TypeORM Development Guidelines
You are an expert in TypeORM, TypeScript, and database design with a focus on the Data Mapper pattern and enterprise application architecture.
Core Principles
- TypeORM supports both Active Record and Data Mapper patterns
- Uses TypeScript decorators for entity and column definitions
- Supports MySQL, PostgreSQL, MariaDB, SQLite, MS SQL Server, Oracle, and more
- Works in Node.js, Browser, Ionic, Cordova, React Native, NativeScript, Expo, and Electron
- First-class support for database migrations
TypeScript Configuration
Required settings in tsconfig.json:
{
"compilerOptions": {
"experimentalDecorators": true,
"emitDecoratorMetadata": true,
"strict": true,
"target": "ES2020",
"module": "commonjs",
"moduleResolution": "node"
}
}Entity Definition
Basic Entity
import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn, UpdateDateColumn } from 'typeorm';
@Entity('users')
export class User {
@PrimaryGeneratedColumn()
id: number;
@Column({ type: 'varchar', length: 255, unique: true })
email: string;
@Column({ type: 'varchar', length: 255, nullable: true })
name: string | null;
@Column({ type: 'boolean', default: true })
isActive: boolean;
@CreateDateColumn()
createdAt: Date;
@UpdateDateColumn()
updatedAt: Date;
}Primary Key Options
// Auto-increment
@PrimaryGeneratedColumn()
id: number;
// UUID
@PrimaryGeneratedColumn("uuid")
id: string;
// Custom primary key
@PrimaryColumn()
id: string;
// Composite primary key
@Entity()
export class OrderItem {
@PrimaryColumn()
orderId: number;
@PrimaryColumn()
productId: number;
}Column Decorators
@Entity()
export class Product {
@PrimaryGeneratedColumn()
id: number;
// String columns
@Column({ type: 'varchar', length: 255 })
name: string;
@Column({ type: 'text', nullable: true })
description: string | null;
// Numeric columns
@Column({ type: 'decimal', precision: 10, scale: 2 })
price: number;
@Column({ type: 'int', default: 0 })
stock: number;
// Boolean
@Column({ type: 'boolean', default: true })
isAvailable: boolean;
// JSON
@Column({ type: 'jsonb', nullable: true })
metadata: Record<string, any> | null;
// Enum
@Column({
type: 'enum',
enum: ['active', 'inactive', 'pending'],
default: 'pending',
})
status: 'active' | 'inactive' | 'pending';
// Timestamps
@CreateDateColumn()
createdAt: Date;
@UpdateDateColumn()
updatedAt: Date;
@DeleteDateColumn()
deletedAt: Date | null; // For soft deletes
// Version column for optimistic locking
@VersionColumn()
version: number;
}Relationships
One-to-One
@Entity()
export class User {
@PrimaryGeneratedColumn()
id: number;
@OneToOne(() => Profile, profile => profile.user, { cascade: true })
@JoinColumn()
profile: Profile;
}
@Entity()
export class Profile {
@PrimaryGeneratedColumn()
id: number;
@Column()
bio: string;
@OneToOne(() => User, user => user.profile)
user: User;
}One-to-Many / Many-to-One
@Entity()
export class User {
@PrimaryGeneratedColumn()
id: number;
@Column()
name: string;
@OneToMany(() => Post, post => post.author)
posts: Post[];
}
@Entity()
export class Post {
@PrimaryGeneratedColumn()
id: number;
@Column()
title: string;
@ManyToOne(() => User, user => user.posts, { onDelete: 'CASCADE' })
@JoinColumn({ name: 'author_id' })
author: User;
@Column()
authorId: number; // Explicit foreign key column
}Many-to-Many
@Entity()
export class Post {
@PrimaryGeneratedColumn()
id: number;
@Column()
title: string;
@ManyToMany(() => Tag, tag => tag.posts)
@JoinTable({
name: 'post_tags',
joinColumn: { name: 'post_id' },
inverseJoinColumn: { name: 'tag_id' },
})
tags: Tag[];
}
@Entity()
export class Tag {
@PrimaryGeneratedColumn()
id: number;
@Column({ unique: true })
name: string;
@ManyToMany(() => Post, post => post.tags)
posts: Post[];
}Repository Pattern
Basic Repository Usage
import { AppDataSource } from './data-source';
import { User } from './entities/User';
const userRepository = AppDataSource.getRepository(User);
// Find all
const users = await userRepository.find();
// Find with conditions
const activeUsers = await userRepository.find({
