Methods
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Instance Public methods
add_column(table_name, column_name, type, options = {})

Adds a new column to the named table. See ActiveRecord::ConnectionAdapters::TableDefinition#column for details of the options you can use.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 187
def add_column(table_name, column_name, type, options = {})
  add_column_sql = "ALTER TABLE #{quote_table_name(table_name)} ADD #{quote_column_name(column_name)} #{type_to_sql(type, options[:limit], options[:precision], options[:scale])}"
  add_column_options!(add_column_sql, options)
  execute(add_column_sql)
end
add_index(table_name, column_name, options = {})

Adds a new index to the table. column_namecan be a single Symbol, or an Array of Symbols.

The index will be named after the table and the first column name, unless you pass :nameas an option.

When creating an index on multiple columns, the first column is used as a name for the index. For example, when you specify an index on two columns [ :first, :last], the DBMS creates an index for both columns as well as an index for the first column :first. Using just the first name for this index makes sense, because you will never have to create a singular index with this name.

Examples
Creating a simple index
add_index(:suppliers, :name)

generates

CREATE INDEX suppliers_name_index ON suppliers(name)
Creating a unique index
add_index(:accounts, [:branch_id, :party_id], :unique => true)

generates

CREATE UNIQUE INDEX accounts_branch_id_party_id_index ON accounts(branch_id, party_id)
Creating a named index
add_index(:accounts, [:branch_id, :party_id], :unique => true, :name => 'by_branch_party')

generates

CREATE UNIQUE INDEX by_branch_party ON accounts(branch_id, party_id)
Creating an index with specific key length
add_index(:accounts, :name, :name => 'by_name', :length => 10)

generates

CREATE INDEX by_name ON accounts(name(10))
add_index(:accounts, [:name, :surname], :name => 'by_name_surname', :length => {:name => 10, :surname => 15})

generates

CREATE INDEX by_name_surname ON accounts(name(10), surname(15))

Note: SQLite doesn't support index length

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 271
def add_index(table_name, column_name, options = {})
  column_names = Array(column_name)
  index_name   = index_name(table_name, :column => column_names)
  if Hash === options # legacy support, since this param was a string
    index_type = options[:unique] ? "UNIQUE" : ""
    index_name = options[:name].to_s if options[:name]
  else
    index_type = options
  end
  if index_name.length > index_name_length
    @logger.warn("Index name '#{index_name}' on table '#{table_name}' is too long; the limit is #{index_name_length} characters. Skipping.")
    return
  end
  if index_exists?(table_name, index_name, false)
    @logger.warn("Index name '#{index_name}' on table '#{table_name}' already exists. Skipping.")
    return
  end
  quoted_column_names = quoted_columns_for_index(column_names, options).join(", ")
  execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{quoted_column_names})"
end
add_order_by_for_association_limiting!(sql, options)

ORDER BY clause for the passed order option. PostgreSQL overrides this due to its stricter standards compliance.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 459
def add_order_by_for_association_limiting!(sql, options)
  sql << " ORDER BY #{options[:order]}"
end
add_timestamps(table_name)

Adds timestamps (created_at and updated_at) columns to the named table.

Examples
add_timestamps(:suppliers)
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 466
def add_timestamps(table_name)
  add_column table_name, :created_at, :datetime
  add_column table_name, :updated_at, :datetime
end
assume_migrated_upto_version(version, migrations_path = ActiveRecord::Migrator.migrations_path)
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 390
def assume_migrated_upto_version(version, migrations_path = ActiveRecord::Migrator.migrations_path)
  version = version.to_i
  sm_table = quote_table_name(ActiveRecord::Migrator.schema_migrations_table_name)
  migrated = select_values("SELECT version FROM #{sm_table}").map(&:to_i)
  versions = Dir["#{migrations_path}/[0-9]*_*.rb"].map do |filename|
    filename.split('/').last.split('_').first.to_i
  end
  unless migrated.include?(version)
    execute "INSERT INTO #{sm_table} (version) VALUES ('#{version}')"
  end
  inserted = Set.new
  (versions - migrated).each do |v|
    if inserted.include?(v)
      raise "Duplicate migration #{v}. Please renumber your migrations to resolve the conflict."
    elsif v < version
      execute "INSERT INTO #{sm_table} (version) VALUES ('#{v}')"
      inserted << v
    end
  end
end
change_column(table_name, column_name, type, options = {})

Changes the column's definition according to the new options. See ActiveRecord::ConnectionAdapters::TableDefinition#column for details of the options you can use.

Examples
change_column(:suppliers, :name, :string, :limit => 80)
change_column(:accounts, :description, :text)
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 210
def change_column(table_name, column_name, type, options = {})
  raise NotImplementedError, "change_column is not implemented"
end
change_column_default(table_name, column_name, default)

Sets a new default value for a column. If you want to set the default value to NULL, you are out of luck. You need to ActiveRecord::ConnectionAdapters::DatabaseStatements#execute the appropriate SQL statement yourself.

