module ActiveRecord::ConnectionAdapters::SchemaStatements

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 588
def add_column(table_name, column_name, type, **options)
  at = create_alter_table table_name
  at.add_column(column_name, type, options)
  execute schema_creation.accept at
end

Add a new type column named column_name to table_name.

The type parameter is normally one of the migrations native types, which is one of the following: :primary_key, :string, :text, :integer, :bigint, :float, :decimal, :numeric, :datetime, :time, :date, :binary, :boolean.

You may use a type not in this list as long as it is supported by your database (for example, “polygon” in MySQL), but this will not be database agnostic and should usually be avoided.

Available options are (none of these exists by default):

• :limit - Requests a maximum column length. This is the number of characters for a :string column and number of bytes for :text, :binary, and :integer columns. This option is ignored by some backends.

• :default - The column's default value. Use nil for NULL.

• :null - Allows or disallows NULL values in the column.

• :precision - Specifies the precision for the :decimal, :numeric, :datetime, and :time columns.

• :scale - Specifies the scale for the :decimal and :numeric columns.

• :collation - Specifies the collation for a :string or :text column. If not specified, the column will have the same collation as the table.

• :comment - Specifies the comment for the column. This option is ignored by some backends.

Note: The precision is the total number of significant digits, and the scale is the number of digits that can be stored following the decimal point. For example, the number 123.45 has a precision of 5 and a scale of 2. A decimal with a precision of 5 and a scale of 2 can range from -999.99 to 999.99.

Please be aware of different RDBMS implementations behavior with :decimal columns:

• The SQL standard says the default scale should be 0, :scale <= :precision, and makes no comments about the requirements of :precision.

• MySQL: :precision [1..63], :scale [0..30]. Default is (10,0).

• PostgreSQL: :precision [1..infinity], :scale [0..infinity]. No default.

• SQLite3: No restrictions on :precision and :scale, but the maximum supported :precision is 16. No default.

• Oracle: :precision [1..38], :scale [-84..127]. Default is (38,0).

• DB2: :precision [1..63], :scale [0..62]. Default unknown.

• SqlServer: :precision [1..38], :scale [0..38]. Default (38,0).

Examples

add_column(:users, :picture, :binary, limit: 2.megabytes)
# ALTER TABLE "users" ADD "picture" blob(2097152)

add_column(:articles, :status, :string, limit: 20, default: 'draft', null: false)
# ALTER TABLE "articles" ADD "status" varchar(20) DEFAULT 'draft' NOT NULL

add_column(:answers, :bill_gates_money, :decimal, precision: 15, scale: 2)
# ALTER TABLE "answers" ADD "bill_gates_money" decimal(15,2)

add_column(:measurements, :sensor_reading, :decimal, precision: 30, scale: 20)
# ALTER TABLE "measurements" ADD "sensor_reading" decimal(30,20)

# While :scale defaults to zero on most databases, it
# probably wouldn't hurt to include it.
add_column(:measurements, :huge_integer, :decimal, precision: 30)
# ALTER TABLE "measurements" ADD "huge_integer" decimal(30)

# Defines a column that stores an array of a type.
add_column(:users, :skills, :text, array: true)
# ALTER TABLE "users" ADD "skills" text[]

# Defines a column with a database-specific type.
add_column(:shapes, :triangle, 'polygon')
# ALTER TABLE "shapes" ADD "triangle" polygon

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 991
def add_foreign_key(from_table, to_table, options = {})
  return unless supports_foreign_keys?

  options = foreign_key_options(from_table, to_table, options)
  at = create_alter_table from_table
  at.add_foreign_key to_table, options

  execute schema_creation.accept(at)
end

Adds a new foreign key. from_table is the table with the key column, to_table contains the referenced primary key.

The foreign key will be named after the following pattern: fk_rails_<identifier>. identifier is a 10 character long string which is deterministically generated from the from_table and column. A custom name can be specified with the :name option.

