I am wondering if any one could explain table relationships for me using
rails. What I am trying to do requires the joining of a product and the
comments for the product, with the user information of whom posted the
comment. So I have a products table that references a comments table
that is referenced by the product_id and the product_type, and the
comments table gets user information from the users table by a user_id.
So right now, I am familiar with has_ and belongs_to, but
don’t know how to make it work with what I am trying to do, and thus the
further explanation.
Thanks for all of that. But how would I create relationships where i use
a foreign key in the has_many and belongs_to declarations? So for
instance if I automatically wanted to return all the comments and the
users of the comments without having to use the :include parameter?
On 7/9/07, Scott Pn [email protected] wrote:
Thanks for all of that. But how would I create relationships where i use
a foreign key in the has_many and belongs_to declarations? So for
instance if I automatically wanted to return all the comments and the
users of the comments without having to use the :include parameter?
I’m not sure what you mean, honestly. has_many and belongs_to rely on
there being a foreign key. The comments table would have a product_id
foreign key to products, as well as a user_id key to users. Having
those keys and the corresponding has_many and belongs_to statements
set up the relationship to be used programmatically.
I don’t know how you would automatically load the associations without
:include. Why do you want to?
The best I think you could do is to write a new finder or override the
default finder, this way you can encapsulate the call.
class Product < ActiveRecord::Base
def self.heavy_find(id, options = {})
find(id, { :include => [ :comments => :users ] }.merge(options))
end
OR
def self.find(id, options = {})
super(id, { :include => [ :comments => :users ] }.merge(options))
end
end
shrug
Pat
On 7/8/07, Scott Pn [email protected] wrote:
–
Posted via http://www.ruby-forum.com/.
Hey Scott,
That’s a pretty easy set up. You won’t have to do any joins, Rails
will take care of everything for you 
Anyway, now that you’ve got the tables set up, you can use AR’s has_*
and belongs_to methods to set up the associations.
class Product
has_many :comments
end
class Comment
belongs_to :user
end
You can set up the reverse associations if you want/need to.
This code will let you do something like:
p = Product.find 1
p.comments.first.user.username # ‘dopey’
comments of course is the collection of all comments, and for each
comment you have access to the user object.
Now one problem is that if you have 1 product with 10 comments, you’ll
end up making 21 db calls. 1 for the product itself, 10 for each of
the comments, and 10 for the associated user. Fortunately Rails lets
you eager load the assocations.
p = Product.find 1, :include => :comments
will take care of the join for you to include comments, so they’re
fetched along with the product. You can also go as deep as you need:
p = Product.find 1, :include => [ :comments => :user ]
This will fetch all the data you need in one query.
Pat
Pat M. wrote:
On 7/9/07, Scott Pn [email protected] wrote:
Funny, http://agilewebdevelopment.com/plugins/includebydefault was
just published to the rails plugins repository. Looks like it ought
to do exactly what you want.Pat
o, awesome, thanks for the find.
On 7/9/07, Scott Pn [email protected] wrote:
Funny, http://agilewebdevelopment.com/plugins/includebydefault was
just published to the rails plugins repository. Looks like it ought
to do exactly what you want.
Pat