在使用mongo驱动程序Api投影字段时“未定义变量的使用”

Question

嗨，我有以下mongo agrgegate查询

我正在尝试转换此usin mongo驱动程序

db.SampleDb.aggregate([{
                $match: {
                    _id: new ObjectId(secId),
                    "visible": true
                }
            }, {
                $unwind: "$ddFields"
            }, {
                $match: {
                    "ddFields.mmList": {
                        $exists: true
                    }
                }
            }, {
                $lookup: {
                    from: "mmList",
                    localField: "ddFields.mmList.id",
                    foreignField: "mmListId",
                    as: "mmList_lookup"
                }
            }, {
                $project: {
                    fieldId: "$ddFields.fId",
                    mmList_lookup: {
                        $filter: {
                            input: "$mmList_lookup",
                            as: "mmList_lookup",
                            cond: {
                                $eq: ["$$mmrList_lookup.sId", new ObjectId(sId)]
                            }
                        }
                    }

                }

            }, {
                $unwind: "$mmList_lookup"
            },
                {
                    $project: {
                        _id: 0,
                        secId: "$_id",
                        fId: "$fieldId",
                        mmListId: "$mmList_lookup.mmListId",
                        refId: "$mList_lookup.refId",
                        mmValues: {
                            $filter: {
                                input: "$mmList_lookup.mmValues",
                                as: "mmValue",
                                cond: {
                                    "$setIsSubset": [["$fId"], "$$mmValue.selected"]
                                }
                            }
                        }

                    }
                }
            ]);

我写了以下

    BasicDBList bb = new BasicDBList();
    basicDBList.add("$fId");

    BasicDBList basicDBList1 = new BasicDBList();
    basicDBList.add("bb");
    basicDBList.add("$$mmValue.assigned");

    AggregateIterable<Document> output = collection.aggregate(Arrays.asList(

            new Document("$match", new Document("_id", secId)
                    .append("visible",true)),
            new Document("$unwind", "$ddFields"),
            new Document("$match", new Document("ddFields.mmList", new Document("$exists",true))),
            new Document("$lookup",
                    new Document("from", "mmLists")
                    .append("localField", "ddFields.mmList.id")
                    .append("foreignField", "mmListId")
                    .append("as", "mmList_lookup")),

            new Document("$project",
                    new Document( "fid", "$ddFields.fid")
                    .append("mmList_lookup",new Document("$filter",
                            new Document("input","$mmList_lookup")
                    .append("as","mmList_lookup")
                    .append("cond",new Document("$eq",basicDBList))))),

                new Document("$unwind", "$mmList_lookup"),

            new Document("$project",new Document("secId","$_id")
            .append("fid","$fid")
            .append("mmListId","$mmList_lookup.mmListId")
            .append("refId","$mmList_lookup.refId")
                    .append("mmValues",new Document("$filter",
                            new Document("input","$mmList_lookup.mmValues")
                                    .append("as","mmValue")
                                    .append("cond",new Document("$setIsSubset",basicDBList1)
                                    )))



            )


            ));

我收到错误消息：“在服务器上使用'未定义的变量：mmValue' 以类似的方式完成此查询中使用的第一个投影的效果如何。 我不明白我在想什么

不确定如何显示未定义的变量