数据有限的$ lookup聚合的MongoDb Post格式 [英] MongoDb Post formatting of $lookup aggregation with limited data

问题描述

我有2个集合coll1和coll2。我想在字段 _id和 comm_field上应用$ lookup，所以我使用了查询：

I have 2 collection coll1 and coll2. I want to apply $lookup on fields "_id" and "comm_field" so I used the query:

db.coll1.aggregate([
    {
      $lookup:
        {
          from: "coll2",
          localField: "_id",
          foreignField: "comm_field",
          as: "inventory_docs"
        }
   },
   {
       $project:{"_id" : 0, "inventory_docs" : 1}
   },
   { $unwind:"$inventory_docs"}
])

并获取输出为：

/* 1 */
{
    "inventory_docs" : {
        "_id" : ObjectId("ssdfsfsdfsdfsfsdfsdfsdfsfsdf"),
        "comm_field" : NumberLong(1111),
        "status" : "active"
    }
}

/* 2 */
{
    "inventory_docs" : {
        "_id" : ObjectId("erteterterterterterterterter"),
        "comm_field" : NumberLong(1111),
        "status" : "active"
    }
}

/* 3 */
{
    "inventory_docs" : {
        "_id" : ObjectId("vbvbfvbdbbcvbvcbcdrgvbcbcbcv"),
        "comm_field" : NumberLong(2222),
        "status" : "active"
    }
}

有没有什么办法可以让我看到输出，如：

Is there any way by which i can see the output like:

        {
            "_id" : ObjectId("ssdfsfsdfsdfsfsdfsdfsdfsfsdf"),
            "comm_field" : NumberLong(1111),
            "status" : "active"
        }
        {
            "_id" : ObjectId("erteterterterterterterterter"),
            "comm_field" : NumberLong(1111),
            "status" : "active"
        }
        {
            "_id" : ObjectId("vbvbfvbdbbcvbvcbcdrgvbcbcbcv"),
            "comm_field" : NumberLong(2222),
            "status" : "active"
        }

所以基本上我希望我的输出格式{---}，而不是{ inventory_docs：{---}}

So basically I want my output in format {---}, not in {"inventory_docs":{---}}

推荐答案

尼尔的答案奏效了。 {$ replaceRoot：{newRoot： $ inventory_docs}} 的添加完成了工作。谢谢尼尔。

Neil's answer worked. Addition of { $replaceRoot: { newRoot: "$inventory_docs" } } did the job. Thanks Neil.

db.coll1.aggregate([
    {
      $lookup:
        {
          from: "coll2",
          localField: "_id",
          foreignField: "comm_field",
          as: "inventory_docs"
        }
   },
   {
       $project:{"_id" : 0, "inventory_docs" : 1}
   },
   { $unwind:"$inventory_docs"},
   { $replaceRoot: { newRoot: "$inventory_docs" } }
])

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