# Challenge **URL:** \ **Category:** Rails\ **Created:** [November 14, 2005, 3:31pm UTC](https://www.ruby-forum.com/t/challenge/95592 "2005-11-14T15:31:59Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![allenbobo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/46a35a/32.png) [@allenbobo](https://www.ruby-forum.com/u/allenbobo)\ **Post date:** [November 14, 2005, 3:31pm UTC](https://www.ruby-forum.com/t/challenge/95592/1 "2005-11-14T15:31:59Z")
i love ROR. but i met a problem : i have a table: users id int not null, name varchar(100)… and i want create a friends association, seems many-to-many self-referential i create a friends table: user\_id int not null, friend\_id int not null, constraint fk\_fu\_user foreign key (user\_id) references users(id), constraint fk\_fu\_friend foreign key (friend\_id) references users(id) … the user Model contains has\_many :friends the friend Model contains belongs\_to :user i hope it’s ok ,but when i test it allways: “Couldn’t find Firend without a ID” so, guys, if you know what’s goning on, please give a hand. all regards ---
**Author:** ![allenbobo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/46a35a/32.png) [@allenbobo](https://www.ruby-forum.com/u/allenbobo)\ **Post date:** [November 14, 2005, 3:38pm UTC](https://www.ruby-forum.com/t/challenge/95592/2 "2005-11-14T15:38:00Z")
There is a good article on this on the wiki [http://wiki.rubyonrails.com/rails/pages/HowToCreateASelfReferentialManyToManyRelationship](http://wiki.rubyonrails.com/rails/pages/HowToCreateASelfReferentialManyToManyRelationship) Maybe this will help Cheers ---
**Author:** ![allenbobo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/46a35a/32.png) [@allenbobo](https://www.ruby-forum.com/u/allenbobo)\ **Post date:** [November 14, 2005, 3:50pm UTC](https://www.ruby-forum.com/t/challenge/95592/3 "2005-11-14T15:50:05Z")
Hello, ``` Don't know if this will help or not, but In the Active Record docs ``` there is an ‘act as tree’ which works as a one to many on itself. It has allot of info about how this is done in the modal, you could most likely get some ideas from that as well. Chanan Braunstein Knovel Corp. Web D. Manager 607-773-1840 x672 [http://www.knovel.com](http://www.knovel.com) * * * From: removed\_email\_address@domain.invalid [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)] On Behalf Of Liquid Sent: Monday, November 14, 2005 9:36 AM To: removed\_email\_address@domain.invalid Subject: Re: [Rails] challenge There is a good article on this on the wiki [http://wiki.rubyonrails.com/rails/pages/HowToCreateASelfReferentialManyToMan](http://wiki.rubyonrails.com/rails/pages/HowToCreateASelfReferentialManyToMan) yRelationship \<[Peak Obsession](http://wiki.rubyonrails.com/rails/pages/HowToCreateASelfReferentialManyToMa) nyRelationship\> Maybe this will help Cheers On 11/15/05, allenbobo [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: i love ROR. but i met a problem : i have a table: users id int not null, name varchar(100)… and i want create a friends association, seems many-to-many self-referential i create a friends table: user\_id int not null, friend\_id int not null, constraint fk\_fu\_user foreign key (user\_id) references users(id), constraint fk\_fu\_friend foreign key (friend\_id) references users(id) … the user Model contains has\_many :friends the friend Model contains belongs\_to :user i hope it’s ok ,but when i test it allways: “Couldn’t find Firend without a ID” so, guys, if you know what’s goning on, please give a hand. all regards ---
**Author:** ![allenbobo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/46a35a/32.png) [@allenbobo](https://www.ruby-forum.com/u/allenbobo)\ **Post date:** [November 14, 2005, 3:53pm UTC](https://www.ruby-forum.com/t/challenge/95592/4 "2005-11-14T15:53:05Z")
“Couldn’t find Firend without a ID” I hope this is a typo and not copied and pasted from the error! In which case you would have to start looking at where you are trying to reference a “Firend” -note the typo regards, Franc Paul ---
**Author:** ![allenbobo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/46a35a/32.png) [@allenbobo](https://www.ruby-forum.com/u/allenbobo)\ **Post date:** [November 14, 2005, 4:42pm UTC](https://www.ruby-forum.com/t/challenge/95592/5 "2005-11-14T16:42:09Z")
thanks all the guys reply my “challenge”. and “liquid” give us a good link it’s solve this kind of problem. here: [http://wiki.rubyonrails.com/rails/pages/HowToCreateASelfReferentialManyToManyRelationship](http://wiki.rubyonrails.com/rails/pages/HowToCreateASelfReferentialManyToManyRelationship) cheers ---
**Author:** ![allenbobo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/46a35a/32.png) [@allenbobo](https://www.ruby-forum.com/u/allenbobo)\ **Post date:** [November 22, 2005, 12:03am UTC](https://www.ruby-forum.com/t/challenge/95592/6 "2005-11-22T00:03:56Z")
I am having a similar problem, I have a category model which is defined to “acts\_as\_tree”. The table structure looks like this: create table categories ( id INT not null auto\_increment, name VARCHAR(200) not null, parent\_id int, description TEXT , created\_on DATETIME null, updated\_on DATETIME null, constraint fk\_categories\_to\_categories foreign key (parent\_id) references categories(id), primary key (id) ); as you can see the foreign key is a reference to another row in the table. For the root category I just have (NULL) specified for the parent\_id. However all of my unit tests are blowing up because it cannot find the parent category for the root category (because it does not exist). ## ERROR MESSAGE: 1. Error: test\_create(CategoryTest): ActiveRecord::StatementInvalid: #23000Cannot delete or update a parent row: a foreign key constraint fails (`itsthes_test/categories`, CONSTRAINT `fk_ categories_to_categories` FOREIGN KEY (`parent_id`) REFERENCES `categories` (`id`)): DELETE FROM categories * * * Does anyone have an idea how to solve this problem? Thanks! Mark ---
**Author:** ![allenbobo](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/46a35a/32.png) [@allenbobo](https://www.ruby-forum.com/u/allenbobo)\ **Post date:** [November 22, 2005, 1:20am UTC](https://www.ruby-forum.com/t/challenge/95592/7 "2005-11-22T01:20:23Z")
Tada! I answered my own question. I am posting my solution in hopes that he helps other developers. The problem I was facing with the unit tests was that the foreign keys needed to be added and deleted from the fixtures in a particular order. The default YAML format was not helpful in this regard. Fortunately there is such a thing as the ordered mapping language independent type : [Ordered Mapping Language-Independent Type for YAML™ Version 1.1](http://yaml.org/type/omap.html) Used in my category example it would look something like this: — !omap - parent: id: 1 parent\_id: NULL title: Parent - child: id: 2 parent\_id: 1 title: Child Later, Mark