How to add filters to a query dynamically in Django?

Question

In my viewSet I am doing a query,

queryset= Books.objects.all();

Now from an ajax call I get my filter values from UI i.e. age,gender, etc. of auther.There will be a total of 5 filters.

Now the problem which I ran into is how am I going to add filters to my query(only those filters which have any value).

What I tried is I checked for individual filter value and did query, but that way it fails as if the user remove the filter value or add multiple filters. Any better suggestion how to accomplish this?

Answer 1

Here's a bit more generic one. It will apply filters to your queryset if they are passed as the GET parameters. If you're doing a POST call, just change the name in the code.

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

Note that you can use lookup expressions in your filters' names. For example, if you want to filter books with price lower or equal to specified in filter, you could just use price__lte as a filter name.

Answer 2

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'])
...

Answer 3

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)

Answer 4

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.

Answer 5

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