Creating a simple foreign key

add_foreign_key :articles, :authors

generates:

ALTER TABLE "articles" ADD CONSTRAINT fk_rails_e74ce85cbc FOREIGN KEY ("author_id") REFERENCES "authors" ("id")

Creating a foreign key on a specific column

add_foreign_key :articles, :users, column: :author_id, primary_key: "lng_id"

generates:

ALTER TABLE "articles" ADD CONSTRAINT fk_rails_58ca3d3a82 FOREIGN KEY ("author_id") REFERENCES "users" ("lng_id")

Creating a cascading foreign key

add_foreign_key :articles, :authors, on_delete: :cascade

generates:

ALTER TABLE "articles" ADD CONSTRAINT fk_rails_e74ce85cbc FOREIGN KEY ("author_id") REFERENCES "authors" ("id") ON DELETE CASCADE

The options hash can include the following keys:

:column

The foreign key column name on from_table. Defaults to to_table.singularize + "_id"

:primary_key

The primary key column name on to_table. Defaults to id.

:name

The constraint name. Defaults to fk_rails_<identifier>.

:on_delete

Action that happens ON DELETE. Valid values are :nullify, :cascade and :restrict

:on_update

Action that happens ON UPDATE. Valid values are :nullify, :cascade and :restrict

:validate

(PostgreSQL only) Specify whether or not the constraint should be validated. Defaults to true.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 785
def add_index(table_name, column_name, options = {})
  index_name, index_type, index_columns, index_options = add_index_options(table_name, column_name, options)
  execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{index_columns})#{index_options}"
end

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

The index will be named after the table and the column name(s), unless you pass :name as an option.

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))

Creating an index with specific key lengths for multiple keys

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.

Creating an index with a sort order (desc or asc, asc is the default)

add_index(:accounts, [:branch_id, :party_id, :surname], order: {branch_id: :desc, party_id: :asc})

generates:

CREATE INDEX by_branch_desc_party ON accounts(branch_id DESC, party_id ASC, surname)

Note: MySQL only supports index order from 8.0.1 onwards (earlier versions accepted the syntax but ignored it).

Creating a partial index

add_index(:accounts, [:branch_id, :party_id], unique: true, where: "active")

generates:

CREATE UNIQUE INDEX index_accounts_on_branch_id_and_party_id ON accounts(branch_id, party_id) WHERE active

Note: Partial indexes are only supported for PostgreSQL and SQLite 3.8.0+.

Creating an index with a specific method

add_index(:developers, :name, using: 'btree')

generates:

CREATE INDEX index_developers_on_name ON developers USING btree (name) -- PostgreSQL
CREATE INDEX index_developers_on_name USING btree ON developers (name) -- MySQL

Note: only supported by PostgreSQL and MySQL

Creating an index with a specific operator class

add_index(:developers, :name, using: 'gist', opclass: :gist_trgm_ops)
# CREATE INDEX developers_on_name ON developers USING gist (name gist_trgm_ops) -- PostgreSQL

add_index(:developers, [:name, :city], using: 'gist', opclass: { city: :gist_trgm_ops })
# CREATE INDEX developers_on_name_and_city ON developers USING gist (name, city gist_trgm_ops) -- PostgreSQL

add_index(:developers, [:name, :city], using: 'gist', opclass: :gist_trgm_ops)
# CREATE INDEX developers_on_name_and_city ON developers USING gist (name gist_trgm_ops, city gist_trgm_ops) -- PostgreSQL

Note: only supported by PostgreSQL

Creating an index with a specific type

add_index(:developers, :name, type: :fulltext)

generates:

CREATE FULLTEXT INDEX index_developers_on_name ON developers (name) -- MySQL

Note: only supported by MySQL.

Creating an index with a specific algorithm

add_index(:developers, :name, algorithm: :concurrently)
# CREATE INDEX CONCURRENTLY developers_on_name on developers (name)

Note: only supported by PostgreSQL.

Concurrently adding an index is not supported in a transaction.

