Michael Kryukov

This looks like same issue with mongomock's implementation of DBRef (which is the core of beanie's links) as discussed in #5. I've created issue at mongomock (mongomock/mongomock#759), but I don't...

What exactly is not working for you? This issue refers to the internal implemetation of beanie that doesn't support some operations with `DBRef` that mongo supports (and beanie uses).

Hi, as far as I can tell, value of "_id" in "$group" stage can be valid expression and any literal will lead to single output document. I didn't found any...

Looks like duplicate of #5 and #20

It's an issue with mongomock (https://github.com/mongomock/mongomock/issues/759) that prevents beanie's `Link` from working. I don't really want to mock anything in this library, so this issue will persisnt until https://github.com/mongomock/mongomock/issues/759 will...

It looks like this issue stems from [mongomock's implementation](https://github.com/mongomock/mongomock/blob/d5c0e8b3e70f74bb0e29819c5a0907c9a03404a2/mongomock/aggregate.py#L798). You might consider reporting it upstream or modifying your implementation to reference inner documents by their IDs rather than using indexes.