Entity definition in NestJS - Mini Project: Build & Apply

Entity Definition in NestJS

📖 Scenario: You are building a simple NestJS application to manage a list of books in a library. Each book has a title, an author, and a year of publication.

🎯 Goal: Create a basic entity class called Book using TypeORM decorators to define the database table and columns.

📋 What You'll Learn

Create a class named Book decorated with @Entity()

Add a primary column id with auto-generated number

Add a column title of type string

Add a column author of type string

Add a column year of type number

💡 Why This Matters

🌍 Real World

Defining entities is essential for building backend applications that interact with databases, such as managing books in a library system.

💼 Career

Understanding entity definition is a key skill for backend developers working with NestJS and TypeORM in real-world projects.

1

Create the Book class with Entity decorator

Create a class called Book and decorate it with @Entity() from typeorm.

NestJS

import { Entity } from 'typeorm';

// Your code here

Need a hint?

Use @Entity() above the class declaration to mark it as a database entity.

2

Add the primary key column id

Import PrimaryGeneratedColumn from typeorm and add a property id decorated with @PrimaryGeneratedColumn() of type number inside the Book class.

NestJS

import { Entity, PrimaryGeneratedColumn } from 'typeorm';

@Entity()
export class Book {
  // Your code here
}

Need a hint?

The id property should have @PrimaryGeneratedColumn() decorator and be of type number.

3

Add columns for title, author, and year

Import Column from typeorm. Add three properties inside the Book class: title and author as strings, and year as a number. Decorate each with @Column().

NestJS

import { Entity, PrimaryGeneratedColumn, Column } from 'typeorm';

@Entity()
export class Book {
  @PrimaryGeneratedColumn()
  id: number;

  // Your code here
}

Need a hint?

Use @Column() decorator for each property and specify the correct types.

4

Export the Book entity class

Make sure the Book class is exported using export class Book so it can be used in other parts of the application.

NestJS

import { Entity, PrimaryGeneratedColumn, Column } from 'typeorm';

// Your code here

Need a hint?

Check that the class declaration starts with export class Book.