Filtering Examples, from Simple To More Complex ones

Plain Vanilla Filtering

To filter any view, override its get_queryset method to return a filtered query set

class HREmployees(generics.ListAPIView):
    def get_queryset(self):
        return Employee.objects.filter(department="Human Resources")

All the API functions will then use the filtered query set for operations. For example, the listing of the above view will only contain employees whose department is Human Resources.

Accessing query parameters in get_queryset

Filtering based on request parameters is easy.

self.request, self.args and self.kwargs are available and point to the current request and its parameters for filtering

def DepartmentEmployees(generics.ListAPIView):
    def get_queryset(self):
        return Employee.objects.filter(department=self.kwargs["department"])

Letting the API parameters decide what to filter

If you want more flexibility and allow the API call to pass in parameters to filter the view, you can plugin filter backends like Django Request Framework(installed via pip)

from rest_framework import filters  

class Employees(generics.ListAPIView):
    queryset=Employee.objects.all()
    filter_backends = (filters.DjangoFilterBackend,)
    filter_fields = ("department", "role",)

Now you can make an API call /api/employees?department=Human Resources and you’ll get a list of employees that belong only to the HR department, or /api/employees?role=manager&department=Human Resources to get only managers in the HR department.

You can combine query set filtering with Django Filter Backend, no problemo. The filters will work on the filtered query set returned by get_queryset

from rest_framework import filters  

class HREmployees(generics.ListAPIView):
    filter_backends = (filters.DjangoFilterBackend,)
    filter_fields = ("department", "role",)

    def get_queryset(self):
        return Employee.objects.filter(department="Human Resources")

FilterSets

So far, you can get by with simple type matches in the above cases.

But what if you want something more complex, like a list of HR employees who are between 25 and 32 years in age?

Answer to problem: Filtersets

Filter sets are classes that define how to filter various fields of the model.

Define em like so

class EmployeeFilter(django_filters.rest_framework.FilterSet):
    min_age = filters.django_filters.NumberFilter(name="age", lookup_expr='gte')
    max_age = filters.django_filters.NumberFilter(name="price", lookup_expr='lte')     

    class Meta:
        model = Employee
        fields = ['age', 'department']

name points to the field which you want to filter

lookup_expr basically refers to the same names you use while filtering query sets, for example you can do a “starts with” match using lookup_expr="startswith" which is equivalent to Employee.objects.filter(department__startswith="Human")

Then use them in your view classes by using filter_class instead of filter_fields

class Employees(generics.ListAPIView):
    queryset=Employee.objects.all()
    filter_backends = (filters.DjangoFilterBackend,)
    filter_class = EmployeeFilter

Now you can do /api/employees?department=Human Resources&min_age=25&max_age=32

Non-exact matches and relationships

Filter classes and expressions are very similar to how you specify filtering in query sets

You can use the ”__” notation to filter fields in relationships, For example, if department was a foreign key from employee, you can add

filter_fields=("department__name",)

and then you can do /api/employees?department__name=Human Resources

Or more elegantly, you can create a filter set, add a filter variable called dept and set its name to department__name, allowing you to do /api/employees?dept=Human Resources