How To Delegate to the Join Model?

Daniel N
Fri, 06 Jul 2007 04:20:13 -0000

Hi,

I''m wondering if someone can help me with this.  I have a situation
where I
need to store information in the join model of a has_many :through to assist
with genearting views.  But I can''t think of an elegant and efficient
solution.


Heres an example of some code:

class Mailbox < AR::B
  has_many :mailbox_contents
  has_many :postcards, :through => ''mailbox_contents''
end

class PostCard < AR::B
  has_many :mailbox_contents
  has_many :mailboxes, :through => ''mailbox_contents''
end

class MailboxContent < AR::B
  belongs_to :mailbox
  belongs_to :postcard
end

So then I want to be able to have a default view for the post card in each
mailbox.

to do this I put a column called default_view into the MailboxContent model
so that I can track default_view per postcard inside each book.

This is because users share postcards.  They can exist in multiple users
mailboxes, and each user may want to see the image, or the text.

I came up with the following in the controller.

def index
  @mailbox = Mailbox.find( :include => :mailbox_contents, :conditions => {
:mailbox_id => params[:mailbox_id] } )
  @postcards = @mailbox.postcards
end

And then in the view

<% @postcards.each do |pc| %>
  View Type
  <%= @mailbox.mailbox_contents.find_by_postcard_id( postcard ).default_view
%>
<% end %>

**shudder** Ugly

I would like to go the other way and use something like

postcard.default_view

but I guess it would  have to be postcard.default_view_for( @mailbox )

I guess the controller code would then change to

def index
  @mailbox = MailBox.find( paras[:id] )
  @postcards = @mailbox.postcards.find( :all, :include =>
[:mailbox_contents] )
end

Then in the postcard model

class Postcard AR::B
  def default_view_for( mailbox )
    self.mailbox_contents.find_by_mailbox_id( mailbox )
  end
end

The question is, would doing this, eager loading in the controller, then
accessing the collection in the model, prevent a whole heap of db requests
in the view?

I''m hoping it will since I think the mailbox_contents association
should be
cached for each model.

Any thoughts on a more elegant and or efficient way of doing this?

Cheers
Daniel

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