Related name for reverse access in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the reverse access name for a ForeignKey with related_name='children'?

Given the following Django models, what is the correct way to access all children of a Parent instance using the related_name?

class Parent(models.Model):
    name = models.CharField(max_length=100)

class Child(models.Model):
    parent = models.ForeignKey(Parent, related_name='children', on_delete=models.CASCADE)
    name = models.CharField(max_length=100)

A parent.children.all()

B child.parent.all()

C parent.child_set.all()

D parent.children_set.all()

💡 Hint

Think about the related_name attribute and how it changes the default reverse accessor.

The related_name='children' sets the reverse accessor from Parent to Child as 'children'. So, to get all children of a parent, you use parent.children.all(). The default would be parent.child_set.all() if related_name was not set.

📝 Syntax

intermediate

Which related_name causes a syntax error in this ForeignKey?

Identify which related_name value will cause a syntax error when used in this Django model:

class Book(models.Model):
    author = models.ForeignKey('Author', related_name=___, on_delete=models.CASCADE)
    title = models.CharField(max_length=200)

A 'books_written'

B 'books123'

C 'books-written'

D 'booksWritten'

💡 Hint

related_name must be a valid Python identifier.

The related_name must be a valid Python attribute name. Hyphens '-' are not allowed in Python identifiers, so 'books-written' causes a syntax error. The others are valid identifiers.

❓ state_output

advanced

What is the output of accessing reverse relation with related_name?

Consider these Django models and code:

class Category(models.Model):
    name = models.CharField(max_length=50)

class Product(models.Model):
    category = models.ForeignKey(Category, related_name='products', on_delete=models.CASCADE)
    name = models.CharField(max_length=100)

cat = Category.objects.create(name='Toys')
Product.objects.create(name='Car', category=cat)
Product.objects.create(name='Doll', category=cat)

print(list(cat.products.values_list('name', flat=True)))

What will be printed?

A []

B ['Car', 'Doll']

C ['Car']

D ['Toys']

💡 Hint

The related_name 'products' allows reverse access from Category to Product.

The related_name 'products' lets us access all Product instances linked to the Category instance 'cat'. So cat.products.all() returns both products. The values_list with 'name' and flat=True returns a list of product names.

🔧 Debug

advanced

Why does this reverse access raise AttributeError?

Given these models:

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    title = models.CharField(max_length=200)

And this code:

author = Author.objects.first()
print(author.books.all())

Why does this raise AttributeError: 'Author' object has no attribute 'books'?

A Because the ForeignKey has no related_name, so default is 'book_set', not 'books'.

B Because the author variable is None and has no attributes.

C Because the Book model is missing a related_name attribute.

D Because the Author model must define a reverse relation explicitly.

💡 Hint

Check the default reverse accessor name when related_name is not set.

When related_name is not set, Django uses the default reverse accessor as modelname_set, here 'book_set'. So author.books does not exist, but author.book_set does.

🧠 Conceptual

expert

How does related_name affect reverse access in multi-level relations?

Given these models:

class Country(models.Model):
    name = models.CharField(max_length=50)

class City(models.Model):
    country = models.ForeignKey(Country, related_name='cities', on_delete=models.CASCADE)
    name = models.CharField(max_length=50)

class Person(models.Model):
    city = models.ForeignKey(City, related_name='residents', on_delete=models.CASCADE)
    name = models.CharField(max_length=100)

Which expression correctly gets all Person instances living in a Country instance named 'country'?

A country.cities.residents_set.all()

B country.residents.all()

C country.cities.residents.all()

D Person.objects.filter(city__country=country)

💡 Hint

Think about how to traverse ForeignKey relations in Django queries.

To get all Person instances living in a Country, you filter Person by city__country=country. The related_name allows reverse access from Country to City as 'cities', and from City to Person as 'residents', but you cannot chain reverse relations directly as attributes without querying.