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# Migrations Constraints

MigrationsConstraints adds the capability to add/drop table constraints or 
specify column constraints during table creation time to 
ActiveRecord::Migrations.

It currently supports the following:

  create_table :users do |t|
    t.column :login, :string, :limit => 20, :null => false, :unique => true
    t.column :type, :string, :limit => 80, :null => false
  end
    
  create_table :projects do |t|
    t.column :owner_id, :integer, :null => false, :references => :users
    t.column :name, :string, :null => false
  end
  
  create_table :line_items do |t|
    t.column :quantity, :integer, :null => false, :check => '> 0'
  end
  
  add_constraint :projects, :unique => :name
  drop_constraint :projects, :unique => :name
  
  add_constraint :project_members, :foreign_key => :project_id, :references => :projects
  add_constraint :project_members, :foreign_key => :user_id, :references => :users
  
  drop_constraint :project_members, :foreign_key => :user_id, :references => :users
  drop_constraint :project_members, :foreign_key => :project_id, :references => :projects
  
  add_constraint :line_items, :name => 'line_items_max_quantity_check', :check => 'quantity < 10000'
  drop_constraint :line_items, :name => 'line_items_max_quantity_check'

## Constraint Naming

Constraints by default are named according to the default naming convention used
by PostgreSQL 8.2.x. That is for a given table +table+, column +column+:

* A unique constraint is named +table_column_uq+.
* A foreign key constraint is named +table_column_fkey+.
* A check constraint is named +table_column_check+.

Otherwise, a constraint's name can be specified explicitly via the +:name+
parameter:

  add_constraint :books, :foreign_key => :author_id, :references => :authors, :name => 'books_authors_fkey'

## Release Notes

MigrationsConstraints is currently being developed and tested using a PostgreSQL
8.2 database back-end.

If the database you're using doesn't follow the same (ANSI SQL 92) data
definition language for specifying database constraints, then please support
this project by contributing to the code. :)

## History

[Alistair A. Israel](http://alistairisrael.wordpress.com/) created this plugin in 2007 ([see the RubyForge project](http://rubyforge.org/projects/mig-constraints/)).