where: { isActive: true },
});
// Find one
const user = await userRepository.findOne({
where: { id: 1 },
});
// Find or fail
const user = await userRepository.findOneOrFail({
where: { id: 1 },
});
// Save
const newUser = userRepository.create({
email: 'user@example.com',
name: 'John Doe',
});
await userRepository.save(newUser);
// Update
await userRepository.update({ id: 1 }, { name: 'Jane Doe' });
// Delete
await userRepository.delete({ id: 1 });
// Soft delete (requires @DeleteDateColumn)
await userRepository.softDelete({ id: 1 });Custom Repository
import { Repository, DataSource } from 'typeorm';
import { User } from './entities/User';
export class UserRepository extends Repository<User> {
constructor(private dataSource: DataSource) {
super(User, dataSource.createEntityManager());
}
async findByEmail(email: string): Promise<User | null> {
return this.findOne({ where: { email } });
}
async findActiveUsers(): Promise<User[]> {
return this.find({
where: { isActive: true },
order: { createdAt: 'DESC' },
});
}
async findWithPosts(userId: number): Promise<User | null> {
return this.findOne({
where: { id: userId },
relations: ['posts'],
});
}
}Query Builder
const users = await userRepository
.createQueryBuilder('user')
.leftJoinAndSelect('user.posts', 'post')
.where('user.isActive = :isActive', { isActive: true })
.andWhere('post.publishedAt IS NOT NULL')
.orderBy('user.createdAt', 'DESC')
.skip(0)
.take(10)
.getMany();
// With raw results
const result = await userRepository
.createQueryBuilder('user')
.select('COUNT(*)', 'count')
.where('user.isActive = :isActive', { isActive: true })
.getRawOne();
// Insert with query builder
await userRepository
.createQueryBuilder()
.insert()
.into(User)
.values([
{ email: 'user1@example.com', name: 'User 1' },
{ email: 'user2@example.com', name: 'User 2' },
])
.execute();Data Source Configuration
// data-source.ts
import { DataSource } from 'typeorm';
import { User } from './entities/User';
import { Post } from './entities/Post';
export const AppDataSource = new DataSource({
type: 'postgres',
host: process.env.DB_HOST || 'localhost',
port: parseInt(process.env.DB_PORT || '5432'),
username: process.env.DB_USERNAME,
password: process.env.DB_PASSWORD,
database: process.env.DB_NAME,
// Entity configuration
entities: [User, Post],
// Or use glob pattern: entities: ["src/entities/**/*.ts"]
// Migrations
migrations: ['src/migrations/**/*.ts'],
// Synchronize - NEVER use in production
synchronize: false,
// Logging
logging: process.env.NODE_ENV === 'development',
// Connection pool
poolSize: 10,
// SSL (for production)
ssl: process.env.NODE_ENV === 'production' ? { rejectUnauthorized: false } : false,
});
// Initialize connection
AppDataSource.initialize()
.then(() => console.log('Data Source initialized'))
.catch(error => console.error('Error initializing Data Source:', error));Migrations
Creating Migrations
# Generate migration from entity changes
npx typeorm migration:generate src/migrations/CreateUsers -d src/data-source.ts
# Create empty migration
npx typeorm migration:create src/migrations/SeedUsers
# Run migrations
npx typeorm migration:run -d src/data-source.ts
# Revert last migration
npx typeorm migration:revert -d src/data-source.tsMigration File Structure
import { MigrationInterface, QueryRunner, Table, TableIndex } from 'typeorm';
export class CreateUsers1234567890 implements MigrationInterface {
public async up(queryRunner: QueryRunner): Promise<void> {
await queryRunner.createTable(
new Table({
name: 'users',
columns: [
{
name: 'id',
type: 'int',
isPrimary: true,
isGenerated: true,
generationStrategy: 'increment',
},
{
name: 'email',
type: 'varchar',
length: '255',
isUnique: true,
},
{
name: 'name',
type: 'varchar',
length: '255',
isNullable: true,
},
{
name: 'is_active',
type: 'boolean',
default: true,
},
{
name: 'created_at',
type: 'timestamp',
default: 'CURRENT_TIMESTAMP',
},
{
name: 'updated_at',
type: 'timestamp',
default: 'CURRENT_TIMESTAMP',
onUpdate: 'CURRENT_TIMESTAMP',
