How to order by a relation field using TypeORM?

In TypeORM, when performing data operations, if you need to sort by a relationship field, you can utilize the order option within QueryBuilder or the find method during query execution. QueryBuilder offers more flexible query building capabilities.

Here is an example of sorting by a relationship field using QueryBuilder. Suppose we have two entities, User and Profile, which have a one-to-one relationship. The User entity contains a relationship field profile pointing to the Profile entity. Now, if we want to sort User based on the age field in Profile, we can do the following:

typescript
import { getRepository } from 'typeorm';
import { User } from './entity/User';

// Create QueryBuilder
const userRepository = getRepository(User);
const users = await userRepository
  .createQueryBuilder('user') // 'user' is the alias for the User entity
  .leftJoinAndSelect('user.profile', 'profile') // Join the Profile entity and alias it as 'profile'
  .orderBy('profile.age', 'ASC') // Sort by the age field in the Profile entity in ascending order
  .getMany(); // Retrieve the results

console.log(users);

In the above code snippet, we first obtain the repository object for the User entity using the getRepository method. Then, we create a new query builder using the createQueryBuilder method, where the string parameter user serves as the alias for the User entity. Next, we use the leftJoinAndSelect method to join the Profile relationship and the orderBy method to specify the sorting field and direction (in this example, sorting User entities by the age field in the Profile entity in ascending order). Finally, we call the getMany method to execute the query and retrieve the results.

If you use the find method, you can do the following:

typescript
import { getRepository } from 'typeorm';
import { User } from './entity/User';

const userRepository = getRepository(User);
const users = await userRepository.find({
  relations: ['profile'], // Specify the related entities to load
  order: {
    'profile.age': 'ASC', // Sort by the relationship field
  },
});

console.log(users);

Here, we use the order parameter of the find method to specify the sorting. Note that relationship fields are treated as nested properties in the order object, with the format { 'relation.field': 'ORDER' }.

The above code snippets demonstrate how to sort by relationship fields using TypeORM. In practical development, you may need to adjust the query construction based on specific business logic and data structures.