[ruby-on-rails] Add a reference column migration in Rails 4

A user has many uploads. I want to add a column to the uploads table that references the user. What should the migration look like?

Here is what I have. I'm not sure if I should use (1) :user_id, :int or (2) :user, :references. I'm not even sure if (2) works. Just trying to do this the "rails" way.

class AddUserToUploads < ActiveRecord::Migration
  def change
    add_column :uploads, :user_id, :integer
  end
end

Relevant question except for Rails 3. Rails 3 migrations: Adding reference column?

Rails 5

You can still use this command to create the migration:

rails g migration AddUserToUploads user:references

The migration looks a bit different to before, but still works:

class AddUserToUploads < ActiveRecord::Migration[5.0]
  def change
    add_reference :uploads, :user, foreign_key: true
  end
end

Note that it's :user, not :user_id

Another syntax of doing the same thing is:

rails g migration AddUserToUpload user:belongs_to

if you like another alternate approach with up and down method try this:

  def up
    change_table :uploads do |t|
      t.references :user, index: true
    end
  end

  def down
    change_table :uploads do |t|
      t.remove_references :user, index: true
    end
  end

Create a migration file

rails generate migration add_references_to_uploads user:references

Default foreign key name

This would create a user_id column in uploads table as a foreign key

class AddReferencesToUploads < ActiveRecord::Migration[5.2]
  def change
    add_reference :uploads, :user, foreign_key: true
  end
end

user model:

class User < ApplicationRecord
  has_many :uploads
end

upload model:

class Upload < ApplicationRecord
  belongs_to :user
end

Customize foreign key name:

add_reference :uploads, :author, references: :user, foreign_key: true

This would create an author_id column in the uploads tables as the foreign key.

user model:

class User < ApplicationRecord
  has_many :uploads, foreign_key: 'author_id'
end

upload model:

class Upload < ApplicationRecord
  belongs_to :user
end

Just to document if someone has the same problem...

In my situation I've been using :uuid fields, and the above answers does not work to my case, because rails 5 are creating a column using :bigint instead :uuid:

add_reference :uploads, :user, index: true, type: :uuid

Reference: Active Record Postgresql UUID

[Using Rails 5]

Generate migration:

rails generate migration add_user_reference_to_uploads user:references

This will create the migration file:

class AddUserReferenceToUploads < ActiveRecord::Migration[5.1]
  def change
    add_reference :uploads, :user, foreign_key: true
  end
end

Now if you observe the schema file, you will see that the uploads table contains a new field. Something like: t.bigint "user_id" or t.integer "user_id".

Migrate database:

rails db:migrate