# Using Migrations to convert join table to join model **URL:** \ **Category:** Rails\ **Created:** [April 20, 2006, 8:02pm UTC](https://www.ruby-forum.com/t/using-migrations-to-convert-join-table-to-join-model/58350 "2006-04-20T20:02:15Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![dawillis](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ebca7d/32.png) [@dawillis](https://www.ruby-forum.com/u/dawillis)\ **Post date:** [April 20, 2006, 8:02pm UTC](https://www.ruby-forum.com/t/using-migrations-to-convert-join-table-to-join-model/58350/1 "2006-04-20T20:02:15Z")
Greetings, I’m trying to convert a HABTM w/attributes join table in my database into a join model table in order to utilize the new has\_many :through functionality introduced in Rails 1.1. Here’s the current table definition: licenses\_user\_groups: license\_id, user\_group\_id, usage\_notes Perhaps it was a mistake, but I made (license\_id, user\_group\_id) the primary key. Now, after playing with has\_many :through, I have discovered that, among other modifications, I really need to add an id column to the table and make it the primary key. However, I cannot figure out how to use the SchemaStatements to add the new column, set it to auto-increment, and then redefine the primary key to be the id column instead of the (license\_id, user\_group\_id) columns. I could use the execute statement and use SQL directly, but I would prefer not to (one of the reasons behind migrations, I thought, was to provide a DB independent way of creating and modifying schemas; using SQL directly makes it possible and likely that database specific changes will be introducted). Any help (or confirmation that execute is the only way to do what I’m looking to do) would be appreciated. Thanks. David. ---
**Author:** ![dawillis](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ebca7d/32.png) [@dawillis](https://www.ruby-forum.com/u/dawillis)\ **Post date:** [April 20, 2006, 10:05pm UTC](https://www.ruby-forum.com/t/using-migrations-to-convert-join-table-to-join-model/58350/2 "2006-04-20T22:05:39Z")
Anyone out there? ---
**Author:** ![dawillis](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ebca7d/32.png) [@dawillis](https://www.ruby-forum.com/u/dawillis)\ **Post date:** [April 20, 2006, 10:23pm UTC](https://www.ruby-forum.com/t/using-migrations-to-convert-join-table-to-join-model/58350/3 "2006-04-20T22:23:27Z")
Hello David, > provide a DB independent way of creating and modifying schemas; > using > SQL directly makes it possible and likely that database specific changes > will be introducted). Maybe I’m wrong but i don’t think it’s possible without a direct SQL execute statement. For me, the primary key is created during a #create\_table call. And there are no methods to suppress or create a primary key (or I haven’t found them yet). The only way I see : create another table with a primary key id, transfer the date into it, suppress the old join model table. Not nice. The simplest way is the SQL statement… ``` -- Jean-François. ``` ---
**Author:** ![dawillis](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ebca7d/32.png) [@dawillis](https://www.ruby-forum.com/u/dawillis)\ **Post date:** [April 20, 2006, 10:40pm UTC](https://www.ruby-forum.com/t/using-migrations-to-convert-join-table-to-join-model/58350/4 "2006-04-20T22:40:17Z")
Jean-François wrote: > Maybe I’m wrong but i don’t think it’s possible without a direct > SQL execute statement. For me, the primary key is created > during a #create\_table call. And there are no methods to suppress > or create a primary key (or I haven’t found them yet). > > The only way I see : create another table with a primary key id, > transfer the date into it, suppress the old join model table. > > Not nice. Yep, that sounds about right to me. There’s a bug in trac to support this funcitonality. Didn’t make it into 1.1, and it’s now slated for 1.2. [http://dev.rubyonrails.org/ticket/3735](http://dev.rubyonrails.org/ticket/3735) – Josh S. [http://blog.hasmanythrough.com](http://blog.hasmanythrough.com) ---
**Author:** ![dawillis](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ebca7d/32.png) [@dawillis](https://www.ruby-forum.com/u/dawillis)\ **Post date:** [April 21, 2006, 12:25am UTC](https://www.ruby-forum.com/t/using-migrations-to-convert-join-table-to-join-model/58350/5 "2006-04-21T00:25:57Z")
Josh S. wrote: Jean-François wrote: Thanks for your responses; it is what I feared, but at least I can do what I need to. Am I just weird? I can’t be the only person running into all of these has\_many :through issues and using migrations to convert a HABTM join table into a has\_many :through join model. I’ve also had issues with migrations not support foreign keys and such; my experiences are making me feel like a lot of RoR features are rather incomplete. Like I said, I appreciate the confirmation both of you provided. David. ---
**Author:** ![dawillis](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/ebca7d/32.png) [@dawillis](https://www.ruby-forum.com/u/dawillis)\ **Post date:** [April 21, 2006, 1:22am UTC](https://www.ruby-forum.com/t/using-migrations-to-convert-join-table-to-join-model/58350/6 "2006-04-21T01:22:46Z")
David W. wrote: > Am I just weird? I can’t be the only person running into all of these > has\_many :through issues and using migrations to convert a HABTM join > table into a has\_many :through join model. I’ve also had issues with > migrations not support foreign keys and such; my experiences are making > me feel like a lot of RoR features are rather incomplete. :through associations are still a relatively new feature, and there are some facets that are incomplete. When you run into missing piece, the best thing you can do is to make sure there is a ticket in trac. Either create a new ticket, or add any pertinent information that is missing from an existing ticket. Test cases can help. And if want to submit a patch (with test cases) to fix the problem, go for it! I gotta say though, you may be borrowing trouble here. Rather than do things the “right” way using database agnostic migrations, just do the simplest thing that will work (without causing you grief later on). – Josh S. [http://blog.hasmanythrough.com](http://blog.hasmanythrough.com)