# (Many-to-many)-to many **URL:** \ **Category:** Rails\ **Created:** [February 23, 2007, 11:50am UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577 "2007-02-23T11:50:16Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [February 23, 2007, 11:50am UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/1 "2007-02-23T11:50:16Z")
I’m very new at rails and wondering if ActiveRecord supports (many-to- many)-to many relationships. For example: I have recipes, ingredients, and cookingmethods. Recipes have many ingredients, and ingredients are in many recipes. For each ingredient in a recipe, there is a different cooking method. For example, potatoes in a salad are diced, but potatoes in potato chips are sliced. Example database tables: recipes: id, name recipes\_ingredients: id, recipe\_id, ingredient\_id ingredients: ingredient\_id, name cookingmethods: id, name recipes\_ingredients\_cookingmethods: recipe\_ingredient\_id, cookingmethod\_id I looked at through associations, but those seemed to deal only with many-to-many relationships. Thanks, Gerry ---
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [February 23, 2007, 12:13pm UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/2 "2007-02-23T12:13:24Z")
I’m, looking at something similar, try this ([http://groups.google.com/group/rubyonrails-talk/browse\_frm/thread/](http://groups.google.com/group/rubyonrails-talk/browse_frm/thread/) b4e27651fb149e48?lnk=igtc) and let me know how you get on? I’d be interested in seeing your model and any extra finder methods you add… Feel free to gTalk me J ---
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [February 23, 2007, 3:05pm UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/3 "2007-02-23T15:05:44Z")
To do this, you have your ingredients, recipes and cooking\_methods tables, as well as a join table… let’s call this recipe\_ingredients. This would have foreign key columns, one for each of the other tables. Recipe has\_many :recipe\_ingredients has\_many :ingredients, :through =\> :recipe\_ingredients has\_many :cooking\_methods, :through =\> :recipe\_ingredients Ingredient has\_many :recipe\_ingredients has\_many :recipes, :through =\> :recipe\_ingredients has\_many :cooking\_methods, :through =\> :recipe\_ingredients CookingMethod has\_many :recipe\_ingredients has\_many :ingredients, :through =\> :recipe\_ingredients has\_many :recipes, :through =\> :recipe\_ingredients RecipeIngredient belongs\_to :recipe belongs\_to :ingredient belongs\_to :cooking\_method There. It’s quite easy really. You just have to break down three-way relationships into two way ones, and that’ll solve any (database) relationship problems. Hope this helps, -Nathan ---
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [February 23, 2007, 3:07pm UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/4 "2007-02-23T15:07:45Z")
\*this would have three foreign key columns, one for each of the other tables. ---
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [February 23, 2007, 9:13pm UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/5 "2007-02-23T21:13:52Z")
Thanks. I’ll try that out. I’ve never gotten such a quick answer from posting a programming question on any forum before. Gerry ---
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [February 23, 2007, 3:54pm UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/6 "2007-02-23T15:54:55Z")
I’d be interested to see how the and controllers and views should be constructed for this model J ---
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [February 24, 2007, 12:17pm UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/7 "2007-02-24T12:17:11Z")
My inner database normalization conscience has some misgivings about this schema. Suppose the number of cooking methods is large compared to the number of recipe/ingredients. So potatoes in potato chips can be sliced, diced, grated… Then I’ll end up duplicating the recipe/ ingredients foreign keys a lot in the join table. Suppose further that people can comment on each recipe/ingredient/ cooking method combination. I would have to add a “comments” column to recipes\_ingredients. Then for each comment, I’ll have to duplicate the keys for recipes/ingredients/cookingmethod…this is clearly unnormalized. So I think my original schema gives me more flexibility in the long run. Any way I can get rails to work with the original schema (see first post in thread)? Thanks for your help. Gerry ---
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [February 26, 2007, 5:37am UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/8 "2007-02-26T05:37:46Z")
On 2/24/07, mastica [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > keys for recipes/ingredients/cookingmethod…this is clearly > unnormalized. normalisation is not necessarily the best design in all cases… but I digress… > So I think my original schema gives me more flexibility in the long > run. Any way I can get rails to work with the original schema (see > first post in thread)? Of course. You need to promote your ingredient/cookingmethod table to a proper first-class model. If you find yourself talking (or thinking) about a join table a lot, it’s usually a sign that it wants to be a model. You’ll also want to read up on has\_many :through. Let’s call that model Preparation. You then have: class Ingredient has\_many :preparations has\_many :cooking\_methods, :through=\>:preparations has\_many :recipes, :through=\>:preparations end class Recipe has\_and\_belongs\_to\_many :preparations has\_many :ingredients, :through=\>:preparations end class CookingMethod has\_many :preparations has\_many :ingredients, :through=\>:preparations end class Preparation has\_and\_belongs\_to\_many :recipes belongs\_to :ingredient belongs\_to :cooking\_method end 5 tables total, one for each of the models, plus a preparations\_recipes table. –max ---
**Author:** ![mastica](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mastica](https://www.ruby-forum.com/u/mastica)\ **Post date:** [March 12, 2007, 3:07pm UTC](https://www.ruby-forum.com/t/many-to-many-to-many/86577/9 "2007-03-12T15:07:43Z")
Im getting an error when running an app under fastCGI file …/public\_html/…/config/…/tmp/sessions//ruby\_sess.(whatver) not readable app works fine under regular cgi. What would cause this?