$lookup across 2 databases

[RindangRamadhan]

Is it possible to do a $lookup aggregation between two databases in Mongodb ?

I try this documentation, but the results is empty array

[steevej (Steeve Juneau)]

It should work as documented. The empty result is probably cause by something else being wrong, like wrong field names, wrong values, wrong operators. It would hel if you share your pipeline.

[RindangRamadhan]

This is my pipeline

db.getSiblingDB("mai_inventory_service").view_product_hpp.aggregate([
    {
      $lookup: {
        localField: '_id',
        from: 'view_main_dealer_package_products',
        foreignField: 'product_id',
        as: 'package_product',
      }
    }
])

[Stennie_X (Stennie)]

Welcome to the community @RindangRamadhan!

As at MongoDB 4.4, $lookup only supports looking up from collections in the same database. Per the $lookup documentation for the from field:

Specifies the collection in the same database to perform the join with. The from collection cannot be sharded.

There is a relevant feature request you can upvote & watch: SERVER-34935: Support cross-database lookup.

Regards,
Stennie