How to override (filter based on particular condition) Django admin filter choices?

Question

My models Django are:

class Brand(models.Model):
    name = models.CharField(max_length=200)

class StanardProduct(models.Model):
    brand = models.ForeignKey(Brand)

class VendorProduct(models.Model):
    standard_product = models.ForeignKey(StanardProduct)

My model admin is:

class StandardProductModelAdmin(admin.ModelAdmin):

    list_filter [
        'brand'
    ]

In the list filter for 'brand', I want to show only those brand choices that satisfy following two conditions:

1. Brand name choice should be referenced by StandardProduct object
2. StandardProduct object should be referenced by VendorProduct object

Using "admin.RelatedOnlyFieldListFilter" in the filter satisfies only condition no. 1 - but not no. 2. I need a way that satisfies both the conditions.

Answer 1

Sub-classing "admin.RelatedOnlyFieldListFilter" and overriding emthod "field_choices" worked!

class CustomRelatedOnlyFieldListFilter(admin.RelatedOnlyFieldListFilter):

    def field_choices(self, field, request, model_admin):
        custom_qs = model_admin.get_queryset(request).exclude(
            vendorproduct=None
        )
        pk_qs = custom_qs.distinct().values_list(
            'brand__pk', flat=True
        )
        return field.get_choices(include_blank=False, limit_choices_to={'pk__in': pk_qs})

And the admin will be:

class StandardProductModelAdmin(admin.ModelAdmin):

    list_filter [
        ('brand', CustomRelatedOnlyFieldListFilter),
    ]