如何在ReactiveMongo聚合框架中使用$ lookup指定多个加入条件？

如何解决如何在ReactiveMongo聚合框架中使用$ lookup指定多个加入条件？

如何在ReactiveMongo（0.17.1）中使用$ lookup指定多个联接条件，并牢记以下几点？ -按照the mongoDB documentation。

用户集合

[
    {
      "name": "dogfrey","field": "cowboy"
    },{
      "name": "catsville","field": "spaceman"
    }
]

角色收集

[
    {
      "id": 0,"userType": "cowboy","spaceman": "fiver","num": 2
    },{
      "id": 1,"userType": "joker","spaceman": "tenner","num": 3
    },{
      "id": 2,"num": 1
    }
]

MongoDb查询

db.users.aggregate([
  {
    "$match": {
      "name": "dogfrey"
    }
  },{
    "$lookup": {
      "from": "roles",let: {
        "users_field": "$field"
      },pipeline: [
        {
          $match: {
            $expr: {
              $eq: [
                "$userType","$$users_field"
              ]
            },}
        },{
          $project: {
            _id: 0
          }
        }
      ],"as": "dogs"
    }
  }
])

See here for the MongoPlayground example

ReactiveMongo documentation没有包含任何这样的示例，表明不可能。任何帮助表示赞赏！

---

也只是添加我尝试过的内容（失败）：

  def getResults(aColl: JSONCollection,bColl: JSONCollection)
                (id: BSONObjectID)(implicit request: Request[AnyContent]) = aColl.aggregateWith[JsObject]() {
    framework => import framework.{Match,Lookup,AddFields,Project,Sort,Ascending,Descending,Filter,Limit,Group,Sum,Push,Slice}

    ...

    val lookupJso = Lookup(
      from = bColl.name,let = Json.obj("fromDate" -> "$varData_e.plan_e.when_e.fromDate","toDate" -> "$varData_e.plan_e.when_e.toDate"),pipeline = Json.arr(
        "$match" -> Json.obj("$expr" ->
            Json.obj("$and" -> Json.arr(
              Json.obj("$gte" -> Json.arr("$varData_e.dateTime",f"$$fromDate")),Json.obj("$lt" -> Json.arr("$varData_e.dateTime",f"$$toDate"))
            )),),"$project" -> Json.obj("_id" -> 0)
      ),"temp_e.lookupTest1_e"
    )

    ...

  }.collect[List](Int.MaxValue,Cursor.FailOnError[List[JsObject]]())

我可以看到Lookup case class看起来像这样：

  case class Lookup(
    from: String,localField: String,foreignField: String,as: String) extends PipelineOperator {
    import builder.{ document,elementProducer => element,string }
    val makePipe: pack.Document = document(Seq(
      element(f"$$lookup",document(Seq(
        element("from",string(from)),element("localField",string(localField)),element("foreignField",string(foreignField)),element("as",string(as)))))))
  }

解决方法

版本0.17.1已有一年以上的历史（最新版本为major 1.0）。

您可以在documentation中看到，可以为API中未提供便捷工厂的阶段定义原始聚合运算符。

import scala.concurrent.ExecutionContext

import reactivemongo.bson._
import reactivemongo.api.collections.bson.BSONCollection

def customAgg(coll: BSONCollection)(implicit ec: ExecutionContext) =
  coll.aggregateWith[BSONDocument]() { framework =>
    import framework.{ Match,PipelineOperator,Project }

    val lookup = PipelineOperator(BSONDocument(f"$$lookup" -> BSONDocument(
      "from" -> "roles","let" -> BSONDocument("users_field" -> f"$$field"),"pipeline" -> Seq(
        Match(BSONDocument(f"$$expr" ->
          BSONDocument(f"$$eq" -> Seq(f"$$userType",f"$$$$users_field")))).
          makePipe,Project(BSONDocument("_id" -> 0)).makePipe),"as" -> "dogs")))

    Match(BSONDocument("name" -> "dogfrey")) -> List(lookup)
  }