TypeORM Has a Free API — Here's How to Build Type-Safe Database Queries

#typeorm #typescript #database #node

TypeORM is a feature-rich ORM for TypeScript and JavaScript that supports PostgreSQL, MySQL, SQLite, MongoDB, and more. It uses decorators for entity definitions and provides both Active Record and Data Mapper patterns.

Installation

npm install typeorm reflect-metadata pg
# Add to tsconfig.json: "emitDecoratorMetadata": true, "experimentalDecorators": true

Entity Definition

import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn, ManyToOne } from "typeorm";

@Entity()
export class User {
  @PrimaryGeneratedColumn("uuid")
  id: string;

  @Column({ unique: true })
  email: string;

  @Column()
  name: string;

  @CreateDateColumn()
  createdAt: Date;

  @OneToMany(() => Post, post => post.author)
  posts: Post[];
}

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

  @Column()
  title: string;

  @Column("text")
  content: string;

  @ManyToOne(() => User, user => user.posts)
  author: User;
}

Data Source Setup

import { DataSource } from "typeorm";

export const AppDataSource = new DataSource({
  type: "postgres",
  host: "localhost",
  port: 5432,
  username: "admin",
  password: "password",
  database: "mydb",
  entities: [User, Post],
  synchronize: true // dev only!
});

await AppDataSource.initialize();

CRUD Operations

const userRepo = AppDataSource.getRepository(User);

// Create
const user = userRepo.create({ email: "dev@example.com", name: "Dev" });
await userRepo.save(user);

// Find with relations
const users = await userRepo.find({
  where: { name: Like("%Dev%") },
  relations: ["posts"],
  order: { createdAt: "DESC" },
  take: 10
});

// Query Builder
const result = await userRepo
  .createQueryBuilder("user")
  .leftJoinAndSelect("user.posts", "post")
  .where("user.email LIKE :email", { email: "%example%" })
  .orderBy("post.id", "DESC")
  .getMany();

Migrations

npx typeorm migration:generate -d src/data-source.ts src/migrations/AddUserTable
npx typeorm migration:run -d src/data-source.ts
npx typeorm migration:revert -d src/data-source.ts

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