For more information see the “Transactional Migrations” section.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 904
def add_reference(table_name, ref_name, **options)
  ReferenceDefinition.new(ref_name, options).add_to(update_table_definition(table_name, self))
end

Adds a reference. The reference column is a bigint by default, the :type option can be used to specify a different type. Optionally adds a _type column, if :polymorphic option is provided. add_reference and add_belongs_to are acceptable.

The options hash can include the following keys:

:type

The reference column type. Defaults to :bigint.

:index

Add an appropriate index. Defaults to true. See add_index for usage of this option.

:foreign_key

Add an appropriate foreign key constraint. Defaults to false.

:polymorphic

Whether an additional _type column should be added. Defaults to false.

:null

Whether the column allows nulls. Defaults to true.

Create a user_id bigint column without an index

add_reference(:products, :user, index: false)

Create a user_id string column

add_reference(:products, :user, type: :string)

Create supplier_id, supplier_type columns

add_reference(:products, :supplier, polymorphic: true)

Create a supplier_id column with a unique index

add_reference(:products, :supplier, index: { unique: true })

Create a supplier_id column with a named index

add_reference(:products, :supplier, index: { name: "my_supplier_index" })

Create a supplier_id column and appropriate foreign key

add_reference(:products, :supplier, foreign_key: true)

Create a supplier_id column and a foreign key to the firms table

add_reference(:products, :supplier, foreign_key: {to_table: :firms})

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 1148
def add_timestamps(table_name, options = {})
  options[:null] = false if options[:null].nil?

  if !options.key?(:precision) && supports_datetime_with_precision?
    options[:precision] = 6
  end

  add_column table_name, :created_at, :datetime, options
  add_column table_name, :updated_at, :datetime, options
end

Adds timestamps (created_at and updated_at) columns to table_name. Additional options (like :null) are forwarded to add_column.

add_timestamps(:suppliers, null: true)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 623
def change_column(table_name, column_name, type, options = {})
  raise NotImplementedError, "change_column is not implemented"
end

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

change_column(:suppliers, :name, :string, limit: 80)
change_column(:accounts, :description, :text)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 1224
def change_column_comment(table_name, column_name, comment_or_changes)
  raise NotImplementedError, "#{self.class} does not support changing column comments"
end

Changes the comment for a column or removes it if nil.

Passing a hash containing :from and :to will make this change reversible in migration:

change_column_comment(:posts, :state, from: "old_comment", to: "new_comment")

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 641
def change_column_default(table_name, column_name, default_or_changes)
  raise NotImplementedError, "change_column_default is not implemented"
end

Sets a new default value for a column:

change_column_default(:suppliers, :qualification, 'new')
change_column_default(:accounts, :authorized, 1)

Setting the default to nil effectively drops the default:

change_column_default(:users, :email, nil)

Passing a hash containing :from and :to will make this change reversible in migration:

change_column_default(:posts, :state, from: nil, to: "draft")

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 661
def change_column_null(table_name, column_name, null, default = nil)
  raise NotImplementedError, "change_column_null is not implemented"
end

Sets or removes a NOT NULL constraint on a column. The null flag indicates whether the value can be NULL. For example

change_column_null(:users, :nickname, false)

says nicknames cannot be NULL (adds the constraint), whereas

change_column_null(:users, :nickname, true)

allows them to be NULL (drops the constraint).

The method accepts an optional fourth argument to replace existing NULLs with some other value. Use that one when enabling the constraint if needed, since otherwise those rows would not be valid.

Please note the fourth argument does not set a column's default.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 471
def change_table(table_name, options = {})
  if supports_bulk_alter? && options[:bulk]
    recorder = ActiveRecord::Migration::CommandRecorder.new(self)
    yield update_table_definition(table_name, recorder)
    bulk_change_table(table_name, recorder.commands)
  else
    yield update_table_definition(table_name, self)
  end
end

A block for changing columns in table.

