mongo-scala driver aggregation lookup with pipeline

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Colin Bester

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Oct 15, 2018, 5:41:35 PM10/15/18

to mongodb-user

I am looking to implement aggregation using new lookup feature using pipeline with mongo-scala-driver version 2.30.

MongoQuery aggregation stage I am trying to implement is:

$lookup: {
    from: "user",
    let: { recipeId: "$_id" },
    pipeline:[
        { $match:
            { $expr: 
                { $in: ["$$recipeId", "$licenses.recipe"] }
            }                
        }
    ],
    as: "users"
}

My current working stage is:

val let = Seq(Variable("recipeId", "$_id"))
val theMatch = Document.apply("""{$match:{$expr:{ $in: ["$$recipeId", "$licenses.recipe"] }}}""").toBsonDocument
val pipeline = Seq(theMatch)
val theLookup = lookup("user", let, pipeline, "users")

//go and run aggregation
val aggr = Seq(
  ...,
  theLookup)

While this does work, I am pretty sure there is better way to use supplied driver library and better implement the Document.apply brute force method I used for, as example, theMatch.

Suggestions appreciated.

Wan Bachtiar

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Oct 23, 2018, 7:56:51 PM10/23/18

to mongodb-user

I am pretty sure there is better way to use supplied driver library and better implement the Document.apply brute force method I used for, as example, theMatch

Hi Colin,

Currently there’s an open ticket to add support for full aggregation expression language builder JAVA-1949 (MongoDB Scala driver implementation is built upon the MongoDB Java driver). Please feel free to upvote/watch the ticket to receive notifications update on the ticket.

In the meantime, building the $expr via Document/BsonDocument is the recommended way.