Rails - Feb 2008 - clear persistent model associations for objects in session

I have an order form that is comprised of a lot of :has_many and
:has_one associations. I want to load the object into the session, with
all associations and edit it.

I want the whole submission process to be done atomically for objects at
once. So if I add or edit items on the order, I don''t want to be saved
to the database until the user clicks submit.

The problem is that I save the order in the session, but the
associations get refreshed every time the page reloads. I looked at the
code in ction_controller/session_management.rb and
clear_persistent_model_associations() takes care of removing
associations.

Any suggestions on how to handle this?
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Constantin Gavrilescu wrote:
> I have an order form that is comprised of a lot of :has_many and
> :has_one associations. I want to load the object into the session, with
> all associations and edit it.
> 
> I want the whole submission process to be done atomically for objects at
> once. So if I add or edit items on the order, I don''t want to be
saved
> to the database until the user clicks submit.
> 
> The problem is that I save the order in the session, but the
> associations get refreshed every time the page reloads. I looked at the
> code in ction_controller/session_management.rb and
> clear_persistent_model_associations() takes care of removing
> associations.
> 
> Any suggestions on how to handle this?
You can serialize and deserialize the whole structure with
to_json and from_json, specifying the includes.

But because cookie sessions are limited to 4KB, you should
probably store associated ids instead. e.g. create a model
attribute that on read converts a has_many to an array of ids,
and on write populates the has_many from an array.  The
association is re-loaded, but you re-create the right set of
associates.

-- 
We develop, watch us RoR, in numbers too big to ignore.


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Mark Reginald James wrote:
> Constantin Gavrilescu wrote:
>> code in ction_controller/session_management.rb and
>> clear_persistent_model_associations() takes care of removing
>> associations.
>> 
>> Any suggestions on how to handle this?
> 
> You can serialize and deserialize the whole structure with
> to_json and from_json, specifying the includes.
Marshal dump() and load() saves associated objects, too. Is there some 
specific reason why I should use json?

Maybe I need to explain what I want to achieve. I have an order with a 
multitude of associated associations which, to further complicate 
things, have more associations, like extra charges.

Something like:
order has many containers
container has many extra charges

The user edits the order, adds or deletes containers, adds or deletes 
extra charges to the containers. The problem is that I want all the 
changes to be saved the the user presses the "Save order" button, not 
when he adds or edits each container or extra charge. I wanted to save 
the whole order and associations in the session until it''s ready to
save
in one atomic operation, but it seems there''s no easy way to do this 
with the way Rails and ActiveRecord works.
>> Order.find(20).containers.size
=> 1
>>
?> o = Order.find(20)
=> #<ImportOrder:0x46b3934 @attributes=....
>> o.containers.size
=> 1
>> o.containers = Hash.new #This will delete all containers in the
database, not just in the memory.
=> {}
>Order.find(20).containers.size
=> 0

So when I work with activerecord objects, they might get commited to the 
database when I don''t really want that.

> But because cookie sessions are limited to 4KB, you should
> probably store associated ids instead. e.g. create a model
> attribute that on read converts a has_many to an array of ids,
> and on write populates the has_many from an array.  The
> association is re-loaded, but you re-create the right set of
> associates.
> 
> --
> We develop, watch us RoR, in numbers too big to ignore.
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Constantin Gavrilescu wrote:
> Maybe I need to explain what I want to achieve. I have an order with a 
> multitude of associated associations which, to further complicate 
> things, have more associations, like extra charges.
> 
> Something like:
> order has many containers
> container has many extra charges
> 
> The user edits the order, adds or deletes containers, adds or deletes 
> extra charges to the containers. The problem is that I want all the 
> changes to be saved the the user presses the "Save order" button,
not
> when he adds or edits each container or extra charge. I wanted to save 
> the whole order and associations in the session until it''s ready
to save
> in one atomic operation
I found a way to keep all my order objects into the session until they 
are ready to be saved: redefine clear_association_cache for class order 
and it''s subclasses.

def clear_association_cache
  return if self.class.to_s =~ /Order$/
  super
end

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This seems to address the same problem that i''m trying to find a 
suitable workaround for.

I''ve tried your solution (redefining the clear_association_cache method
on the parent object) and on first try it looks to be achieving the 
desired effect of maintaining the child data in the session.

I was just wondering if this solution ended up working for you 
long-term, or if any undesirable side effects appeared?

Thanks very much for your time,

jesse

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