Active Record objects don't specify their attributes directly, but rather infer them from the table definition with which they're linked. Adding, removing, and changing attributes and their type is done directly in the database. Any change is instantly reflected in the Active Record objects. The mapping that binds a given Active Record class to a certain database table will happen automatically in most common cases, but can be overwritten for the uncommon ones.

See the mapping rules in ::table_name and the full example in files/README.html for more insight.


Active Records accept constructor parameters either in a hash or as a block. The hash method is especially useful when you're receiving the data from somewhere else, like an HTTP request. It works like this:

user = => "David", :occupation => "Code Artist") # => "David"

You can also use block initialization:

user = do |u| = "David"
  u.occupation = "Code Artist"

And of course you can just create a bare object and specify the attributes after the fact:

user = = "David"
user.occupation = "Code Artist"


Conditions can either be specified as a string, array, or hash representing the WHERE-part of an SQL statement. The array form is to be used when the condition input is tainted and requires sanitization. The string form can be used for statements that don't involve tainted data. The hash form works much like the array form, except only equality and range is possible. Examples:

class User < ActiveRecord::Base
  def self.authenticate_unsafely(user_name, password)
    find(:first, :conditions => "user_name = '#{user_name}' AND password = '#{password}'")
  def self.authenticate_safely(user_name, password)
    find(:first, :conditions => [ "user_name = ? AND password = ?", user_name, password ])
  def self.authenticate_safely_simply(user_name, password)
    find(:first, :conditions => { :user_name => user_name, :password => password })

The authenticate_unsafelymethod inserts the parameters directly into the query and is thus susceptible to SQL-injection attacks if the user_nameand passwordparameters come directly from an HTTP request. The authenticate_safelyand authenticate_safely_simplyboth will sanitize the user_nameand passwordbefore inserting them in the query, which will ensure that an attacker can't escape the query and fake the login (or worse).

When using multiple parameters in the conditions, it can easily become hard to read exactly what the fourth or fifth question mark is supposed to represent. In those cases, you can resort to named bind variables instead. That's done by replacing the question marks with symbols and supplying a hash with values for the matching symbol keys:

Company.find(:first, :conditions => [
  "id = :id AND name = :name AND division = :division AND created_at > :accounting_date",
  { :id => 3, :name => "37signals", :division => "First", :accounting_date => '2005-01-01' }

Similarly, a simple hash without a statement will generate conditions based on equality with the SQL AND operator. For instance:

Student.find(:all, :conditions => { :first_name => "Harvey", :status => 1 })
Student.find(:all, :conditions => params[:student])

A range may be used in the hash to use the SQL BETWEEN operator:

Student.find(:all, :conditions => { :grade => 9..12 })

An array may be used in the hash to use the SQL IN operator:

Student.find(:all, :conditions => { :grade => [9,11,12] })

Overwriting default accessors

All column values are automatically available through basic accessors on the Active Record object, but sometimes you want to specialize this behavior. This can be done by overwriting the default accessors (using the same name as the attribute) and calling read_attribute(attr_name)and write_attribute(attr_name, value) to actually change things. Example:

class Song < ActiveRecord::Base
  # Uses an integer of seconds to hold the length of the song
  def length=(minutes)
    write_attribute(:length, minutes.to_i * 60)
  def length
    read_attribute(:length) / 60

You can alternatively use self[:attribute]=(value)and self[:attribute]instead of write_attribute(:attribute, value) and read_attribute(:attribute)as a shorter form.

Attribute query methods

In addition to the basic accessors, query methods are also automatically available on the Active Record object. Query methods allow you to test whether an attribute value is present.

For example, an Active Record User with the nameattribute has a name?method that you can call to determine whether the user has a name:

user = => "David") # => true
anonymous = => "") # => false

Accessing attributes before they have been typecasted

Sometimes you want to be able to read the raw attribute data without having the column-determined typecast run its course first. That can be done by using the <attribute>_before_type_castaccessors that all attributes have. For example, if your Account model has a balanceattribute, you can call account.balance_before_type_castor account.id_before_type_cast.

This is especially useful in validation situations where the user might supply a string for an integer field and you want to display the original string back in an error message. Accessing the attribute normally would typecast the string to 0, which isn't what you want.

Dynamic attribute-based finders

Dynamic attribute-based finders are a cleaner way of getting (and/or creating) objects by simple queries without turning to SQL. They work by appending the name of an attribute to find_by_, find_last_by_, or find_all_by_, so you get finders like Person.find_by_user_name, Person.find_all_by_last_name, and Payment.find_by_transaction_id. So instead of writing Person.find(:first, :conditions => ["user_name = ?", user_name]) , you just do Person.find_by_user_name(user_name). And instead of writing Person.find(:all, :conditions => ["last_name = ?", last_name]) , you just do Person.find_all_by_last_name(last_name).

It's also possible to use multiple attributes in the same find by separating them with “ and”, so you get finders like Person.find_by_user_name_and_passwordor even Payment.find_by_purchaser_and_state_and_country. So instead of writing Person.find(:first, :conditions => ["user_name = ? AND password = ?", user_name, password]), you just do Person.find_by_user_name_and_password(user_name, password).

It's even possible to use all the additional parameters to find. For example, the full interface for Payment.find_all_by_amountis actually Payment.find_all_by_amount(amount, options). And the full interface to Person.find_by_user_nameis actually Person.find_by_user_name(user_name, options). So you could call Payment.find_all_by_amount(50, :order => "created_on") . Also you may call Payment.find_last_by_amount(amount, options)returning the last record matching that amount and options.

The same dynamic finder style can be used to create the object if it doesn't already exist. This dynamic finder is called with find_or_create_by_and will return the object if it already exists and otherwise creates it, then returns it. Protected attributes won't be set unless they are given in a block. For example:

# No 'Summer' tag exists
Tag.find_or_create_by_name("Summer") # equal to Tag.create(:name => "Summer")
# Now the 'Summer' tag does exist
Tag.find_or_create_by_name("Summer") # equal to Tag.find_by_name("Summer")
# Now 'Bob' exist and is an 'admin'
User.find_or_create_by_name('Bob', :age => 40) { |u| u.admin = true }

Use the find_or_initialize_by_finder if you want to return a new record without saving it first. Protected attributes won't be set unless they are given in a block. For example:

# No 'Winter' tag exists
winter = Tag.find_or_initialize_by_name("Winter")
winter.new_record? # true

To find by a subset of the attributes to be used for instantiating a new object, pass a hash instead of a list of parameters. For example:

Tag.find_or_create_by_name(:name => "rails", :creator => current_user)

That will either find an existing tag named “rails”, or create a new one while setting the user that created it.

Saving arrays, hashes, and other non-mappable objects in text columns

Active Record can serialize any object in text columns using YAML. To do so, you must specify this with a call to the class method serialize. This makes it possible to store arrays, hashes, and other non-mappable objects without doing any additional work. Example:

class User < ActiveRecord::Base
  serialize :preferences
user = User.create(:preferences => { "background" => "black", "display" => large })
User.find( # => { "background" => "black", "display" => large }

You can also specify a class option as the second parameter that'll raise an exception if a serialized object is retrieved as a descendant of a class not in the hierarchy. Example:

class User < ActiveRecord::Base
  serialize :preferences, Hash
user = User.create(:preferences => %w( one two three ))
User.find(    # raises SerializationTypeMismatch

Single table inheritance

Active Record allows inheritance by storing the name of the class in a column that by default is named “type” (can be changed by overwriting Base.inheritance_column). This means that an inheritance looking like this:

class Company < ActiveRecord::Base; end
class Firm < Company; end
class Client < Company; end
class PriorityClient < Client; end

When you do Firm.create(:name => "37signals"), this record will be saved in the companies table with type = “Firm”. You can then fetch this row again using Company.find(:first, "name = '37signals'") and it will return a Firm object.

If you don't have a type column defined in your table, single-table inheritance won't be triggered. In that case, it'll work just like normal subclasses with no special magic for differentiating between them or reloading the right type with find.

Note, all the attributes for all the cases are kept in the same table. Read more:

Connection to multiple databases in different models

Connections are usually created through ::establish_connection and retrieved by #connection. All classes inheriting from ActiveRecord::Base will use this connection. But you can also set a class-specific connection. For example, if Course is an ActiveRecord::Base, but resides in a different database, you can just say Course.establish_connectionand Course and all of its subclasses will use this connection instead.

This feature is implemented by keeping a connection pool in ActiveRecord::Base that is a Hash indexed by the class. If a connection is requested, the ::retrieve_connection method will go up the class-hierarchy until a connection is found in the connection pool.


  • ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.

  • AdapterNotSpecified - The configuration hash used in establish_connectiondidn't include an :adapterkey.

  • AdapterNotFound - The :adapterkey used in establish_connection specified a non-existent adapter (or a bad spelling of an existing one).

  • AssociationTypeMismatch - The object assigned to the association wasn't of the type specified in the association definition.

  • SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.

  • ConnectionNotEstablished+ - No connection has been established. Use establish_connectionbefore querying.

