嵌套工厂的意义是什么？

Question

I just don't know what they're for. Before I thought they were for populating foreign keys easily but now I see that's not the case.

# User attributes: id, name, password
factory :user_0, class: User do
    id 0
    name "Jimmy"
    password "Jimson"
end

# Status attributes: id, user_id, content
factory :user_0_statuses, class: Status do
    association :user, factory: :user_0

    factory :user_0_status_0 do
        id 0
        content "noo"
    end
    factory :user_0_status_1 do
        id 1
        content "yees"
    end
end

When :user_0_status_0 and :user_0_status_1 factories are .create d in a spec, I thought that this factory setup would create the following in the database (note the status' user_id entries.):

users    
id | name  | password
0  | Jimmy | Jimson

statuses
id | user_id | content
0  | 0       | noo
1  | 0       | yees

But instead it creates this:

users    
id | name  | password
0  | Jimmy | Jimson
0  | Jimmy | Jimson

statuses
id | user_id | content
0  | nil     | noo
1  | nil     | yees

Basically, a brand new user based on the user_0 factory is created for every nested status factory, and the user_id of the status isn't set at all. How is this behaviour useful?

I just can't see any use at all regarding nested factories. What are they, and the association method, for?

Answer 1

When a factory is nested inside another factory definition, it inherits the attributes defined in the parent factory. If you had a User factory, you could nest an "admin_user" factory inside of it that would have all the base user characteristics plus whatever makes an user an admin without having to redefine the base attributes twice.

(slightly unrelated: I'm not sure if setting the primary key (is Status is an ActiveRecord class) is a reliable practice, and I'd advise finding another way to solve that problem.)