Defining models with fields in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Django model field default value?

Consider this Django model field definition:

age = models.IntegerField(default=20)

What will be the value of age if a new model instance is created without specifying age?

A The age field will raise a validation error for missing value.

B The age field will be set to None.

C The age field will be set to 20 by default.

D The age field will be set to 0 by default.

💡 Hint

Think about what the default parameter does in Django model fields.

The default parameter sets the value automatically if none is provided. Here, age will be 20 if not specified.

📝 Syntax

intermediate

Which option correctly defines a CharField with max length 50 and allows blank values?

You want to define a Django model field that stores text up to 50 characters and can be left blank. Which option is correct?

A name = models.CharField(max_length=50, blank=True)

B name = models.CharField(max_length=50, null=True)

C name = models.CharField(blank=True)

D name = models.CharField(max_length=50, blank=False)

💡 Hint

Remember that max_length is required for CharField and blank=True allows empty input.

max_length is mandatory for CharField. blank=True allows form validation to accept empty values.

🔧 Debug

advanced

What error does this model field definition cause?

Examine this Django model field:

price = models.DecimalField(max_digits=5, decimal_places=2, max_length=10)

What error will this cause when running migrations?

A ValueError: max_digits must be greater than decimal_places

B TypeError: DecimalField got an unexpected keyword argument 'max_length'

C No error, field is valid

D SyntaxError: invalid syntax in field definition

💡 Hint

Check the valid parameters for DecimalField.

DecimalField does not accept max_length parameter, so it raises a TypeError.

❓ state_output

advanced

What is the value of 'is_active' after saving this model instance?

Given this model field:

is_active = models.BooleanField(default=True)

And this code:

obj = MyModel()
obj.is_active = False
obj.save()

What will be the value of is_active in the database?

A False, because the field was explicitly set before saving.

B True, because default=True overrides assigned values.

C Raises IntegrityError due to missing value.

D None, because BooleanField cannot be set to False.

💡 Hint

Default is only used if no value is assigned.

Explicitly setting is_active to False overrides the default. The saved value is False.

🧠 Conceptual

expert

Which field option combination ensures a unique, non-null email field that can be blank in forms?

You want to define an email field in a Django model that:
- Must be unique in the database
- Cannot be null in the database
- Can be left blank in forms (optional input)
Which option correctly achieves this?

A email = models.EmailField(unique=True, null=True, blank=True)

B email = models.EmailField(unique=True, null=True, blank=False)

C email = models.EmailField(unique=False, null=False, blank=True)

D email = models.EmailField(unique=True, null=False, blank=True)

💡 Hint

null controls database nullability; blank controls form validation.

null=False means database column cannot be null, blank=True allows empty form input, unique=True enforces uniqueness.