# change_table() yields a Table instance
change_table(:suppliers) do |t|
  t.column :name, :string, limit: 60
  # Other column alterations here
end

The options hash can include the following keys:

:bulk

Set this to true to make this a bulk alter query, such as

ALTER TABLE `users` ADD COLUMN age INT, ADD COLUMN birthdate DATETIME ...

Defaults to false.

Only supported on the MySQL and PostgreSQL adapter, ignored elsewhere.

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(bigint) 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(bigint) 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 transformations.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 1214
def change_table_comment(table_name, comment_or_changes)
  raise NotImplementedError, "#{self.class} does not support changing table comments"
end

Changes the comment for a table or removes it if nil.

Passing a hash containing :from and :to will make this change reversible in migration:

change_table_comment(:posts, from: "old_comment", to: "new_comment")

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 133
def column_exists?(table_name, column_name, type = nil, **options)
  column_name = column_name.to_s
  checks = []
  checks << lambda { |c| c.name == column_name }
  checks << lambda { |c| c.type == type.to_sym rescue nil } if type
  column_options_keys.each do |attr|
    checks << lambda { |c| c.send(attr) == options[attr] } if options.key?(attr)
  end

  columns(table_name).any? { |c| checks.all? { |check| check[c] } }
end

Checks to see if a column exists in a given table.

# Check a column exists
column_exists?(:suppliers, :name)

# Check a column exists of a particular type
column_exists?(:suppliers, :name, :string)

# Check a column exists with a specific definition
column_exists?(:suppliers, :name, :string, limit: 100)
column_exists?(:suppliers, :name, :string, default: 'default')
column_exists?(:suppliers, :name, :string, null: false)
column_exists?(:suppliers, :tax, :decimal, precision: 8, scale: 2)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 112
def columns(table_name)
  table_name = table_name.to_s
  column_definitions(table_name).map do |field|
    new_column_from_field(table_name, field)
  end
end

Returns an array of Column objects for the table specified by table_name.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 374
def create_join_table(table_1, table_2, column_options: {}, **options)
  join_table_name = find_join_table_name(table_1, table_2, options)

  column_options.reverse_merge!(null: false, index: false)

  t1_ref, t2_ref = [table_1, table_2].map { |t| t.to_s.singularize }

  create_table(join_table_name, options.merge!(id: false)) do |td|
    td.references t1_ref, column_options
    td.references t2_ref, column_options
    yield td if block_given?
  end
end

Creates a new join table with the name created using the lexical order of the first two arguments. These arguments can be a String or a Symbol.

# Creates a table called 'assemblies_parts' with no id.
create_join_table(:assemblies, :parts)

You can pass an options hash which can include the following keys:

:table_name

Sets the table name, overriding the default.

:column_options

Any extra options you want appended to the columns definition.

: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.

Note that create_join_table does not create any indices by default; you can use its block form to do so yourself:

create_join_table :products, :categories do |t|
  t.index :product_id
  t.index :category_id
end

Add a backend specific option to the generated SQL (MySQL)

create_join_table(:assemblies, :parts, options: 'ENGINE=InnoDB DEFAULT CHARSET=utf8')

generates:

CREATE TABLE assemblies_parts (
  assembly_id bigint NOT NULL,
  part_id bigint NOT NULL,
) ENGINE=InnoDB DEFAULT CHARSET=utf8

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 294
def create_table(table_name, **options)
  td = create_table_definition(table_name, options)

  if options[:id] != false && !options[:as]
    pk = options.fetch(:primary_key) do
      Base.get_primary_key table_name.to_s.singularize
    end

    if pk.is_a?(Array)
      td.primary_keys pk
    else
      td.primary_key pk, options.fetch(:id, :primary_key), options.except(:comment)
    end
  end

  yield td if block_given?

  if options[:force]
    drop_table(table_name, options.merge(if_exists: true))
  end

  result = execute schema_creation.accept td

  unless supports_indexes_in_create?
    td.indexes.each do |column_name, index_options|
      add_index(table_name, column_name, index_options)
    end
  end

  if supports_comments? && !supports_comments_in_create?
    if table_comment = options[:comment].presence
      change_table_comment(table_name, table_comment)
    end

    td.columns.each do |column|
      change_column_comment(table_name, column.name, column.comment) if column.comment.present?
    end
  end

  result
end

Creates a new table with the name table_name. table_name may 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

