问题描述

我正在尝试在 Ruby on Rails 应用程序中修改数据库迁移.我使用 MySQL 作为我的数据库，并希望将外键添加到正在创建的表中.我正在使用以下代码，并且在遵循在适当列上创建空值的规范时，没有应用外键约束.

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

推荐答案

你可以使用 Foreigner宝石.

然后将您的迁移更改为:

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

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