Cursor pagination first: 0 returns all items

[stefansundin]

Describe the bug

Passing first: 0 to findByCursor returns all items.

I have a situation where, in the front-end, I want to just retrieve the total count of items. I don't have an endpoint to just get meta information, so I am just issuing a query to list zero items and then reading the page information. Unfortunately, right now this retrieves all items which is a major performance issue. So as a workaround I am requesting a single item with first: 1.

Since limit: 0 returns zero items, I think first: 0 also should return zero items.

Reproduction

https://github.com/stefansundin/mikro-orm-reproduction/tree/first-0

test('basic CRUD example', async () => {
  for (let i=0; i < 100; i++) {
    orm.em.create(User, { name: `Foo ${i}` });
  }
  await orm.em.flush();
  orm.em.clear();

  // {limit: 0} works
  const [limitResult, limitTotalCount] = await orm.em.findAndCount(User, {}, { limit: 0 });
  expect(limitTotalCount).toBe(100);
  expect(limitResult.length).toBe(0);

  // {first: 1} works
  const result1 = await orm.em.findByCursor(User, {}, { first: 1, orderBy: [{name: 'ASC'}] });
  expect(result1.totalCount).toBe(100);
  expect(result1.length).toBe(1);

  // {first: 0} is a performance trap!
  const result2 = await orm.em.findByCursor(User, {}, { first: 0, orderBy: [{name: 'ASC'}] });
  expect(result2.totalCount).toBe(100);
  expect(result2.length).toBe(0); // <-- bug
});

What driver are you using?

@mikro-orm/postgresql

MikroORM version

6.2.1

Node.js version

18.20.2

Operating system

No response

Validations

• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Slack.
• The provided reproduction is a minimal reproducible example of the bug.

[B4nan]

Note that first: 0 shouldn't result in limit 0 but rather to limit 1, as with cursor based pagination we are overfetching by default to know whether there is a next page. You can disable that via overfetch: false.