Creating a belongs_to relationship with a model from the main app from an engine model

问题

I've built myself a Rails Engine that requires that the main app have a Users table. I need to be able to create a relationship between one of the models in my engine and the Users table in the main app. Is this more complicated than just saying belongs_to :user? I'm getting an error that says the User object is nil, but when I use the console it returns the right user. My assumption is that Rails assumed my belongs_to :user call meant a User's class in the same namespace as the engine, i.e. MyEngine::User. Is there a way for me to explicitly specify that the User class is in the main app's namespace and not the engine's?

回答1:

In your association set the class name explicitly, including the namespace:

belongs_to :user, :class_name => "MyEngine::User"

回答2:

I dont know much about engines, but you use :: to refer to the root namespace, so you could use ::User I guess

回答3:

Turns out the engine recognizes the MainApp's user class by default just by saying belongs_to :user. I was doing something else wrong :/.

来源：https://stackoverflow.com/questions/11707639/creating-a-belongs-to-relationship-with-a-model-from-the-main-app-from-an-engine