Rails - Dec 2009 - Validating the presence of two associated objects from both models

I have a model “Conversation” and a model “Leader”. A Conversation is always led
by exactly 1 Leader.

I’ve overridden Conversation’s “validate” method to validate the presence of an
associated Leader model.

If I add a similar validation to the Leader model, however, Conversations can no
longer be saved on creation because the Leader model is invalid.

On creation of both a new Conversation and new Leader how can I validate in each
model that it is associated with the other? Is there a best practice? The
closest I’ve come is to override Leader’s “validate_on_update” method to ensure
the presence of a Conversation but that still allows new Leader objects to be
created without a Conversation, filling my tables with junk.

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How about this:

class Conversation < ActiveRecord::Base
  validates_presence_of :leader
end

That way you can''t save a conversation without assigning it a leader,
but the leader doesn''t have to be saved yet.

On Dec 30, 3:30 pm, Evan Chaney
<evancha...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I have a model “Conversation” and a model “Leader”. A Conversation is
always led by exactly 1 Leader.
>
> I’ve overridden Conversation’s “validate” method to validate the presence
of an associated Leader model.
>
> If I add a similar validation to the Leader model, however, Conversations
can no longer be saved on creation because the Leader model is invalid.
>
> On creation of both a new Conversation and new Leader how can I validate in
each model that it is associated with the other? Is there a best practice? The
closest I’ve come is to override Leader’s “validate_on_update” method to ensure
the presence of a Conversation but that still allows new Leader objects to be
created without a Conversation, filling my tables with junk.
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> That way you can''t save a conversation without assigning it a
leader,
> but the leader doesn''t have to be saved yet.
Well, that’s where I’m at right now. I’d like to be in a situation where
Conversation validates that it has a Leader and Leader validates it has a
Conversation before either is saved.

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Evan,

Don''t overdo your requirements. Take your requirements lightly.

From what I can see in your example, Leader plays a larger role in your
domain, so it has priority over the Conversation.

I would model Leader having zero or more (0..*) Conversations, Conversation
having 1 Leader. A simple one to many relationship between those domain
objects.

As from what I can tell, your are trying to create both at the same time in
the view, thus sending both objects over to the controller.

While creating a Conversation, you could give the user the opportunity to
create a Leader, if its currently not available, or he wants to get a new
one. You could use AJAX to access the create action in the leader controller
having it available prior to saving the Conversation.

Check out this resource by Ryan Bates.
http://railscasts.com/episodes/57-create-model-through-text-field

Regards,
Rodrigo Dellacqua
IBM - IGF Project Manager
"Communication is the key"

On Wed, Dec 30, 2009 at 8:50 PM, Evan Chaney
<evanchaney-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > That way you can''t save a conversation without assigning it a
leader,
> > but the leader doesn''t have to be saved yet.
>
> Well, that’s where I’m at right now. I’d like to be in a situation where
> Conversation validates that it has a Leader and Leader validates it has a
> Conversation before either is saved.
>
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Evan Chaney wrote:
>> That way you can''t save a conversation without assigning it a
leader,
>> but the leader doesn''t have to be saved yet.
> 
> Well, that�s where I�m at right now. I�d like to be in a situation where 
> Conversation validates that it has a Leader and Leader validates it has 
> a Conversation before either is saved.
>
Just validate that there are keys: Conversation validates_presence_of 
:leader, Leader validates_presence_of :conversation (perhaps).  Do the 
rest with foreign key constraints in the DB.  As you''ve discovered, the
application layer is the wrong place for this sort of simple integrity 
check.
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Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
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Posted via http://www.ruby-forum.com/.

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