TypeORM

Common errors

• Cannot delete without criteria. Pass 'true' to delete all entities.

  cause Attempting to delete all entities by calling `repository.delete({})` without explicitly confirming the intent to delete all. This behavior changed in 0.3.23 to prevent accidental mass deletion.
  fix If you intend to delete all entities, change the call to `repository.delete(true)`.

• TypeError: Reflect.decorate is not a function

  cause The `reflect-metadata` polyfill, essential for TypeScript decorators used by TypeORM, has not been installed or imported at the application's entry point.
  fix Install `reflect-metadata` (`npm install reflect-metadata`) and add `import "reflect-metadata";` as the very first line in your application's entry file.

• No driver for database type "..." was found installed. Try to install the corresponding driver for your database.

  cause TypeORM requires a specific database driver (e.g., `pg` for PostgreSQL, `mysql2` for MySQL) to be installed as a peer dependency, but it's missing for the configured database type.
  fix Install the correct database driver for your chosen database, e.g., `npm install pg` for PostgreSQL or `npm install mysql2` for MySQL.

• No entities were found in the given directory: ...

  cause The `entities` array in your `DataSource` configuration is empty, or the glob patterns/paths specified for your entities are incorrect, preventing TypeORM from discovering your entity classes.
  fix Ensure your `DataSource` configuration's `entities` array correctly lists your entity classes or provides accurate glob patterns to their location (e.g., `[User, Post]`, `["**/*.entity{.ts,.js}"]`).

• Cannot read properties of undefined (reading 'sync')

  cause This error was a bug in previous versions of TypeORM related to an upgrade of the `glob` package.
  fix Update TypeORM to version `0.3.19` or later, as this issue was resolved in `0.3.19` and confirmed fixed in `0.3.20`.

Warnings

• breaking Calling `repository.delete({})` or `repository.update({}, data)` no longer deletes/updates all rows. Instead, it throws an error to prevent accidental mass deletion/updates.
  Fix: To delete/update all entities, pass `true` as the criteria (e.g., `repository.delete(true)`).
• gotcha The `reflect-metadata` polyfill is required for TypeORM's decorators to work but must be explicitly installed and imported once at the top of your application's entry file.
  Fix: Install `reflect-metadata` (`npm install reflect-metadata`) and add `import "reflect-metadata";` at the very top of your main entry file (e.g., `main.ts` or `app.ts`).
• gotcha When using MySQL, TypeORM now defaults `connectionOptions.extra.stringifyObjects` to `true` to mitigate a potential security vulnerability in underlying MySQL drivers.
  Fix: If you encounter issues or need to revert to the old behavior, set `connectionOptions.extra.stringifyObjects = false` in your data source configuration.
• deprecated For SAP HANA connections, TypeORM now utilizes the built-in connection pooling from the `@sap/hana-client` library. The external `hdb-pool` library is deprecated.
  Fix: Remove `hdb-pool` from your project dependencies and update your SAP HANA connection configuration to rely on the built-in pooling.

Install

• npm install typeorm npm
• yarn add typeorm yarn
• pnpm add typeorm pnpm

Imports

• DataSource
  wrong:

  const DataSource = require('typeorm')

  correct:

  import { DataSource } from 'typeorm'

  TypeORM 0.3.x is designed for modern JavaScript environments (ES2021+) and strongly encourages ESM imports.

Quickstart

This example demonstrates how to initialize a TypeORM DataSource with SQLite, define a simple User entity, create its schema, and then perform basic save and find operations. It highlights the core steps for getting started with TypeORM in a TypeScript environment.

import "reflect-metadata";
import { DataSource, Entity, PrimaryGeneratedColumn, Column, Repository } from "typeorm";

@Entity()
class User {
    @PrimaryGeneratedColumn()
    id!: number;

    @Column()
    firstName!: string;

    @Column()
    lastName!: string;
}

async function run() {
    const AppDataSource = new DataSource({
        type: "sqlite",
        database: "database.sqlite",
        synchronize: true, // For development, automatically create schema
        entities: [User],
        logging: false,
    });

    await AppDataSource.initialize();
    console.log("Data Source has been initialized!");

    const userRepository: Repository<User> = AppDataSource.getRepository(User);

    const user = new User();
    user.firstName = "John";
    user.lastName = "Doe";
    await userRepository.save(user);
    console.log("User saved:", user);

    const allUsers = await userRepository.find();
    console.log("All users:", allUsers);

    await AppDataSource.destroy();
    console.log("Data Source has been destroyed!");
}

run().catch(error => console.error("Error:", error));