Ruby-on-rails 关于空的belongs_to 关联的最佳实践

Best practice about empty belongs_to association

提问by Jo?o Daniel

Imagine the following situation:

想象一下以下情况：

I have a dogmodel and a housemodel. A dog can belong to a house, and a house can have many dogs, so:

我有一个dog模型和一个house模型。一只狗可以属于一个房子，一个房子可以有很多狗，所以：

Class Dog <  ActiveRecord::Base
  belongs_to :house
end

Class House < ActiveRecord::Base
  has_many :dogs
end

Now, imagine that I also want to create dogs that don't have a house. They don't belong to house. Can I still use that relationship structure and simply don't inform a :house_idwhen creating it?

现在，想象一下我也想创造没有房子的狗。他们不属于房子。我是否仍然可以使用该关系结构并且:house_id在创建它时不通知 a ？

Is there a better practice?

有没有更好的做法？

Obs.: I used this analogy to simplify my problem, but my real situation is: I have a model a user can generate instances of it. He can also create collections of those instances, but he can leave an instance outside a collection.

观察：我用这个比喻来简化我的问题，但我的真实情况是：我有一个模型，用户可以生成它的实例。他还可以创建这些实例的集合，但他可以将实例留在集合之外。

采纳答案by Flexoid

I think it is absolutely normal approach.

我认为这是绝对正常的方法。

You can just leave house_idwith nullvalue in database for the models which don't belong to other.

你可以只留下house_id与null价值在数据库中不属于其他车型。

回答by Wibbly

Be careful with this in Rails 5 ...

在 Rails 5 中小心这一点......

belongs_to is required by default

From now on every Rails application will have a new configuration option config.active_record.belongs_to_required_by_default = true, it will trigger a validation error when trying to save a model where belongs_to associations are not present.

config.active_record.belongs_to_required_by_default can be changed to false and with this keep old Rails behavior or we can disable this validation on each belongs_to definition, just passing an additional option optional: true as follows:

class Book < ActiveRecord::Base
    belongs_to :author, optional: true
end

默认情况下需要belongs_to

从现在开始，每个 Rails 应用程序都会有一个新的配置选项 config.active_record.belongs_to_required_by_default = true，它会在尝试保存不存在关联的模型时触发验证错误。

config.active_record.belongs_to_required_by_default 可以更改为 false 并保持旧的 Rails 行为，或者我们可以在每个belongs_to 定义上禁用此验证，只需传递一个附加选项 optional: true 如下：

class Book < ActiveRecord::Base
    belongs_to :author, optional: true
end

from: http://blog.michelada.io/whats-new-in-rails-5

来自：http: //blog.michelada.io/whats-new-in-rails-5