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DEPRECATED: This plugin is not updated anymore. I recommend you SchemaPlus:

Foreign Key Migrations

Foreign Key Migrations is a plugin that automatically generates foreign-key constraints when creating tables. It uses SQL-92 syntax and as such should be compatible with most databases that support foreign-key constraints.

In the simplest case, the plugin assumes that if you have a column named customer_id that you want a foreign-key constraint generated that references the id column in the customers table:

create_table :orders do |t|
  t.column :customer_id, :integer, :null => false

If you have multiple columns referencing a table or for whatever reason, your column name isn't the same as the referenced table name, you can use the :references option:

create_table :orders do |t|
  t.column :ordered_by_id, :integer, :null => false, :references => :customers

If you have a column with a name ending in _id for which you do not wish a foreign-key to be generated, you can use :references => nil:

create_table :orders do |t|
  t.column :external_id, :integer, :null => false, :references => nil

Sometimes you may (for legacy reasons) need to reference a primary key column that is named something other than id. In this case you can specify the name of the column:

create_table :orders do |t|
  t.column :ordered_by_pk, :integer, :null => false, :references => [:customers, :pk]

You also have the option of specifying what to do on delete/update using :on_delete/:on_update, respectively to one of: :cascade; :restrict; and :set_null:

create_table :orders do |t|
  t.column :customer_id, :integer, :on_delete => :set_null, :on_update => :cascade

If your database supports it (for example PostgreSQL) you can also mark the constraint as deferrable:

create_table :orders do |t|
  t.column :customer_id, :integer, :deferrable => true

By convention, if a column is named parent_id it will be treated as a circular reference to the table in which it is defined.

Sometimes you may (for legacy reasons) need to name your primary key column such that it would be misinterpreted as a foreign-key (say for example if you named the primary key order_id). In this case you can manually create the primary key as follows:

create_table :orders, :id => false do |t|
  t.primary_key :order_id, :references => nil

There is also a generator for creating foreign keys on a database that currently has none:

ruby script/generate foreign_key_migration

The plugin fully supports and understands the following active-record configuration properties:

  • config.active_record.pluralize_table_names
  • config.active_record.table_name_prefix
  • config.active_record.table_name_suffix


  • RedHill on Rails Core (redhillonrails_core).

See Also

  • Foreign Key Associations (foreign_key_associations).


This plugin is copyright 2006 by RedHill Consulting, Pty. Ltd. and is released under the MIT license.

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