add_reference

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.

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, pass true to add. In case the join table can’t be inferred from the association pass :to_table with the appropriate table name.

: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 1095
      def add_reference(table_name, ref_name, **options)
        ReferenceDefinition.new(ref_name, **options).add(table_name, self)
      end