Rails - Jun 2006 - how to delete a parent record and child records?

Wow, got myself lost as *soon* as I left the hand-holding exercises in 
the books.

I''m trying to set it up so when I click the (scaffold-generated) 
''destroy'' link on one (of a list) of parent MySQL records, the
children
records in a different table get deleted also.

Very simple setup: my tables are ''customers'' and
''accounts''

class Customer < ActiveRecord::Base
    has_many :accounts, :order => "cmp_code"
end

class Account < ActiveRecord::Base
  belongs_to :customer
end

I used migrate to create the tables.
The table ''accounts'' has a field called customer_id (int).

It was easy to add a "add new account to this customer" form to the 
show.rhtml for my ''list'' view. That works great. And I can
destroy a
customer record just fine (using the auto-generated destroy link). But I 
can''t figure out how to also destroy the accounts that are associated 
with a customer via customer_id.

I have a
   class ListController < ApplicationController
that lists all the customers, no problem.

That ListController class has the default destroy method that deletes 
the selected customer from the database, simply:
      Customer.find(params[:id]).destroy

My questions:
1) Should a MySQL foreign key have been created (either automatically or 
by me) in the database? Because MySql Admin does not show any foreign 
keys.

2) Should a destroy on the parent in ''customers'' destroy the
children in
''accounts'' due to the dynamically-created has_many and
belongs_to
relationships? (It doesn''t, hence this post) I thought that was one of 
the purposes of the has_many and belongs_to ?

3) Assuming the answer to (2) is ''no'' and I have to do that 
destroy-children records manually, what code would I add to the destroy 
method so the accounts are deleted where accounts[customer_id] = the id 
for the record whose ''destroy'' link is clicked? I''m
sure it;s simple,
but I tried several things with no luck.

Thanks!

-- 
Posted via http://www.ruby-forum.com/.

On 6/16/06, william Jo <william@essay.com> wrote:
>
> Wow, got myself lost as *soon* as I left the hand-holding exercises in
> the books.
>
> I''m trying to set it up so when I click the (scaffold-generated)
> ''destroy'' link on one (of a list) of parent MySQL
records, the children
> records in a different table get deleted also.

This is a lot simpler than you might think in Rails.  You don''t need to
do
anything special to your database,unless you want to of course;)  You need
to add an option to your has_many method call.  :dependent => :destroy
Thats it.  Add this to each has many in a chain of parent child eg
parent -> child -> grandchild

There will be a has_many in the parent and the child.  If you put in the
:dependent option in these calls, they will be called automatically when an
object is destroyed.

Note that it must be destroyed an not deleted.

You can read more about it at the dox for has_many
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html#M000530

Very simple setup: my tables are ''customers'' and
''accounts''
>
> class Customer < ActiveRecord::Base
>     has_many :accounts, :order => "cmp_code"
> end
>
> class Account < ActiveRecord::Base
>   belongs_to :customer
> end
>
> I used migrate to create the tables.
> The table ''accounts'' has a field called customer_id
(int).
>
> It was easy to add a "add new account to this customer" form to
the
> show.rhtml for my ''list'' view. That works great. And I
can destroy a
> customer record just fine (using the auto-generated destroy link). But I
> can''t figure out how to also destroy the accounts that are
associated
> with a customer via customer_id.
>
> I have a
>    class ListController < ApplicationController
> that lists all the customers, no problem.
>
> That ListController class has the default destroy method that deletes
> the selected customer from the database, simply:
>       Customer.find(params[:id]).destroy
>
> My questions:
> 1) Should a MySQL foreign key have been created (either automatically or
> by me) in the database? Because MySql Admin does not show any foreign
> keys.
>
> 2) Should a destroy on the parent in ''customers'' destroy
the children in
> ''accounts'' due to the dynamically-created has_many and
belongs_to
> relationships? (It doesn''t, hence this post) I thought that was
one of
> the purposes of the has_many and belongs_to ?
>
> 3) Assuming the answer to (2) is ''no'' and I have to do
that
> destroy-children records manually, what code would I add to the destroy
> method so the accounts are deleted where accounts[customer_id] = the id
> for the record whose ''destroy'' link is clicked?
I''m sure it;s simple,
> but I tried several things with no luck.
>
> Thanks!
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>
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Daniel ----- wrote:
> This is a lot simpler than you might think in Rails.  You don''t
need to
> do
> anything special to your database,unless you want to of course;)  You 
> need
> to add an option to your has_many method call.  :dependent => :destroy
> Thats it.  Add this to each has many in a chain of parent child eg
OMG. That''s kinda cool. Thank you!


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