Examples
change_column_default(:suppliers, :qualification, 'new')
change_column_default(:accounts, :authorized, 1)
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 220
def change_column_default(table_name, column_name, default)
  raise NotImplementedError, "change_column_default is not implemented"
end
change_table(table_name)

A block for changing columns in table.

Example

# change_table() yields a Table instance
change_table(:suppliers) do |t|
  t.column :name, :string, :limit => 60
  # Other column alterations here
end
Examples
Add a column
change_table(:suppliers) do |t|
  t.column :name, :string, :limit => 60
end
Add 2 integer columns
change_table(:suppliers) do |t|
  t.integer :width, :height, :null => false, :default => 0
end
Add created_at/updated_at columns
change_table(:suppliers) do |t|
  t.timestamps
end
Add a foreign key column
change_table(:suppliers) do |t|
  t.references :company
end

Creates a company_id(integer)column

Add a polymorphic foreign key column
change_table(:suppliers) do |t|
  t.belongs_to :company, :polymorphic => true
end

Creates company_type(varchar)and company_id(integer)columns

Remove a column
change_table(:suppliers) do |t|
  t.remove :company
end
Remove several columns
change_table(:suppliers) do |t|
  t.remove :company_id
  t.remove :width, :height
end
Remove an index
change_table(:suppliers) do |t|
  t.remove_index :company_id
end

See also Table for details on all of the various column transformation

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 169
def change_table(table_name)
  yield Table.new(table_name, self)
end
columns(table_name, name = nil)

Returns an array of Column objects for the table specified by table_name. See the concrete implementation for details on the expected parameter values.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 27
def columns(table_name, name = nil) end
create_table(table_name, options = {})

Creates a new table with the name table_name. table_namemay either be a String or a Symbol.

There are two ways to work with create_table. You can use the block form or the regular form, like this:

Block form

# create_table() passes a TableDefinition object to the block.
# This form will not only create the table, but also columns for the
# table.
create_table(:suppliers) do |t|
  t.column :name, :string, :limit => 60
  # Other fields here
end

Regular form

# Creates a table called 'suppliers' with no columns.
create_table(:suppliers)
# Add a column to 'suppliers'.
add_column(:suppliers, :name, :string, {:limit => 60})

The optionshash can include the following keys:

:id

Whether to automatically add a primary key column. Defaults to true. Join tables for has_and_belongs_to_manyshould set :id => false .

:primary_key

The name of the primary key, if one is to be added automatically. Defaults to id.

:options

Any extra options you want appended to the table definition.

:temporary

Make a temporary table.

:force

Set to true to drop the table before creating it. Defaults to false.

Examples
Add a backend specific option to the generated SQL (MySQL)
create_table(:suppliers, :options => 'ENGINE=InnoDB DEFAULT CHARSET=utf8')

generates:

CREATE TABLE suppliers (
  id int(11) DEFAULT NULL auto_increment PRIMARY KEY
) ENGINE=InnoDB DEFAULT CHARSET=utf8
Rename the primary key column
create_table(:objects, :primary_key => 'guid') do |t|
  t.column :name, :string, :limit => 80
end

generates:

CREATE TABLE objects (
  guid int(11) DEFAULT NULL auto_increment PRIMARY KEY,
  name varchar(80)
)
Do not add a primary key column
create_table(:categories_suppliers, :id => false) do |t|
  t.column :category_id, :integer
  t.column :supplier_id, :integer
end

generates:

CREATE TABLE categories_suppliers (
  category_id int,
  supplier_id int
)

See also ActiveRecord::ConnectionAdapters::TableDefinition#column for details on how to create columns.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 95
def create_table(table_name, options = {})
  table_definition = TableDefinition.new(self)
  table_definition.primary_key(options[:primary_key] || Base.get_primary_key(table_name.to_s.singularize)) unless options[:id] == false
  yield table_definition if block_given?
  if options[:force] && table_exists?(table_name)
    drop_table(table_name, options)
  end
  create_sql = "CREATE#{' TEMPORARY' if options[:temporary]} TABLE "
  create_sql << "#{quote_table_name(table_name)} ("
  create_sql << table_definition.to_sql
  create_sql << ") #{options[:options]}"
  execute create_sql
end
distinct(columns, order_by)

SELECT DISTINCT clause for a given set of columns and a given ORDER BY clause. Both PostgreSQL and Oracle overrides this for custom DISTINCT syntax.

distinct("posts.id", "posts.created_at desc")
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 453
def distinct(columns, order_by)
  "DISTINCT #{columns}"
end
drop_table(table_name, options = {})

Drops a table from the database.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 181
def drop_table(table_name, options = {})
  execute "DROP TABLE #{quote_table_name(table_name)}"
end
index_exists?(table_name, index_name, default)

Verify the existence of an index.

