Active Record Attribute Methods

Namespace
Methods
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Included Modules
Instance Public methods
[](attr_name)

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 Date.new(2004, 12, 12)). It raises ActiveModel::MissingAttributeErrorif the identified attribute is missing.

Alias for the read_attributemethod.

class Person < ActiveRecord::Base
  belongs_to :organization
end

person = Person.new(name: 'Francesco', age: '22')
person[:name] # => "Francesco"
person[:age]  # => 22

person = Person.select('id').first
person[:name]            # => ActiveModel::MissingAttributeError: missing attribute: name
person[:organization_id] # => ActiveModel::MissingAttributeError: missing attribute: organization_id
# File activerecord/lib/active_record/attribute_methods.rb, line 326
def [](attr_name)
  read_attribute(attr_name) { |n| missing_attribute(n, caller) }
end
[]=(attr_name, value)

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

class Person < ActiveRecord::Base
end

person = Person.new
person[:age] = '22'
person[:age] # => 22
person[:age] # => Fixnum
# File activerecord/lib/active_record/attribute_methods.rb, line 340
def []=(attr_name, value)
  write_attribute(attr_name, value)
end
attribute_for_inspect(attr_name)

Returns an #inspect-like string for the value of the attribute attr_name. String attributes are truncated upto 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)

person.attribute_for_inspect(:name)
# => "\"David Heinemeier Hansson David Heinemeier Hansson D...\""

person.attribute_for_inspect(:created_at)
# => "\"2012-10-22 00:15:07\""
# File activerecord/lib/active_record/attribute_methods.rb, line 260
def attribute_for_inspect(attr_name)
  value = read_attribute(attr_name)

  if value.is_a?(String) && value.length > 50
    "#{value[0..50]}...".inspect
  elsif value.is_a?(Date) || value.is_a?(Time)
    %Q("#{value.to_s(:db)}")
  else
    value.inspect
  end
end
attribute_names()

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

class Person < ActiveRecord::Base
end

person = Person.new
person.attribute_names
# => ["id", "created_at", "updated_at", "name", "age"]
# File activerecord/lib/active_record/attribute_methods.rb, line 229
def attribute_names
  @attributes.keys
end
attribute_present?(attribute)

Returns trueif the specified attributehas been set by the user or by a database load and is neither nilnor empty?(the latter only applies to objects that respond to empty?, most notably Strings). Otherwise, false. Note that it always returns truewith boolean attributes.

class Task < ActiveRecord::Base
end

person = Task.new(title: '', is_done: false)
person.attribute_present?(:title)   # => false
person.attribute_present?(:is_done) # => true
person.name = 'Francesco'
person.is_done = true
person.attribute_present?(:title)   # => true
person.attribute_present?(:is_done) # => true
# File activerecord/lib/active_record/attribute_methods.rb, line 287
def attribute_present?(attribute)
  value = read_attribute(attribute)
  !value.nil? && !(value.respond_to?(:empty?) && value.empty?)
end
attributes()

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

class Person < ActiveRecord::Base
end

person = Person.create(name: 'Francesco', age: 22)
person.attributes
# => {"id"=>3, "created_at"=>Sun, 21 Oct 2012 04:53:04, "updated_at"=>Sun, 21 Oct 2012 04:53:04, "name"=>"Francesco", "age"=>22}
# File activerecord/lib/active_record/attribute_methods.rb, line 241
def attributes
  attribute_names.each_with_object({}) { |name, attrs|
    attrs[name] = read_attribute(name)
  }
end
column_for_attribute(name)

Returns the column object for the named attribute. Returns nil if the named attribute not exists.

class Person < ActiveRecord::Base
end

person = Person.new
person.column_for_attribute(:name) # the result depends on the ConnectionAdapter
# => #<ActiveRecord::ConnectionAdapters::SQLite3Column:0x007ff4ab083980 @name="name", @sql_type="varchar(255)", @null=true, ...>

person.column_for_attribute(:nothing)
# => nil
# File activerecord/lib/active_record/attribute_methods.rb, line 304
def column_for_attribute(name)
  # FIXME: should this return a null object for columns that don't exist?
  self.class.columns_hash[name.to_s]
end
has_attribute?(attr_name)

Returns trueif the given attribute is in the attributes hash, otherwise false.

class Person < ActiveRecord::Base
end

person = Person.new
person.has_attribute?(:name)    # => true
person.has_attribute?('age')    # => true
person.has_attribute?(:nothing) # => false
# File activerecord/lib/active_record/attribute_methods.rb, line 217
def has_attribute?(attr_name)
  @attributes.has_key?(attr_name.to_s)
end
respond_to?(name, include_private = false)

A Person object with a name attribute can ask person.respond_to?(:name), person.respond_to?(:name=), and person.respond_to?(:name?)which will all return true. It also define the attribute methods if they have not been generated.

class Person < ActiveRecord::Base
end

person = Person.new
person.respond_to(:name)    # => true
person.respond_to(:name=)   # => true
person.respond_to(:name?)   # => true
person.respond_to('age')    # => true
person.respond_to('age=')   # => true
person.respond_to('age?')   # => true
person.respond_to(:nothing) # => false
# File activerecord/lib/active_record/attribute_methods.rb, line 189
def respond_to?(name, include_private = false)
  name = name.to_s
  self.class.define_attribute_methods unless self.class.attribute_methods_generated?
  result = super

  # If the result is false the answer is false.
  return false unless result

  # If the result is true then check for the select case.
  # For queries selecting a subset of columns, return false for unselected columns.
  # We check defined?(@attributes) not to issue warnings if called on objects that
  # have been allocated but not yet initialized.
  if defined?(@attributes) && @attributes.present? && self.class.column_names.include?(name)
    return has_attribute?(name)
  end

  return true
end