# Non Master **URL:** \ **Category:** Rails\ **Created:** [October 13, 2006, 9:14pm UTC](https://www.ruby-forum.com/t/non-master/72045 "2006-10-13T21:14:39Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![kumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/9f8e36/32.png) [@kumar](https://www.ruby-forum.com/u/kumar)\ **Post date:** [October 13, 2006, 9:14pm UTC](https://www.ruby-forum.com/t/non-master/72045/1 "2006-10-13T21:14:39Z")
How to handle a non-master table which is a mapping between 3 master tables. I have defined the appropriate has\_and\_belongs\_to\_many associations but when I enter data for a course I get 2 entries in course\_prerequisites table 1 2 null 1 null 3 Basically I am not able to make ROR understand that group\_id and exam\_id that I am entering belong to a single tuple. Any solution? Kumar. ---
**Author:** ![kumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/9f8e36/32.png) [@kumar](https://www.ruby-forum.com/u/kumar)\ **Post date:** [October 13, 2006, 10:27pm UTC](https://www.ruby-forum.com/t/non-master/72045/2 "2006-10-13T22:27:11Z")
Can I get more specific answer? ☹ ---
**Author:** ![kumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/9f8e36/32.png) [@kumar](https://www.ruby-forum.com/u/kumar)\ **Post date:** [October 13, 2006, 10:05pm UTC](https://www.ruby-forum.com/t/non-master/72045/3 "2006-10-13T22:05:03Z")
On 10/13/06, Kumar [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > exam\_id that I am entering belong to a single tuple. > Any solution? The most straight way is to introduce another model for that non-master table. It’s not about just creating another AR class, but adjusting your vision of the problem domain. Then you’ll be able to use has\_many :through (if it will be still be needed). ---
**Author:** ![kumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/9f8e36/32.png) [@kumar](https://www.ruby-forum.com/u/kumar)\ **Post date:** [October 13, 2006, 10:33pm UTC](https://www.ruby-forum.com/t/non-master/72045/4 "2006-10-13T22:33:40Z")
On 10/14/06, Kumar [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Can I get more specific answer? ☹ I doubt you can without being more specific about your problem. ---
**Author:** ![kumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/9f8e36/32.png) [@kumar](https://www.ruby-forum.com/u/kumar)\ **Post date:** [October 13, 2006, 10:45pm UTC](https://www.ruby-forum.com/t/non-master/72045/5 "2006-10-13T22:45:58Z")
No doubt… I mean I didnt got that answer correctly. Want in detail. ☹ Kumar ---
**Author:** ![kumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/9f8e36/32.png) [@kumar](https://www.ruby-forum.com/u/kumar)\ **Post date:** [October 13, 2006, 10:27pm UTC](https://www.ruby-forum.com/t/non-master/72045/6 "2006-10-13T22:27:11Z")
Can I get more specific answer? ☹ ---
**Author:** ![kumar](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/9f8e36/32.png) [@kumar](https://www.ruby-forum.com/u/kumar)\ **Post date:** [October 13, 2006, 10:56pm UTC](https://www.ruby-forum.com/t/non-master/72045/7 "2006-10-13T22:56:03Z")
On 10/14/06, Kumar [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > No doubt… I mean I didnt got that answer correctly. > Want in detail. ☹ E.g, you have models A, B and C and a “non-master” table to link them together. Then you can create model D that will represent some meanful entity in your A / B / C model. Then you can do “A has\_many :bs, :through =\> :d” and vice versa.