Prisma migrations in NestJS - Step-by-Step Execution

Concept Flow - Prisma migrations

Write schema.prisma

↓

Run prisma migrate dev

↓

Migration files created

↓

Database schema updated

↓

Application uses updated schema

↓

Repeat for new changes

This flow shows how you write your Prisma schema, run migrations to update the database, and then use the updated schema in your NestJS app.

Execution Sample

NestJS

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

// Run: npx prisma migrate dev --name init

Defines a User model and runs a migration to create the corresponding database table.

Execution Table

Step	Action	Input/Command	Effect	Output/Result
1	Write schema	Add User model to schema.prisma	Schema file updated	User model defined
2	Run migration	npx prisma migrate dev --name init	Migration process starts	Migration files created
3	Apply migration	Database updated	Database schema matches User model	User table created
4	Generate client	Prisma client updated	Client reflects new schema	Client ready to use
5	Use in app	NestJS uses Prisma client	App can query User table	Data operations succeed
6	Exit	No more migrations	Process ends	Database and app in sync

💡 No more schema changes, migration process complete

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
schema.prisma	empty or old schema	User model added	User model unchanged	User model unchanged	User model unchanged	User model defined
migration files	none	none	init migration created	init migration applied	init migration applied	init migration applied
database schema	old or empty	old or empty	old or empty	User table created	User table created	User table created
Prisma client	old version	old version	old version	updated with User model	updated with User model	updated with User model

Key Moments - 2 Insights

Why do we need to run 'prisma migrate dev' after changing schema.prisma?

Because the migration command creates files and updates the database schema to match your Prisma schema. Without it, the database won't reflect your changes (see execution_table step 2 and 3).

What happens if you change schema.prisma but don't generate the Prisma client?

Your app will use an outdated client that doesn't know about new models or fields. Step 4 in the execution_table shows client generation is needed to keep the client in sync.

Visual Quiz - 3 Questions

Look at the execution_table, what is created at step 2?

A Database tables

B Migration files

C Prisma client

D NestJS modules

💡 Hint

Check the 'Effect' and 'Output/Result' columns in step 2 of the execution_table.

At which step does the database schema get updated?

A Step 3

B Step 1

C Step 4

D Step 5

💡 Hint

Look for 'Database schema matches User model' in the 'Effect' column.

If you skip step 4, what problem will you face?

A Migration files won't be created

B Database schema won't update

C Prisma client won't reflect schema changes

D NestJS app won't start

💡 Hint

Refer to the 'Prisma client' variable in variable_tracker after step 4.

Concept Snapshot

Prisma migrations let you update your database schema safely.
1. Edit schema.prisma to define models.
2. Run 'npx prisma migrate dev --name <desc>' to create migration files and update DB.
3. Prisma client regenerates to match schema.
4. Use updated client in NestJS app.
Repeat for every schema change.

Full Transcript

Prisma migrations in NestJS start by writing or updating the schema.prisma file to define your data models. Then, you run the command 'npx prisma migrate dev --name <migration_name>' which creates migration files and applies changes to your database schema. After the database updates, Prisma regenerates its client to reflect the new schema. Finally, your NestJS application uses this updated client to interact with the database. This process repeats whenever you change your data models, ensuring your database and app stay in sync.

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