How to paginate results when filtering on left join table column - mikro-orm

Question

Let's define for example these entities:
#Entity()
export class Author {
#OneToMany(() => Book, book => book.author)
books = new Collection<Book>(this);
}
#Entity()
export class Book {
#Property()
name: string;
#ManyToOne()
author: Author;
}
const authors = await authorRepository.find({ books: {name: 'Test'} }, {
limit: 10
});
As you can see i want to select all authors that have books with name 'Test', but this will generate the following query:
select `e0`.* from `author` as `e0`
left join `book` as `e1` on `e0`.`id` = `e1`.`author_id`
where `e1`.`name` = 'Test' limit 10
The problem is when i have more than 2 authors and each of them has more than 10 books with name 'Test', this query will return only the first author because of the limit clause.
I am not sure if this is a bug in the ORM or it's a expected behavior.
One way to fix that is to select all rows without the limit clause and do the pagination in memory like they are doing in hibernate, but i am not sure how much memory will be used with very large tables and this might block the event loop in NodeJS while processing them.

Answer 1

You could fallback to query builder here to apply group by clause:
const qb = await authorRepository.createQueryBuilder('a');
qb.select('a.*').where({ books: { name: 'Test' } }).limit(10).groupBy('a.id');
const authors = await qb.getResult();
Will think about how to support this use case directly via EM/repository API.