Ruby-on-rails – Rails Migration: add_reference to Table but Different Column Name For Foreign Key Than Rails Convention

rails-migrationsruby-on-rails

I have the following two Models:

class Store < ActiveRecord::Base
    belongs_to :person
end

class Person < ActiveRecord::Base
    has_one :store
end

Here is the issue: I am trying to create a migration to create the foreign key within the people table. However, the column referring to the foreign key of Store is not named store_id as would be rails convention but is instead named foo_bar_store_id.

If I was following the rails convention I would do the migration like this:

class AddReferencesToPeople < ActiveRecord::Migration
  def change
    add_reference :people, :store, index: true
  end
end

However this will not work because the column name is not store_id but is foo_bar_store_id. So how do I specify that the foreign key name is just different, but still maintain index: true to maintain fast performance?

Best Answer

in rails 5.x you can add a foreign key to a table with a different name like this:

class AddFooBarStoreToPeople < ActiveRecord::Migration[5.0]
  def change
    add_reference :people, :foo_bar_store, foreign_key: { to_table: :stores }
  end
end

Inside a create_table block

t.references :feature, foreign_key: {to_table: :product_features}

Related Solutions

Ruby-on-rails – Defining foreign key relationships for Rails’ models

The Rails default behaviour is that the column used to hold the foreign key on a model is the name of the association with the suffix _id added. The :foreign_key option lets you set the name of the foreign key directly. The associations between your Post and Comment model classes should look like this:

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

—Note that you don't need :class_name => "Post" in your Comment model. Rails already has that information. You should only be specifying :class_name and :foreign_key when you need to override the Rails' conventions.

You're correct that Rails maintains the foreign key relationships for you. You can enforce them in the database layer if you want by adding foreign key constraints.

I think you would benefit from reading A Guide to ActiveRecord Associations.

Ruby-on-rails – Rails: How to rename a database column in a Ruby on Rails migration

rename_column :table, :old_column, :new_column

You'll probably want to create a separate migration to do this. (Rename FixColumnName as you will.):

script/generate migration FixColumnName
# creates  db/migrate/xxxxxxxxxx_fix_column_name.rb

Then edit the migration to do your will:

# db/migrate/xxxxxxxxxx_fix_column_name.rb
class FixColumnName < ActiveRecord::Migration
  def self.up
    rename_column :table_name, :old_column, :new_column
  end

  def self.down
    # rename back if you need or do something else or do nothing
  end
end

For Rails 3.1 use:

While, the up and down methods still apply, Rails 3.1 receives a change method that "knows how to migrate your database and reverse it when the migration is rolled back without the need to write a separate down method".

See "Active Record Migrations" for more information.

rails g migration FixColumnName

class FixColumnName < ActiveRecord::Migration
  def change
    rename_column :table_name, :old_column, :new_column
  end
end

If you happen to have a whole bunch of columns to rename, or something that would have required repeating the table name over and over again:

rename_column :table_name, :old_column1, :new_column1
rename_column :table_name, :old_column2, :new_column2
...

You could use change_table to keep things a little neater:

class FixColumnNames < ActiveRecord::Migration
  def change
    change_table :table_name do |t|
      t.rename :old_column1, :new_column1
      t.rename :old_column2, :new_column2
      ...
    end
  end
end

Then just db:migrate as usual or however you go about your business.

For Rails 4:

While creating a Migration for renaming a column, Rails 4 generates a change method instead of up and down as mentioned in the above section. The generated change method is:

$ > rails g migration ChangeColumnName

which will create a migration file similar to:

class ChangeColumnName < ActiveRecord::Migration
  def change
    rename_column :table_name, :old_column, :new_column
  end
end

Best Answer

Related Solutions

Ruby-on-rails – Defining foreign key relationships for Rails’ models

Ruby-on-rails – Rails: How to rename a database column in a Ruby on Rails migration

Related Topic