CRUD with Prisma in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Prisma create operation?

Given the following NestJS Prisma service code, what will be the output when creating a new user with name 'Alice' and email '[e-mail]'?

NestJS

async createUser() {
  const user = await this.prisma.user.create({
    data: { name: 'Alice', email: '[e-mail]' }
  });
  return user;
}

A Returns null because no user was found

B {"id": 1, "name": "Alice", "email": "[e-mail]"}

C Throws a runtime error because 'id' is missing in data

D {"name": "Alice", "email": "[e-mail]"}

💡 Hint

Prisma automatically generates the 'id' field if it is set as an auto-increment primary key.

The create method returns the full created record including the auto-generated id. The data object only needs the fields to set; Prisma adds the id.

❓ state_output

intermediate

What is the result of this Prisma update operation?

Consider this update method in a NestJS Prisma service. What will be the returned value after updating the user with id 5 to have name 'Bob'?

NestJS

async updateUser() {
  const updatedUser = await this.prisma.user.update({
    where: { id: 5 },
    data: { name: 'Bob' }
  });
  return updatedUser;
}

A {"id": 5, "name": "Bob", "email": "[e-mail]"}

B null because user with id 5 does not exist

C {"name": "Bob"}

D Throws a PrismaClientKnownRequestError because user with id 5 does not exist

💡 Hint

Prisma throws an error if you try to update a record that does not exist.

The update method throws a PrismaClientKnownRequestError if no record matches the where condition.

🔧 Debug

advanced

Why does this Prisma delete operation fail?

This NestJS Prisma service method tries to delete a user by id but fails with a runtime error. What is the cause?

NestJS

async deleteUser(id: number) {
  await this.prisma.user.delete({
    where: { userId: id }
  });
}

A The field 'userId' does not exist in the Prisma schema; it should be 'id'.

B The method is missing an await keyword before the delete call.

C The delete method requires a 'data' property, not 'where'.

D Prisma delete cannot delete by id, only by unique email.

💡 Hint

Check the exact field names in your Prisma schema for the User model.

The where clause must use the exact unique field name defined in the Prisma schema. If the primary key is id, using userId causes an error.

📝 Syntax

advanced

Which option correctly fetches all users with Prisma in NestJS?

Select the correct Prisma query to fetch all users from the database.

A const users = await this.prisma.user.getMany();

B const users = await this.prisma.user.findAll();

C const users = await this.prisma.user.findMany();

D const users = await this.prisma.user.fetchAll();

💡 Hint

Check the Prisma Client API for fetching multiple records.

The correct method to fetch multiple records is findMany(). Other methods do not exist in Prisma Client.

🧠 Conceptual

expert

What happens if you call Prisma update with no matching record?

In NestJS Prisma, what is the behavior when you call prisma.user.update with a where clause that matches no records?

A Prisma throws a PrismaClientKnownRequestError indicating no record found.

B Prisma returns null without error.

C Prisma creates a new record with the update data.

D Prisma silently ignores the update and returns the previous data.

💡 Hint

Consider how Prisma handles updates on non-existent records.

The update method requires an existing record. If none matches, Prisma throws a PrismaClientKnownRequestError.