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
  ...
end

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
  ...
end

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
  ...
end

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]
  ...
end

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
  ...
end

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
  ...
end

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
end

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:

Dependencies

See Also

Installation

EDGE

To install using SVN:
ruby script/plugin install svn://rubyforge.org/var/svn/redhillonrails/trunk/vendor/plugins/foreign_key_migrations

or using HTTP:
ruby script/plugin install http://redhillonrails.rubyforge.org/svn/trunk/vendor/plugins/foreign_key_migrations

2.0 Stable

To install using SVN:
ruby script/plugin install svn://rubyforge.org/var/svn/redhillonrails/branches/stable-2.0/vendor/plugins/foreign_key_migrations

or using HTTP:
ruby script/plugin install http://redhillonrails.rubyforge.org/svn/branches/stable-2.0/vendor/plugins/foreign_key_migrations

1.2 Stable

To install using SVN:
ruby script/plugin install svn://rubyforge.org/var/svn/redhillonrails/branches/stable-1.2/vendor/plugins/foreign_key_migrations

or using HTTP:
ruby script/plugin install http://redhillonrails.rubyforge.org/svn/branches/stable-1.2/vendor/plugins/foreign_key_migrations

1.1.6 Release

To install using SVN:
ruby script/plugin install svn://rubyforge.org/var/svn/redhillonrails/tags/release-1.1.6/vendor/plugins/foreign_key_migrations

or using HTTP:
ruby script/plugin install http://redhillonrails.rubyforge.org/svn/tags/release-1.1.6/vendor/plugins/foreign_key_migrations