# Question about Associations **URL:** \ **Category:** Rails\ **Created:** [April 20, 2006, 11:21pm UTC](https://www.ruby-forum.com/t/question-about-associations/58368 "2006-04-20T23:21:57Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![johnt519](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/cab0a1/32.png) [@johnt519](https://www.ruby-forum.com/u/johnt519)\ **Post date:** [April 20, 2006, 11:21pm UTC](https://www.ruby-forum.com/t/question-about-associations/58368/1 "2006-04-20T23:21:57Z")
Hi all. Got a stupid-simple question about associations. I have two models - school and course. There are a fixed number of schools (set up in the migration). Each course is assigned a school and a school will be associated with multiple courses… How do I set up the associations? Do (can) I have School :has\_one :course and Course :has\_many :schools? Does the schools table then get a course\_id field or the other way around? I don’t think I should have course :belongs\_to School, as there will only be one instance of a school in the Schools table. Thanks! jt ---
**Author:** ![johnt519](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/cab0a1/32.png) [@johnt519](https://www.ruby-forum.com/u/johnt519)\ **Post date:** [April 20, 2006, 11:40pm UTC](https://www.ruby-forum.com/t/question-about-associations/58368/2 "2006-04-20T23:40:22Z")
On Apr 20, 2006, at 05:16 PM, John T. wrote: > Hi all. Got a stupid-simple question about associations. I have two > models - school and course. There are a fixed number of schools (set > up in the migration). Each course is assigned a school and a school > will be associated with multiple courses… > > How do I set up the associations? Do (can) I have School :has\_one > :course and Course :has\_many :schools? If “a school will be associated with multiple courses”, then School has\_many: courses, which means Course belongs\_to :school. The fact that there are a fixed number of schools is actually irrelevant to how the two tables of data relate to each other. You only use has\_one when a row from table a is related to one, and only one, row from table b. That’s not what you’ve described here. > Does the schools table then get a course\_id field or the other way > around? Again, if a “course is assigned a [to a] school”, then the courses table has a shool\_id field. This is also specified by the association. > I don’t think I should have course :belongs\_to School, as there will > only be one instance of a school in the Schools table. Honestly, I’ve never thought about which model I “wanted” to have the belongs\_to association defined in. That was always done naturally by the nature of the relation. Obviously, in a 1-to-1 relation, it’s possible to swap the has\_one and belongs\_to, but I would say that which ever model you expect to refer to, most often, gets the has\_one, and the not-most-often model gets the belongs\_to. -Brian ---
**Author:** ![johnt519](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/cab0a1/32.png) [@johnt519](https://www.ruby-forum.com/u/johnt519)\ **Post date:** [April 21, 2006, 12:07am UTC](https://www.ruby-forum.com/t/question-about-associations/58368/3 "2006-04-21T00:07:58Z")
On 4/20/06, Brian V Hughes [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > If “a school will be associated with multiple courses”, then School > has\_many: courses, which means Course belongs\_to :school. The fact > that there are a fixed number of schools is actually irrelevant to > how the two tables of data relate to each other. You only use has\_one > when a row from table a is related to one, and only one, row from > table b. That’s not what you’ve described here. Thanks for the info. I think I did get it figured out, with some help from the IRC chat. I have it set up with school :has\_many courses and the courses table will have a school\_id. And course :belongs\_to schools. > > Does the schools table then get a course\_id field or the other way > > around? > > Again, if a “course is assigned a [to a] school”, then the courses > table has a shool\_id field. This is also specified by the association. Correct, as was pointed out to me. > -Brian I was looking too close to the problem - I was getting a little confused because I knew that the model that had the “belongs\_to” is the one that has the foreign key (per the docs). Just took a second opinion to see the light 🙂 Thanks again ---
**Author:** ![johnt519](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/cab0a1/32.png) [@johnt519](https://www.ruby-forum.com/u/johnt519)\ **Post date:** [April 21, 2006, 12:14am UTC](https://www.ruby-forum.com/t/question-about-associations/58368/4 "2006-04-21T00:14:18Z")
Hi – On Thu, 20 Apr 2006, John T. wrote: > > > How do I set up the associations? Do (can) I have School :has\_one > > > :course and Course :has\_many :schools? A small, but not really small, point: it’s has\_one and has\_many, not :has\_one and :has\_many. They’re method calls, not symbols 🙂 David – David A. Black (removed\_email\_address@domain.invalid) Ruby Power and Light, LLC ([http://www.rubypowerandlight.com](http://www.rubypowerandlight.com)) “Ruby for Rails” PDF now on sale! [Ruby for Rails](http://www.manning.com/black) Paper version coming in early May! ---
**Author:** ![johnt519](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/cab0a1/32.png) [@johnt519](https://www.ruby-forum.com/u/johnt519)\ **Post date:** [April 21, 2006, 12:17am UTC](https://www.ruby-forum.com/t/question-about-associations/58368/5 "2006-04-21T00:17:27Z")
On 4/20/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > How do I set up the associations? Do (can) I have School :has\_one > > > > :course and Course :has\_many :schools? > > A small, but not really small, point: it’s has\_one and has\_many, not > :has\_one and :has\_many. They’re method calls, not symbols 🙂 Heh… of course. Got a little over zealous with the colon key 😉 jt