如何创建使用on-delete级联约束更新外键的Rails迁移？

Question

我正在使用Rails 4.2.3和PostgreSQL数据库.我想写一个迁移来更新我的一个外键以具有on-delete级联约束,所以我创建了以下内容:

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,我收到以下错误:

$ 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'

我该如何编写迁移来更新外键？

Answer 1

你需要改变这条线,

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

简单的区别是cascade应该是symbol(:cascade)或string('cascade').

希望这可以帮助.

问候,