automatic_foreign_key

= 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.

As a bonus, the extension also allows you to create indices on columns via options to the schema column definition statements.

=== Installation

gem install automatic_foreign_key
rails generate automatic_foreign_key:install

=== Rails 3.1 compatibility

You need at least 1.3.0 version. Also explicit reference to redhillonrails_core 2.0.0.pre must be set.

gem "automatic_foreign_key", "~> 1.3.0"
gem "redhillonrails_core", "~> 2.0.0.pre"

=== Rails 3.0 compatibility

Fully compatible with Rails 3.

=== Rails 2.x compatibility

Only generator is not compatible

=== Usage

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 rails generate automatic_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

=== Auto Indices

It's very common to create an index on foreign key. You can instruct AutomaticForeignKey to add an index after adding foreign key.

create_table :orders, :id => false do |t| ... t.integer :order_id, :index => true end

If you want to pass some options for index use hash params.

create_table :bills, :id => false do |t| ... t.integer :order_id, :index => { :unique => true, :name => 'foo_index' } end

==== NOTE

Auto indexing option is useless for MySQL users as their RDBMS adds indices on foreign keys by default. However PostgreSQL users may have fun with that feature.

=== Column Indices

You can create an index on any column by specifying the +:index+ option.

create_table :users do |t| ... t.string :role, :index => true end

If you want to pass some options for rails' +add_index()+ you can use hash params.

create_table :users do |t| ... t.string :userid, :index => { :unique => true } end

You can also define a multi-column index by specifying a +:with+ option listing one or more additional columns to be passed to +add_index()+.

create_table :users do |t| t.integer :group_id t.integer :member_number, :index => { :with => :group_id, :unique => true } t.integer :country_code t.string :area_code t.string :local_phone, :index => { :with => [:country_code, :area_code], :unique => true } end

=== Configuration

For customization purposes create config/initializers/automatic_foreign_key.rb file:

AutomaticForeignKey.setup do |config| config.auto_index = true # create indices on FKs by default config.on_update = :cascade # cascade as default on_update action config.on_delete = :restrict # restrict as default on_delete action

config.disable = false # set to true if you want to disable auto foreign keys

end

=== Dependencies

• RedHill on Rails Core (redhillonrails_core).

=== Support

Don't hesitate to ask questions on our mailing list. http://groups.google.com/group/rails-db

=== NOTE

• Code was created by harukizaemon(http://github.com/harukizaemon) but is not supported currently by him.
• Former name was foreign_key_migrations

=== License

This plugin is copyright 2011 by Michał Łomnicki and is released under the MIT license.