Rails - Sep 2007 - Is "has_many ... :through" faster?

I have a table which maps users to photo album as hosts:


   | Album table |   =>  | Hosts |  <=>  | Users |


Sometimes I need to query if a user is a host of an album:

   if album.hosts.include? user

Which I cannot do because "hosts" is an array of Host models -- not
users.   I was wondering which solution be faster, or perform better.

This:

   has_many :host_users, :through => :hosts, :source => :user

Or:

   def host_users

      # Create table as instance variable
      if !@hostUsersTbl
         hosts.each do |h|
            @hostUsersTbl[h.user.id] = h
         end
      end

      @hostUsersTbl
   end

The first solution would make an extra call to the DB, but the second
is manually creating the list.  I guess I could also do this instead:

   has_and_belongs_to_many :hosts, :class_name => "User",
:join_table
=> "hosts"

But then I wouldn''t have the Host model array to manipulate (i.e.
create, delete), right?  Please advise.

Thanks,
Jeremy


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Hey Jeremy,
The way I''d do this is with a

has_many :users, :through => :hosts

I''m of course presuming that the Host model belongs to album and user,
and of course that you already have the has_many :hosts in both
user.rb and album.rb if not classes should look like

class Album<ActiveRecord:Base
  has_many :hosts
  has_many :users, :through => :hosts
end

class User<ActiveRecord:Base
  has_many :hosts
  has_many :albums, :through => :hosts
end

class Host<ActiveRecord:Base
  belongs_to :user
  belongs_to :album
end

I think this would be faster as it will only call the database when it
is needed so it won''t overload your objects or your database with
unnecessary transactions.

Hope this helps.
Cam


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