  • RecordNotFound - No record responded to the findmethod. Either the row with the given ID doesn't exist or the row didn't meet the additional restrictions. Some findcalls do not raise this exception to signal nothing was found, please check its documentation for further details.

  • StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.

  • MultiparameterAssignmentErrors - Collection of errors that occurred during a mass assignment using the attributes=method. The errorsproperty of this exception contains an array of AttributeAssignmentError objects that should be inspected to determine which attributes triggered the errors.

  • AttributeAssignmentError - An error occurred while doing a mass assignment through the attributes=method. You can inspect the attribute property of the exception object to determine which attribute triggered the error.

Note: The attributes listed are class-level attributes (accessible from both the class and instance level). So it's possible to assign a logger to the class through Base.logger=which will then be used by all instances in the current object space.

VALID_FIND_OPTIONS = [ :conditions, :include, :joins, :limit, :offset, :order, :select, :readonly, :group, :having, :from, :lock ]
[RW] abstract_class

Set this to true if this is an abstract class (see abstract_class?).

Class Public methods

Overwrite the default class equality method to provide support for association proxies.

# File activerecord/lib/active_record/base.rb, line 1488
def ===(object)

Returns whether this class is a base AR class. If A is a base class and B descends from A, then B.base_class will return B.

# File activerecord/lib/active_record/base.rb, line 1504
def abstract_class?
  defined?(@abstract_class) && @abstract_class == true

This is an alias for find(:all). You can pass in all the same arguments to this method as you can to find(:all)

# File activerecord/lib/active_record/base.rb, line 638
def all(*args)
  find(:all, *args)

Deprecated and no longer has any effect.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 92
def allow_concurrency
  ActiveSupport::Deprecation.warn("ActiveRecord::Base.allow_concurrency has been deprecated and no longer has any effect. Please remove all references to allow_concurrency.")

Deprecated and no longer has any effect.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 97
def allow_concurrency=(flag)
  ActiveSupport::Deprecation.warn("ActiveRecord::Base.allow_concurrency= has been deprecated and no longer has any effect. Please remove all references to allow_concurrency=.")

Specifies a white list of model attributes that can be set via mass-assignment, such as new(attributes), update_attributes(attributes), or attributes=(attributes)

This is the opposite of the attr_protectedmacro: Mass-assignment will only set attributes in this list, to assign to the rest of attributes you can use direct writer methods. This is meant to protect sensitive attributes from being overwritten by malicious users tampering with URLs or forms. If you'd rather start from an all-open default and restrict attributes as needed, have a look at attr_protected.

class Customer < ActiveRecord::Base
  attr_accessible :name, :nickname
customer = => "David", :nickname => "Dave", :credit_rating => "Excellent")
customer.credit_rating # => nil
customer.attributes = { :name => "Jolly fellow", :credit_rating => "Superb" }
customer.credit_rating # => nil
customer.credit_rating = "Average"
customer.credit_rating # => "Average"
# File activerecord/lib/active_record/base.rb, line 1085
def attr_accessible(*attributes)
  write_inheritable_attribute(:attr_accessible, + (accessible_attributes || []))

Attributes named in this macro are protected from mass-assignment, such as new(attributes), update_attributes(attributes), or attributes=(attributes).

Mass-assignment to these attributes will simply be ignored, to assign to them you can use direct writer methods. This is meant to protect sensitive attributes from being overwritten by malicious users tampering with URLs or forms.

class Customer < ActiveRecord::Base
  attr_protected :credit_rating
customer ="name" => David, "credit_rating" => "Excellent")
customer.credit_rating # => nil
customer.attributes = { "description" => "Jolly fellow", "credit_rating" => "Superb" }
customer.credit_rating # => nil
customer.credit_rating = "Average"
customer.credit_rating # => "Average"

To start from an all-closed default and enable attributes as needed, have a look at attr_accessible.

# File activerecord/lib/active_record/base.rb, line 1052
def attr_protected(*attributes)
  write_inheritable_attribute(:attr_protected, + (protected_attributes || []))

Attributes listed as readonly can be set for a new record, but will be ignored in database updates afterwards.

# File activerecord/lib/active_record/base.rb, line 1095
def attr_readonly(*attributes)
  write_inheritable_attribute(:attr_readonly, + (readonly_attributes || []))

Returns the base AR subclass that this class descends from. If A extends AR::Base, A.base_class will return A. If B descends from A through some arbitrarily deep hierarchy, B.base_class will return A.

# File activerecord/lib/active_record/base.rb, line 1495
def base_class
benchmark(title, log_level = Logger::DEBUG, use_silence = true)

Log and benchmark multiple statements in a single block. Example:

Project.benchmark("Creating project") do
  project = Project.create("name" => "stuff")
  project.create_manager("name" => "David")
  project.milestones << Milestone.find(:all)

The benchmark is only recorded if the current level of the logger is less than or equal to the log_level, which makes it easy to include benchmarking statements in production software that will remain inexpensive because the benchmark will only be conducted if the log level is low enough.

The logging of the multiple statements is turned off unless use_silenceis set to false.

# File activerecord/lib/active_record/base.rb, line 1468
def benchmark(title, log_level = Logger::DEBUG, use_silence = true)
  if logger && logger.level <= log_level
    result = nil
    ms = { result = use_silence ? silence { yield } : yield }
    logger.add(log_level, '%s (%.1fms)' % [title, ms])

Determines whether to use ANSI codes to colorize the logging statements committed by the connection adapter. These colors make it much easier to overview things during debugging (when used through a reader like tailand on a black background), but may complicate matters if you use software like syslog. This is true, by default.

# File activerecord/lib/active_record/base.rb, line 491
cattr_accessor :colorize_logging, :instance_writer => false

Returns an array of column names as strings.

# File activerecord/lib/active_record/base.rb, line 1317
def column_names
  @column_names ||= { |column| }

Returns an array of column objects for the table associated with this class.

# File activerecord/lib/active_record/base.rb, line 1303
def columns
  unless defined?(@columns) && @columns
    @columns = connection.columns(table_name, "#{name} Columns")
    @columns.each { |column| column.primary = == primary_key }

Returns a hash of column objects for the table associated with this class.

# File activerecord/lib/active_record/base.rb, line 1312
def columns_hash
  @columns_hash ||= columns.inject({}) { |hash, column| hash[] = column; hash }

Contains the database configuration - as is typically stored in config/database.yml - as a Hash.

For example, the following database.yml…

  adapter: sqlite3
  database: db/development.sqlite3
  adapter: sqlite3
  database: db/production.sqlite3

…would result in ::configurations to look like this:

   'development' => {
      'adapter'  => 'sqlite3',
      'database' => 'db/development.sqlite3'
   'production' => {
      'adapter'  => 'sqlite3',
      'database' => 'db/production.sqlite3'
# File activerecord/lib/active_record/base.rb, line 448
cattr_accessor :configurations, :instance_writer => false

Returns true if ActiveRecordis connected.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 127
def connected?

Returns the connection currently associated with the class. This can also be used to “borrow” the connection to do database work unrelated to any of the specific Active Records.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 114
def connection

The connection handler

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 13
class_attribute :connection_handler
# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 118
def connection_pool

Returns an array of column objects where the primary id, all columns ending in “_id” or “_count”, and columns used for single table inheritance have been removed.

# File activerecord/lib/active_record/base.rb, line 1323
def content_columns
  @content_columns ||= columns.reject { |c| c.primary || =~ /(_id|_count)$/ || == inheritance_column }

Returns the result of an SQL statement that should only include a COUNT(*) in the SELECT part. The use of this method should be restricted to complicated SQL queries that can't be executed using the ActiveRecord::Calculations class methods. Look into those before using this.


  • sql- An SQL statement which should return a count query from the database, see the example below.


Product.count_by_sql "SELECT COUNT(*) FROM sales s, customers c WHERE s.customer_id ="
# File activerecord/lib/active_record/base.rb, line 918
def count_by_sql(sql)
  sql = sanitize_conditions(sql)
  connection.select_value(sql, "#{name} Count").to_i
create(attributes = nil, &block)

Creates an object (or multiple objects) and saves it to the database, if validations pass. The resulting object is returned whether the object was saved successfully to the database or not.

The attributesparameter can be either be a Hash or an Array of Hashes. These Hashes describe the attributes on the objects that are to be created.


# Create a single new object
User.create(:first_name => 'Jamie')
# Create an Array of new objects
User.create([{ :first_name => 'Jamie' }, { :first_name => 'Jeremy' }])
# Create a single object and pass it into a block to set other attributes.
User.create(:first_name => 'Jamie') do |u|
  u.is_admin = false
# Creating an Array of new objects using a block, where the block is executed for each object:
User.create([{ :first_name => 'Jamie' }, { :first_name => 'Jeremy' }]) do |u|
  u.is_admin = false
# File activerecord/lib/active_record/base.rb, line 721
def create(attributes = nil, &block)
  if attributes.is_a?(Array)
    attributes.collect { |attr| create(attr, &block) }
    object = new(attributes)
    yield(object) if block_given?
decrement_counter(counter_name, id)

Decrement a number field by one, usually representing a count.

