We help IT Professionals succeed at work.

Many to Many relations between 3 tables

Last Modified: 2013-11-13
Hi all,

I have four tables.


Now I want to establish Many to Many relationship between Projects, Roles, Users.

I have search on the net for many to many relation and found lot of examples specifying relationship on two table using has_and_belongs_to or has many through options. How can i achieve this task of specifying many to many relationship between three tables using has_and_belongs_to and has_many through options.

Watch Question

This one is on us!
(Get your first solution completely free - no credit card required)


Here is how I would do it:

Let's call your Projects_Users_Roles something a little bit more intuitive, such as RoleMapping

class RoleMapping < ActiveRecords::Base
  belongs_to :project
  belongs_to :user
  belongs_to :role

Then each other class would use has_many :through relationships.

For example, the role class would have:

class Role < ActiveRecord::Base
  has_many :project_user_roles
  has_many :projects, :through => :project_user_roles
  has_many :users, :through => :project_user_roles

If you have a moment, please let me know what I could have provided to get an A on this question so that I can improve in the future.



Thanks for your reply, You solution worked for me. You have used has_and_belongs_to relationship in your example but i was looking for resolution in both the ways using has_and_belongs_to and has_many through. I am still not clear when to use has_and_belongs_to and when to use has_many through.
If you need to access extra information on the junction table, use :through.
If not, use HABTM for simplicity.

Gain unlimited access to on-demand training courses with an Experts Exchange subscription.

Get Access
Why Experts Exchange?

Experts Exchange always has the answer, or at the least points me in the correct direction! It is like having another employee that is extremely experienced.

Jim Murphy
Programmer at Smart IT Solutions

When asked, what has been your best career decision?

Deciding to stick with EE.

Mohamed Asif
Technical Department Head

Being involved with EE helped me to grow personally and professionally.

Carl Webster
CTP, Sr Infrastructure Consultant
Empower Your Career
Did You Know?

We've partnered with two important charities to provide clean water and computer science education to those who need it most. READ MORE

Ask ANY Question

Connect with Certified Experts to gain insight and support on specific technology challenges including:

  • Troubleshooting
  • Research
  • Professional Opinions
Unlock the solution to this question.
Join our community and discover your potential

Experts Exchange is the only place where you can interact directly with leading experts in the technology field. Become a member today and access the collective knowledge of thousands of technology experts.

*This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.


Please enter a first name

Please enter a last name

8+ characters (letters, numbers, and a symbol)

By clicking, you agree to the Terms of Use and Privacy Policy.