将JOIN查询转换为Rails Active Record关联

Question

I have 3 different Models

class GroupMember < ActiveRecord::Base
attr_accessible :group_id, :user_id, :owner_id
has_one :user
end

class Group < ActiveRecord::Base
attr_accessible :name, :owner, :permission
has_many :groupMembers
end

class User < ActiveRecord::Base
end

and when im in the groups_controller.rb i want realize the following query with associations

SELECT * FROM groups 
LEFT JOIN  group_members ON groups.id = group_members.group_id 
LEFT JOIN users ON group_members.user_id = users.id WHERE users.id = 1

or the joins query

Group.joins('LEFT JOIN  group_members ON groups.id = group_members.group_id LEFT JOIN users ON group_members.user_id = users.id').where('users.id = ?', current_user.id );

Is this possible?

 Group.joins(:user_id => current_user.id)

Answer 1

I believe it is possible but it is a bit difficult to test as soon as I don't have a DB with these tables. Probably something like:

Groups.joins(:group_members, :user).merge(User.where(:id => current_user.id))

---

But the design is a bit strange. I suppose you want to fetch all groups for a certain user, and it is best put like this:

@user = User.find_by_id(current_user.id)
@groups = @user.groups

for this to work you should have groups association in your User model.

It is also unclear for me why you have GroupMember has_one :user . I understand that group member is related to only one user, but can a user be represented as several group members, of different groups? If yes, the Rails way to design it would be:

class GroupMember < ActiveRecord::Base
  attr_accessible :group_id, :user_id, :owner_id
  belongs_to :user
  belongs_to :group
end

class Group < ActiveRecord::Base
  attr_accessible :name, :owner, :permission
  has_many :group_members
  has_many :users, :through => :group_members
end

class User < ActiveRecord::Base
  has_many :group_members
  has_many :groups, :through => :group_members
end