This works the same as ::increment_counter but reduces the column value by 1 instead of increasing it.


  • counter_name- The name of the field that should be decremented.

  • id- The id of the object that should be decremented.


# Decrement the post_count column for the record with an id of 5
DiscussionBoard.decrement_counter(:post_count, 5)
# File activerecord/lib/active_record/base.rb, line 1024
def decrement_counter(counter_name, id)
  update_counters(id, counter_name => -1)

Determines whether to use Time.local (using :local) or Time.utc (using :utc) when pulling dates and times from the database. This is set to :local by default.

# File activerecord/lib/active_record/base.rb, line 498
cattr_accessor :default_timezone, :instance_writer => false

Deletes the row with a primary key matching the idargument, using a SQL DELETEstatement, and returns the number of rows deleted. Active Record objects are not instantiated, so the object's callbacks are not executed, including any :dependent association options or Observer methods.

You can delete multiple rows at once by passing an Array of ids.

Note: Although it is often much faster than the alternative, #destroy, skipping callbacks might bypass business logic in your application that ensures referential integrity or performs other essential jobs.


# Delete a single row
# Delete multiple rows
# File activerecord/lib/active_record/base.rb, line 779
def delete(id)
  delete_all([ "#{connection.quote_column_name(primary_key)} IN (?)", id ])
delete_all(conditions = nil)

Deletes the records matching conditionswithout instantiating the records first, and hence not calling the destroymethod nor invoking callbacks. This is a single SQL DELETE statement that goes straight to the database, much more efficient than destroy_all. Be careful with relations though, in particular :dependentrules defined on associations are not honored. Returns the number of rows affected.


  • conditions- Conditions are specified the same way as with findmethod.


Post.delete_all("person_id = 5 AND (category = 'Something' OR category = 'Else')")
Post.delete_all(["person_id = ? AND (category = ? OR category = ?)", 5, 'Something', 'Else'])

Both calls delete the affected posts all at once with a single DELETE statement. If you need to destroy dependent associations or call your before_*or after_destroycallbacks, use the destroy_allmethod instead.

# File activerecord/lib/active_record/base.rb, line 901
def delete_all(conditions = nil)
  sql = "DELETE FROM #{quoted_table_name} "
  add_conditions!(sql, conditions, scope(:find))
  connection.delete(sql, "#{name} Delete all")

True if this isn't a concrete subclass needing a STI type condition.

# File activerecord/lib/active_record/base.rb, line 1419
def descends_from_active_record?
  if superclass.abstract_class?
    superclass == Base || !columns_hash.include?(inheritance_column)

Destroy an object (or multiple objects) that has the given id, the object is instantiated first, therefore all callbacks and filters are fired off before the object is deleted. This method is less efficient than ActiveRecord#delete but allows cleanup methods and other actions to be run.

This essentially finds the object (or multiple objects) with the given id, creates a new object from the attributes, and then calls destroy on it.


  • id- Can be either an Integer or an Array of Integers.


# Destroy a single object
# Destroy multiple objects
todos = [1,2,3]
# File activerecord/lib/active_record/base.rb, line 802
def destroy(id)
  if id.is_a?(Array) { |one_id| destroy(one_id) }
destroy_all(conditions = nil)

Destroys the records matching conditionsby instantiating each record and calling its destroymethod. Each object's callbacks are executed (including :dependentassociation options and before_destroy/ after_destroy Observer methods). Returns the collection of objects that were destroyed; each will be frozen, to reflect that no changes should be made (since they can't be persisted).

Note: Instantiation, callback execution, and deletion of each record can be time consuming when you're removing many records at once. It generates at least one SQL DELETEquery per record (or possibly more, to enforce your callbacks). If you want to delete many rows quickly, without concern for their associations or callbacks, use delete_all instead.


  • conditions- A string, array, or hash that specifies which records to destroy. If omitted, all records are destroyed. See the Conditions section in the introduction to ActiveRecord::Base for more information.


Person.destroy_all("last_login < '2004-04-04'")
Person.destroy_all(:status => "inactive")
# File activerecord/lib/active_record/base.rb, line 880
def destroy_all(conditions = nil)
  find(:all, :conditions => conditions).each { |object| object.destroy }
establish_connection(spec = nil)

Establishes the connection to the database. Accepts a hash as input where the :adapterkey must be specified with the name of a database adapter (in lower-case) example for regular databases (MySQL, Postgresql, etc):

  :adapter  => "mysql",
  :host     => "localhost",
  :username => "myuser",
  :password => "mypass",
  :database => "somedatabase"

Example for SQLite database:

  :adapter => "sqlite",
  :database  => "path/to/dbfile"

Also accepts keys as strings (for parsing from YAML for example):

  "adapter" => "sqlite",
  "database"  => "path/to/dbfile"

The exceptions AdapterNotSpecified, AdapterNotFound and ArgumentError may be returned on an error.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 51
def self.establish_connection(spec = nil)
  case spec
    when nil
      raise AdapterNotSpecified unless defined? RAILS_ENV
    when ConnectionSpecification
      self.connection_handler.establish_connection(name, spec)
    when Symbol, String
      if configuration = configurations[spec.to_s]
        raise AdapterNotSpecified, "#{spec} database is not configured"
      spec = spec.symbolize_keys
      unless spec.key?(:adapter) then raise AdapterNotSpecified, "database configuration does not specify adapter" end
        require 'rubygems'
        gem "activerecord-#{spec[:adapter]}-adapter"
        require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
      rescue LoadError
          require "active_record/connection_adapters/#{spec[:adapter]}_adapter"
        rescue LoadError
          raise "Please install the #{spec[:adapter]} adapter: `gem install activerecord-#{spec[:adapter]}-adapter` (#{$!})"
      adapter_method = "#{spec[:adapter]}_connection"
      if !respond_to?(adapter_method)
        raise AdapterNotFound, "database configuration specifies nonexistent #{spec[:adapter]} adapter"
      establish_connection(, adapter_method))
exists?(id_or_conditions = {})

Returns true if a record exists in the table that matches the idor conditions given, or false otherwise. The argument can take five forms:

  • Integer - Finds the record with this primary key.

  • String - Finds the record with a primary key corresponding to this string (such as '5').

  • Array - Finds the record that matches these find-style conditions (such as ['color = ?', 'red']).

  • Hash - Finds the record that matches these find-style conditions (such as {:color => 'red'} ).

  • No args - Returns false if the table is empty, true otherwise.

For more information about specifying conditions as a Hash or Array, see the Conditions section in the introduction to ActiveRecord::Base.

Note: You can't pass in a condition as a string (like name = 'Jamie' ), since it would be sanitized and then queried against the primary key column, like id = 'name = \'Jamie\'' .


Person.exists?(:name => "David")
Person.exists?(['name LIKE ?', "%#{query}%"])
# File activerecord/lib/active_record/base.rb, line 693
def exists?(id_or_conditions = {})
    :select => "#{quoted_table_name}.#{primary_key}",
    :conditions => expand_id_conditions(id_or_conditions)) ? true : false

Find operates with four different retrieval approaches:

  • Find by id - This can either be a specific id (1), a list of ids (1, 5, 6), or an array of ids ([5, 6, 10]). If no record can be found for all of the listed ids, then RecordNotFound will be raised.

  • Find first - This will return the first record matched by the options used. These options can either be specific conditions or merely an order. If no record can be matched, nilis returned. Use Model.find(:first, *args)or its shortcut Model.first(*args).

  • Find last - This will return the last record matched by the options used. These options can either be specific conditions or merely an order. If no record can be matched, nilis returned. Use Model.find(:last, *args)or its shortcut Model.last(*args).

  • Find all - This will return all the records matched by the options used. If no records are found, an empty array is returned. Use Model.find(:all, *args)or its shortcut Model.all(*args).

All approaches accept an options hash as their last parameter.


  • :conditions- An SQL fragment like “administrator = 1”, [ "user_name = ?", username ], or ["user_name = :user_name", { :user_name => user_name }] . See conditions in the intro.

  • :order- An SQL fragment like “created_at DESC, name”.

  • :group- An attribute name by which the result should be grouped. Uses the GROUP BYSQL-clause.

  • :having- Combined with :groupthis can be used to filter the records that a GROUP BYreturns. Uses the HAVINGSQL-clause.

  • :limit- An integer determining the limit on the number of rows that should be returned.

  • :offset- An integer determining the offset from where the rows should be fetched. So at 5, it would skip rows 0 through 4.

  • :joins- Either an SQL fragment for additional joins like “LEFT JOIN comments ON comments.post_id = id” (rarely needed), named associations in the same form used for the :includeoption, which will perform an INNER JOINon the associated table(s), or an array containing a mixture of both strings and named associations. If the value is a string, then the records will be returned read-only since they will have attributes that do not correspond to the table's columns. Pass :readonly => falseto override.

  • :include- Names associations that should be loaded alongside. The symbols named refer to already defined associations. See eager loading under Associations.

