Option to limit list_filter to related_objects of instances of the list

[Stanislas Guerra <stan@…>]

I know there are many snippets and blog entries to do that but it is a common use case to limit the FK/related model choices to the very objects displayed in the list and maybe the core team would consider to implement it directly in the Django admin.

The +10 lines patch I provide allow you to limit the choices for a FK/M2M to the current object list by adding the attribute RELATED_FIELD_filter_related_only=True to your ModelAdmin.

By example :

class Order(models.Model):
    ...
    support = models.ForeignKey(Support)
    parutions = models.ManyToManyField(Parution, through='OrderParution', related_name='order')


class OrderAdmin(admin.ModelAdmin):
    ...
    list_filter = ('support', 'agency', 'parutions')
    parutions_filter_related_only=True
    support_filter_related_only=True

[Stanislas Guerra <stan@…>]

Patch for django 1.3

[Matt@…]

Bad choice using a dict as a default argument. If you add something to this, it will be changed in all calls to the method. Use None instead.

[Russell Keith-Magee]

Procedurally -- the dict argument is important feedback. The patch also requires tests and documentation.

I'm inclined to say that this shouldn't be a top-level ModelAdmin argument, but a configuration option of the list_filter item itself. The new ListFilter class (in trunk) should provide a better interface to handle this.

[Matthew Schinckel]

Yeah, sorry that was a bit terse. Written in bed from iPad, wife complained about tap-tap-tap.

What it should say is:

When you have a literal dict or list as a default argument to a function or method, this generally results in undesired behaviour. If you modify this variable, rather than assign to it, then you change the default value for _every_ call to the function/method.

ie (this is a list, but a dict is the same behaviour):

def foo(bar=[]):
  return bar
 
baz = foo()
baz # =>[]
baz.append(None)
baz # => [None]
foo() # => [None]

You almost always expect that last call to foo() to return [], not [None].

[Julien Phalip]

I agree with russellm for the API design; the class you specifically want to look at is contrib.admin.filters.RelatedFieldListFilter. The functionality of that class could be extended to accept configuration options. The developer could then assign a custom filter class to a given field:

class MyModelAdmin(ModelAdmin):
    list_filter = (('my_field', MyRelatedFieldListFilter),)

[Stanislas Guerra <stan@…>]

Thanks for the feedback.

I have rewritten the patch for the trunk according to your suggestions and the usage is now :

from django.contrib.admin.filters import RelatedOnlyFieldListFilter

class OrderAdmin(admin.ModelAdmin):
    ...
    list_filter = ('support', 'agency', ('parutions', RelatedOnlyFieldListFilter))

Writting some tests now.

By the way, is list_filer a typo in contrib.admin.views.main (line 82) ?

           for list_filer in self.list_filter:
                if callable(list_filer):
                    # This is simply a custom list filter class.
                    spec = list_filer(request, cleaned_params,
                        self.model, self.model_admin)
                else:
                    field_path = None
                    if isinstance(list_filer, (tuple, list)):
                        # This is a custom FieldListFilter class for a given field.
                        field, field_list_filter_class = list_filer
                    else:
                        # This is simply a field name, so use the default
                        # FieldListFilter class that has been registered for
                        # the type of the given field.
                        field, field_list_filter_class = list_filer, FieldListFilter.create

[Stan <stanislas.guerra@…>]

Patch against trunk with a subclass of RelatedFieldListFilter.

[Jannis Leidel]

In [16445]:

Fixed typos in admin views wrt list_filter. Refs #16311.

[Stanislas Guerra <stan@…>]

Regresssion tests added.

[Stanislas <stanislas.guerra@…>]

Patch against Django-1.4.1.

[stanislas.guerra@…]

Patch against 1.5.x : ​https://github.com/Starou/django/compare/django:stable/1.5.x...ticket_16311_1_5?expand=1

[stanislas.guerra@…]

PR against master : ​https://github.com/django/django/pull/2695

[Tim Graham]

The PR lacks documentation.

[stanislas.guerra@…]

Replying to timo:

The PR lacks documentation.

Hi Timo,

PR updated.

[Tim Graham <timograham@…>]

In 98e8da3709e400d549e87c7ff1450a2685c0adcf:

Fixed #16311 -- Added a RelatedOnlyFieldListFilter class in admin.filters.

[Tim Graham <timograham@…>]

In b50ea73e1e0179c1925167832318a6d0316ee50b:

Fixed two tests in previous commit; refs #16311.

[stanislas.guerra@…]

That is great, many thanks Tim!