Has Many Through Question

Rails
1

I have a relations question. I have an events table where each event is
owned by a user. So…

class Event < ActiveRecord::Base
belongs_to :user
end

And a user…

class User < ActiveRecord::Base
has_many :events
end

But, I also have an attendance_lists table so that other users can say
they are attending an event (or not attending). So…

class AttendanceList < ActiveRecord::Base
belongs_to :users
belongs_to :events
end

But now, if I’m going to add the relations to the user and event
models, it would seem I would have…

class Event < ActiveRecord::Base
belongs_to :user
has_many :attendance_lists
has_many :users, :through => :attendance_lists
end
class User < ActiveRecord::Base
has_many :events
has_many :attendance_lists
has_many :events, :through => :attendance_lists
end

My question is whether ActiveRecord will be able to differentiate,
using the relations above, the events a user is in charge of and events
a user is attending. In the user model, will having two has_many
:events, even though one has a :through clause, confuse ActiveRecord?
Am I confused and not including something I should be?

2

Dylan B. wrote:

I have a relations question. I have an events table where each event is
owned by a user. So…

class Event < ActiveRecord::Base
belongs_to :user
end

And a user…

class User < ActiveRecord::Base
has_many :events
end

But, I also have an attendance_lists table so that other users can say
they are attending an event (or not attending). So…

class AttendanceList < ActiveRecord::Base
belongs_to :users
belongs_to :events
end

But now, if I’m going to add the relations to the user and event
models, it would seem I would have…

class Event < ActiveRecord::Base
belongs_to :user
has_many :attendance_lists
has_many :users, :through => :attendance_lists
end
class User < ActiveRecord::Base
has_many :events
has_many :attendance_lists
has_many :events, :through => :attendance_lists
end

My question is whether ActiveRecord will be able to differentiate,
using the relations above, the events a user is in charge of and events
a user is attending. In the user model, will having two has_many
:events, even though one has a :through clause, confuse ActiveRecord?
Am I confused and not including something I should be?

Just name the associations so that you (and ActiveRecord) can
distinguish them. By default AR will infer things like class and foreign
key from the association name, but you can override those things using
:class_name and :foreign_key options on the association. I have many
examples of doing that on my blog, particularly these:
http://blog.hasmanythrough.com/articles/2006/04/21/self-referential-through
http://blog.hasmanythrough.com/articles/2006/05/06/through_gets_uniq

–
Josh S.
http://blog.hasmanythrough.com

3

Thanks! I actually dug through your blog looking for something, but I
think I just didn’t know what I was looking for yet. I replaced this…

has_many :events, :through => :attendance_lists

…with this…

has_many :events_to_attend, :through => :attendance_lists,
:foreign_key => “event_id”, :class_name => “Event”

Thanks for the help!

4

Okay, looking at this again, I think I was wrong. Looking in the API
docs, it seems I would need to do…

has_many :events_to_attend, :through => :attendance_lists, :source =>
:event

Is that right?