Prisma migrations in NestJS - Mini Project: Build & Apply

Prisma Migrations with NestJS

📖 Scenario: You are building a simple NestJS backend application that manages a list of books. You want to use Prisma ORM to handle your database schema and migrations.This project will guide you through setting up Prisma migrations step-by-step to create and update your database schema safely.

🎯 Goal: By the end, you will have a Prisma schema file defining a Book model, a migration created and applied to your database, and a NestJS service ready to use Prisma Client to access the Book table.

📋 What You'll Learn

Create a Prisma schema file with a Book model

Configure the database connection URL

Generate and apply a Prisma migration

Use Prisma Client in a NestJS service to query books

💡 Why This Matters

🌍 Real World

Prisma migrations help developers safely evolve their database schema as application requirements change, avoiding manual database edits.

💼 Career

Understanding Prisma migrations and integrating Prisma Client in NestJS is valuable for backend developers working with modern Node.js frameworks and relational databases.

1

Create Prisma schema with Book model

Create a file named schema.prisma with a datasource block for PostgreSQL using the URL postgresql://user:password@localhost:5432/mydb. Then add a generator block for Prisma Client. Finally, define a model Book with fields: id Int @id @default(autoincrement()), title String, and author String.

NestJS

// Create schema.prisma with datasource, generator, and Book model
// Your code here

Hint

Remember to define datasource and generator blocks before the model.

2

Configure environment variable for database URL

Create a file named .env in your project root. Add a line setting DATABASE_URL="postgresql://user:password@localhost:5432/mydb". Then update schema.prisma to use env("DATABASE_URL") for the url in the datasource block.

NestJS

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

// Create .env file with DATABASE_URL
// Your code here

Hint

Use env("DATABASE_URL") in schema.prisma and set the exact DATABASE_URL in .env.

3

Generate and apply Prisma migration

Run the command npx prisma migrate dev --name init in your terminal to create and apply the initial migration based on your schema.

NestJS

// Run the migration command below
// Your code here

Hint

This command creates a migration folder and updates your database schema.

4

Use Prisma Client in NestJS service

In your NestJS service file, import PrismaClient from @prisma/client. Create a class BooksService with a private prisma property initialized as new PrismaClient(). Add an async method getAllBooks() that returns this.prisma.book.findMany().

NestJS

// Import PrismaClient and create BooksService class
// Your code here

Hint

Use new PrismaClient() to access your database and return all books with findMany().

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