Ruby-on-rails Rails中has_one和belongs_to的区别？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/861144/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Difference between has_one and belongs_to in Rails?
提问by Moon
I am trying to understand has_onerelationship in RoR.
我试图了解has_oneRoR 中的关系。
Let's say I have two models - Personand Cell:
假设我有两个模型 -Person和Cell：
class Person < ActiveRecord::Base
has_one :cell
end
class Cell < ActiveRecord::Base
belongs_to :person
end
Can I just use has_one :personinstead of belongs_to :personin Cellmodel?
我可以只使用has_one :person而不是belongs_to :person在Cell模型中吗？
Isn't it the same?
不是一样吗？
回答by Sarah Mei
No, they are not interchangable, and there are some real differences.
不，它们不可互换，并且存在一些真正的差异。
belongs_tomeans that the foreign key is in the table for this class. So belongs_tocan ONLY go in the class that holds the foreign key.
belongs_to意味着外键在这个类的表中。所以belongs_to只能进入持有外键的类。
has_onemeans that there is a foreign key in another table that references this class. So has_onecan ONLY go in a class that is referenced by a column in another table.
has_one意味着在另一个表中有一个引用这个类的外键。所以has_one只能进入由另一个表中的列引用的类。
So this is wrong:
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
And this is also wrong:
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
The correct way is (if Cellcontains person_idfield):
正确的方法是（如果Cell包含person_id字段）：
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
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.
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。即使对于单向关联，使用哪一个也很重要。
回答by Pablo Fernandez
If you add "belongs_to" then you got a bidirectional association. That means you can get a person from the cell and a cell from the person.
如果您添加“belongs_to”，那么您将获得双向关联。这意味着你可以从细胞中得到一个人，也可以从这个人那里得到一个细胞。
There's no real difference, both approaches (with and without "belongs_to") use the same database schema (a person_id field in the cells database table).
没有真正的区别，两种方法（有和没有“belongs_to”）都使用相同的数据库模式（单元数据库表中的 person_id 字段）。
To summarize: Do not add "belongs_to" unless you need bidirectional associations between models.
总结一下：除非您需要模型之间的双向关联，否则不要添加“belongs_to”。
回答by Jarrod
Using both allows you to get info from both Person and Cell models.
使用两者可以让您从 Person 和 Cell 模型中获取信息。
@cell.person.whatever_info and @person.cell.whatever_info.
