Forum: Rails Engines adding belongs_to to an application model from an engine

Hi,

I have an Instance model in my application, to which I want to add a
has_many :web_file_attachment from the plugin.
I tried putting this in my plugin's app/model/instance.rb :
  class Instance < ActiveRecord::Base
    has_many :web_file_attachments , :dependent => :destroy
  end

but it doesn't seem to work.

What's the way to get this working?

Thanks

Raph

On 30 Oct 2008, at 13:35, Raphael Bauduin wrote:

> Hi,
>
> I have an Instance model in my application, to which I want to add a
> has_many :web_file_attachment from the plugin.
> I tried putting this in my plugin's app/model/instance.rb :
>  class Instance < ActiveRecord::Base
>    has_many :web_file_attachments , :dependent => :destroy
>  end
>
> but it doesn't seem to work.

The engines plugin doesn't mix model code (yet), so it's unlikely that
your plugin model is being loaded.

A better way to do this would be to add a 'macro' method to
ActiveRecord::Base, which you can then call in your main application
model, along the lines of

   app/models/instance.rb

   class Instance < ActiveRecord::Base
      # other stuff...
      has_web_file_attachments
   end

This would give you more flexibility, I think.

The main reason why your current setup doesn't work, is that the
engines plugin isn't loading your plugin model.

James

On Thu, Oct 30, 2008 at 2:45 PM, James Adam <james@lazyatom.com> wrote:
>>
>
>  class Instance < ActiveRecord::Base
>     # other stuff...
>     has_web_file_attachments
>  end
>
> This would give you more flexibility, I think.

Yes, but I'm looking at engines to be able to add this without
touching the main app.
Actually I'm building a new datatype for dedomenon.org , and it would
be great if it was possible without touching the main application's
code: just install the engine and you're done.
Isn't there a way to achieve this?

Thanks for your help!

Raph

On 30 Oct 2008, at 13:56, Raphael Bauduin wrote:
> Yes, but I'm looking at engines to be able to add this without
> touching the main app.
> Actually I'm building a new datatype for dedomenon.org , and it would
> be great if it was possible without touching the main application's
> code: just install the engine and you're done.
> Isn't there a way to achieve this?
>
> Thanks for your help!

In this case, you'll need to ensure that the main application
instance.rb model is loaded before you reopen the class in your
plugin. I would probably do something along the lines of

my_plugin/init.rb

   require 'instance_extensions'

my_plugin/lib/instance_extensions.rb

   require 'instance' # maybe raise an error here if it's missing in
the main app
   Instance.class_eval do
     has_many :web_file_attachments # ....
   end

Hope that helps,

James

On Thu, Oct 30, 2008 at 2:59 PM, James Adam <james@lazyatom.com> wrote:
>
>  require 'instance' # maybe raise an error here if it's missing in the main
> app
>  Instance.class_eval do
>    has_many :web_file_attachments # ....
>  end
>
> Hope that helps,

It's going in the right direction, but it's not working yet as I get
this error when starting the application:

=> Booting WEBrick...
/home/rb/dev/dedomenon/vendor/rails/activerecord/lib/active_record/associations.rb:1273:in
`before_destroy': wrong number of arguments (1 for 0) (ArgumentError)
        from 
/home/rb/dev/dedomenon/vendor/rails/activerecord/lib/active_record/associations.rb:1273:in
`configure_dependency_for_has_many'
        from 
/home/rb/dev/dedomenon/vendor/rails/activerecord/lib/active_record/associations.rb:711:in
`has_many'
        from 
/home/rb/dev/dedomenon/vendor/plugins/web_file_attachment/lib/instance_extensions.rb:3
        from 
/home/rb/dev/dedomenon/vendor/plugins/web_file_attachment/lib/instance_extensions.rb:2:in
`class_eval'
        from 
/home/rb/dev/dedomenon/vendor/plugins/web_file_attachment/lib/instance_extensions.rb:2
        from 
/usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:27:in
`gem_original_require'
        from 
/usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:27:in
`require'
        from 
/home/rb/dev/dedomenon/vendor/rails/activesupport/lib/active_support/dependencies.rb:509:in
`require'
         ... 26 levels...
        from 
/home/rb/dev/dedomenon/vendor/rails/activesupport/lib/active_support/dependencies.rb:509:in
`require'
        from 
/home/rb/dev/dedomenon/vendor/rails/railties/lib/commands/server.rb:39
        from ./script/server:3:in `require'
        from ./script/server:3


The line causing the problem is
  has_many :web_file_attachments , :dependent => :destroy
This exact same line put in the Instance class of the application works 
fine.

Any hints?

Thanks!

Raph