# User has many topics or subtopics **URL:** \ **Category:** Rails\ **Created:** [June 27, 2009, 5:27am UTC](https://www.ruby-forum.com/t/user-has-many-topics-or-subtopics/171155 "2009-06-27T05:27:44Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![ADADAD](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/85e7bf/32.png) [@ADADAD](https://www.ruby-forum.com/u/ADADAD)\ **Post date:** [June 27, 2009, 5:27am UTC](https://www.ruby-forum.com/t/user-has-many-topics-or-subtopics/171155/1 "2009-06-27T05:27:44Z")
Hi, So i have users in the system and i have topics. Topics also have\_many subtopics. What is the cleanest way to setup the AR relationships if a user can either have\_many topics or subtopics ? Its basically a dual select box dropdown, where the second dropdown is optional. Is the best to have user\_topics, and user\_subtopics tables and manage that way ? or combine into one table with STI and a type ? Thanks AD ---
**Author:** ![ADADAD](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/85e7bf/32.png) [@ADADAD](https://www.ruby-forum.com/u/ADADAD)\ **Post date:** [June 27, 2009, 10:42am UTC](https://www.ruby-forum.com/t/user-has-many-topics-or-subtopics/171155/2 "2009-06-27T10:42:45Z")
AD wrote: > Hi, > > So i have users in the system and i have topics. Topics also > have\_many subtopics. What is the cleanest way to setup the AR > relationships if a user can either have\_many topics or subtopics ? > Its basically a dual select box dropdown, where the second dropdown is > optional. > > Is the best to have user\_topics, and user\_subtopics tables and manage > that way ? or combine into one table with STI and a type ? > > Thanks > AD Maybe better like this: topic.rb belongs\_to :user has\_many :subtopics user.rb has\_many :topics has\_many :subtopics, :through =\> :topics subtopic.rb belongs\_to :user belongs\_to :topic Try smth like this, and read this one: > **[Active Record Associations — Ruby on Rails Guides](https://guides.rubyonrails.org/association_basics.html#the-has-many-through-association)** > > Active Record AssociationsThis guide covers the association features of Active Record.After reading this guide, you will know: How to declare associations between Active Record models. How to understand the various types of Active Record... ---
**Author:** ![ADADAD](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/85e7bf/32.png) [@ADADAD](https://www.ruby-forum.com/u/ADADAD)\ **Post date:** [June 27, 2009, 10:52am UTC](https://www.ruby-forum.com/t/user-has-many-topics-or-subtopics/171155/3 "2009-06-27T10:52:19Z")
2009/6/27 Andrey O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > > Â Is the best to have user\_topics, and user\_subtopics tables and manage > > user.rb > has\_many :topics > has\_many :subtopics, :through =\> :topics > > subtopic.rb > belongs\_to :user > belongs\_to :topic I imagine it may need HABTM relationships for users\_topics and users\_subtopics if topics and subtopics can belong to multiple users. Also I think the above will not allow a user to have a subtopic without a topic, which I think AD asked for, though he/she may not have meant that. Though if this was meant then I would suggest maybe an error in the design. AD can you clarify the requirement? Colin ---
**Author:** ![ADADAD](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/85e7bf/32.png) [@ADADAD](https://www.ruby-forum.com/u/ADADAD)\ **Post date:** [June 27, 2009, 9:09pm UTC](https://www.ruby-forum.com/t/user-has-many-topics-or-subtopics/171155/4 "2009-06-27T21:09:44Z")
yea sorry if you have a subtopic, you have a topic since a subtopic belongs to a topic. So if I have TopicA, TopicB, and TopicA has SubTopicD and SubTopicE, a user can have TopicB, SubtopicE. Since SubTopicE belongs to TopicA they would also have that. The requirement was really that they didnt have to choose a subtopic if they only wanted to choose a Topic. But choosing a subtopic intrinsically gets you a topic by association of that subtopic to its parent topic. AD ---
**Author:** ![ADADAD](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/85e7bf/32.png) [@ADADAD](https://www.ruby-forum.com/u/ADADAD)\ **Post date:** [June 29, 2009, 3:23am UTC](https://www.ruby-forum.com/t/user-has-many-topics-or-subtopics/171155/5 "2009-06-29T03:23:45Z")
yes sorry, a topic can belong to many users. For subtopics we had went the subtopics\_users approach, but now that a new requirement came in to support a user having either a topic with no subtopic as well as a subtopic directly (impying topic). Thanks ---
**Author:** ![ADADAD](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/85e7bf/32.png) [@ADADAD](https://www.ruby-forum.com/u/ADADAD)\ **Post date:** [June 27, 2009, 9:30pm UTC](https://www.ruby-forum.com/t/user-has-many-topics-or-subtopics/171155/6 "2009-06-27T21:30:49Z")
2009/6/27 AD [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > AD You have not clarified whether a topic can belong to more one user. If so then you need HABTM associations. Do you need further help? I presume you have worked through the rails guide on associations. Colin ---
**Author:** ![ADADAD](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/85e7bf/32.png) [@ADADAD](https://www.ruby-forum.com/u/ADADAD)\ **Post date:** [June 29, 2009, 4:30am UTC](https://www.ruby-forum.com/t/user-has-many-topics-or-subtopics/171155/7 "2009-06-29T04:30:02Z")
AD wrote: > yes sorry, a topic can belong to many users. For subtopics we had > went the subtopics\_users approach, but now that a new requirement came > in to support a user having either a topic with no subtopic as well as > a subtopic directly (impying topic). If I were to jump in late, and only read that graph, without reading the rest of the thread (purely as a rhetorical technique, mind you)… Then u appear to have the Composite Design Pattern. Give each topic a super\_topic\_id. If a topic has a pointer to another topic, it’s a subtopic. Forcing them all to belong to the same user is then a business rules issue, not a database issue. I suspect that system is most flexible… – Phlip [http://twitter.com/Pen\_Bird](http://twitter.com/Pen_Bird)