Support basic aggregation pipelines

[ferretdb-bot]

Tasks

Beta Give feedback

1. Implement aggregate command stub #969
   code/chore +1
   
2. Support aggregation pipelines for Tigris #1891
   code/feature +1
   
3. Implement $sort aggregation pipeline stage #1439
   code/feature +1
   
4. Implement aggregate command #1410
   code/feature +1
   
5. Implement $match aggregation pipeline stage #1428
   code/feature +1
   
6. Implement $count aggregation pipeline stage #1417
   code/feature +1
   
7. Implement $group aggregation pipeline stage #1423
   code/feature +1
   
8. Support query pushdown for $match aggregation stage #1894
   code/enhancement +1
   

[xqzhou]

Just curious, how is this going to be implemented?

[AlekSi]

Just like everything else in FerretDB: by generating one or more queries, sending them to PostgreSQL, converting results. We don't know better yet.

[psini]

I think that also [$unwind]
(https://www.mongodb.com/docs/manual/reference/operator/aggregation/unwind/#mongodb-pipeline-pipe.-unwind) is a very common use case could be added to the plan. We do an extensive use of it in our project .

[AlekSi]

We will do #1442 soon

[gwozdzm]

psini

[$unwind] is done! Do you need any other feature to achieve FerretDB compatibility with your project?