# How to retrieve attributes from HABTM? **URL:** \ **Category:** Rails\ **Created:** [March 1, 2006, 4:23pm UTC](https://www.ruby-forum.com/t/how-to-retrieve-attributes-from-habtm/75250 "2006-03-01T16:23:08Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![yash](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f17d59/32.png) [@yash](https://www.ruby-forum.com/u/yash)\ **Post date:** [March 1, 2006, 4:23pm UTC](https://www.ruby-forum.com/t/how-to-retrieve-attributes-from-habtm/75250/1 "2006-03-01T16:23:08Z")
We have tables Users and Communities linked by has\_an\_belongs\_to\_many. The join table Communities\_Users has additional fields [ is\_active, is\_blocked, join\_date] etc. These are populated using @user.push\_with\_attributes(:is\_active =\> true,…). Later on how do we update or retrieve the attributes in the link table for a given user or a community with doing it explicitly using SQL? Thanks, Yash ---
**Author:** ![yash](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f17d59/32.png) [@yash](https://www.ruby-forum.com/u/yash)\ **Post date:** [March 1, 2006, 8:45pm UTC](https://www.ruby-forum.com/t/how-to-retrieve-attributes-from-habtm/75250/2 "2006-03-01T20:45:09Z")
Why don’t you create a model for the join table? ---
**Author:** ![yash](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f17d59/32.png) [@yash](https://www.ruby-forum.com/u/yash)\ **Post date:** [March 2, 2006, 12:47am UTC](https://www.ruby-forum.com/t/how-to-retrieve-attributes-from-habtm/75250/3 "2006-03-02T00:47:31Z")
Yash \ writes: > We have tables Users and Communities linked by has\_an\_belongs\_to\_many. > The join table Communities\_Users has additional fields [ is\_active, > is\_blocked, join\_date] etc. These are populated using > user.push\_with\_attributes(:is\_active =\> true,…). > Later on how do we update or retrieve the attributes in the link table > for a given user or a community with doing it explicitly using SQL? Without creating a separate model for the join table, there appears to be no easy way to update a HABTM join’s attributes. I usually have to delete the associated object and add it back in again with the changed atttributes. Retrieval is OK. community.users should provide you with the join table attributes merged into the users attributes. If have any fields named the same thing, I think they get clobbered. Or you could create your own model for the join table. However this involves its own problems. Do you make a fake autonumber/serial primary key field for the table then? If you do, Rails should work fine, although you’ve lost the purity of the join table in the process. If you choose leave your table with a composite primary key of (user\_id, community\_id) (or whatever), Rails will have a very hard time dealing with it. Update and destroy methods will not work (I usually override the update method in the model with a custom SQL statement). Record inserts will work, although Rails automatically tries to go get the ID field from the last inserted row (in PostgreSQL, by selecting the current value from an appropriately named sequence). But since the PK is not an autonumber/serial, there is no sequence, so Rails fails. I get around this by setting the (nonexistant) ID attribute before I save it (model\_record[‘id’] = some\_bogus\_value). That seems to fool Rails well enough. Really, the HABTM support in Rails is pretty lame. It’s been one of the most frustrating aspects of ActiveRecord for me. Unfortunately, given how zealous DHH is about every table having an ID primary key, I don’t see this getting fixed anytime soon. ---
**Author:** ![yash](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f17d59/32.png) [@yash](https://www.ruby-forum.com/u/yash)\ **Post date:** [March 2, 2006, 1:06am UTC](https://www.ruby-forum.com/t/how-to-retrieve-attributes-from-habtm/75250/4 "2006-03-02T01:06:24Z")
I’ll chime in on going with the join model approach. It just works better with Rails. I’m doing a multi-part essay on my blog about things you can do with them, so instead of repeating myself I’ll refer you there 🙂 [http://blog.hasmanythrough.com](http://blog.hasmanythrough.com) –josh KW wrote: > Yash \ writes: > > > We have tables Users and Communities linked by has\_an\_belongs\_to\_many. > > The join table Communities\_Users has additional fields [ is\_active, > > is\_blocked, join\_date] etc. These are populated using > > user.push\_with\_attributes(:is\_active =\> true,…). > > Later on how do we update or retrieve the attributes in the link table > > for a given user or a community with doing it explicitly using SQL? ---
**Author:** ![yash](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f17d59/32.png) [@yash](https://www.ruby-forum.com/u/yash)\ **Post date:** [March 2, 2006, 2:30pm UTC](https://www.ruby-forum.com/t/how-to-retrieve-attributes-from-habtm/75250/5 "2006-03-02T14:30:29Z")
Yash wrote: > We have tables Users and Communities linked by has\_an\_belongs\_to\_many. > The join table Communities\_Users has additional fields [ is\_active, > is\_blocked, join\_date] etc. These are populated using > @user.push\_with\_attributes(:is\_active =\> true,…). > Later on how do we update or retrieve the attributes in the link table > for a given user or a community with doing it explicitly using SQL? As the others have said this is a good case for a separate domain model say Membership. See the Agile book page 241 \_tony ---
**Author:** ![yash](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f17d59/32.png) [@yash](https://www.ruby-forum.com/u/yash)\ **Post date:** [April 16, 2007, 7:41am UTC](https://www.ruby-forum.com/t/how-to-retrieve-attributes-from-habtm/75250/6 "2007-04-16T07:41:09Z")
you could also use sql to update the join table: ActiveRecord::Base.connection.execute(sql) should work fine. However, if you really see yourself using and interacting with the join table, go the :through route… ---
**Author:** ![yash](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f17d59/32.png) [@yash](https://www.ruby-forum.com/u/yash)\ **Post date:** [March 2, 2006, 12:40pm UTC](https://www.ruby-forum.com/t/how-to-retrieve-attributes-from-habtm/75250/7 "2006-03-02T12:40:57Z")
is this the same issue? although i’m too newby to know if it’s just me, i’ve run into problems with HABTM as well [http://dev.rubyonrails.org/ticket/1031](http://dev.rubyonrails.org/ticket/1031)