Mongodb聚合和展开行为 - 重复

我目前正在使用以下查询来展开并“加入”多个集合：

User.aggregate([{
                "$match": {
                    "verified": true,
                    "active_account": true
                }
            },
            {
                "$lookup": {
                    "from": "screens",
                    "localField": "_id",
                    "foreignField": "user_obj",
                    "as": "screenings"
                }
            },
            {
                "$unwind": "$screens"
            },
            {
                "$lookup": {
                    "from": "drinks",
                    "localField": "_id",
                    "foreignField": "user_id",
                    "as": "drinks"
                }
            },
            {
                "$unwind": "$drinks"
            },
            {
                "$group": {
                    "_id": "$_id",
                    "smsmobile": {
                        "$first": "$smsmobile"
                    },
                    "screens": {
                        "$push": "$screens"
                    },
                    "drinks": {
                        "$push": "$drinks"
                    }
                }
            }
        ]...

我目前遇到的问题是，对于饮料和屏幕，它们每个都有重复的记录 - 但是在实际数据库中它们是单个项目 . 例如，数据库中的屏幕只有两个记录，但在上面的过程中输出了四个 .

似乎聚合展开过程正在生成这些重复项 . 我对此表示欢迎 .

屏幕的示例输出如下 . 注意_id，它自己的集合没有重复的罪 .

[ { _id: 58e901837a085502ec6b4b6b,
    updatedAt: 2017-04-08T15:28:03.153Z,
    createdAt: 2017-04-08T15:28:03.153Z,
    user_obj: 58e901267a085502ec6b4b69,
    screen: 1,
    difficult_sit: 1,
    group: 2,
    __v: 0 },
  { _id: 58e901837a085502ec6b4b6b,
    updatedAt: 2017-04-08T15:28:03.153Z,
    createdAt: 2017-04-08T15:28:03.153Z,
    user_obj: 58e901267a085502ec6b4b69,
    screen: 1,
    difficult_sit: 1,
    group: 2,
    __v: 0 },
  { _id: 58eb4001ee18b403f05a9043,
    updatedAt: 2017-04-10T08:19:13.857Z,
    createdAt: 2017-04-10T08:19:13.857Z,
    user_obj: 58e901267a085502ec6b4b69,
    screen: 1,
    difficult_sit: null,
    group: 2,
    __v: 0 },
  { _id: 58eb4001ee18b403f05a9043,
    updatedAt: 2017-04-10T08:19:13.857Z,
    createdAt: 2017-04-10T08:19:13.857Z,
    user_obj: 58e901267a085502ec6b4b69,
    screen: 1,
    difficult_sit: null,
    group: 2,
    __v: 0 } ]