How to find data rows using foreign key in TypeORM

In TypeORM, a common approach for querying data using foreign keys involves retrieving related data through association relationships. We can implement this using several methods, including QueryBuilder, the relations parameter in the find method, or EntityManager. Below are specific examples of these techniques:

1. Using QueryBuilder

Assume we have two entities: User and Photo, where the Photo entity has a foreign key referencing the User entity. We can use QueryBuilder to fetch all photos for a specific user:

typescript
import { getRepository } from "typeorm";

async function findPhotosByUser(userId: number) {
  const photoRepository = getRepository(Photo);
  const photos = await photoRepository
    .createQueryBuilder("photo")
    .innerJoinAndSelect("photo.user", "user")
    .where("user.id = :userId", { userId })
    .getMany();

  return photos;
}

In this example, the innerJoinAndSelect method joins the Photo and User tables while also selecting the User table's content, enabling direct access to the user data linked to each photo.

2. Using the relations Parameter in the find Method

Another method for querying foreign-key-related data is to utilize the relations parameter within the find method. This approach offers more concise code:

typescript
import { getRepository } from "typeorm";

async function findPhotosByUser(userId: number) {
  const userRepository = getRepository(User);
  const userWithPhotos = await userRepository.findOne(userId, {
    relations: ["photos"]
  });

  return userWithPhotos?.photos;
}

Here, we specify the relations option directly when querying User, which causes TypeORM to automatically load the associated Photo data for the user.

3. Using EntityManager

For greater control over database operations, you can employ EntityManager:

typescript
import { getManager } from "typeorm";

async function findPhotosByUser(userId: number) {
  const entityManager = getManager();
  const photos = await entityManager
    .createQueryBuilder(Photo, "photo")
    .innerJoinAndSelect("photo.user", "user")
    .where("user.id = :userId", { userId })
    .getMany();

  return photos;
}

This method parallels using getRepository but directly leverages EntityManager, which may provide enhanced flexibility for complex query scenarios.

Summary

In TypeORM, querying data with foreign keys can be achieved through multiple approaches, and the optimal method depends on the specific application context and personal preference. The examples above demonstrate how TypeORM offers flexible and robust tools for handling related data queries in databases.