如何创建 Rails 迁移以使用删除级联约束更新外键？

Question

我正在使用 Rails 4.2.3 和 PostgreSQL 数据库。我想编写一个迁移来更新我的一个外键以具有删除级联约束，因此我创建了以下内容：

class UpdateForeignKeyAddOnDeleteConstraint < ActiveRecord::Migration
  def change
    remove_foreign_key :my_object_times, :my_objects
    add_foreign_key :my_object_times, :my_objects, on_delete: cascade
  end
end

但是当我运行迁移时，出现以下错误：

$ rake db:migrate
== 20160525203028 UpdateForeignKeyAddOnDeleteConstraint: migrating ============
-- remove_foreign_key(:my_object_times, :my_objects)
   -> 0.0454s
-- cascade()
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

undefined local variable or method `cascade' for #<UpdateForeignKeyAddOnDeleteConstraint:0x007f82f2c71998>
/Users/davea/.rvm/gems/ruby-2.3.0@global/gems/activerecord-4.2.5.1/lib/active_record/migration.rb:664:in `block in method_missing'
/Users/davea/.rvm/gems/ruby-2.3.0@global/gems/activerecord-4.2.5.1/lib/active_record/migration.rb:634:in `block in say_with_time'
/Users/davea/.rvm/gems/ruby-2.3.0@global/gems/activerecord-4.2.5.1/lib/active_record/migration.rb:634:in `say_with_time'
/Users/davea/.rvm/gems/ruby-2.3.0@global/gems/activerecord-4.2.5.1/lib/active_record/migration.rb:654:in `method_missing'

我应该如何编写迁移来更新外键？

Answer 1

您需要更改此行，

add_foreign_key :my_object_times, :my_objects, on_delete: cascade

有了这个：

add_foreign_key :my_object_times, :my_objects, on_delete: :cascade

简单的区别就是cascade应该是一个符号（:cascade）或者一个字符串（'cascade'）。

有关详细信息，请参阅 documentation on add_foreign_key。

希望对您有所帮助。

如何创建 Rails 迁移以使用删除级联约束更新外键？

How do I create a Rails migration that updates a foreign key with an on-delete cascade constraint?

ruby-on-rails-4

foreign-keys

migration

constraints

cascade