Question

I have the following many-to-many relationship:

class Assignment < ActiveRecord::Base
  belongs_to :programmer
  belongs_to :project
end

class Programmer < ActiveRecord::Base
  has_many :assignments
  has_many :projects, :through => :assignments
end

class Project < ActiveRecord::Base
  has_many :assignments
  has_many :programmers, :through => :assignments
end

And in my db:migrate I have the following:

class CreateAssignments < ActiveRecord::Migration
  def self.up
    create_table :assignments do |t|
      t.integer :programmer_id
      t.integer :project_id
      t.boolean :owner, :default => false
      t.timestamps
   end
  end

 def self.down
    drop_table :assignments
 end
end

This means that I can load a project belonging to a programmer, by doing this:

@my_programmer.projects.find params[:id]

But if you see my migration, each assignment also has a “owner” flag that indicates whether or not the programmer is the owner of that project. My problem is that this query will only give me the project, and not access to the “owner” flag.

So how do I know whether the programmer is the owner? I could do another call to get the collaboration, but it seems stupid as it’s already doing a JOIN on assignments?

Is there a way to get the properties on the :through class, without needing to do a specific database call?

Answer 1

It is quite strange architecture of your database. But you can try this

class Programmer < ActiveRecord::Base
  has_many :assignments
  has_many :projects, :through => :assignments

  def own_projects
    projects.where(:owner => true)
  end
end

class Project < ActiveRecord::Base
  has_many :assignments
  has_many :programmers, :through => :assignments

  def owners
    programmers.where(:owner => true)
  end

  def collaborators
    programmers.where(:owner => false)
  end
end

@my_programmer.own_projects
@my_project.owners
@my_project.owners.include? @my_programmer
@my_project.colaborators

UPD

Another solution for using eager loading:

class Programmer < ActiveRecord::Base
  has_many :assignments
  has_many :projects, :through => :assignments
  has_many :own_projects, :class_name => "Project", :through => :assignments, :conditions => ['assignments.owner = ?', true], :source => :project
end

class Project < ActiveRecord::Base
  has_many :assignments
  has_many :programmers, :through => :assignments
  has_many :owners, :class_name => "Programmer", :through => :assignments, :conditions => ['assignments.owner = ?', true], :source => :programmer
  has_many :collaborators, :class_name => "Programmer", :through => :assignments, :conditions => ['assignments.owner = ?', false], :source => :programmer
end

@my_programmer.projects.includes(:owners).each do |project|
  project.owner
end