Repository pattern in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Repository class from TypeORM.

NestJS

import { [1] } from 'typeorm';

Drag options to blanks, or click blank then click option'

AModule

BRepository

CController

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Service or Controller instead of Repository.

Forgetting to import from 'typeorm'.

The Repository class is imported from typeorm to use the repository pattern in NestJS.

2fill in blank

medium

Complete the code to inject the repository for the User entity using @InjectRepository.

NestJS

constructor(@InjectRepository([1]) private userRepository: Repository<User>) {}

Drag options to blanks, or click blank then click option'

AUser

BUserService

CUserModule

DUserController

Attempts:

3 left

💡 Hint

Common Mistakes

Passing service or module names instead of the entity class.

Omitting the entity class inside @InjectRepository.

The @InjectRepository decorator takes the entity class, here User, to inject its repository.

3fill in blank

hard

Fix the error in the method to find a user by id using the repository.

NestJS

async findUserById(id: number): Promise<User | null> {
  return await this.userRepository.[1]({ id });
}

Drag options to blanks, or click blank then click option'

AfindOneById

BfindById

CfindOne

DgetOne

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like findOneById or findById.

Using getOne which is not a repository method.

The correct method to find one entity by id in TypeORM repository is findOne.

4fill in blank

hard

Fill both blanks to create a new user entity and save it using the repository.

NestJS

const newUser = this.userRepository.[1](userData);
await this.userRepository.[2](newUser);

Drag options to blanks, or click blank then click option'

Acreate

Bsave

Cinsert

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using insert instead of save after create.

Using update instead of save for new entities.

Use create to make a new entity instance and save to store it in the database.

5fill in blank

hard

Fill all three blanks to update a user's email by id using the repository.

NestJS

await this.userRepository.[1]({ id: userId }, { [2]: [3] });

Drag options to blanks, or click blank then click option'

Aupdate

Bemail

CnewEmail

Dsave

Attempts:

3 left

💡 Hint

Common Mistakes

Using save instead of update for partial updates.

Mixing up field names or values in the update object.

The update method takes a condition object and a partial entity with fields to update. Here, we update the email field to newEmail.

Practice

1. What is the main purpose of the Repository pattern in NestJS?

easy

A. To separate data access logic from business logic

B. To handle HTTP requests directly

C. To manage application configuration settings

D. To create UI components

Solution

1. Step 1: Understand the role of Repository pattern

   The Repository pattern is designed to isolate data access logic from the rest of the application.

2. Step 2: Identify what Repository does in NestJS

   In NestJS, repositories handle database operations, keeping business logic clean and testable.

3. Final Answer:

   To separate data access logic from business logic -> Option A

4. Quick Check:

   Repository pattern = separate data access [OK]

Hint: Repository = data access layer, not UI or config [OK]

Common Mistakes:

• Confusing repository with controller responsibilities
• Thinking repository manages UI or HTTP directly
• Mixing repository with configuration management

2. Which of the following is the correct way to inject a repository in a NestJS service using TypeORM?

easy

A. @Inject(UserRepository) private userRepository: Repository<User>;

B. @InjectableRepository(User) private userRepository: Repository<User>;

C. @RepositoryInject(User) private userRepository: Repository<User>;

D. @InjectRepository(User) private userRepository: Repository<User>;

Solution

1. Step 1: Recall the correct decorator for repository injection

   In NestJS with TypeORM, @InjectRepository() is used to inject repositories.

2. Step 2: Match the syntax with the correct option

   @InjectRepository(User) private userRepository: Repository<User>; uses @InjectRepository(User) which is the official and correct syntax.

3. Final Answer:

   @InjectRepository(User) private userRepository: Repository<User>; -> Option D

4. Quick Check:

   @InjectRepository = correct injection [OK]

Hint: Use @InjectRepository to inject TypeORM repositories [OK]

Common Mistakes:

• Using wrong decorator names like @InjectableRepository
• Confusing @Inject with @InjectRepository
• Omitting the entity inside @InjectRepository()

3. Given the following NestJS service code, what will findAll() return?

import { Injectable } from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { User } from './user.entity';

@Injectable()
export class UserService {
  constructor(@InjectRepository(User) private userRepo: Repository<User>) {}

  async findAll() {
    return await this.userRepo.find();
  }
}

medium

A. Undefined, because find() is not a valid method

B. A single User entity

C. An array of all User entities from the database

D. A Promise that resolves to null

Solution

1. Step 1: Understand what this.userRepo.find() does

   The find() method of TypeORM repository returns all records of the entity as an array.

2. Step 2: Analyze the return type of findAll()

   Since find() returns a Promise resolving to an array of User entities, findAll() returns that array.

3. Final Answer:

   An array of all User entities from the database -> Option C

4. Quick Check:

   Repository.find() returns array [OK]

Hint: Repository.find() returns all records as an array [OK]

Common Mistakes:

• Thinking find() returns a single entity
• Assuming find() is not a valid method
• Confusing Promise with null return

4. Identify the error in this NestJS repository injection code snippet:

@Injectable()
export class ProductService {
  constructor(private productRepository: Repository<Product>) {}
}

medium

A. Missing @InjectRepository decorator for productRepository

B. Repository should be injected using @InjectableRepository

C. Constructor should not have parameters

D. Repository cannot be injected in services

Solution

1. Step 1: Check how repositories are injected in NestJS

   Repositories must be injected with @InjectRepository(Entity) decorator to work properly.

2. Step 2: Identify missing decorator in the code

   The code misses @InjectRepository(Product) before the repository parameter.

3. Final Answer:

   Missing @InjectRepository decorator for productRepository -> Option A

4. Quick Check:

   Repository injection needs @InjectRepository [OK]

Hint: Always use @InjectRepository for repositories in constructor [OK]

Common Mistakes:

• Forgetting @InjectRepository decorator
• Using wrong decorator names
• Assuming repositories inject automatically without decorators

5. You want to create a custom method findActiveUsers() in your UserRepository that returns only users with isActive = true. Which approach correctly applies the Repository pattern in NestJS?

hard

A. Add findActiveUsers() method directly in the UserService without modifying repository

B. Extend the Repository class and add findActiveUsers() method, then inject this custom repository

C. Use a global function outside repository and service to filter active users

D. Modify the User entity to include a static method findActiveUsers()

Solution

1. Step 1: Understand extending repository for custom methods

   To add custom queries, extend the Repository class and add methods like findActiveUsers().

2. Step 2: Confirm proper injection of custom repository

   Inject the custom repository in services to keep data access logic encapsulated.

3. Final Answer:

   Extend the Repository class and add findActiveUsers() method, then inject this custom repository -> Option B

4. Quick Check:

   Custom repo methods = extend Repository [OK]

Hint: Add custom queries by extending Repository class [OK]

Common Mistakes:

• Putting query logic in service instead of repository
• Using global functions outside repository pattern
• Adding static methods to entity instead of repository