Deep relationships in Rails - ruby-on-rails

Question

I have some projects. Those projects have users through memberships.
However, those users belong to companies. Question is, how do I find out which companies can access a project?
Ideally I'd be able to do project.users.companies, but that won't work.
Is there a nice, pleasant way of doing this?

Answer 1

I'm assuming that you have this:
class Project < ActiveRecord::Base
has_and_belongs_to_many :users
end
class User < ActiveRecord::Base
has_and_belongs_to_many :projects
belongs_to :company
end
class Company < ActiveRecord::Base
has_many :users
end
And you want to get project.companies. The less painful one I can imagine is:
class Project < ActiveRecord::Base
has_and_belongs_to_many :users
def companies
Company.all(
:joins => {:users => :projects},
:conditions => {'projects_users.project_id' => self.id}
).uniq
end
end
Notice the uniq at the end. It will remove duplicated companies.

Answer 2

The other answers appear to be neglecting memberships that you mentioned. If those are actual objects which you have a recording of, then what you choose to do depends on the size of your tables. If they aren't terribly huge, then the "more OO" solution would probably look something like this:
class Project < ActiveRecord::Base
has_many :memberships
has_many :users, :through => :memberships
def user_companies
self.users.map {|user| user.companies}.flatten.uniq
end
end
class Membership < ActiveRecord::Base
belongs_to :user
belongs_to :project
end
class User < ActiveRecord::Base
has_many :memberships
has_many :projects, :through => :memberships
belongs_to :company
end
class Company < ActiveRecord::Base
has_many :users
end
This might not perform great, as it pulls a lot of data from the database and then does all the filtering in memory, but it's pretty intuitive to read. If you wanted to shove all the computing down into the database, I think a good solution would likely look something like this in the Project class instead:
def user_companies
Company.find_by_sql("SELECT company.*
FROM companies, users, memberships
WHERE companies.id = users.company_id
AND users.id = memberships.user_id
AND memberships.project_id = #{self.id}")
end
It's a little less clean but will put most of the processing nearest the data, and at only a three table join should not end up generating such a huge number of tuples that your DBMS falls apart at the seems.

Answer 3

I think you can do something like this.
class Project < ActiveRecord::Base
def self.companies
Company.all(:conditions => { :users => { :project_id => #project.id } }, :include => :users)
end
end
But it's been a while since I have used these features, so I may be rusty.
Edit: this may not work. Not sure if I got the :include or :join right. But like I said, I'm rusty.

Answer 4

You should be able to set the relationships up to allow: project.users.companies.
The associations are:
Project has_one User belongs_to Company