Question

I am trying to modify a database Migration in a Ruby on Rails application. I am using MySQL as my database and would like to add foreign keys to the table that is being created. I am using the following code and while the specifications for creating null values on appropriate columns is being followed no foreign key constraints are being applied.

class CreateBookCheckOuts < ActiveRecord::Migration
  def self.up
    create_table :book_check_outs do |t|
      t.integer :book_id, :null => false, :options =>
        "CONSTRAINT fk_book_check_out_books REFERENCES books(id)"
      t.integer :person_id, :null => false, :options =>
        "CONSTRAINT fk_book_check_out_people REFERENCES people(id)"
      t.datetime :OutDate, :null => false
      t.datetime :ReturnDate, :null => true

      t.timestamps
    end
  end

  def self.down
    drop_table :book_check_outs
  end
end

Answer 1

You can use the Foreigner gem.

Then change your migration to this:

class CreateBookCheckOuts < ActiveRecord::Migration
  def self.up
    create_table :book_check_outs do |t|
      t.integer :book_id, :null => false
      t.integer :person_id, :null => false
      t.datetime :OutDate, :null => false
      t.datetime :ReturnDate, :null => true

      t.timestamps
    end
    add_foreign_key(:book_check_outs, :books)
    add_foreign_key(:book_check_outs, :people)
  end

  def self.down
    remove_foreign_key(:book_check_outs, :books)
    remove_foreign_key(:book_check_outs, :people)
    drop_table :book_check_outs
  end
end