Add a reference column migration in Rails 5

rails-activerecordrails-migrationsruby-on-rails-5

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?

Related question for Rails 3: Rails 3 migrations: Adding reference column?

Related question for Rails 4: Add a reference column migration in Rails 4

Related question for Rails 6: How to add reference column migration in Rails 6 with SQLite

Best Answer

As with prior versions of Rails, you may use the following command to create the migration:

rails g migration AddUserToUploads user:references

Unlike prior versions of Rails, the migration looks like:

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

Related Solutions

Mysql – Rolling back a failed Rails migration

Unfortunately, you must manually clean up failed migrations for MySQL. MySQL does not support transactional database definition changes.

Rails 2.2 includes transactional migrations for PostgreSQL. Rails 2.3 includes transactional migrations for SQLite.

This doesn't really help you for your problem right now, but if you have a choice of database on future projects, I recommend using one with support for transactional DDL because it makes migrations much more pleasant.

Update - this is still true in 2017, on Rails 4.2.7 and MySQL 5.7, reported by Alejandro Babio in another answer here.

Ruby-on-rails – Rails migrations: Undo default setting for a column

Rails 5+

def change
  change_column_default( :table_name, :column_name, from: nil, to: false )
end

Rails 3 and Rails 4

def up
  change_column_default( :table_name, :column_name, nil )
end

def down
  change_column_default( :table_name, :column_name, false )
end

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