ActiveRecordSchema

ActiveRecordSchema is an ActiveRecord extension that allows you to write database schema for a model within the model itself and to generate migrations directly from models.

Unlike other libraries (eg. mini_record) ActiveRecordSchema is not an alternative to Rails migrations, but rather a tool to simplify their use.

Features

• Defining columns and indexes directly in model
• Generation of migration from the model taking into account the current state of the database

• Automatically add code to migrate associations:

  • Foreign key for belongs_to
  • Join table for has_and_belongs_to_many

• Automatic indexing of foreign keys for both belongs_to and has_and_belongs_to_many (configurable)

Installation

Put this in your Gemfile

gem 'active_record_schema'

and update your bundle

bundle install

NOTE: ActiveRecordSchema depends on rails ~> 3.0 and not only ActiveRecord

Usage

Create a model and use the class method #field to define columns

class Post < ActiveRecord::Base
    field :title
    field :body, :as => :text
    belongs_to :author, :class_name => "User"
end

Now run rails g migration with --from option

rails g migration init_posts_schema --from Post

and the following migration will be generated

class InitPostsSchema < ActiveRecord::Migration
  def change
    add_column :posts, :title, :string
    add_column :posts, :body, :text

    add_column :author_id, :integer
    index :author_id
  end
end

Generating a migration for new columns is the same, lets add a new field to Post (eg. pubdate):

class Post < ActiveRecord::Base
    field :title
    field :body, :as => :text
    belongs_to :author, :class_name => "User"

    field :pubdate, :as => :datetime
end

Now run

rails g migration add_pubdate_to_posts --from Post

that will generate:

class AddPubdateToPosts < ActiveRecord::Migration
  def change
    add_column :posts, :pubdate, :datetime
  end
end

Has and Belongs To Many (HBTM) associations

Lets try to add a HBTM association to our Post model

ex.

# content.rb
class Post < ActiveRecord::Base
  field :title
  field :body, :as => :text
  belongs_to :author, :class_name => "User"
  field :pubdate, :as => :datetime

  has_and_belongs_to_many :voters, :class_name => "User"
end

Now running

rails g migration add_voters_to_posts --from Post

will generate:

    class AddVotersToPosts < ActiveRecord::Migration
      def change
        create_table :contents_users, :id => false do |t|
          t.integer  "content_id"
          t.integer  "user_id"
        end
        add_index :contents_users, "content_id"
        add_index :contents_users, "user_id"
      end
    end

Single Table Inheritance (STI)

Call #inheritable inside the base class of your hierarchy to add the inheritance column required by Single Table Inheritance.

ex.

# content.rb
class Content < ActiveRecord::Base
  inheritable

  field :title

  has_and_belongs_to_many :voters, :class_name => "User"
  belongs_to              :author, :class_name => "User"

  timestamps
end


# article.rb
class Article < Content
  field :body, :as => :text
end


# video.rb
class Video < Content
  field :url
end

Running

rails g migration init_contents --from Content

same as

rails g migration init_contents --from Article

same as

rails g migration init_contents --from Video

will generate the following migration

class InitContents < ActiveRecord::Migration
  def change
    add_column :contents, :type, :string
    add_column :contents, :title, :string
    add_column :contents, :author_id, :string
    add_column :contents, :body, :text
    add_column :contents, :url, :string

    add_index :contents, :author_id

    create_table :contents_users, :id => false do |t|
      t.integer  "content_id"
      t.integer  "user_id"
    end
    add_index :contents_users, "content_id"
    add_index :contents_users, "user_id"
  end  
end

Mixins

Probably one of the most significant advantage given by ActiveRecordSchema is to allow the definition of fields in modules and reuse them through mixin

ex.

module Profile
  extend ActiveSupport::Concern
  included do
    field :name
    field :age, :as => :integer

  end
end

class User < ActiveRecord::Base
  include Profile

end

class Player < ActiveRecord::Base
  include Profile

end

DSL (Domain Specific Language) reference

• field(name, *args)

  Adds a new column with name name to the schema. The type of column can be passed either as second argument or as option, if not specified is intended to be :string

  options

  • :as or :type : Specify the type of the column. The value can be a String, a Symbol or a Class, default to :string
  • :index : Specify wether or not the field should be indexed, default to false

  examples

  field :name
  
  field :name, :string
  field :name, "string"
  field :name, String
  
  field :name, :as => :string
  field :name, :as => "string"
  field :name, :as => String
  
  field :name, :type => :string
  field :name, :type => "string"
  field :name, :type => String
  
  field :age, :as => :integer, :index => true
  

• belongs_to(name, options = {})

  Adds a new foreign key column for the association to the schema and then delegates to ActiveRecord::Base.belongs_to. If the association is polimorphic a column for foreign type is also generated.

  options

  • :index : Specify wether or not the foreing key column should be indexed, default to true. If the association is polimorphic creates an index on both foreign key and foreing type

• has_and_belongs_to_many(name, options = {}, &extension)

  Adds a new join table for the association to the schema and then delegates to ActiveRecord::Base.has_and_belongs_to_many

• index(column_name, options = {})

  Adds a new index for column_name column to the schema

• timestamps

  Same as

  field :created_at, :datetime
  field :updated_at, :datetime
  

• inheritable

  Same as

  field :"#{inheritance_column}"
  

Why do not also generate irreversible changes (change/remove columns or indexes)?

ActiveRecordSchema does not take into account the removal of columns and indexes or changes in the types of columns. The reason for this is that these changes are not reversible, so it's a better idea to introduce them by hand rather than let them be generated automatically. Anyway the need to resort to harsh measures such as irreversible changes is limited to non-routine situations.

Contributing to active_record_schema

• Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet.
• Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it.
• Fork the project.
• Start a feature/bugfix branch.
• Commit and push until you are happy with your contribution.
• Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
• Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.

---

Copyright (c) 2012 mcasimir

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.