Prisma migrations in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of Prisma migrations in a NestJS project?

Prisma migrations help manage and apply changes to the database schema in a safe and organized way. They keep the database structure in sync with your Prisma schema file.

beginner

Which command creates a new migration file after updating the Prisma schema?

The command npx prisma migrate dev --name your_migration_name creates a new migration file and applies it to the database during development.

intermediate

How does Prisma ensure migrations are applied in the correct order?

Prisma stores migration history in a special table in the database. It applies migrations sequentially based on this history to keep the database consistent.

intermediate

What should you do before running migrations in a production environment?

You should review migration files carefully, back up your database, and run npx prisma migrate deploy to apply migrations safely without prompts.

beginner

Why is it important to commit migration files to version control?

Committing migration files lets your team share database changes and ensures everyone applies the same schema updates, avoiding conflicts and errors.

Which Prisma command applies migrations during development and updates the database?

A npx prisma generate

B npx prisma migrate dev --name migration_name

C npx prisma studio

D npx prisma migrate deploy

The migrate dev command creates and applies migrations during development.

Where does Prisma store the migration history to track applied migrations?

A In a special table inside the database

B In the Prisma schema file

C In a JSON file in the project root

D In environment variables

Prisma uses a dedicated table in the database to track migration history.

What is the recommended command to apply migrations in a production environment?

A npx prisma migrate reset

B npx prisma migrate dev

C npx prisma migrate deploy

D npx prisma generate

The migrate deploy command applies migrations safely in production.

Why should migration files be committed to version control?

A To share schema changes with the team

B To speed up the application runtime

C To store database credentials

D To generate Prisma client

Committing migration files helps the team stay in sync with database changes.

What happens if you change the Prisma schema but do not create a migration?

A The Prisma client will update automatically

B The database will reset

C The migration will be created automatically on app start

D The database schema will not update

Without creating a migration, the database schema stays unchanged.

Explain the steps to create and apply a new Prisma migration in a NestJS project.

Think about how you change the schema and then update the database safely.

Describe how Prisma migrations help keep your database consistent across different environments.

Consider how migrations track and share changes to avoid conflicts.

Practice

1. What is the main purpose of Prisma migrations in a NestJS project?

easy

A. To optimize API response times

B. To generate frontend UI components automatically

C. To manage user authentication and sessions

D. To keep the database schema in sync with the application code

Solution

1. Step 1: Understand Prisma migrations role

   Prisma migrations help update the database schema to match changes in your code models.

2. Step 2: Compare options

   Options A, B, and C relate to performance, UI, and authentication, which are unrelated to migrations.

3. Final Answer:

   To keep the database schema in sync with the application code -> Option D

4. Quick Check:

   Prisma migrations = sync DB schema [OK]

Hint: Migrations sync DB schema with code changes [OK]

Common Mistakes:

• Confusing migrations with frontend code generation
• Thinking migrations handle user sessions
• Assuming migrations optimize API speed

2. Which command correctly creates a new migration during development with Prisma in NestJS?

easy

A. npx prisma migrate dev --name addUserTable

B. npx prisma migrate deploy --name addUserTable

C. npx prisma generate --name addUserTable

D. npx prisma migrate reset --name addUserTable

Solution

1. Step 1: Identify the correct command for creating migrations

   The command npx prisma migrate dev --name is used to create and apply migrations during development.

2. Step 2: Eliminate incorrect commands

   migrate deploy applies migrations in production, generate creates Prisma client code, and migrate reset resets the database.

3. Final Answer:

   npx prisma migrate dev --name addUserTable -> Option A

4. Quick Check:

   Dev migrations use migrate dev [OK]

Hint: Use migrate dev to create migrations in development [OK]

Common Mistakes:

• Using migrate deploy instead of migrate dev for new migrations
• Confusing generate with migration commands
• Trying to reset DB when creating migrations

3. Given the following Prisma schema change and migration command, what will happen?

model User {
  id    Int    @id @default(autoincrement())
  email String @unique
  name  String?
}

// Command run:
npx prisma migrate dev --name addNameField

medium

A. The database schema remains unchanged

B. An error occurs because 'name' field is optional

C. A migration file is created adding the optional 'name' field to User table

D. The User table is deleted and recreated

Solution

1. Step 1: Analyze schema change

   The schema adds an optional 'name' field to the User model, which is a valid change.

2. Step 2: Understand migrate dev behavior

   Running npx prisma migrate dev --name addNameField creates a migration file reflecting this change and applies it to the database.

3. Final Answer:

   A migration file is created adding the optional 'name' field to User table -> Option C

4. Quick Check:

   Optional field added = migration created [OK]

Hint: Optional fields create migrations without errors [OK]

Common Mistakes:

• Thinking optional fields cause errors
• Assuming schema stays unchanged without manual DB update
• Believing migrate dev deletes tables

4. You run npx prisma migrate deploy in production but get an error saying migrations are missing. What is the likely cause?

medium

A. You forgot to create migration files locally before deploying

B. The database connection string is incorrect

C. You ran migrate dev instead of migrate deploy

D. Prisma client was not generated

Solution

1. Step 1: Understand migrate deploy requirements

   migrate deploy applies existing migration files to production; it does not create them.

2. Step 2: Identify cause of missing migrations error

   If migration files were not created locally (e.g., with migrate dev), deploy will fail due to missing files.

3. Final Answer:

   You forgot to create migration files locally before deploying -> Option A

4. Quick Check:

   Deploy needs existing migrations [OK]

Hint: Create migrations locally before deploying to production [OK]

Common Mistakes:

• Confusing migrate dev and migrate deploy roles
• Ignoring missing migration files
• Assuming wrong DB connection causes missing migrations error

5. You want to add a new required field age Int to your User model in Prisma. However, your database already has existing users without this field. What is the best way to handle this migration safely?

hard

A. Delete all existing users before running migration

B. Add the field as optional first, run a migration, then update data and make it required in a second migration

C. Add the required field directly and run migrate dev once

D. Skip migrations and manually update the database schema

Solution

1. Step 1: Understand required field impact

   Adding a required field means existing rows must have a value, or migration will fail.

2. Step 2: Apply a two-step migration strategy

   First add the field as optional, migrate, update existing data with values, then change field to required and migrate again.

3. Final Answer:

   Add the field as optional first, run a migration, then update data and make it required in a second migration -> Option B

4. Quick Check:

   Two-step migration avoids missing data errors [OK]

Hint: Add required fields in two steps to avoid errors [OK]

Common Mistakes:

• Adding required fields directly causing migration failure
• Deleting data unnecessarily
• Skipping migrations and editing DB manually