},
],
}),
true,
);
await queryRunner.createIndex(
'users',
new TableIndex({
name: 'IDX_USERS_EMAIL',
columnNames: ['email'],
}),
);
}
public async down(queryRunner: QueryRunner): Promise<void> {
await queryRunner.dropIndex('users', 'IDX_USERS_EMAIL');
await queryRunner.dropTable('users');
}
}Transactions
// Using QueryRunner
const queryRunner = AppDataSource.createQueryRunner();
await queryRunner.connect();
await queryRunner.startTransaction();
try {
const user = queryRunner.manager.create(User, {
email: 'user@example.com',
name: 'User',
});
await queryRunner.manager.save(user);
const post = queryRunner.manager.create(Post, {
title: 'First Post',
author: user,
});
await queryRunner.manager.save(post);
await queryRunner.commitTransaction();
} catch (error) {
await queryRunner.rollbackTransaction();
throw error;
} finally {
await queryRunner.release();
}
// Using transaction method
await AppDataSource.transaction(async manager => {
const user = manager.create(User, {
email: 'user@example.com',
name: 'User',
});
await manager.save(user);
const post = manager.create(Post, {
title: 'First Post',
author: user,
});
await manager.save(post);
});NestJS Integration
// app.module.ts
import { Module } from '@nestjs/common';
import { TypeOrmModule } from '@nestjs/typeorm';
import { User } from './entities/user.entity';
import { UsersModule } from './users/users.module';
@Module({
imports: [
TypeOrmModule.forRoot({
type: 'postgres',
host: 'localhost',
port: 5432,
username: 'user',
password: 'password',
database: 'db',
entities: [User],
synchronize: false,
}),
UsersModule,
],
})
export class AppModule {}
// users/users.module.ts
@Module({
imports: [TypeOrmModule.forFeature([User])],
providers: [UsersService],
controllers: [UsersController],
})
export class UsersModule {}
// users/users.service.ts
@Injectable()
export class UsersService {
constructor(
@InjectRepository(User)
private usersRepository: Repository<User>,
) {}
findAll(): Promise<User[]> {
return this.usersRepository.find();
}
findOne(id: number): Promise<User | null> {
return this.usersRepository.findOneBy({ id });
}
}Best Practices
Use Migrations in Production
Never use synchronize: true in production. Always use migrations:
// Development: Use migrations, not sync
synchronize: false,Eager vs Lazy Loading
// Eager loading - loads relations automatically
@OneToMany(() => Post, (post) => post.author, { eager: true })
posts: Post[];
// Lazy loading - loads relations on access
@OneToMany(() => Post, (post) => post.author)
posts: Promise<Post[]>;
// Explicit loading (recommended)
const user = await userRepository.findOne({
where: { id: 1 },
relations: ["posts"],
});Avoid N+1 Queries
// Bad: N+1 queries
const users = await userRepository.find();
for (const user of users) {
console.log(user.posts); // Separate query for each user
}
// Good: Eager load relations
const users = await userRepository.find({
relations: ['posts'],
});Use Indexes
@Entity()
@Index(['email'])
@Index(['firstName', 'lastName'])
export class User {
@Column()
@Index()
email: string;
@Column()
firstName: string;
@Column()
lastName: string;
}Cascade Operations
@OneToMany(() => Post, (post) => post.author, {
cascade: true, // Saves/removes related posts
onDelete: "CASCADE", // Database-level cascade
})
posts: Post[];Naming Strategies
For consistent naming between TypeScript and database:
import { DefaultNamingStrategy, NamingStrategyInterface } from "typeorm";
import { snakeCase } from "typeorm/util/StringUtils";
export class SnakeNamingStrategy extends DefaultNamingStrategy implements NamingStrategyInterface {
tableName(targetName: string, userSpecifiedName: string | undefined): string {
return userSpecifiedName ? userSpecifiedName : snakeCase(targetName);
}
columnName(propertyName: string, customName: string, embeddedPrefixes: string[]): string {
return snakeCase(embeddedPrefixes.join("_")) + (customName ? customName : snakeCase(propertyName));
}
}
// Use in data source config
namingStrategy: new SnakeNamingStrategy(),