  • :select- By default, this is “*” as in “SELECT * FROM”, but can be changed if you, for example, want to do a join but not include the joined columns. Takes a string with the SELECT SQL fragment (e.g. “id, name”).

  • :from- By default, this is the table name of the class, but can be changed to an alternate table name (or even the name of a database view).

  • :readonly- Mark the returned records read-only so they cannot be saved or updated.

  • :lock- An SQL fragment like “FOR UPDATE” or “LOCK IN SHARE MODE”. :lock => truegives connection's default exclusive lock, usually “FOR UPDATE”.


# find by id
Person.find(1)       # returns the object for ID = 1
Person.find(1, 2, 6) # returns an array for objects with IDs in (1, 2, 6)
Person.find([7, 17]) # returns an array for objects with IDs in (7, 17)
Person.find([1])     # returns an array for the object with ID = 1
Person.find(1, :conditions => "administrator = 1", :order => "created_on DESC")

Note that returned records may not be in the same order as the ids you provide since database rows are unordered. Give an explicit :orderto ensure the results are sorted.


# find first
Person.find(:first) # returns the first object fetched by SELECT * FROM people
Person.find(:first, :conditions => [ "user_name = ?", user_name])
Person.find(:first, :conditions => [ "user_name = :u", { :u => user_name }])
Person.find(:first, :order => "created_on DESC", :offset => 5)
# find last
Person.find(:last) # returns the last object fetched by SELECT * FROM people
Person.find(:last, :conditions => [ "user_name = ?", user_name])
Person.find(:last, :order => "created_on DESC", :offset => 5)
# find all
Person.find(:all) # returns an array of objects for all the rows fetched by SELECT * FROM people
Person.find(:all, :conditions => [ "category IN (?)", categories], :limit => 50)
Person.find(:all, :conditions => { :friends => ["Bob", "Steve", "Fred"] }
Person.find(:all, :offset => 10, :limit => 10)
Person.find(:all, :include => [ :account, :friends ])
Person.find(:all, :group => "category")

Example for find with a lock: Imagine two concurrent transactions: each will read person.visits == 2, add 1 to it, and save, resulting in two saves of person.visits = 3. By locking the row, the second transaction has to wait until the first is finished; we get the expected person.visits == 4.

Person.transaction do
  person = Person.find(1, :lock => true)
  person.visits += 1!
# File activerecord/lib/active_record/base.rb, line 611
def find(*args)
  options = args.extract_options!
  case args.first
    when :first then find_initial(options)
    when :last  then find_last(options)
    when :all   then find_every(options)
    else             find_from_ids(args, options)

Executes a custom SQL query against your database and returns all the results. The results will be returned as an array with columns requested encapsulated as attributes of the model you call this method from. If you call Product.find_by_sqlthen the results will be returned in a Product object with the attributes you specified in the SQL query.

If you call a complicated SQL query which spans multiple tables the columns specified by the SELECT will be attributes of the model, whether or not they are columns of the corresponding table.

The sqlparameter is a full SQL query as a string. It will be called as is, there will be no database agnostic conversions performed. This should be a last resort because using, for example, MySQL specific terms will lock you to using that particular database engine or require you to change your call if you switch engines.


# A simple SQL query spanning multiple tables
Post.find_by_sql "SELECT p.title, FROM posts p, comments c WHERE = c.post_id"
> [#<Post:0x36bff9c @attributes={"title"=>"Ruby Meetup", "first_name"=>"Quentin"}>, ...]
# You can use the same string replacement techniques as you can with ActiveRecord#find
Post.find_by_sql ["SELECT title FROM posts WHERE author = ? AND created > ?", author_id, start_date]
> [#<Post:0x36bff9c @attributes={"first_name"=>"The Cheap Man Buys Twice"}>, ...]
# File activerecord/lib/active_record/base.rb, line 664
def find_by_sql(sql)
  connection.select_all(sanitize_sql(sql), "#{name} Load").collect! { |record| instantiate(record) }

A convenience wrapper for find(:first, *args). You can pass in all the same arguments to this method as you can to find(:first).

# File activerecord/lib/active_record/base.rb, line 626
def first(*args)
  find(:first, *args)
human_attribute_name(attribute_key_name, options = {})

Transforms attribute key names into a more humane format, such as “First name” instead of “first_name”. Example:

Person.human_attribute_name("first_name") # => "First name"

This used to be depricated in favor of humanize, but is now preferred, because it automatically uses the I18n module now. Specify optionswith additional translating options.

# File activerecord/lib/active_record/base.rb, line 1395
def human_attribute_name(attribute_key_name, options = {})
  defaults = do |klass|
  defaults << options[:default] if options[:default]
  defaults << attribute_key_name.to_s.humanize
  options[:count] ||= 1
  I18n.translate(defaults.shift, options.merge(:default => defaults, :scope => [:activerecord, :attributes]))
human_name(options = {})

Transform the modelname into a more humane format, using I18n. Defaults to the basic humanize method. Default scope of the translation is activerecord.models Specify optionswith additional translating options.

# File activerecord/lib/active_record/base.rb, line 1410
def human_name(options = {})
  defaults = do |klass|
  defaults <<
  I18n.translate(defaults.shift, {:scope => [:activerecord, :models], :count => 1, :default => defaults}.merge(options))
increment_counter(counter_name, id)

Increment a number field by one, usually representing a count.

This is used for caching aggregate values, so that they don't need to be computed every time. For example, a DiscussionBoard may cache post_count and comment_count otherwise every time the board is shown it would have to run an SQL query to find how many posts and comments there are.


  • counter_name- The name of the field that should be incremented.

  • id- The id of the object that should be incremented.


# Increment the post_count column for the record with an id of 5
DiscussionBoard.increment_counter(:post_count, 5)
# File activerecord/lib/active_record/base.rb, line 1007
def increment_counter(counter_name, id)
  update_counters(id, counter_name => 1)

Defines the column name for use with single table inheritance – can be set in subclasses like so: self.inheritance_column = “type_id”

# File activerecord/lib/active_record/base.rb, line 1215
def inheritance_column
  @inheritance_column ||= "type".freeze
inheritance_column=(value = nil, &block)

Returns a string like 'Post id:integer, title:string, body:text'

# File activerecord/lib/active_record/base.rb, line 1433
def inspect
  if self == Base
  elsif abstract_class?
  elsif table_exists?
    attr_list = { |c| "#{}: #{c.type}" } * ', '
    "#{super}(Table doesn't exist)"

A convenience wrapper for find(:last, *args). You can pass in all the same arguments to this method as you can to find(:last).

# File activerecord/lib/active_record/base.rb, line 632
def last(*args)
  find(:last, *args)

Merges conditions so that the result is a valid condition

# File activerecord/lib/active_record/base.rb, line 1523
def merge_conditions(*conditions)
  segments = []
  conditions.each do |condition|
    unless condition.blank?
      sql = sanitize_sql(condition)
      segments << sql unless sql.blank?
  "(#{segments.join(') AND (')})" unless segments.empty?
new(attributes = nil)

New objects can be instantiated as either empty (pass no construction parameter) or pre-set with attributes but not yet saved (pass a hash with key names matching the associated table column names). In both instances, valid attribute keys are determined by the column names of the associated table – hence you can't have attributes that aren't part of the table columns.

# File activerecord/lib/active_record/base.rb, line 2480
def initialize(attributes = nil)
  @attributes = attributes_from_column_definition
  @attributes_cache = {}
  @new_record = true
  self.attributes = attributes unless attributes.nil?
  assign_attributes(self.class.send(:scope, :create)) if self.class.send(:scoped?, :create)
  result = yield self if block_given?
  callback(:after_initialize) if respond_to_without_attributes?(:after_initialize)

Indicates whether table names should be the pluralized versions of the corresponding class names. If true, the default table name for a Product class will be products. If false, it would just be product. See ::table_name for the full rules on table/class naming. This is true, by default.

# File activerecord/lib/active_record/base.rb, line 483
cattr_accessor :pluralize_table_names, :instance_writer => false

Defines the primary key field – can be overridden in subclasses. Overwriting will negate any effect of the ::primary_key_prefix_type setting, though.

# File activerecord/lib/active_record/base.rb, line 1188
def primary_key
primary_key=(value = nil, &block)

Accessor for the prefix type that will be prepended to every primary key column name. The options are :::table_name and :table_name_with_underscore. If the first is specified, the Product class will look for “productid” instead of “id” as the primary column. If the latter is specified, the Product class will look for “product_id” instead of “id”. Remember that this is a global setting for all Active Records.

# File activerecord/lib/active_record/base.rb, line 457
cattr_accessor :primary_key_prefix_type, :instance_writer => false

Returns an array of all the attributes that have been specified as readonly.

# File activerecord/lib/active_record/base.rb, line 1100
def readonly_attributes
remove_connection(klass = self)
# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 131
def remove_connection(klass = self)

Resets all the cached information about columns, which will cause them to be reloaded on the next request.

