Query builder in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Query Builder in NestJS?

A Query Builder in NestJS is a tool that helps you create database queries step-by-step using code instead of writing raw SQL. It makes queries easier to build, read, and maintain.

beginner

How do you start a Query Builder for a User entity in NestJS using TypeORM?

You use the repository for the User entity and call createQueryBuilder(). For example: const query = this.userRepository.createQueryBuilder('user');

beginner

What method do you use to add a WHERE condition in a NestJS Query Builder?

You use the .where() method. For example: query.where('user.age > :age', { age: 18 }) adds a condition to filter users older than 18.

intermediate

How can you join related tables using Query Builder in NestJS?

You use .leftJoinAndSelect() or .innerJoinAndSelect() methods to join related tables and select their data. For example: query.leftJoinAndSelect('user.profile', 'profile') joins the profile table.

beginner

Why is using a Query Builder better than raw SQL in NestJS?

Query Builder helps avoid SQL syntax errors, improves security by preventing SQL injection, and makes queries easier to read and maintain with code instead of raw strings.

Which method starts a Query Builder for an entity in NestJS?

A createQueryBuilder()

B find()

C execute()

D connect()

createQueryBuilder() is the method used to start building a query for an entity.

How do you add a WHERE clause in a NestJS Query Builder?

A .orderBy()

B .join()

C .select()

D .where()

The .where() method adds conditions to filter results.

Which method joins related tables and selects their data?

A .leftJoinAndSelect()

B .groupBy()

C .limit()

D .insert()

.leftJoinAndSelect() joins tables and includes their data in the result.

What is a key benefit of using Query Builder over raw SQL?

A Requires no database connection

B Prevents SQL injection

C Runs faster than SQL

D Automatically creates tables

Query Builder helps prevent SQL injection by safely handling parameters.

In NestJS, which object do you usually call createQueryBuilder() on?

A Service

B Controller

C Repository

D Module

You call createQueryBuilder() on the repository of the entity.

Explain how to build a query with a WHERE condition and a JOIN using NestJS Query Builder.

Think about chaining methods to build the query step-by-step.

Describe the advantages of using Query Builder in NestJS compared to writing raw SQL queries.

Focus on safety, readability, and flexibility.