Complex forms: only one level of “arrayn ess” is allowed?

Rails
1

Hi all,

I thought I was trying to do something rather simple, but it has
caused me a lot of headaches. Here it is:

  • in my program: model_a has_many model_b. model_b has_many model_c.

  • in the user interface, I would like the user to be able to fill the
    information for one model_a, one or more associated model_bs
    (corresponding fields could be added with a set of links ‘add/remove a
    model_b’), and for each model_b added, one or more model_c (with the
    same mechanism).

Thanks to the great tutorial “Handle multiple models in one form”,
it’s easy to handle the first step (any number of model_b per
model_a), but I can’t get the second step to work. The natural
indexing should (I think) be:

“model_a[model_b_attributes][][model_c_attributes][][an_attribute]”

But it doesn’t seem to work. I read here

that “only one level of “arrayness” is allowed” and that I should use
hashes instead, but I am not quite sure I understand how to do it.

Do you have any idea?

Thanks a lot
PJ

2

On Apr 15, 1:07 am, PJ [email protected] wrote:

“model_a[model_b_attributes][][model_c_attributes][][an_attribute]”

But it doesn’t seem to work. I read herehttp://guides.rubyonrails.org/form_helpers.html
that “only one level of “arrayness” is allowed” and that I should use
hashes instead, but I am not quite sure I understand how to do it.

Do you have any idea?

What that comment is saying is that you can replace an array eg
[a,b,c] with a hash eg {1 => a, 2=> b, 3=>c}
Generating those keys is up to your client side code, approaches
included using a number you increment or going for some unique thing
you generate on the spot (eg time in milliseconds concatenated with a
random number) so that you don’t have to keep track of how many fields
and what not you have created clientside.

Fred

3

Thanks Fred.

Considering there is a bit of “wizardry” that needs to be done and
that Rails doesn’t include helpers to do this simply, does it mean it
is not recommended to build such complex forms?

I am not very experienced with Rails, but I love the fact it is very
“clean” and I feel a bit cautious having to generate keys manually.

PJ

On Apr 15, 9:05 am, Frederick C. [email protected]

4

PJ wrote:
[…]

The natural
indexing should (I think) be:

“model_a[model_b_attributes][][model_c_attributes][][an_attribute]”

But it doesn’t seem to work.
[…]

There is a bug in Rails at least up to 2.2.2 that you may be running
into. I reported it on this list around Christmas 2008. If you search
the archives for my name around that time, you will find the ensuing
discussion and a patch that Fred submitted for the bug. Good luck!

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

5

On Apr 15, 5:09 pm, PJ [email protected] wrote:

Thanks Fred.

Considering there is a bit of “wizardry” that needs to be done and
that Rails doesn’t include helpers to do this simply, does it mean it
is not recommended to build such complex forms?

I am not very experienced with Rails, but I love the fact it is very
“clean” and I feel a bit cautious having to generate keys manually.

There is the nested forms stuff in rails 2.3 (unfortunately not yet
documented in the guide).

Fred