Filtering with django-filter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this django-filter setup?

Given a Django model Book with fields title (string) and year (integer), and this filter class:

import django_filters

class BookFilter(django_filters.FilterSet):
    class Meta:
        model = Book
        fields = {"year": ["gte", "lte"]}

What will BookFilter({'year__gte': 2000}).qs return?

Django

import django_filters

class BookFilter(django_filters.FilterSet):
    class Meta:
        model = Book
        fields = {"year": ["gte", "lte"]}

# Assume Book.objects.all() contains books with years 1995, 2000, 2005

A A queryset of books with year >= 2000

B A queryset of books with year <= 2000

C Raises a TypeError due to incorrect filter syntax

D A queryset of all books ignoring the filter

💡 Hint

Look at the filter field name and the query parameter key.

The filter year__gte applies a 'greater than or equal' filter on the year field, so only books from 2000 and later are included.

📝 Syntax

intermediate

Which option correctly defines a filter for a CharField with case-insensitive contains?

Choose the correct django-filter field definition to filter a name CharField with case-insensitive substring matching.

Django

import django_filters

class PersonFilter(django_filters.FilterSet):
    name = ???

    class Meta:
        model = Person
        fields = ['name']

A name = django_filters.CharFilter(lookup_expr='contains')

B name = django_filters.CharFilter(lookup_expr='icontains')

C name = django_filters.CharFilter(lookup_expr='iexact')

D name = django_filters.CharFilter(lookup_expr='startswith')

💡 Hint

Look for the lookup expression that ignores case and checks substring.

icontains means case-insensitive substring match, which fits the requirement.

🔧 Debug

advanced

Why does this filter raise a FieldError?

Given this filter class:

class ProductFilter(django_filters.FilterSet):
    price = django_filters.NumberFilter(lookup_expr='gte')

    class Meta:
        model = Product
        fields = ['price', 'category']

And the query ProductFilter({'price__gte': 100}).qs raises django.core.exceptions.FieldError. Why?

Django

class ProductFilter(django_filters.FilterSet):
    price = django_filters.NumberFilter(lookup_expr='gte')

    class Meta:
        model = Product
        fields = ['price', 'category']

# Product model has fields: price (DecimalField), category (ForeignKey)

A Because 'category' field is missing a filter definition

B Because 'price__gte' is not a valid query parameter for NumberFilter with lookup_expr='gte'

C Because the Product model does not have a 'price' field

D Because the filter field 'price' already uses 'gte', the query param should be 'price' not 'price__gte'

💡 Hint

Check how django-filter builds query parameters from filter fields and lookup expressions.

When you set lookup_expr='gte' on a filter field named 'price', the filter expects query param 'price', not 'price__gte'. Using 'price__gte' causes a FieldError.

❓ state_output

advanced

What is the count of items in the filtered queryset?

Given a model Order with a status CharField and this filter:

class OrderFilter(django_filters.FilterSet):
    status = django_filters.CharFilter(lookup_expr='exact')

    class Meta:
        model = Order
        fields = ['status']

# Assume Order.objects.all() has 10 orders: 4 with status 'pending', 6 with status 'shipped'

What is OrderFilter({'status': 'pending'}).qs.count()?

Django

class OrderFilter(django_filters.FilterSet):
    status = django_filters.CharFilter(lookup_expr='exact')

    class Meta:
        model = Order
        fields = ['status']

# Orders: 4 pending, 6 shipped

A 4

B 6

C 10

D 0

💡 Hint

Filter matches exact status 'pending'.

The filter returns only orders with status exactly 'pending', which are 4.

🧠 Conceptual

expert

Which option best explains how django-filter applies filters internally?

How does django-filter apply filters to a queryset when you call FilterSet(data).qs?

A It modifies the original queryset in place by removing items that don't match the filter criteria.

B It converts the filter data into raw SQL and executes it directly on the database.

C It builds a Django ORM query by chaining <code>filter()</code> calls using the filter fields and their lookup expressions with the provided data.

D It loads all objects into memory and filters them using Python list comprehensions.

💡 Hint

Think about how Django ORM queries are built and executed lazily.

django-filter builds a queryset by chaining filter() calls with the lookup expressions and data, which Django ORM translates to SQL and executes lazily.