Chaining Filters with Django-Filter and Django-Autocomplete-Light

I see you're having issues with chaining filters when integrating Django-Filter with Django-Autocomplete-Light. The main issue in your code appears to be how you're trying to reference the selected values in your queryset definitions.

The Problem

In your current implementation, you're trying to use the filter field variables directly in the queryset definitions:

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queryset=Region.objects.filter(country__name__iexact=country)

This won't work because country here is just the variable name of your filter field, not the selected value.

Solution

You need to modify your approach to properly chain the filters. Here's how you can fix it:

1. First, define your filter fields without the dependent querysets:

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class RoomFilter(FilterSet):
    country = ModelChoiceFilter(
        lookup_expr="iexact",
        queryset=Country.objects.all(), 
        widget=autocomplete.ModelSelect2(
            url="auth_app:country-autocomplete", 
            attrs={"class": "form-control"}
        ), 
        label=_("Country")
    )
    
    region = ModelChoiceFilter(
        lookup_expr="iexact", 
        queryset=Region.objects.all(),  # We'll override this in __init__
        widget=autocomplete.ModelSelect2(
            url="auth_app:region-autocomplete", 
            attrs={"class": "form-control"}, 
            forward=["country"]
        ), 
        label=_("Region")
    )
    
    city = ModelChoiceFilter(
        lookup_expr="iexact", 
        queryset=City.objects.all(),  # We'll override this in __init__
        widget=autocomplete.ModelSelect2(
            url="auth_app:city-autocomplete", 
            attrs={"class": "form-control"}, 
            forward=["region"]
        ), 
        label=_("City")
    )
    
    # Other filters remain the same
    
    class Meta:
        model = Room
        fields = ["country", "region", "city", "ethnicity", "age"]
    
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        
        # Get the current values from data (if any)
        country_id = self.data.get('country') if self.data else None
        region_id = self.data.get('region') if self.data else None
        
        # Adjust the querysets based on the selected values
        if country_id:
            self.filters['region'].queryset = Region.objects.filter(country_id=country_id)
        else:
            self.filters['region'].queryset = Region.objects.none()
            
        if region_id:
            self.filters['city'].queryset = City.objects.filter(region_id=region_id)
        else:
            self.filters['city'].queryset = City.objects.none()

2. Make sure your autocomplete views properly handle the forwarded parameters:

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class RegionAutocomplete(autocomplete.Select2QuerySetView):
    def get_queryset(self):
        if not self.request.user.is_authenticated:
            return Region.objects.none()
            
        qs = Region.objects.all()
        
        country = self.forwarded.get('country', None)
        if country:
            qs = qs.filter(country_id=country)
        
        if self.q:
            qs = qs.filter(name__icontains=self.q)
        
        return qs

class CityAutocomplete(autocomplete.Select2QuerySetView):
    def get_queryset(self):
        if not self.request.user.is_authenticated:
            return City.objects.none()
            
        qs = City.objects.all()
        
        region = self.forwarded.get('region', None)
        if region:
            qs = qs.filter(region_id=region)
        
        if self.q:
            qs = qs.filter(name__icontains=self.q)
        
        return qs

This approach properly handles the chaining of filters by:

1. Setting up the initial querysets
2. Dynamically updating the querysets based on selected values
3. Ensuring the autocomplete views respect the forwarded parameters

The key is using the __init__ method to dynamically adjust the querysets based on the current form data, rather than trying to reference the filter fields directly in the queryset definitions.