The most common usage pattern for this method is probably in a migration, when just after creating a table you want to populate it with some default values, eg:

class CreateJobLevels < ActiveRecord::Migration
  def self.up
    create_table :job_levels do |t|
      t.integer :id
      t.string :name
    %w{assistant executive manager director}.each do |type|
      JobLevel.create(:name => type)
  def self.down
    drop_table :job_levels
# File activerecord/lib/active_record/base.rb, line 1367
def reset_column_information
  generated_methods.each { |name| undef_method(name) }
  @column_names = @columns = @columns_hash = @content_columns = @dynamic_methods_hash = @generated_methods = @inheritance_column = nil
reset_counters(id, *counters)

Resets one or more counter caches to their correct value using an SQL count query. This is useful when adding new counter caches, or if the counter has been corrupted or modified directly by SQL.


  • id- The id of the object you wish to reset a counter on.

  • counters- One or more counter names to reset


# For Post with id #1 records reset the comments_count
Post.reset_counters(1, :comments)
# File activerecord/lib/active_record/base.rb, line 936
      def reset_counters(id, *counters)
        object = find(id)
        counters.each do |association|
          child_class = reflect_on_association(association.to_sym).klass
          belongs_name =
          counter_name = child_class.reflect_on_association(belongs_name).counter_cache_column
          value = object.send(association).count
          connection.update("            UPDATE #{quoted_table_name}
            SET #{connection.quote_column_name(counter_name)} = #{value}
            WHERE #{connection.quote_column_name(primary_key)} = #{quote_value(}
", "#{name} UPDATE")
        return true
respond_to?(method_id, include_private = false)
# File activerecord/lib/active_record/base.rb, line 1508
def respond_to?(method_id, include_private = false)
  if match = DynamicFinderMatch.match(method_id)
    return true if all_attributes_exists?(match.attribute_names)
  elsif match = DynamicScopeMatch.match(method_id)
    return true if all_attributes_exists?(match.attribute_names)
# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 122
def retrieve_connection

Specifies the format to use when dumping the database schema with Rails' Rakefile. If :sql, the schema is dumped as (potentially database- specific) SQL statements. If :ruby, the schema is dumped as an ActiveRecord::Schema file which can be loaded into any database that supports migrations. Use :ruby if you want to have different database adapters for, e.g., your development and test environments.

# File activerecord/lib/active_record/base.rb, line 509
cattr_accessor :schema_format , :instance_writer => false
sequence_name=(value = nil, &block)
serialize(attr_name, class_name = Object)

If you have an attribute that needs to be saved to the database as an object, and retrieved as the same object, then specify the name of that attribute using this method and it will be handled automatically. The serialization is done through YAML. If class_nameis specified, the serialized object must be of that class on retrieval or SerializationTypeMismatch will be raised.


  • attr_name- The field name that should be serialized.

  • class_name- Optional, class name that the object type should be equal to.


# Serialize a preferences attribute
class User
  serialize :preferences
# File activerecord/lib/active_record/base.rb, line 1119
def serialize(attr_name, class_name = Object)
  serialized_attributes[attr_name.to_s] = class_name

Returns a hash of all the attributes that have been specified for serialization as keys and their class restriction as values.

# File activerecord/lib/active_record/base.rb, line 1124
def serialized_attributes
  read_inheritable_attribute(:attr_serialized) or write_inheritable_attribute(:attr_serialized, {})
set_inheritance_column(value = nil, &block)

Sets the name of the inheritance column to use to the given value, or (if the value # is nil or false) to the value returned by the given block.

class Project < ActiveRecord::Base
  set_inheritance_column do
    original_inheritance_column + "_id"
Also aliased as: inheritance_column=
# File activerecord/lib/active_record/base.rb, line 1263
def set_inheritance_column(value = nil, &block)
  define_attr_method :inheritance_column, value, &block
set_primary_key(value = nil, &block)

Sets the name of the primary key column to use to the given value, or (if the value is nil or false) to the value returned by the given block.

class Project < ActiveRecord::Base
  set_primary_key "sysid"
Also aliased as: primary_key=
# File activerecord/lib/active_record/base.rb, line 1249
def set_primary_key(value = nil, &block)
  define_attr_method :primary_key, value, &block
set_sequence_name(value = nil, &block)

Sets the name of the sequence to use when generating ids to the given value, or (if the value is nil or false) to the value returned by the given block. This is required for Oracle and is useful for any database which relies on sequences for primary key generation.

If a sequence name is not explicitly set when using Oracle or Firebird, it will default to the commonly used pattern of: #{::table_name}_seq

If a sequence name is not explicitly set when using PostgreSQL, it will discover the sequence corresponding to your primary key for you.

class Project < ActiveRecord::Base
  set_sequence_name "projectseq"   # default would have been "project_seq"
Also aliased as: sequence_name=
# File activerecord/lib/active_record/base.rb, line 1282
def set_sequence_name(value = nil, &block)
  define_attr_method :sequence_name, value, &block
set_table_name(value = nil, &block)

Sets the table name to use to the given value, or (if the value is nil or false) to the value returned by the given block.

class Project < ActiveRecord::Base
  set_table_name "project"
Also aliased as: table_name=
# File activerecord/lib/active_record/base.rb, line 1237
def set_table_name(value = nil, &block)
  define_attr_method :table_name, value, &block

Silences the logger for the duration of the block.

# File activerecord/lib/active_record/base.rb, line 1480
def silence
  old_logger_level, logger.level = logger.level, Logger::ERROR if logger
  logger.level = old_logger_level if logger
# File activerecord/lib/active_record/base.rb, line 1518
def sti_name
  store_full_sti_class ? name : name.demodulize

Indicates whether the table associated with this class exists

# File activerecord/lib/active_record/base.rb, line 1298
def table_exists?

Guesses the table name (in forced lower-case) based on the name of the class in the inheritance hierarchy descending directly from ActiveRecord::Base. So if the hierarchy looks like: Reply < Message < ActiveRecord::Base, then Message is used to guess the table name even when called on Reply. The rules used to do the guess are handled by the Inflector class in Active Support, which knows almost all common English inflections. You can add new inflections in config/initializers/inflections.rb.

Nested classes are given table names prefixed by the singular form of the parent's table name. Enclosing modules are not considered.


class Invoice < ActiveRecord::Base; end;
file                  class               table_name
invoice.rb            Invoice             invoices
class Invoice < ActiveRecord::Base; class Lineitem < ActiveRecord::Base; end; end;
file                  class               table_name
invoice.rb            Invoice::Lineitem   invoice_lineitems
module Invoice; class Lineitem < ActiveRecord::Base; end; end;
file                  class               table_name
invoice/lineitem.rb   Invoice::Lineitem   lineitems

Additionally, the class-level table_name_prefixis prepended and the table_name_suffixis appended. So if you have “myapp_” as a prefix, the table name guess for an Invoice class becomes “myapp_invoices”. Invoice::Lineitem becomes “myapp_invoice_lineitems”.

You can also overwrite this class method to allow for unguessable links, such as a Mouse class with a link to a “mice” table. Example:

class Mouse < ActiveRecord::Base
  set_table_name "mice"
# File activerecord/lib/active_record/base.rb, line 1161
def table_name
table_name=(value = nil, &block)

Accessor for the name of the prefix string to prepend to every table name. So if set to “basecamp_”, all table names will be named like “basecamp_projects”, “basecamp_people”, etc. This is a convenient way of creating a namespace for tables in a shared database. By default, the prefix is the empty string.

If you are organising your models within modules you can add a prefix to the models within a namespace by defining a singleton method in the parent module called ::table_name_prefix which returns your chosen prefix.

# File activerecord/lib/active_record/base.rb, line 468
cattr_accessor :table_name_prefix, :instance_writer => false

Works like table_name_prefix, but appends instead of prepends (set to “_basecamp” gives “projects_basecamp”, “people_basecamp”). By default, the suffix is the empty string.

# File activerecord/lib/active_record/base.rb, line 475
cattr_accessor :table_name_suffix, :instance_writer => false

Specify whether or not to use timestamps for migration numbers

# File activerecord/lib/active_record/base.rb, line 515
cattr_accessor :timestamped_migrations , :instance_writer => false
update(id, attributes)

Updates an object (or multiple objects) and saves it to the database, if validations pass. The resulting object is returned whether the object was saved successfully to the database or not.


  • id- This should be the id or an array of ids to be updated.

  • attributes- This should be a hash of attributes to be set on the object, or an array of hashes.


# Updating one record:
Person.update(15, :user_name => 'Samuel', :group => 'expert')
# Updating multiple records:
people = { 1 => { "first_name" => "David" }, 2 => { "first_name" => "Jeremy" } }
Person.update(people.keys, people.values)
# File activerecord/lib/active_record/base.rb, line 748
def update(id, attributes)
  if id.is_a?(Array)
    idx = -1
    id.collect { |one_id| idx += 1; update(one_id, attributes[idx]) }
    object = find(id)
update_all(updates, conditions = nil, options = {})

Updates all records with details given if they match a set of conditions supplied, limits and order can also be supplied. This method constructs a single SQL UPDATE statement and sends it straight to the database. It does not instantiate the involved models and it does not trigger Active Record callbacks.


  • updates- A string of column and value pairs that will be set on any records that match conditions. This creates the SET clause of the generated SQL.

