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
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
On 4/20/06, Brian V Hughes [email protected] 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
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 ([email protected])
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)
“Ruby for Rails” PDF now on sale! Ruby for Rails
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On 4/20/06, [email protected] [email protected] 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