Block form, with shorthand

# You can also use the column types as method calls, rather than calling the column method.
create_table(:suppliers) do |t|
  t.string :name, 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 options hash can include the following keys:

:id

Whether to automatically add a primary key column. Defaults to true. Join tables for ActiveRecord::Base.has_and_belongs_to_many should set it to false.

A Symbol can be used to specify the type of the generated primary key column.

:primary_key

The name of the primary key, if one is to be added automatically. Defaults to id. If :id is false, then this option is ignored.

If an array is passed, a composite primary key will be created.

Note that Active Record models will automatically detect their primary key. This can be avoided by using self.primary_key= on the model to define the key explicitly.

: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. Set to :cascade to drop dependent objects as well. Defaults to false.

:if_not_exists

Set to true to avoid raising an error when the table already exists. Defaults to false.

:as

SQL to use to generate the table. When this option is used, the block is ignored, as are the :id and :primary_key options.

Add a backend specific option to the generated SQL (MySQL)

create_table(:suppliers, options: 'ENGINE=InnoDB DEFAULT CHARSET=utf8mb4')

generates:

CREATE TABLE suppliers (
  id bigint auto_increment PRIMARY KEY
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4

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 bigint auto_increment PRIMARY KEY,
  name varchar(80)
)

Change the primary key column type

create_table(:tags, id: :string) do |t|
  t.column :label, :string
end

generates:

CREATE TABLE tags (
  id varchar PRIMARY KEY,
  label varchar
)

Create a composite primary key

create_table(:orders, primary_key: [:product_id, :client_id]) do |t|
  t.belongs_to :product
  t.belongs_to :client
end

generates:

CREATE TABLE order (
    product_id bigint NOT NULL,
    client_id bigint NOT NULL
);

ALTER TABLE ONLY "orders"
  ADD CONSTRAINT orders_pkey PRIMARY KEY (product_id, client_id);

Do not add a primary key column

create_table(:categories_suppliers, id: false) do |t|
  t.column :category_id, :bigint
  t.column :supplier_id, :bigint
end

generates:

CREATE TABLE categories_suppliers (
  category_id bigint,
  supplier_id bigint
)

Create a temporary table based on a query

create_table(:long_query, temporary: true,
  as: "SELECT * FROM orders INNER JOIN line_items ON order_id=orders.id")

generates:

CREATE TEMPORARY TABLE long_query AS
  SELECT * FROM orders INNER JOIN line_items ON order_id=orders.id

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 46
def data_source_exists?(name)
  query_values(data_source_sql(name), "SCHEMA").any? if name.present?
rescue NotImplementedError
  data_sources.include?(name.to_s)
end

Checks to see if the data source name exists on the database.

data_source_exists?(:ebooks)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 36
def data_sources
  query_values(data_source_sql, "SCHEMA")
rescue NotImplementedError
  tables | views
end

Returns the relation names useable to back Active Record models. For most adapters this means all tables and views.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 394
def drop_join_table(table_1, table_2, options = {})
  join_table_name = find_join_table_name(table_1, table_2, options)
  drop_table(join_table_name)
end

Drops the join table specified by the given arguments. See create_join_table for details.

Although this command ignores the block if one is given, it can be helpful to provide one in a migration's change method so it can be reverted. In that case, the block will be used by create_join_table.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 501
def drop_table(table_name, options = {})
  execute "DROP TABLE#{' IF EXISTS' if options[:if_exists]} #{quote_table_name(table_name)}"
end

Drops a table from the database.

:force

Set to :cascade to drop dependent objects as well. Defaults to false.

:if_exists

Set to true to only drop the table if it exists. Defaults to false.