  • conditions- An SQL fragment like “administrator = 1” or [ “user_name = ?”, username ]. See conditions in the intro for more info.

  • options- Additional options are :limitand :order, see the examples for usage.


# Update all billing objects with the 3 different attributes given
Billing.update_all( "category = 'authorized', approved = 1, author = 'David'" )
# Update records that match our conditions
Billing.update_all( "author = 'David'", "title LIKE '%Rails%'" )
# Update records that match our conditions but limit it to 5 ordered by date
Billing.update_all( "author = 'David'", "title LIKE '%Rails%'",
                      :order => 'created_at', :limit => 5 )
# File activerecord/lib/active_record/base.rb, line 831
def update_all(updates, conditions = nil, options = {})
  sql  = "UPDATE #{quoted_table_name} SET #{sanitize_sql_for_assignment(updates)} "
  scope = scope(:find)
  select_sql = ""
  add_conditions!(select_sql, conditions, scope)
  if options.has_key?(:limit) || (scope && scope[:limit])
    # Only take order from scope if limit is also provided by scope, this
    # is useful for updating a has_many association with a limit.
    add_order!(select_sql, options[:order], scope)
    add_limit!(select_sql, options, scope)
    sql.concat(connection.limited_update_conditions(select_sql, quoted_table_name, connection.quote_column_name(primary_key)))
    add_order!(select_sql, options[:order], nil)
  connection.update(sql, "#{name} Update")
update_counters(id, counters)

A generic “counter updater” implementation, intended primarily to be used by ::increment_counter and ::decrement_counter, but which may also be useful on its own. It simply does a direct SQL update for the record with the given ID, altering the given hash of counters by the amount given by the corresponding value:


  • id- The id of the object you wish to update a counter on or an Array of ids.

  • counters- An Array of Hashes containing the names of the fields to update as keys and the amount to update the field by as values.


# For the Post with id of 5, decrement the comment_count by 1, and
# increment the action_count by 1
Post.update_counters 5, :comment_count => -1, :action_count => 1
# Executes the following SQL:
# UPDATE posts
#    SET comment_count = comment_count - 1,
#        action_count = action_count + 1
#  WHERE id = 5
# For the Posts with id of 10 and 15, increment the comment_count by 1
Post.update_counters [10, 15], :comment_count => 1
# Executes the following SQL:
# UPDATE posts
#    SET comment_count = comment_count + 1,
#  WHERE id IN (10, 15)
# File activerecord/lib/active_record/base.rb, line 982
def update_counters(id, counters)
  updates = do |counter_name, value|
    operator = value < 0 ? '-' : '+'
    quoted_column = connection.quote_column_name(counter_name)
    "#{quoted_column} = COALESCE(#{quoted_column}, 0) #{operator} #{value.abs}"
  update_all(updates.join(', '), primary_key => id )

Deprecated and no longer has any effect.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 102
def verification_timeout
  ActiveSupport::Deprecation.warn("ActiveRecord::Base.verification_timeout has been deprecated and no longer has any effect. Please remove all references to verification_timeout.")

Deprecated and no longer has any effect.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 107
def verification_timeout=(flag)
  ActiveSupport::Deprecation.warn("ActiveRecord::Base.verification_timeout= has been deprecated and no longer has any effect. Please remove all references to verification_timeout=.")
Class Protected methods
# File activerecord/lib/active_record/base.rb, line 2291
def aggregate_mapping(reflection)
  mapping = reflection.options[:mapping] || [,]
  mapping.first.is_a?(Array) ? mapping : [mapping]

Returns the class descending directly from ActiveRecord::Base or an abstract class, if any, in the inheritance hierarchy.

# File activerecord/lib/active_record/base.rb, line 2249
def class_of_active_record_descendant(klass)
  if klass.superclass == Base || klass.superclass.abstract_class?
  elsif klass.superclass.nil?
    raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"

Returns the class type of the record using the current module as a prefix. So descendants of MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.

# File activerecord/lib/active_record/base.rb, line 2236
def compute_type(type_name)
  modularized_name = type_name_with_module(type_name)
  silence_warnings do
      class_eval(modularized_name, __FILE__)
    rescue NameError
      class_eval(type_name, __FILE__)
default_scope(options = {})

Sets the default options for the model. The format of the optionsargument is the same as in find.

class Person < ActiveRecord::Base
  default_scope :order => 'last_name, first_name'
# File activerecord/lib/active_record/base.rb, line 2208
def default_scope(options = {})
  self.default_scoping << { :find => options, :create => options[:conditions].is_a?(Hash) ? options[:conditions] : {} }

Accepts a hash of SQL conditions and replaces those attributes that correspond to a composed_ofrelationship with their expanded aggregate attribute values. Given:

class Person < ActiveRecord::Base
  composed_of :address, :class_name => "Address",
    :mapping => [%w(address_street street), %w(address_city city)]


{ :address =>"813 abc st.", "chicago") }
  # => { :address_street => "813 abc st.", :address_city => "chicago" }
# File activerecord/lib/active_record/base.rb, line 2307
def expand_hash_conditions_for_aggregates(attrs)
  expanded_attrs = {}
  attrs.each do |attr, value|
    unless (aggregation = reflect_on_aggregation(attr)).nil?
      mapping = aggregate_mapping(aggregation)
      mapping.each do |field_attr, aggregate_attr|
        if mapping.size == 1 && !value.respond_to?(aggregate_attr)
          expanded_attrs[field_attr] = value
          expanded_attrs[field_attr] = value.send(aggregate_attr)
      expanded_attrs[attr] = value
sanitize_conditions(condition, table_name = quoted_table_name)
sanitize_sql(condition, table_name = quoted_table_name)
Also aliased as: sanitize_conditions

Accepts an array of conditions. The array has each value sanitized and interpolated into the SQL statement.

["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"
# File activerecord/lib/active_record/base.rb, line 2383
def sanitize_sql_array(ary)
  statement, *values = ary
  if values.first.is_a?(Hash) and statement =~ /:\w+/
    replace_named_bind_variables(statement, values.first)
  elsif statement.include?('?')
    replace_bind_variables(statement, values)
    statement % values.collect { |value| connection.quote_string(value.to_s) }

Accepts an array, hash, or string of SQL conditions and sanitizes them into a valid SQL fragment for a SET clause.

{ :name => nil, :group_id => 4 }  returns "name = NULL , group_id='4'"
# File activerecord/lib/active_record/base.rb, line 2283
def sanitize_sql_for_assignment(assignments)
  case assignments
    when Array; sanitize_sql_array(assignments)
    when Hash;  sanitize_sql_hash_for_assignment(assignments)
    else        assignments
sanitize_sql_for_conditions(condition, table_name = quoted_table_name)

Accepts an array, hash, or string of SQL conditions and sanitizes them into a valid SQL fragment for a WHERE clause.

["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"
{ :name => "foo'bar", :group_id => 4 }  returns "name='foo''bar' and group_id='4'"
"name='foo''bar' and group_id='4'" returns "name='foo''bar' and group_id='4'"
Also aliased as: sanitize_sql
# File activerecord/lib/active_record/base.rb, line 2269
def sanitize_sql_for_conditions(condition, table_name = quoted_table_name)
  return nil if condition.blank?
  case condition
    when Array; sanitize_sql_array(condition)
    when Hash;  sanitize_sql_hash_for_conditions(condition, table_name)
    else        condition
sanitize_sql_hash(attrs, default_table_name = quoted_table_name, top_level = true)

Sanitizes a hash of attribute/value pairs into SQL conditions for a SET clause.

{ :status => nil, :group_id => 1 }
  # => "status = NULL , group_id = 1"
# File activerecord/lib/active_record/base.rb, line 2374
def sanitize_sql_hash_for_assignment(attrs) do |attr, value|
    "#{connection.quote_column_name(attr)} = #{quote_bound_value(value)}"
  end.join(', ')
sanitize_sql_hash_for_conditions(attrs, default_table_name = quoted_table_name, top_level = true)

Sanitizes a hash of attribute/value pairs into SQL conditions for a WHERE clause.

{ :name => "foo'bar", :group_id => 4 }
  # => "name='foo''bar' and group_id= 4"
{ :status => nil, :group_id => [1,2,3] }
  # => "status IS NULL and group_id IN (1,2,3)"
{ :age => 13..18 }
  # => "age BETWEEN 13 AND 18"
{ '' => 7 }
  # => "`other_records`.`id` = 7"
{ :other_records => { :id => 7 } }
  # => "`other_records`.`id` = 7"

And for value objects on a composed_of relationship:

{ :address =>"123 abc st.", "chicago") }
  # => "address_street='123 abc st.' and address_city='chicago'"
Also aliased as: sanitize_sql_hash
# File activerecord/lib/active_record/base.rb, line 2340
def sanitize_sql_hash_for_conditions(attrs, default_table_name = quoted_table_name, top_level = true)
  attrs = expand_hash_conditions_for_aggregates(attrs)
  return '1 = 2' if !top_level && attrs.is_a?(Hash) && attrs.empty?
  conditions = do |attr, value|
    table_name = default_table_name
    if not value.is_a?(Hash)
      attr = attr.to_s
      # Extract table name from qualified attribute names.
      if attr.include?('.') and top_level
        attr_table_name, attr = attr.split('.', 2)
        attr_table_name = connection.quote_table_name(attr_table_name)
        attr_table_name = table_name
      attribute_condition("#{attr_table_name}.#{connection.quote_column_name(attr)}", value)
    elsif top_level
      sanitize_sql_hash_for_conditions(value, connection.quote_table_name(attr.to_s), false)
      raise ActiveRecord::StatementInvalid
  end.join(' AND ')
  replace_bind_variables(conditions, expand_range_bind_variables(attrs.values))
with_exclusive_scope(method_scoping = {}, &block)

Works like ::with_scope, but discards any nested properties.

