Rails 3 迁移 update_all 与关系/连接
鉴于以下模型，
class User
has_many :conversations
end
class Conversation
belongs_to :user
has_many :messages
end
class Message
belongs_to :conversation
end
我想删除对话模型并将对用户的引用迁移到消息。 通常我会使用类似
add_column :messages, :user_id, :integer
Message.reset_column_information
Message.all.each do |message|
message.user_id = message.conversation.user_id
end
remove_column :messages, :conversation_id
但在生产迁移中在代码更新后运行的内容。因此这会引发错误。
也许我只需要一点提示。
Given Following Models
class User
has_many :conversations
end
class Conversation
belongs_to :user
has_many :messages
end
class Message
belongs_to :conversation
end
I want to remove the Conversation model and migrate the reference to a user to Message.
Normally I would use something like
add_column :messages, :user_id, :integer
Message.reset_column_information
Message.all.each do |message|
message.user_id = message.conversation.user_id
end
remove_column :messages, :conversation_id
But in Production migrations run after the code was updated. Therefore this would throw an error.
Probably I just need a little hint.
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即使您删除了“belongs: to”关系，消息仍应将“conversation_id”作为字段，对吧？
那么如果你这样做了怎么办：
message.user_id = User.find_by_id(message.conversation_id).user_id
Message should still have 'conversation_id' as a field even though you removed the belongs: to relationship right?
So what if you did:
message.user_id = User.find_by_id(message.conversation_id).user_id
一个好的解决方案是在迁移中定义一个临时模型 -> 来源：Rails 指南
A good solution is to define a temporary model inside the migration -> Source: Rails Guides