Although this command ignores most options and the block if one is given, it can be helpful to provide these in a migration's change method so it can be reverted. In that case, options and the block will be used by create_table.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 1048
def foreign_key_exists?(from_table, to_table = nil, **options)
  foreign_key_for(from_table, to_table: to_table, **options).present?
end

Checks to see if a foreign key exists on a table for a given foreign key definition.

# Checks to see if a foreign key exists.
foreign_key_exists?(:accounts, :branches)

# Checks to see if a foreign key on a specified column exists.
foreign_key_exists?(:accounts, column: :owner_id)

# Checks to see if a foreign key with a custom name exists.
foreign_key_exists?(:accounts, name: "special_fk_name")

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 943
def foreign_keys(table_name)
  raise NotImplementedError, "foreign_keys is not implemented"
end

Returns an array of foreign keys for the given table. The foreign keys are represented as ForeignKeyDefinition objects.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 101
def index_exists?(table_name, column_name, options = {})
  column_names = Array(column_name).map(&:to_s)
  checks = []
  checks << lambda { |i| Array(i.columns) == column_names }
  checks << lambda { |i| i.unique } if options[:unique]
  checks << lambda { |i| i.name == options[:name].to_s } if options[:name]

  indexes(table_name).any? { |i| checks.all? { |check| check[i] } }
end

Checks to see if an index exists on a table for a given index definition.

# Check an index exists
index_exists?(:suppliers, :company_id)

# Check an index on multiple columns exists
index_exists?(:suppliers, [:company_id, :company_type])

# Check a unique index exists
index_exists?(:suppliers, :company_id, unique: true)

# Check an index with a custom name exists
index_exists?(:suppliers, :company_id, name: "idx_company_id")

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 853
def index_name_exists?(table_name, index_name)
  index_name = index_name.to_s
  indexes(table_name).detect { |i| i.name == index_name }
end

Verifies the existence of an index with a given name.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 83
def indexes(table_name)
  raise NotImplementedError, "#indexes is not implemented"
end

Returns an array of indexes for the given table.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 16
def native_database_types
  {}
end

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 146
def primary_key(table_name)
  pk = primary_keys(table_name)
  pk = pk.first unless pk.size > 1
  pk
end

Returns just a table's primary key

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 613
def remove_column(table_name, column_name, type = nil, options = {})
  execute "ALTER TABLE #{quote_table_name(table_name)} #{remove_column_for_alter(table_name, column_name, type, options)}"
end

Removes the column from the table definition.

remove_column(:suppliers, :qualification)

The type and options parameters will be ignored if present. It can be helpful to provide these in a migration's change method so it can be reverted. In that case, type and options will be used by add_column. Indexes on the column are automatically removed.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 598
def remove_columns(table_name, *column_names)
  raise ArgumentError.new("You must specify at least one column name. Example: remove_columns(:people, :first_name)") if column_names.empty?
  column_names.each do |column_name|
    remove_column(table_name, column_name)
  end
end

Removes the given columns from the table definition.

remove_columns(:suppliers, :qualification, :experience)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 1026
def remove_foreign_key(from_table, to_table = nil, **options)
  return unless supports_foreign_keys?

  fk_name_to_delete = foreign_key_for!(from_table, to_table: to_table, **options).name

  at = create_alter_table from_table
  at.drop_foreign_key fk_name_to_delete

  execute schema_creation.accept(at)
end

Removes the given foreign key from the table. Any option parameters provided will be used to re-add the foreign key in case of a migration rollback. It is recommended that you provide any options used when creating the foreign key so that the migration can be reverted properly.

Removes the foreign key on accounts.branch_id.

remove_foreign_key :accounts, :branches

Removes the foreign key on accounts.owner_id.

remove_foreign_key :accounts, column: :owner_id

Removes the foreign key on accounts.owner_id.

remove_foreign_key :accounts, to_table: :owners

Removes the foreign key named special_fk_name on the accounts table.

remove_foreign_key :accounts, name: :special_fk_name

The options hash accepts the same keys as #add_foreign_key with an addition of

:to_table

The name of the table that contains the referenced primary key.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 817
def remove_index(table_name, options = {})
  index_name = index_name_for_remove(table_name, options)
  execute "DROP INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)}"
end

Removes the given index from the table.