# File activerecord/lib/active_record/base.rb, line 2193
def with_exclusive_scope(method_scoping = {}, &block)
  with_scope(method_scoping, :overwrite, &block)
with_scope(method_scoping = {}, action = :merge, &block)

Scope parameters to method calls within the block. Takes a hash of method_name => parameters hash. method_name may be :findor :create. :findparameters may include the :conditions, :joins, :include, :offset, :limit, and :readonly options. :createparameters are an attributes hash.

class Article < ActiveRecord::Base
  def self.create_with_scope
    with_scope(:find => { :conditions => "blog_id = 1" }, :create => { :blog_id => 1 }) do
      find(1) # => SELECT * from articles WHERE blog_id = 1 AND id = 1
      a = create(1)
      a.blog_id # => 1

In nested scopings, all previous parameters are overwritten by the innermost rule, with the exception of :conditions, :include, and :joinsoptions in :find, which are merged.

:joinsoptions are uniqued so multiple scopes can join in the same table without table aliasing problems. If you need to join multiple tables, but still want one of the tables to be uniqued, use the array of strings format for your joins.

class Article < ActiveRecord::Base
  def self.find_with_scope
    with_scope(:find => { :conditions => "blog_id = 1", :limit => 1 }, :create => { :blog_id => 1 }) do
      with_scope(:find => { :limit => 10 })
        find(:all) # => SELECT * from articles WHERE blog_id = 1 LIMIT 10
      with_scope(:find => { :conditions => "author_id = 3" })
        find(:all) # => SELECT * from articles WHERE blog_id = 1 AND author_id = 3 LIMIT 1

You can ignore any previous scopings by using the with_exclusive_scopemethod.

class Article < ActiveRecord::Base
  def self.find_with_exclusive_scope
    with_scope(:find => { :conditions => "blog_id = 1", :limit => 1 }) do
      with_exclusive_scope(:find => { :limit => 10 })
        find(:all) # => SELECT * from articles LIMIT 10

Note: the :findscope also has effect on update and deletion methods, like update_alland delete_all.

# File activerecord/lib/active_record/base.rb, line 2132
def with_scope(method_scoping = {}, action = :merge, &block)
  method_scoping = method_scoping.method_scoping if method_scoping.respond_to?(:method_scoping)
  # Dup first and second level of hash (method and params).
  method_scoping = method_scoping.inject({}) do |hash, (method, params)|
    hash[method] = (params == true) ? params : params.dup
  method_scoping.assert_valid_keys([ :find, :create ])
  if f = method_scoping[:find]
    set_readonly_option! f
  # Merge scopings
  if [:merge, :reverse_merge].include?(action) && current_scoped_methods
    method_scoping = current_scoped_methods.inject(method_scoping) do |hash, (method, params)|
      case hash[method]
        when Hash
          if method == :find
            (hash[method].keys + params.keys).uniq.each do |key|
              merge = hash[method][key] && params[key] # merge if both scopes have the same key
              if key == :conditions && merge
                if params[key].is_a?(Hash) && hash[method][key].is_a?(Hash)
                  hash[method][key] = merge_conditions(hash[method][key].deep_merge(params[key]))
                  hash[method][key] = merge_conditions(params[key], hash[method][key])
              elsif key == :include && merge
                hash[method][key] = merge_includes(hash[method][key], params[key]).uniq
              elsif key == :joins && merge
                hash[method][key] = merge_joins(params[key], hash[method][key])
                hash[method][key] = hash[method][key] || params[key]
            if action == :reverse_merge
              hash[method] = hash[method].merge(params)
              hash[method] = params.merge(hash[method])
          hash[method] = params
  self.scoped_methods << method_scoping
Instance Public methods

Returns true if the comparison_objectis the same object, or is of the same type and has the same id.

# File activerecord/lib/active_record/base.rb, line 2861
def ==(comparison_object)
  comparison_object.equal?(self) ||
    (comparison_object.instance_of?(self.class) && == id &&

Returns the value of the attribute identified by attr_name after it has been typecast (for example, “2004-12-12” in a data column is cast to a date object, like, 12, 12)). (Alias for the protected read_attribute method).

# File activerecord/lib/active_record/base.rb, line 2759
def [](attr_name)
[]=(attr_name, value)

Updates the attribute identified by attr_namewith the specified value. (Alias for the protected write_attribute method).

# File activerecord/lib/active_record/base.rb, line 2765
def []=(attr_name, value)
  write_attribute(attr_name, value)

Returns an #inspect-like string for the value of the attribute attr_name. String attributes are elided after 50 characters, and Date and Time attributes are returned in the :dbformat. Other attributes return the value of #inspectwithout modification.

person = Person.create!(:name => "David Heinemeier Hansson " * 3)
# => '"David Heinemeier Hansson David Heinemeier Hansson D..."'
# => '"2009-01-12 04:48:57"'
# File activerecord/lib/active_record/base.rb, line 2826
def attribute_for_inspect(attr_name)
  value = read_attribute(attr_name)
  if value.is_a?(String) && value.length > 50
  elsif value.is_a?(Date) || value.is_a?(Time)

Returns an array of names for the attributes available on this object sorted alphabetically.

# File activerecord/lib/active_record/base.rb, line 2851
def attribute_names

Returns true if the specified attributehas been set by the user or by a database load and is neither nil nor empty? (the latter only applies to objects that respond to empty?, most notably Strings).

# File activerecord/lib/active_record/base.rb, line 2840
def attribute_present?(attribute)
  value = read_attribute(attribute)

Returns a hash of all the attributes with their names as keys and the values of the attributes as values.

# File activerecord/lib/active_record/base.rb, line 2799
def attributes
  attrs = {}
  attribute_names.each { |name| attrs[name] = read_attribute(name) }
attributes=(new_attributes, guard_protected_attributes = true)

Allows you to set all the attributes at once by passing in a hash with keys matching the attribute names (which again matches the column names).

If guard_protected_attributesis true (the default), then sensitive attributes can be protected from this form of mass-assignment by using the attr_protectedmacro. Or you can alternatively specify which attributes canbe accessed with the attr_accessiblemacro. Then all the attributes not included in that won't be allowed to be mass-assigned.

class User < ActiveRecord::Base
  attr_protected :is_admin
user =
user.attributes = { :username => 'Phusion', :is_admin => true }
user.username   # => "Phusion"
user.is_admin?  # => false
user.send(:attributes=, { :username => 'Phusion', :is_admin => true }, false)
user.is_admin?  # => true
# File activerecord/lib/active_record/base.rb, line 2789
def attributes=(new_attributes, guard_protected_attributes = true)
  return if new_attributes.nil?
  attributes = new_attributes.dup
  attributes = remove_attributes_protected_from_mass_assignment(attributes) if guard_protected_attributes
  assign_attributes(attributes) if attributes and attributes.any?

Returns a hash of attributes before typecasting and deserialization.

# File activerecord/lib/active_record/base.rb, line 2806
def attributes_before_type_cast
  self.attribute_names.inject({}) do |attrs, name|
    attrs[name] = read_attribute_before_type_cast(name)

Returns an instance of the specified klasswith the attributes of the current record. This is mostly useful in relation to single-table inheritance structures where you want a subclass to appear as the superclass. This can be used along with record identification in Action Pack to allow, say, Client < Companyto do something like render :partial => @client.becomes(Company)to render that instance using the companies/company partial instead of clients/client.

Note: The new instance will share a link to the same attributes as the original class. So any change to the attributes in either instance will affect the other.

# File activerecord/lib/active_record/base.rb, line 2656
def becomes(klass) do |became|
    became.instance_variable_set("@attributes", @attributes)
    became.instance_variable_set("@attributes_cache", @attributes_cache)
    became.instance_variable_set("@new_record", new_record?)

Returns a cache key that can be used to identify this record.

Examples     # => "products/new"
Product.find(5).cache_key # => "products/5" (updated_at not available)
Person.find(5).cache_key  # => "people/5-20071224150000" (updated_at available)
# File activerecord/lib/active_record/base.rb, line 2538
def cache_key
  when new_record?
  when timestamp = self[:updated_at]

Returns a clone of the record that hasn't been assigned an id yet and is treated as a new record. Note that this is a “shallow” clone: it copies the object's attributes only, not its associations. The extent of a “deep” clone is application-specific and is therefore left to the application to implement according to its need.

