How to add filters to a query dynamically in Django?

You haven't shown any code, so you haven't really explained what the problem is:

Start with the queryset Book.objects.all(). For each filter, check if there is a value for the filter in request.POST, and if so, filter the queryset. Django querysets are lazy, so only the final queryset will be evaluated.

queryset = Book.objects.all()
if request.POST.get('age'):
    queryset = queryset.filter(author__age=request.POST['age'])
if request.POST.get('gender'):
    queryset = queryset.filter(author__gender=request.POST['gender'])
...

You can simply get the request.GET content as a dict (making sure to convert the values to string or a desired type as they'd be list by default i.e: dict(request.GET) would give you something like {u'a': [u'val']}.

Once you are sure you have a dictionary of keys matching your model fields, you can simply do:

filtered = queryset.filter(**dict_container)

this worked for me, I've merged Alex Morozov answer with Dima answer

import operator

def your_view(self, request, *args, **kwargs):
    # Here you list all your filter names
    filter_names = ('filter_one', 'filter_two', 'another_one', )

    queryset = Books.objects.all(); 
    filter_clauses = [Q(**{filter: request.GET[filter]})
                  for filter in filter_names
                  if request.GET.get(filter)]
    if filter_clauses:
    queryset = queryset.filter(reduce(operator.and_, filter_clauses))

    # rest of your view

Maybe django-filter would help simplify the solutions others have given?

Something like:

class BookFilter(django_filters.FilterSet):
    class Meta:
        model = Book
        fields = ['author__age', 'author__gender', ...]

Then the view looks like:

def book_list(request):
    f = BookFilter(request.GET, queryset=Book.objects.all())
    return render_to_response('my_app/template.html', {'filter': f})

For more information see the documentation.

You can do something like that

class BooksAPI(viewsets.ModelViewSet):
    queryset = Books.objects.none()


def get_queryset(self):
    argumentos = {}
    if self.request.query_params.get('age'):
        argumentos['age'] = self.request.query_params.get('age')
    if self.request.query_params.get('gender'):
        argumentos['gender'] = self.request.query_params.get('gender')
    if len(argumentos) > 0:
        books = Books.objects.filter(**argumentos)
    else:
        books = Books.objects.all()
    return books

For a very simple equality check, here is my solution using a helper function in a ModelViewSet.

1. The helper function check_for_params creates a dictionary of request parameters passed in the URL.

2. Alter the ModelViewSet get_queryset() method by filtering the Django QuerySet with a single filter clause which prevents multiple queries being called by chaining filters.

I could tried to use the Django Q() object but could not get it to only make a single call.

def check_for_params(request, param_check_list: List) -> dict:
    """
    Create a dictionary of params passed through URL.

    Parameters
    ----------
    request - DRF Request object.
    param_check_list - List of params potentially passed in the url.
    """
    if not param_check_list:
        print("No param_check_list passed.")
    else:
        param_dict = {}
        for p in param_check_list:
            param_dict[p] = request.query_params.get(p, None)
        return param_dict
    

class MyModelViewSet(viewsets.ModelViewSet):
    queryset = MyModel.objects.all()
    serializer_class = MyModelSerializer
    authentication_classes = [SessionAuthentication]
    permission_classes = [IsAuthenticated]

    def get_queryset(self):
        """
        Return a queryset and apply filters, if applicable.
        
        Info
        ----
        Building the queryset.filter method by unpacking the key-value pairs this way,
        creates a single filter clause and prevents multiple queries from being called
        by chaining filters.
        """
        queryset = MyModel.objects.all()

        param_check_list = ['param1', 'param2', 'param3']
        params = check_for_params(self.request, param_check_list)
        filtered = {k: v for k, v in params.items() if v}

        # Calling filter() only once here prevents multiple queries. 
        return queryset.filter(**filtered)