Removes the index on branch_id in the accounts table if exactly one such index exists.

remove_index :accounts, :branch_id

Removes the index on branch_id in the accounts table if exactly one such index exists.

remove_index :accounts, column: :branch_id

Removes the index on branch_id and party_id in the accounts table if exactly one such index exists.

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

Removes the index named by_branch_party in the accounts table.

remove_index :accounts, name: :by_branch_party

Removes the index named by_branch_party in the accounts table concurrently.

remove_index :accounts, name: :by_branch_party, algorithm: :concurrently

Note: only supported by PostgreSQL.

Concurrently removing an index is not supported in a transaction.

For more information see the “Transactional Migrations” section.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 924
def remove_reference(table_name, ref_name, foreign_key: false, polymorphic: false, **options)
  if foreign_key
    reference_name = Base.pluralize_table_names ? ref_name.to_s.pluralize : ref_name
    if foreign_key.is_a?(Hash)
      foreign_key_options = foreign_key
    else
      foreign_key_options = { to_table: reference_name }
    end
    foreign_key_options[:column] ||= "#{ref_name}_id"
    remove_foreign_key(table_name, foreign_key_options)
  end

  remove_column(table_name, "#{ref_name}_id")
  remove_column(table_name, "#{ref_name}_type") if polymorphic
end

Removes the reference(s). Also removes a type column if one exists. remove_reference and remove_belongs_to are acceptable.

Remove the reference

remove_reference(:products, :user, index: false)

Remove polymorphic reference

remove_reference(:products, :supplier, polymorphic: true)

Remove the reference with a foreign key

remove_reference(:products, :user, foreign_key: true)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 1163
def remove_timestamps(table_name, options = {})
  remove_column table_name, :updated_at
  remove_column table_name, :created_at
end

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

remove_timestamps(:suppliers)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 669
def rename_column(table_name, column_name, new_column_name)
  raise NotImplementedError, "rename_column is not implemented"
end

Renames a column.

rename_column(:suppliers, :description, :name)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 828
def rename_index(table_name, old_name, new_name)
  validate_index_length!(table_name, new_name)

  # this is a naive implementation; some DBs may support this more efficiently (PostgreSQL, for instance)
  old_index_def = indexes(table_name).detect { |i| i.name == old_name }
  return unless old_index_def
  add_index(table_name, old_index_def.columns, name: new_name, unique: old_index_def.unique)
  remove_index(table_name, name: old_name)
end

Renames 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 485
def rename_table(table_name, new_name)
  raise NotImplementedError, "rename_table is not implemented"
end

Renames a table.

rename_table('octopuses', 'octopi')

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 30
def table_alias_for(table_name)
  table_name[0...table_alias_length].tr(".", "_")
end

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

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 25
def table_comment(table_name)
  nil
end

Returns the table comment that's stored in database metadata.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 61
def table_exists?(table_name)
  query_values(data_source_sql(table_name, type: "BASE TABLE"), "SCHEMA").any? if table_name.present?
rescue NotImplementedError
  tables.include?(table_name.to_s)
end

Checks to see if the table table_name exists on the database.

table_exists?(:developers)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 53
def tables
  query_values(data_source_sql(type: "BASE TABLE"), "SCHEMA")
end

Returns an array of table names defined in the database.

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 76
def view_exists?(view_name)
  query_values(data_source_sql(view_name, type: "VIEW"), "SCHEMA").any? if view_name.present?
rescue NotImplementedError
  views.include?(view_name.to_s)
end

Checks to see if the view view_name exists on the database.

view_exists?(:ebooks)

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 68
def views
  query_values(data_source_sql(type: "VIEW"), "SCHEMA")
end

Returns an array of view names defined in the database.