Query builder in NestJS - Mini Project: Build & Apply

Building a Simple Query with NestJS Query Builder

📖 Scenario: You are creating a small NestJS service to fetch users from a database. You want to build a query that filters users by their age.

🎯 Goal: Build a NestJS query builder that selects users from a users table and filters those whose age is greater than a given threshold.

📋 What You'll Learn

Create a variable with the initial query builder for the users table

Add a variable for the age threshold filter

Use the query builder to filter users with age greater than the threshold

Complete the query builder chain with a call to getMany() to fetch the results

💡 Why This Matters

🌍 Real World

Filtering database records dynamically is common in web apps to show users only relevant data.

💼 Career

Understanding query builders is essential for backend developers working with databases and NestJS.

1

Create the initial query builder

Create a variable called queryBuilder that uses this.userRepository.createQueryBuilder('user') to start building a query for the users table.

NestJS

# Your code here
// Create the initial query builder for users

Need a hint?

Use this.userRepository.createQueryBuilder('user') to start the query.

2

Add an age threshold variable

Create a variable called ageThreshold and set it to 30 to use as the minimum age filter.

NestJS

const queryBuilder = this.userRepository.createQueryBuilder('user');
// Create an age threshold variable
# Your code here

Need a hint?

Set ageThreshold to 30.

3

Add the age filter to the query builder

Use queryBuilder.where('user.age > :age', { age: ageThreshold }) to filter users older than ageThreshold.

NestJS

const queryBuilder = this.userRepository.createQueryBuilder('user');
const ageThreshold = 30;
// Add a where clause to filter users by age
# Your code here

Need a hint?

Use where with a parameter :age and pass { age: ageThreshold }.

4

Complete the query with getMany()

Add const users = await queryBuilder.getMany() to execute the query and get the list of users older than ageThreshold.

NestJS

const queryBuilder = this.userRepository.createQueryBuilder('user');
const ageThreshold = 30;
queryBuilder.where('user.age > :age', { age: ageThreshold });
// Execute the query to get users
# Your code here

Need a hint?

Use await queryBuilder.getMany() to fetch the results.