Prisma Client usage in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Prisma Client query in NestJS?

Consider a Prisma Client query fetching a user by ID. What will be the output if the user does not exist?

NestJS

const user = await prisma.user.findUnique({ where: { id: 999 } });
console.log(user);

A {} (empty object)

B undefined

C Throws an error

D null

💡 Hint

Think about what Prisma returns when no record matches the query.

Prisma Client returns null when findUnique finds no matching record.

❓ state_output

intermediate

What is the value of 'createdUser' after this Prisma create call?

Given the following Prisma Client code in a NestJS service, what does 'createdUser' contain?

NestJS

const createdUser = await prisma.user.create({
  data: { email: '[e-mail]', name: 'Test User' }
});
console.log(createdUser);

A { email: '[e-mail]', name: 'Test User' }

B { id: number, email: '[e-mail]', name: 'Test User', createdAt: Date }

C null

D Throws a runtime error

💡 Hint

Prisma returns the full created record including auto-generated fields.

The create method returns the full record including generated fields like id and createdAt.

📝 Syntax

advanced

Which option correctly updates a user's name using Prisma Client in NestJS?

Select the correct Prisma Client syntax to update the name of a user with id 5 to 'Alice'.

A await prisma.user.update({ where: { id: 5 }, data: { name: 'Alice' } });

B await prisma.user.update({ data: { name: 'Alice' }, where: { id: 5 } });

C await prisma.user.update({ id: 5, name: 'Alice' });

D await prisma.user.update({ where: { id: 5 }, name: 'Alice' });

💡 Hint

Check the order and keys required by Prisma's update method.

The update method requires where and data keys. The order of keys does not matter, but the structure must be correct.

🔧 Debug

advanced

What error does this Prisma Client code produce?

Analyze the following code snippet and identify the error it causes.

NestJS

const user = await prisma.user.findUnique({ where: { email: '[e-mail]' } });
console.log(user.name);

A No error, prints undefined

B ReferenceError: user is not defined

C TypeError: Cannot read property 'name' of null

D SyntaxError: Unexpected token '.'

💡 Hint

Consider what happens when findUnique returns null and you try to access a property.

If findUnique returns null, accessing user.name causes a TypeError.

🧠 Conceptual

expert

Which option best describes Prisma Client's transaction behavior in NestJS?

When using Prisma Client's $transaction method in NestJS, what happens if one query inside the transaction fails?

A All queries inside the transaction are rolled back; no changes are saved.

B Only the failed query is rolled back; others remain committed.

C The transaction ignores errors and commits all queries anyway.

D Prisma Client throws an error but commits successful queries.

💡 Hint

Think about the atomic nature of transactions.

Prisma Client's $transaction ensures atomicity: if any query fails, all changes are rolled back.