Taking Advantage of Your Rails Model Generator

This is a quick trick I haven’t explored until now (no really, didn’t know it like 5 minute ago).

When you’re calling rails g model to generate your models, you have the option to pass in the field names inline, like this:

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$ rails g model UserRole user_id:integer role_id:integer extra_permissions:text

The example above has something interesting: you create two columns of type integer: role_id and user_id. What you really want to express, however, is that you want ot hook up two associations in your UserRole model: belongs_to :role and belongs_to :user. After you generate this migration, you may have to do a couple of things by hand:

• add add_index commands on the migration to create the index on role_id and user_id before running rake db:migrate
• add belongs_to associations in app/models/user_role.rb

Well, all of this manual typing can be just eliminated if you use this syntax instead:

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$ rails g model UserRole user:belongs_to role:belongs_to extra_permissions:text

That’s it! We express the model with its data relations instead of raw database columns. As you can see in the generated code, rails already included the appropriate belongs_to and indexes to the files, like below:

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class UserRole < ActiveRecord::Base
  belongs_to :user
  belongs_to :role
end

And to the migration file:

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class CreateUserRoles < ActiveRecord::Migration
  def change
    create_table :user_roles do |t|
      t.belongs_to :user, index: true
      t.belongs_to :role, index: true
      t.text :extra_permissions

      t.timestamps
    end
  end
end

All done in a single call to rails g. Hope you enjoy!