Ruby-on-rails Rails (ActiveRecord) 多对多表
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Rails (ActiveRecord) many to many table
提问by Ori
I have two models, Users and Groups. Each group can have many users and each user can be in many groups.
我有两个模型，用户和组。每个组可以有多个用户，每个用户可以在多个组中。
I currently have something simple like:
我目前有一些简单的东西：
User:
用户：
has_many :groups
Group:
团体：
has_many :users
So I have a groups_users table which is just creating rows with group_id and user_id. I want to add another column to this, (which I have), the question is how do I access it from a model without using a custom SQL call? In the group model I can go self.users and in user I can go self.groups
所以我有一个groups_users 表，它只是用group_id 和user_id 创建行。我想为此添加另一列（我有），问题是如何在不使用自定义 SQL 调用的情况下从模型访问它？在组模型中我可以去 self.users 而在用户中我可以去 self.groups
Is there a way to change the third column in this table from a user model?
有没有办法从用户模型更改此表中的第三列？
Sorry if this is confusing, please advise on this
对不起，如果这令人困惑，请就此提出建议
回答by dave elkins
Here are a couple of tutorials that should help. Basically there two approaches to make many-to-many work, either has_and_belongs_to_many or has_many :through (recommended).
这里有几个教程应该会有所帮助。基本上有两种方法可以进行多对多工作，has_and_belongs_to_many 或 has_many :through（推荐）。
links:
链接：
回答by bigpotato
In Rails 3 you want to make a join table for many to many relationships, using the plural names of the tables you want to join in alphabetical order. So in this case it would be groups_users.
在 Rails 3 中，您想为多对多关系创建一个连接表，使用要按字母顺序连接的表的复数名称。所以在这种情况下它会是groups_users.
models
楷模
class GroupsUser < ActiveRecord::Base
belongs_to :user
belongs_to :group
end
class User < ActiveRecord::Base
has_many :groups_users
has_many :groups, :through => :groups_users
end
class Group < ActiveRecord::Base
has_many :groups_users
has_many :users, :through => :groups_users
end
回答by Ethan
I [added] another column to [
users_groups]...The question is how do I access it from a model without using a custom SQL call?
我 [添加] 另一列到 [
users_groups]...问题是如何在不使用自定义 SQL 调用的情况下从模型访问它？
It sounds like you want to access a column of your user_groupstable by calling a method on your Usermodel or your Groupmodel.
听起来您想user_groups通过调用User模型或Group模型上的方法来访问表的列。
Some suggestions:
一些建议：
I'd name the table "user_groups" to work with ActiveRecord's pluralization expectations, but I'm not sure if that's essential.
我将表命名为 " user_groups" 以符合 ActiveRecord 的复数期望，但我不确定这是否必要。
Following Dave's advice, you'd want to set things up using the "has_many :through" technique...
按照 Dave 的建议，您可能希望使用“ has_many :through”技术进行设置...
# Declare a Model based on the many-to-many linking table.
class UserGroup < ActiveRecord::Base
belongs_to :user
belongs_to :group
end
class User < ActiveRecord::Base
has_many :user_groups
has_many :groups, :through => :user_groups
end
class Group < ActiveRecord::Base
has_many :user_groups
has_many :users, :through => :user_groups
end
Is there a way to change the third column in this table from a user model?
有没有办法从用户模型更改此表中的第三列？
This is a little unclear, but keep in mind that each Usercan have a lot of UserGroups. So if you wanted to change that third column you'd have to find the particular one you're looking for.
这有点不清楚，但请记住，每个都User可以有很多UserGroups. 因此，如果您想更改第三列，则必须找到您要查找的特定列。
