Aggregate help joining documents

[Eman Nollase]

Please see the code below

val nameProp = Product::name
        val descProp = Product::description
        val userProp = User::username


        val pipeline: List<Bson> = listOf(
            lookup("users", Product::user.name, User::id.name, "user"),
            unwind("\$user"),
            project(
                fields(
                    include(nameProp, descProp, userProp),
                    excludeId()
                )
            )
        )

        val products = productTable.aggregate<Document>(pipeline).toList()
        println(products)

the products always empty? any idea? thanks

[Eman Nollase]

Hi i manage to make it work but the new problem i'm having is that  it returns all the field of the user.

How can I limit the relation field to be returned?

thanks

[Teo Fonrouge]

Hi,

You need to use a lookup with a pipeline, and you can use a $project stage in order to filter what fields will be returned.

Check the $lookup with pipeline documentation:  https://www.mongodb.com/docs/manual/reference/operator/aggregation/lookup/

best regards,

Teo