typeorm

What this skill does

# 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:

```json
{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "strict": true,
    "target": "ES2020",
    "module": "commonjs",
    "moduleResolution": "node"
  }
}
```

## Entity Definition

### Basic Entity

```typescript
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

```typescript
// 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

```typescript
@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

```typescript
@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

```typescript
@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

```typescript
@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

```typescript
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: "[email protected]",
  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

```typescript
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

```typescript
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: "[email protected]", name: "User 1" },
    { email: "[email protected]", name: "User 2" },
  ])
  .execute();
```

## Data Source Configuration

```typescript
// 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

```bash
# 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 migr