Rails中has_one和belongs_to的区别? [英] Difference between has_one and belongs_to in Rails?

问题描述

我正在尝试了解 RoR 中的 has_one 关系.

I am trying to understand has_one relationship in RoR.

假设我有两个模型 - Person 和 Cell:

Let's say I have two models - Person and Cell:

class Person < ActiveRecord::Base
  has_one :cell
end

class Cell < ActiveRecord::Base
  belongs_to :person
end

我可以在 Cell 模型中使用 has_one :person 而不是 belongs_to :person 吗?

Can I just use has_one :person instead of belongs_to :person in Cell model?

不一样吗?

推荐答案

不，它们不可互换，并且存在一些实际差异.

No, they are not interchangable, and there are some real differences.

belongs_to 表示外键在该类的表中.所以 belongs_to 只能进入持有外键的类.

belongs_to means that the foreign key is in the table for this class. So belongs_to can ONLY go in the class that holds the foreign key.

has_one 表示另一个表中存在引用此类的外键.所以 has_one 只能进入另一个表中的列引用的类.

has_one means that there is a foreign key in another table that references this class. So has_one can ONLY go in a class that is referenced by a column in another table.

所以这是错误的:

class Person < ActiveRecord::Base
  has_one :cell # the cell table has a person_id
end

class Cell < ActiveRecord::Base
  has_one :person # the person table has a cell_id
end

这也是错误的:

class Person < ActiveRecord::Base
  belongs_to :cell # the person table has a cell_id
end

class Cell < ActiveRecord::Base
  belongs_to :person # the cell table has a person_id
end

正确的方法是(如果 Cell 包含 person_id 字段):

The correct way is (if Cell contains person_id field):

class Person < ActiveRecord::Base
  has_one :cell # the person table does not have 'joining' info
end

class Cell < ActiveRecord::Base
  belongs_to :person # the cell table has a person_id
end

对于双向关联，您需要每个关联一个，并且他们必须进入正确的班级.即使是单向关联，使用哪一种也很重要.

For a two-way association, you need one of each, and they have to go in the right class. Even for a one-way association, it matters which one you use.

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