CODEWITHSUNDEEP
ruby-on-railsrubyactiverecordmany-to-many
Ori
Ori

Reputation: 5081

Rails (ActiveRecord) many to many table

I have two models, Users and Groups. Each group can have many users and each user can be in many groups.

I currently have something simple like:

User:

has_many    :groups

Group:

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

Is there a way to change the third column in this table from a user model?

Sorry if this is confusing, please advise on this

Upvotes: 13

Views: 25264

Answers (3)

bigpotato
bigpotato

Reputation: 27557

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.

models

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

Upvotes: 13

dave elkins
dave elkins

Reputation: 331

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).

links:

  1. http://blog.hasmanythrough.com/2006/4/20/many-to-many-dance-off
  2. http://railscasts.com/episodes/47-two-many-to-many
  3. http://railscasts.com/episodes/154-polymorphic-association

Upvotes: 15

Ethan
Ethan

Reputation: 60179

I [added] another column to [users_groups]...The question is how do I access it from a model without using a custom SQL call?

It sounds like you want to access a column of your user_groups table by calling a method on your User model or your Group model.

Some suggestions:

I'd name the table "user_groups" to work with ActiveRecord's pluralization expectations, but I'm not sure if that's essential.

Following Dave's advice, you'd want to set things up using the "has_many :through" technique...

# 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?

This is a little unclear, but keep in mind that each User can 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.

Upvotes: 4

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