Migrations concept and workflow in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens after running python manage.py migrate?

You have created a new model in your Django app and run python manage.py makemigrations. What is the immediate effect of running python manage.py migrate?

A It restarts the Django development server automatically.

B It deletes all existing data in the database tables.

C It only creates migration files but does not change the database.

D It applies the new migration files to update the database schema accordingly.

💡 Hint

Think about what changes the database structure.

Running migrate applies the migration files to the database, updating its schema to match your models.

📝 Syntax

intermediate

Identify the correct migration command to create migration files

Which command correctly creates migration files after you change your Django models?

A python manage.py makemigrations

B python manage.py migrate

C python manage.py runserver

D python manage.py collectstatic

💡 Hint

This command prepares the changes but does not apply them yet.

makemigrations creates migration files based on model changes.

🔧 Debug

advanced

Why does this migration fail with an error?

You added a new non-nullable field without a default to an existing model and ran makemigrations. The migration fails when applying. Why?

Django

class Book(models.Model):
    title = models.CharField(max_length=100)
    published_date = models.DateField()
    author = models.CharField(max_length=100, null=False)  # New field added without default

A Because the <code>author</code> field should be a ForeignKey, not CharField.

B Because the migration files were not created with <code>makemigrations</code>.

C Because the new field is non-nullable and existing rows have no value, so the database rejects the migration.

D Because Django does not support adding new fields to models.

💡 Hint

Think about what happens to existing data when adding a required field.

Adding a non-nullable field without a default causes the database to fail because existing rows have no value for that field.

🧠 Conceptual

advanced

What is the role of the Migration class in Django migration files?

Each migration file contains a Migration class. What does this class define?

A It defines the operations to apply or reverse changes to the database schema.

B It contains the Django model definitions for the app.

C It manages user authentication during migrations.

D It stores the database connection settings.

💡 Hint

Think about what migrations do to the database.

The Migration class lists operations like creating or altering tables to apply or undo schema changes.

❓ state_output

expert

What is the state of the database after running these commands in order?

You run these commands in your Django project:

1. python manage.py makemigrations
2. python manage.py migrate
3. You modify a model by renaming a field
4. python manage.py makemigrations
5. python manage.py migrate

What is true about the database after step 5?

A The database schema is reset to the initial state before any migrations.

B The database schema matches the latest model changes, including the renamed field.

C The database schema has duplicate columns for old and new field names.

D The database schema still has the old field name because migrations do not rename fields.

💡 Hint

Consider what migrations do when you rename a field and apply migrations.

Django generates a migration to rename the field and applies it, so the database schema updates accordingly.