Automatic Foreign Key
Automatic Foreign Key is an ActiveRecord extension 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:
-
config.active_record.pluralize_table_names
-
config.active_record.table_name_prefix
-
config.active_record.table_name_suffix
Rails 3 compatibility
Automatic foreign key is fully compatibly with Rails 3.
Rails 2.x compatibility
Everything but generator is compatible
Dependencies
-
RedHill on Rails Core (redhillonrails_core).
NOTE
-
Code was created by harukizaemon(github.com/harukizaemon) but is not supported currently by him.
-
Former name was foreign_key_migrations
License
This plugin is copyright 2010 by Michał Łomnicki and is released under the MIT license.