Ruby-on-rails 外国人 - 删除外键
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foreigner - remove foreign key
提问by Mel
I am trying to use mailboxer in my rails 4 app. A problem is arising when i try to deploy the db. The error occurs in creating the mailboxer conversations table, which has dependencies in notifications table.
我正在尝试在我的 rails 4 应用程序中使用邮箱。当我尝试部署数据库时出现问题。在创建邮箱会话表时发生错误，该表在通知表中具有依赖关系。
I am trying to remove the foreign key for notifications conversations.
我正在尝试删除通知对话的外键。
I created a migration which says:
我创建了一个迁移，它说：
change_table :notifications do |t|
t.remove_foreign_key :conversations
However, the rake aborts and says a foreign key does not exist.
但是，rake 中止并说外键不存在。
rake aborted!
An error has occurred, this and all later migrations canceled:
PG::UndefinedObject: ERROR: constraint "notifications_conversation_id_fk" of relation "notifications" does not exist
My schema includes: add_foreign_key "notifications", "conversations", name: "notifications_on_conversation_id"
我的架构包括：add_foreign_key“notifications”，“conversations”，名称：“notifications_on_conversation_id”
I tried to rake db:migrate:down the original migration that created mailboxer, but also got an error saying 'command not found'.
我试图将 db:migrate:down 原始迁移创建邮箱，但也收到一条错误消息，提示“未找到命令”。
Can anyone help? Thank you.
任何人都可以帮忙吗？谢谢你。
回答by cschroed
The add_foreign_keycommand in your schema gave your foreign key the name notifications_on_conversation_id. This name is different than the default name that foreigner would normally assign based on the column name, which is notifications_conversation_id_fk. So your remove_foreign_keycommand must specify the existing foreign key name instead of the column name. Try:
add_foreign_key架构中的命令为您的外键指定了 name notifications_on_conversation_id。此名称不同于外国人通常根据列名称分配的默认名称，即notifications_conversation_id_fk. 因此您的remove_foreign_key命令必须指定现有的外键名称而不是列名称。尝试：
remove_foreign_key :notifications, name: "notifications_on_conversation_id"
回答by Dorian
# Removes the given foreign key from the table.
# Removes the foreign key on +accounts.branch_id+.
remove_foreign_key :accounts, :branches
# Removes the foreign key on +accounts.owner_id+.
remove_foreign_key :accounts, column: :owner_id
# Removes the foreign key named +special_fk_name+ on the +accounts+ table.
remove_foreign_key :accounts, name: :special_fk_name
官方文档：http: //api.rubyonrails.org/v4.2/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-remove_foreign_key
回答by CodingBingo
When I ran that I got:
当我跑的时候，我得到了：
NoMethodError: undefined method `remove_foreign_key' for #<ActiveRecord::ConnectionAdapters::Table:0x00007faa35e94aa8>
Did you mean? remove_index
Words of wisdom- never use anything except an id integer for a foreign key. I used a title param while practicing on a fake app and it causes:
智慧之言 - 除了外键的 id 整数外，永远不要使用任何东西。我在一个假的应用程序上练习时使用了一个标题参数，它导致：
ActiveRecord::AssociationTypeMismatch (Company(#70210936585940) expected, got "Company4" which is an instance of String(#70210933923380))
