ManyToMany through parameter bug workaround.

[Nicolas Emiliani]

Hi,

I was trying to create an m2m relationship using the 'through' parameter  because

I want to have an additional field in the relation table. The idea was to render this

using CheckboxSelectMultiple.

The thing is that when I add the model m2m field to the 'fieldset' field at the 

ModelForm it throws an exception :

'HomeAdmin.fieldsets[4][1]['fields']' can't include the ManyToManyField field 'attributes' because 'attributes' manually specifies a 'through' model.

Apparently this is a BUG pointed out here :

https://groups.google.com/forum/?fromgroups#!topic/django-users/nWpb0RjoTJ0%5B1-25%5D

Basically if you use the 'through' parameter to use a relation table that contains an extra field/s

you can't render it using a CheckboxSelectMultple widget, not even if the extra field allows null

values.

I thought of fixing it this way (a nasty hack) :

class A(models.Model):

      .

      .

      foos = models.ManyToManyField('Foo')

class Foo(models.Model):

      name = CharField

And here comes the nasssty

class FooRelationshipValue(models.Model):

      a   =  ForeingKey(A)

      foo = ForeingKey(Foo) 

      value = DateField

Here I can store the value for the relationship when saving the Model in the DB.

If anyone has a better solution, suggestion, comment or thinks this is going 

to make me rot in hell please let me know.

Thanks.

--
Nicolas Emiliani

Lo unico instantaneo en la vida es el cafe, y es bien feo.

[Nicolas Emiliani]

Here I can store the value for the relationship when saving the Model in the DB.

If anyone has a better solution, suggestion, comment or thinks this is going 

to make me rot in hell please let me know.

Well, I kept on reading and I found a clean solution :

It's explained here, the same happened to this guy and a workaround is provided.

The code in  MHCs response example has a few errors, but the idea is pretty clear.

http://stackoverflow.com/questions/2854350/django-admin-many-to-many-listbox-doesnt-show-up-with-a-through-parameter

Hope it saves some headaches.

 

-- 

Nicolas Emiliani

Lo unico instantaneo en la vida es el cafe, y es bien feo.