Question

如何通过添加外键来指定不同的表名。例如

我有一个类似

的模型

class MyPost < ActiveRecord::Base
  has_many :comments, class_name: PostComment
end

class PostComment < ActiveRecord::Base
  belongs_to :post, class_name: MyPost
end

现在我想改变我的迁移文件：

class CreatePostComments < ActiveRecord::Migration
  def change
    create_table :post_comments do |t|
     t.belongs_to :post, index: true
     t.timestamps null: false
    end
    add_foreign_key :post, :class_name => MyPost
  end
end

但它不起作用。迁移正在取消。如何更改我的迁移文件以使用我的模型结构。

Answer 1

您可以传递外键的选项，如下所示：

class CreatePostComments < ActiveRecord::Migration
  def change
    create_table :post_comments do |t|
      t.references :post, foreign_key: { to_table: :my_posts }, index: true
      t.timestamps null: false
    end
  end
end

如果您想添加唯一约束，则对于索引选项也是如此：

t.references :post, foreign_key: { to_table: :my_posts }, index: { unique: true}

顺便说一下，引用是belongs_to的别名，或者更确切地说，belongs_to是引用的别名。

查看实施中的详细信息rails 5.0.rc2＆amp; rails 4.2

Answer 2

It should look like this:

class CreatePostComments < ActiveRecord::Migration
  def change
    create_table :post_comments do |t|
     t.belongs_to :post, index: true
     t.timestamps null: false
    end
    add_foreign_key :post_comments, :my_posts, column: :post_id
  end
end

Take a look at the documentation: http://apidock.com/rails/ActiveRecord/ConnectionAdapters/SchemaStatements/add_foreign_key

You use the column option when the column is named differently.

如何使用不同的表名在rails迁移中添加外键

2 个答案: