# Creating a child object - handling the parent reference?

**URL:** <https://www.ruby-forum.com/t/creating-a-child-object-handling-the-parent-reference/70791>\
**Category:** Rails\
**Created:** [October 3, 2006, 1:09am UTC](https://www.ruby-forum.com/t/creating-a-child-object-handling-the-parent-reference/70791 "2006-10-03T01:09:24Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\
**Post date:** [October 3, 2006, 1:09am UTC](https://www.ruby-forum.com/t/creating-a-child-object-handling-the-parent-reference/70791/1 "2006-10-03T01:09:24Z")

</div>

All,

Looking for a best practice here. I have an object, List, that I’m  
editing in a form. List is a collection of Target objects.

One of the things that I can do in my List edit is create a new Target.  
I am trying to come up with the best way to be able to assign my new  
Target object to my List object.

I know that I can:

1. Create a hidden field in my form that holds the list id and get  
access to it that way in my “create\_target” action.

2. I could store the list id in the session (in a key such as  
“current\_list”) as soon as I hit the “edit list” function and have  
access to it that way.

Are there any other options?

Anyone care to advise on a best practice?

Thanks,  
Wes

---

<div class="post-metadata">

**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\
**Post date:** [October 3, 2006, 2:22am UTC](https://www.ruby-forum.com/t/creating-a-child-object-handling-the-parent-reference/70791/2 "2006-10-03T02:22:23Z")

</div>

Quickly, here’s what I did:

Parent controller (ListController):

def add\_target  
flash[:current\_list\_id] = @target\_list.id  
redirect\_to(:controller =\> ‘target’, :action =\> ‘create’)  
end

Child controller (Target):

def create  
@target = Target.new  
@target.target\_list = TargetList.find(flash[:current\_list\_id]) if  
flash[:current\_list\_id]  
session[:new\_target] = @target  
render(:action =\> ‘edit’)  
end

I think this, and allowing for quick on-screen messages is the only  
reason to use the flash - but it is very handy for these cases when I  
have complete control over the requests.

Fear not, the session[:new\_target] object is set to nil upon the  
successful save of the target.

Thanks,  
Wes

---

<div class="post-metadata">

**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\
**Post date:** [October 3, 2006, 8:20am UTC](https://www.ruby-forum.com/t/creating-a-child-object-handling-the-parent-reference/70791/3 "2006-10-03T08:20:02Z")

</div>

Max,

I see your point on the session issue and I can agree on your two  
potential solutions for getting around using the flash.

However, the session[:new\_target] object is really what I’d call a “form  
bean” in the Java world - it is the new target object until it  
successfully gets created in the database upon the first successful  
save.

I’m not a big fan of creating stuff in the database until it is really  
necessary, so I need someplace to store the new target until it is  
saved. What are your thoughts?

In general, the synchronization issue that you bring up where one user  
may interact through my application through many browsers is valid.  
Although I think you probably run into this issue as soon as you store  
_anything_ in the session, not just the stuff that I was proposing. I  
can’t remember if/how we ever got around that in Java - based Web apps.  
I believe a custom request - synchronization scheme would be required,  
no?

Wes

---

<div class="post-metadata">

**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\
**Post date:** [October 3, 2006, 2:46am UTC](https://www.ruby-forum.com/t/creating-a-child-object-handling-the-parent-reference/70791/4 "2006-10-03T02:46:25Z")

</div>

On 10/3/06, Wes G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> I know that I can:  
> Anyone care to advise on a best practice?

Storing this kind of information in the session is generally a bad  
idea. There are always those power users that insist on opening  
several browser windows for the same session. In that case, you open  
up the possibility of invalid data being written to the db. Of course,  
you can get around this with some sort of request key mechanism that  
detects double posting, but that’s more trouble than it’s worth.

Two ways of handling this are posting the parent id in a hidden field,  
or making the parent id part of the url the form is posted to:  
/targets/add\_to\_list/3 where 3 is the id of the list. Or (with slight  
semantic breakage of the controller separation) /lists/add\_target/3  
where the target creation is handled in the lists\_controller code.

Cheers,  
Max

---

<div class="post-metadata">

**Author:** ![weyus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ab992/32.png) [@weyus](https://www.ruby-forum.com/u/weyus)\
**Post date:** [October 3, 2006, 11:44pm UTC](https://www.ruby-forum.com/t/creating-a-child-object-handling-the-parent-reference/70791/5 "2006-10-03T23:44:44Z")

</div>

> I am trying to come up with the best way to be able to assign my new  
> Target object to my List object.

Below is what I do. Can someone enlighten me if this is the “right” way  
to do things? I remember hearing some philosophies on when to send data  
with GET versus POST. I like to POST the “new data” and send the parent  
info in the URL…

For your new target form:

\<%= form\_tag :controller =\> ‘target’, :action =\> ‘create’, :list =\>  
@list.id %\>

In your target ‘create’ method:

if params[:list]  
@list = List.find(params[:list])  
@target = Target.new(params[:target])  
@target.list = @list  
@target.save  
end