get() for single objects in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does get() return when the object exists?

Consider a Django model Book with a record where id=1. What does Book.objects.get(id=1) return?

Django

book = Book.objects.get(id=1)
print(type(book))

A A QuerySet containing the record with id=1

B An instance of the Book model representing the record with id=1

C A list containing the record with id=1

D None, if the record exists

💡 Hint

Remember, get() returns a single object, not a list or QuerySet.

The get() method returns a single model instance matching the query. It does not return a QuerySet or list.

🔧 Debug

intermediate

What error occurs if get() finds no matching object?

What error will this code raise if no Book with id=999 exists?

Book.objects.get(id=999)

Django

Book.objects.get(id=999)

A Book.DoesNotExist

B ValueError

C KeyError

D MultipleObjectsReturned

💡 Hint

Think about what happens when no object matches the query.

If get() finds no matching object, Django raises DoesNotExist specific to the model.

📝 Syntax

advanced

Which get() call causes MultipleObjectsReturned error?

Given multiple Book records with author='Alice', which code raises MultipleObjectsReturned?

Django

Book.objects.get(author='Alice')

A Book.objects.get(id=1)

B Book.objects.get(title='Unique Title')

C Book.objects.get(author='Alice')

D Book.objects.get(pk=999)

💡 Hint

get() expects exactly one match, not many.

If more than one object matches the query, get() raises MultipleObjectsReturned.

❓ state_output

advanced

What is the output of this get() usage with try-except?

What will this code print if no Book with id=10 exists?

try:
    book = Book.objects.get(id=10)
    print('Found:', book.title)
except Book.DoesNotExist:
    print('No book found')

Django

try:
    book = Book.objects.get(id=10)
    print('Found:', book.title)
except Book.DoesNotExist:
    print('No book found')

A No book found

B Prints nothing

C Raises MultipleObjectsReturned error

D Found: <title of book with id=10>

💡 Hint

The except block runs if get() finds no object.

The code catches the DoesNotExist error and prints 'No book found' if no matching record exists.

🧠 Conceptual

expert

Why prefer get() over filter() when expecting a single object?

Which reason best explains why get() is preferred over filter() when you expect exactly one object?

A filter() raises an error if no objects are found, while get() returns None

B filter() returns a single object directly without wrapping in a QuerySet

C get() returns a QuerySet which is easier to chain with other queries

D get() raises errors if zero or multiple objects found, helping catch unexpected data issues

💡 Hint

Think about error detection when data does not match expectations.

get() helps catch problems by raising errors if the data is missing or duplicated, unlike filter() which silently returns empty or multiple results.

Practice

1. What does the Django get() method do when used on a model's manager?

easy

A. It updates the object matching the filter.

B. It returns a list of all objects matching the filter.

C. It returns exactly one object matching the filter or raises an error.

D. It deletes the object matching the filter.

Solution

1. Step 1: Understand the purpose of get()

   The get() method is designed to find exactly one object that matches the given filter criteria.

2. Step 2: Recognize behavior on multiple or zero matches

   If no objects or more than one object match, get() raises an error instead of returning multiple objects or none.

3. Final Answer:

   It returns exactly one object matching the filter or raises an error. -> Option C

4. Quick Check:

   get() returns one object or error [OK]

Hint: Remember: get() expects one object, else error [OK]

Common Mistakes:

• Thinking get() returns multiple objects like filter()
• Assuming get() updates or deletes objects
• Expecting get() to return None if no match

2. Which of the following is the correct syntax to get a single Book object with id=5 using Django ORM?

easy

A. Book.objects.get(id=5)

B. Book.get.objects(id=5)

C. Book.objects.filter(id=5)

D. Book.objects.get.filter(id=5)

Solution

1. Step 1: Recall correct method call order

   In Django ORM, get() is called on the model manager accessed by objects.

2. Step 2: Verify syntax correctness

   The correct syntax is Book.objects.get(id=5). Other options misuse method chaining or order.

3. Final Answer:

   Book.objects.get(id=5) -> Option A

4. Quick Check:

   Correct syntax = Book.objects.get(id=5) [OK]

Hint: Use Model.objects.get(field=value) syntax [OK]

Common Mistakes:

• Swapping method and manager order
• Calling get() after filter() incorrectly
• Using get() as an attribute instead of method

3. Given the model Author with two entries having name='Alice', what happens when you run Author.objects.get(name='Alice')?

medium

A. Returns the first Author object with name 'Alice'.

B. Returns a list of Author objects with name 'Alice'.

C. Raises a DoesNotExist exception.

D. Raises a MultipleObjectsReturned exception.

Solution

1. Step 1: Understand get() behavior with multiple matches

   If more than one object matches the filter, get() raises a MultipleObjectsReturned exception.

2. Step 2: Apply to given scenario

   Since two Authors have name='Alice', calling get(name='Alice') triggers this exception.

3. Final Answer:

   Raises a MultipleObjectsReturned exception. -> Option D

4. Quick Check:

   Multiple matches cause MultipleObjectsReturned [OK]

Hint: Multiple matches with get() cause MultipleObjectsReturned error [OK]

Common Mistakes:

• Assuming get() returns first match silently
• Expecting get() to return a list
• Confusing DoesNotExist with multiple matches

4. What is wrong with this code snippet?

user = User.objects.get(username='john')
print(user.email)

Assuming no user with username 'john' exists.

medium

A. It will print an empty string for email.

B. It will raise a DoesNotExist exception.

C. It will raise a MultipleObjectsReturned exception.

D. It will return None and cause AttributeError on print.

Solution

1. Step 1: Check behavior when no object matches get()

   If no object matches the filter, get() raises a DoesNotExist exception.

2. Step 2: Apply to given code

   Since no user with username 'john' exists, User.objects.get(username='john') raises DoesNotExist before print runs.

3. Final Answer:

   It will raise a DoesNotExist exception. -> Option B

4. Quick Check:

   No match with get() causes DoesNotExist [OK]

Hint: No match with get() raises DoesNotExist error [OK]

Common Mistakes:

• Expecting get() to return None if no match
• Assuming print runs without error
• Confusing DoesNotExist with MultipleObjectsReturned

5. You want to get a single Product with sku='12345'. If it doesn't exist, you want to create it with name='New Product'. Which code correctly does this using get()?

hard

A. try:
product = Product.objects.get(sku='12345')
except Product.DoesNotExist:
product = Product.objects.create(sku='12345', name='New Product')

B. product = Product.objects.get_or_create(sku='12345', name='New Product')

C. product = Product.objects.get(sku='12345') or Product.objects.create(sku='12345', name='New Product')

D. product = Product.objects.filter(sku='12345').get_or_create(name='New Product')

Solution

1. Step 1: Understand get() behavior and exception handling

   get() raises DoesNotExist if no object matches, so use try-except to handle this.

2. Step 2: Review options for correct usage

   try: product = Product.objects.get(sku='12345') except Product.DoesNotExist: product = Product.objects.create(sku='12345', name='New Product') uses try-except with get() and creates the object if not found, which is correct. product = Product.objects.get_or_create(sku='12345', name='New Product') uses get_or_create() which is a different method, not get(). The other options misuse method chaining and will cause errors.

3. Final Answer:

   Use try-except with get() and create if not found. -> Option A

4. Quick Check:

   Handle DoesNotExist with try-except for get() [OK]

Hint: Use try-except DoesNotExist to handle get() missing object [OK]

Common Mistakes:

• Using get_or_create() instead of get()
• Assuming get() returns None if no match
• Chaining get_or_create() after filter() incorrectly