# Join tables, must they be created manually? **URL:** \ **Category:** Rails\ **Created:** [May 19, 2007, 5:16am UTC](https://www.ruby-forum.com/t/join-tables-must-they-be-created-manually/104545 "2007-05-19T05:16:55Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![mcampbell](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mcampbell](https://www.ruby-forum.com/u/mcampbell)\ **Post date:** [May 19, 2007, 5:16am UTC](https://www.ruby-forum.com/t/join-tables-must-they-be-created-manually/104545/1 "2007-05-19T05:16:55Z")
I’m sure this is a silly question, but I’ve been reading through the agile rails book and no surprises about using join tables so far. But I looked into the rails cookbook and it has this to say on the matter: “The many-to-many relationship between recipes and tags also needs the help of Active Record declarations. We’ve added has\_and\_belongs\_to\_many :tags to recipes.rb and has\_and\_belongs\_to\_many :recipes to tags.rb. There’s no sign of the intermediate join table, recipes\_tags; this is by design. Active Record handles the complexities of maintaining many-to-many relationships and provides an intuitive interface for accessing them from within Rails.” I also looked through the sitepoint rails book and there wasn’t even a mention of defining ‘join tables’ for use with has\_and\_belongs\_to\_many. So now I’m confused, agile rails seems like a highly credible book but as far as I can tell it defines the manual creation of join tables as necessary, while the other two books either don’t mention them at all or give the impression they are maintained internally, or at least can be. I realize I’m probably overlooking something very obvious, but I’ll accept my humiliation for an answer to my dilemma 🙂 ---
**Author:** ![mcampbell](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mcampbell](https://www.ruby-forum.com/u/mcampbell)\ **Post date:** [May 19, 2007, 11:30am UTC](https://www.ruby-forum.com/t/join-tables-must-they-be-created-manually/104545/2 "2007-05-19T11:30:21Z")
All table must be created manually or (preferably) in a migration. By default (name conventings can be configured to some extent), habtm expects a table named recipes\_tags (alphabetical order) with a recipe\_id field and a tag\_id field AND NOTHING ELSE. So if you are creating it in a migration, you have to make sure you don’t get an id field. It’s easy for that to happen since migrations add it silently by default. You will want to add :id =\> false when you call create\_table in the migration On May 18, 9:16 pm, Michael C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![mcampbell](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mcampbell](https://www.ruby-forum.com/u/mcampbell)\ **Post date:** [May 19, 2007, 5:30pm UTC](https://www.ruby-forum.com/t/join-tables-must-they-be-created-manually/104545/3 "2007-05-19T17:30:56Z")
Interesting. I have not had the time to re-create the application in the Sitepoint ruby on rails book, so am I to assume there are no circumstances under which habtm could work without manually defining a join table, thus the application in the book would fail? ---
**Author:** ![mcampbell](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mcampbell](https://www.ruby-forum.com/u/mcampbell)\ **Post date:** [May 19, 2007, 10:42pm UTC](https://www.ruby-forum.com/t/join-tables-must-they-be-created-manually/104545/4 "2007-05-19T22:42:27Z")
It’s hard to believe they would overlook something that obvious. They don’t define the join table where they define the other tables? On May 19, 9:30 am, Michael C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) ---
**Author:** ![mcampbell](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/8e7dd6/32.png) [@mcampbell](https://www.ruby-forum.com/u/mcampbell)\ **Post date:** [May 20, 2007, 4:10am UTC](https://www.ruby-forum.com/t/join-tables-must-they-be-created-manually/104545/5 "2007-05-20T04:10:51Z")
On second look the habtm relationship isn’t used in the demo application, it’s merely mentioned separately, although again, there is no mention of join tables. It is a ‘beginner’ book so I suppose it’s more of a “do further research” factor rather than “forgot to include something important” factor. As for the Rails Cookbook suggesting there is “no sign of join table by design”, I’m assuming this probably means not that there isn’t a join table, but rather there doesn’t need to be a mention of it in the model. Seems like nothing more than a bit of misunderstanding on my part, thanks.