# File activerecord/lib/active_record/base.rb, line 2641
def clone
  attrs = clone_attributes(:read_attribute_before_type_cast)
  record =
  record.send :instance_variable_set, '@attributes', attrs

Returns the column object for the named attribute.

# File activerecord/lib/active_record/base.rb, line 2856
def column_for_attribute(name)

Returns the connection currently associated with the class. This can also be used to “borrow” the connection to do database work that isn't easily done without going straight to SQL.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb, line 19
def connection
decrement(attribute, by = 1)

Initializes attributeto zero if niland subtracts the value passed as by(default is 1). The decrement is performed directly on the underlying attribute, no setter is invoked. Only makes sense for number-based attributes. Returns self.

# File activerecord/lib/active_record/base.rb, line 2713
def decrement(attribute, by = 1)
  self[attribute] ||= 0
  self[attribute] -= by
decrement!(attribute, by = 1)

Wrapper around decrementthat saves the record. This method differs from its non-bang version in that it passes through the attribute setter. Saving is not subjected to validation checks. Returns trueif the record could be saved.

# File activerecord/lib/active_record/base.rb, line 2723
def decrement!(attribute, by = 1)
  decrement(attribute, by).update_attribute(attribute, self[attribute])

Deletes the record in the database and freezes this instance to reflect that no changes should be made (since they can't be persisted). Returns the frozen instance.

The row is simply removed with a SQL DELETEstatement on the record's primary key, and no callbacks are executed.

To enforce the object's before_destroyand after_destroycallbacks, Observer methods, or any :dependentassociation options, use #destroy.

# File activerecord/lib/active_record/base.rb, line 2615
def delete
  self.class.delete(id) unless new_record?
  @destroyed = true

Deletes the record in the database and freezes this instance to reflect that no changes should be made (since they can't be persisted).

# File activerecord/lib/active_record/base.rb, line 2623
def destroy
  unless new_record?
      "DELETE FROM #{self.class.quoted_table_name} " +
      "WHERE #{connection.quote_column_name(self.class.primary_key)} = #{quoted_id}",
      "#{} Destroy"
  @destroyed = true

Returns trueif the record has been destroyed.

# File activerecord/lib/active_record/base.rb, line 2890
def destroyed?

Delegates to ==

# File activerecord/lib/active_record/base.rb, line 2869
def eql?(comparison_object)
  self == (comparison_object)

Freeze the attributes hash such that associations are still accessible, even on destroyed records.

# File activerecord/lib/active_record/base.rb, line 2880
def freeze
  @attributes.freeze; self

Returns trueif the attributes hash has been frozen.

# File activerecord/lib/active_record/base.rb, line 2885
def frozen?

Returns true if the given attribute is in the attributes hash

# File activerecord/lib/active_record/base.rb, line 2846
def has_attribute?(attr_name)

Delegates to id in order to allow two records of the same type and id to work with something like:

[ Person.find(1), Person.find(2), Person.find(3) ] & [ Person.find(1), Person.find(4) ] # => [ Person.find(1) ]
# File activerecord/lib/active_record/base.rb, line 2875
def hash

A model instance's primary key is always available as whether you name it the default 'id' or set it to something else.

# File activerecord/lib/active_record/base.rb, line 2494
def id
  attr_name = self.class.primary_key
  column = column_for_attribute(attr_name)
  self.class.send(:define_read_method, :id, attr_name, column)
  # now that the method exists, call it
  self.send attr_name.to_sym

Sets the primary ID.

# File activerecord/lib/active_record/base.rb, line 2558
def id=(value)
  write_attribute(self.class.primary_key, value)
increment(attribute, by = 1)

Initializes attributeto zero if niland adds the value passed as by(default is 1). The increment is performed directly on the underlying attribute, no setter is invoked. Only makes sense for number-based attributes. Returns self.

# File activerecord/lib/active_record/base.rb, line 2696
def increment(attribute, by = 1)
  self[attribute] ||= 0
  self[attribute] += by
increment!(attribute, by = 1)

Wrapper around incrementthat saves the record. This method differs from its non-bang version in that it passes through the attribute setter. Saving is not subjected to validation checks. Returns trueif the record could be saved.

# File activerecord/lib/active_record/base.rb, line 2706
def increment!(attribute, by = 1)
  increment(attribute, by).update_attribute(attribute, self[attribute])

Returns the contents of the record as a nicely formatted string.

# File activerecord/lib/active_record/base.rb, line 2906
def inspect
  attributes_as_nice_string = self.class.column_names.collect { |name|
    if has_attribute?(name) || new_record?
      "#{name}: #{attribute_for_inspect(name)}"
  }.compact.join(", ")
  "#<#{self.class} #{attributes_as_nice_string}>"

Returns true if this object hasn't been saved yet – that is, a record for the object doesn't exist yet; otherwise, returns false.

# File activerecord/lib/active_record/base.rb, line 2563
def new_record?
  @new_record || false

Marks this record as read only.

# File activerecord/lib/active_record/base.rb, line 2901
def readonly!
  @readonly = true

Returns trueif the record is read only. Records loaded through joins with piggy-back attributes will be marked as read only since they cannot be saved.

# File activerecord/lib/active_record/base.rb, line 2896
def readonly?
  defined?(@readonly) && @readonly == true
reload(options = nil)

Reloads the attributes of this object from the database. The optional options argument is passed to find when reloading so you may do e.g. record.reload(:lock => true) to reload the same record with an exclusive row lock.

# File activerecord/lib/active_record/base.rb, line 2748
def reload(options = nil)
  @attributes.update(self.class.send(:with_exclusive_scope) { self.class.find(, options) }.instance_variable_get('@attributes'))
  @attributes_cache = {}
save(perform_validation = true)

Saves the model.

If the model is new a record gets created in the database, otherwise the existing record gets updated.

If perform_validationis true validations run. If any of them fail the action is cancelled and savereturns false. If the flag is false validations are bypassed altogether. See ActiveRecord::Validations for more information.

There's a series of callbacks associated with save. If any of the before_*callbacks return falsethe action is cancelled and savereturns false. See ActiveRecord::Callbacks for further details.

# File activerecord/lib/active_record/base.rb, line 2584
def save

Saves the model.

If the model is new a record gets created in the database, otherwise the existing record gets updated.

With save!validations always run. If any of them fail ActiveRecord::RecordInvalid gets raised. See ActiveRecord::Validations for more information.

There's a series of callbacks associated with save!. If any of the before_*callbacks return falsethe action is cancelled and save!raises ActiveRecord::RecordNotSaved. See ActiveRecord::Callbacks for further details.

# File activerecord/lib/active_record/base.rb, line 2601
def save!
  create_or_update || raise(RecordNotSaved)

Returns a String, which Action Pack uses for constructing an URL to this object. The default implementation returns this record's id as a String, or nil if this record's unsaved.

For example, suppose that you have a User model, and that you have a map.resources :usersroute. Normally, user_path will construct a path with the user object's 'id' in it:

user = User.find_by_name('Phusion')
user_path(user)  # => "/users/1"

You can override to_paramin your model to make user_pathconstruct a path using the user's name instead of the user's id:

class User < ActiveRecord::Base
  def to_param  # overridden
user = User.find_by_name('Phusion')
user_path(user)  # => "/users/Phusion"
# File activerecord/lib/active_record/base.rb, line 2526
def to_param
  # We can't use alias_method here, because method 'id' optimizes itself on the fly.
  (id = ? id.to_s : nil # Be sure to stringify the id for routes

Assigns to attributethe boolean opposite of attribute?. So if the predicate returns truethe attribute will become false. This method toggles directly the underlying value without calling any setter. Returns self.

# File activerecord/lib/active_record/base.rb, line 2731
def toggle(attribute)
  self[attribute] = !send("#{attribute}?")

Wrapper around togglethat saves the record. This method differs from its non-bang version in that it passes through the attribute setter. Saving is not subjected to validation checks. Returns trueif the record could be saved.

# File activerecord/lib/active_record/base.rb, line 2740
def toggle!(attribute)
  toggle(attribute).update_attribute(attribute, self[attribute])
update_attribute(name, value)

Updates a single attribute and saves the record without going through the normal validation procedure. This is especially useful for boolean flags on existing records. The regular update_attributemethod in Base is replaced with this when the validations module is mixed in, which it is by default.

# File activerecord/lib/active_record/base.rb, line 2667
def update_attribute(name, value)
  send(name.to_s + '=', value)

Updates all the attributes from the passed-in Hash and saves the record. If the object is invalid, the saving will fail and false will be returned.

# File activerecord/lib/active_record/base.rb, line 2674
def update_attributes(attributes)
  with_transaction_returning_status(:update_attributes_inside_transaction, attributes)

Updates an object just like #update_attributes but calls save! instead of save so an exception is raised if the record is invalid.

# File activerecord/lib/active_record/base.rb, line 2684
def update_attributes!(attributes)
  with_transaction_returning_status(:update_attributes_inside_transaction!, attributes)