Django Admin custom list filter different model

Question

I'm using Django 2.1 and I need to add a list filter on model(#1) admin page referencing a field from a different model(#2)(which has a foreign key referencing the current model(#1) These are my 2 models:

class ParentProduct(models.Model):
    parent_id = models.CharField(max_length=255, validators=[ParentIDValidator])
    name = models.CharField(max_length=255, validators=[ProductNameValidator])
    parent_slug = models.SlugField(max_length=255)
    parent_brand = models.ForeignKey(Brand, related_name='parent_brand_product', blank=False, on_delete=models.CASCADE)
    ...

class ParentProductCategory(models.Model):
    parent_product = models.ForeignKey(ParentProduct, related_name='parent_product_pro_category', on_delete=models.CASCADE)
    category = models.ForeignKey(Category, related_name='parent_category_pro_category', on_delete=models.CASCADE)
    created_at = models.DateTimeField(auto_now_add=True)
    modified_at = models.DateTimeField(auto_now=True)

Here is my admin class for model 'ParentProduct':

class ParentProductAdmin(admin.ModelAdmin):
    resource_class = ParentProductResource
    form = ParentProductForm

    class Media:
        pass

    change_list_template = 'admin/products/parent_product_change_list.html'
    actions = [deactivate_selected_products, approve_selected_products]
    list_display = [
        'parent_id', 'name', 'parent_brand', 'product_hsn', 'gst', 'product_image', 'status'
    ]
    inlines = [
        ParentProductCategoryAdmin
    ]
    list_filter = [ParentBrandFilter, 'status']

Here is the ParentBrandFilter:

class ParentBrandFilter(AutocompleteFilter):
    title = 'Brand'
    field_name = 'parent_brand'

This works correctly because the field 'parent_brand' exists on my model 'ParentProduct'. How do I get the same autocomplete type list filter for the field category which is actually inside the 'ParentProductCategory' model.

Note: 'ParentProductCategory' -> 'ParentProduct' is a many-to-one mapping.

Note #2: Django admin add custom filter. I tried going through this question but couldn't get through with the approach and also my requirement is different. I need an autocomplete type filter.

Note #3: If autocomplete is not possible, is there a way to have a dropdown with only existing 'category' values in it?

Answer 1

try this in your ParentProductAdmin class

list_filter = ['parent_product__parent_brand', 'status']