The default argument is returned if the underlying implementation does not define the indexes method, as there's no way to determine the correct answer in that case.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 348
def index_exists?(table_name, index_name, default)
  return default unless respond_to?(:indexes)
  index_name = index_name.to_s
  indexes(table_name).detect { |i| i.name == index_name }
end
initialize_schema_migrations_table()

Should not be called normally, but this operation is non-destructive. The migrations module handles this automatically.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 367
def initialize_schema_migrations_table
  sm_table = ActiveRecord::Migrator.schema_migrations_table_name
  unless tables.detect { |t| t == sm_table }
    create_table(sm_table, :id => false) do |schema_migrations_table|
      schema_migrations_table.column :version, :string, :null => false
    end
    add_index sm_table, :version, :unique => true,
      :name => "#{Base.table_name_prefix}unique_schema_migrations#{Base.table_name_suffix}"
    # Backwards-compatibility: if we find schema_info, assume we've
    # migrated up to that point:
    si_table = Base.table_name_prefix + 'schema_info' + Base.table_name_suffix
    if tables.detect { |t| t == si_table }
      old_version = select_value("SELECT version FROM #{quote_table_name(si_table)}").to_i
      assume_migrated_upto_version(old_version)
      drop_table(si_table)
    end
  end
end
native_database_types()

Returns a Hash of mappings from the abstract data types to the native database types. See ActiveRecord::ConnectionAdapters::TableDefinition#column for details on the recognized abstract data types.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 7
def native_database_types
  {}
end
remove_column(table_name, *column_names)

Removes the column(s) from the table definition.

Examples
remove_column(:suppliers, :qualification)
remove_columns(:suppliers, :qualification, :experience)
Also aliased as: remove_columns
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 197
def remove_column(table_name, *column_names)
  raise ArgumentError.new("You must specify at least one column name.  Example: remove_column(:people, :first_name)") if column_names.empty?
  column_names.flatten.each do |column_name|
    execute "ALTER TABLE #{quote_table_name(table_name)} DROP #{quote_column_name(column_name)}"
  end
end
remove_columns(table_name, *column_names)
remove_index(table_name, options = {})

Remove the given index from the table.

Remove the suppliers_name_index in the suppliers table.

remove_index :suppliers, :name

Remove the index named accounts_branch_id_index in the accounts table.

remove_index :accounts, :column => :branch_id

Remove the index named accounts_branch_id_party_id_index in the accounts table.

remove_index :accounts, :column => [:branch_id, :party_id]

Remove the index named by_branch_party in the accounts table.

remove_index :accounts, :name => :by_branch_party
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 305
def remove_index(table_name, options = {})
  index_name = index_name(table_name, options)
  unless index_exists?(table_name, index_name, true)
    @logger.warn("Index name '#{index_name}' on table '#{table_name}' does not exist. Skipping.")
    return
  end
  remove_index!(table_name, index_name)
end
remove_timestamps(table_name)

Removes the timestamp columns (created_at and updated_at) from the table definition.

Examples
remove_timestamps(:suppliers)
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 474
def remove_timestamps(table_name)
  remove_column table_name, :updated_at
  remove_column table_name, :created_at
end
rename_column(table_name, column_name, new_column_name)

Renames a column.

Example
rename_column(:suppliers, :description, :name)
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 227
def rename_column(table_name, column_name, new_column_name)
  raise NotImplementedError, "rename_column is not implemented"
end
rename_index(table_name, old_name, new_name)

Rename an index.

Rename the index_people_on_last_name index to index_users_on_last_name

rename_index :people, 'index_people_on_last_name', 'index_users_on_last_name'
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 322
def rename_index(table_name, old_name, new_name)
  # this is a naive implementation; some DBs may support this more efficiently (Postgres, for instance)
  old_index_def = indexes(table_name).detect { |i| i.name == old_name }
  return unless old_index_def
  remove_index(table_name, :name => old_name)
  add_index(table_name, old_index_def.columns, :name => new_name, :unique => old_index_def.unique)
end
rename_table(table_name, new_name)

Renames a table.

Example
rename_table('octopuses', 'octopi')
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 176
def rename_table(table_name, new_name)
  raise NotImplementedError, "rename_table is not implemented"
end
structure_dump()

Returns a string of CREATE TABLESQL statement(s) for recreating the entire structure of the database.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 356
def structure_dump
end
table_alias_for(table_name)

Truncates a table alias according to the limits of the current adapter.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 12
def table_alias_for(table_name)
  table_name[0..table_alias_length-1].gsub(/\./, '_')
end
table_exists?(table_name)

def tables(name = nil) end

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 18
def table_exists?(table_name)
  tables.include?(table_name.to_s)
end
Instance Protected methods
options_include_default?(options)
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 485
def options_include_default?(options)
  options.include?(:default) && !(options[:null] == false && options[:default].nil?)
end
quoted_columns_for_index(column_names, options = {})

Overridden by the mysql adapter for supporting index lengths

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 481
def quoted_columns_for_index(column_names, options = {})
  column_names.map {|name| quote_column_name(name) }
end