Rails - Oct 2005 - habtm and eager loading

OK, bare (bear?) with me here :)

I have three tables... users, groups and meetings

users habtm groups         via join table groups_users
users habtm meetings     via join_table attendees
groups habtm users         via join table groups_users
groups habtm meetings  via groups_meetings
meetings habtm users     via attendees
meetings habtm groups  via groups_meetings

The attendees join table provides some rich assoociation attributes,  
such as attendance status, special requirements, that sort of thing

So, we have a triangular set of tables each with many-many  
relationships. The users-meetings association is needed due to the  
extra user specific information it provides.

Anyway... I''m having some difficulties grasping how I might undertake  
eager loading of associations in a couple of scenarios. For instance,  
I want to get a list of meetings for a user... easy, I simply call  
user.meetings and bingo! There it is. BUT, iterating through those  
meetings and retrieving the attendee list for each one results in a  
LOT of queries. I''ve looked at eager loading but can''t really
work
out how to apply it here.

I''ve checked the documentation and the wiki and kind of understand I  
should do something like:

Meeting.find(:all, :include => :users)

But what I don''t understand is what conditions I need to provide to  
limit it to just this users'' meetings.

I would appreciate any help/advice/word of wisdom muchly.

Ta,
Steve

On 4 Oct 2005, at 16:43, Steven Mohapi-Banks wrote:
> OK, bare (bear?) with me here :)
Well, I''ll bear. But whatever floats your boat. ;)
> Meeting.find(:all, :include => :users)
>
> But what I don''t understand is what conditions I need to provide
to
> limit it to just this users'' meetings.
You could build an ''in'' condition. Off the top of my head:

   user_meeting_ids = user.meetings.map {|m| m.id }

   Meeting.find(:all, :include => :users,
     :conditions => [''meetings.id in (?)'',
user_meeting_ids.join('','')])

Or somesuch. Maybe there''s a neater way of doing this?

Hope this helps.

	Mike

Cheers Mike,

Just a quick note to say that the call to join in the conditions  
statement is unnecessary.

Seems to have done the job though. Ace!

Steve

On 4 Oct 2005, at 17:18, Michael Houghton wrote:
>
> On 4 Oct 2005, at 16:43, Steven Mohapi-Banks wrote:
>
>
>> OK, bare (bear?) with me here :)
>>
>
> Well, I''ll bear. But whatever floats your boat. ;)
>
>
>> Meeting.find(:all, :include => :users)
>>
>> But what I don''t understand is what conditions I need to
provide
>> to limit it to just this users'' meetings.
>>
>
> You could build an ''in'' condition. Off the top of my
head:
>
>   user_meeting_ids = user.meetings.map {|m| m.id }
>
>   Meeting.find(:all, :include => :users,
>     :conditions => [''meetings.id in (?)'',
user_meeting_ids.join('','')])
>
> Or somesuch. Maybe there''s a neater way of doing this?
>
> Hope this helps.
>
>     Mike
>
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>

On 4 Oct 2005, at 17:50, Steven Mohapi-Banks wrote:
> Cheers Mike,
>
> Just a quick note to say that the call to join in the conditions 
> statement is unnecessary.
Really? it joins with a comma by itself? cool :)