Question

我有两个系列，水果和推销员。我希望查询返回所有以逗号分隔的水果。

推销员文档具有一组水果ID

水果文档具有ID，名称，........ 推销员表具有ID，名称，水果[apple_id，mango_id .......]，...

db.getCollection('fruit').aggregate([{ "$unwind": "$fruits" }, { "$lookup": {
       "from": "salesman",
       "localField": "fruits",
       "foreignField": "_id",
       "as": "fruitObjects"
    }},
    { "$unwind": "$fruitObjects" } ])

即使该查询也没有给出$ fruitObjects的结果。？

水果文档

{
    "_id" : ObjectId("5b101caddcab7850a4ba32eb"),
    "name" : "Mango"
}

{
    "_id" : ObjectId("5b101caddcab7850a4ba32ec"),
    "name" : "Pears"
}

{
   "_id" : ObjectId("5b101caddcab7850a4ba32de"),
    "name" : "apple"
}

{
   "_id" : ObjectId("5b101caddcab7850a4ba32fe"),
    "name" : "guava"
}

推销员文档

{
    "_id" : ObjectId("5b101caddcab7850a4ba3257"),
    "name" : "xyz",
    "fruits":["5b101caddcab7850a4ba32ec","5b101caddcab7850a4ba32de","5b101caddcab7850a4ba32fe"]
}

{
    "_id" : ObjectId("5b101caddcab7850a4ba3258"),
    "name" : "abc",
    "fruits":["5b101caddcab7850a4ba32eb","5b101caddcab7850a4ba32de"]
}

{
   "_id" : ObjectId("5b101caddcab7850a4ba3259"),
    "name" : "def",
    "fruits":["5b101caddcab7850a4ba32ec"]
}

{
   "_id" : ObjectId("5b101caddcab7850a4ba3260"),
    "name" : "zxc",
    "fruits":["5b101caddcab7850a4ba32ec","5b101caddcab7850a4ba32de","5b101caddcab7850a4ba32eb"]
}
``````````````````````````

Answer 1

有帮助吗？

db.salesman.aggregate([
  { $unwind : "$fruits" },
  { $addFields : { "fruitObjectId": { $toObjectId: "$fruits" } } },
  { $lookup : {
      "from" : "fruit",
      "localField" : "fruitObjectId",
      "foreignField" : "_id",
      "as" : "fruitObjects"
    }
  } 
])

或者，也许是相反的观点？

db.fruit.aggregate([
  { $project : {
      _id : { $toString : "$_id" },
      name : 1
    }
  },
  { $lookup : {
      "from" : "salesman",
      "localField" : "_id",
      "foreignField" : "fruits",
      "as" : "fruitObjects"      
    }
  }
])

Answer 2

是@barrypicker是正确的-字段类型不匹配，导致salesman上的字段为空，请尝试存储相同类型的字段。同时，您实际上可以将一种转换为其他类型-每次进行查询时，也不需要执行$unwind，请尝试以下查询：

查询1：

db.fruit.aggregate([
    {
        $lookup:
        {
            from: "salesman",
            let: { fruitName: { $toString: '$_id' } },
            pipeline: [
                {
                    $match:
                    {
                        $expr:
                            { $in: ["$$fruitName", "$fruits"] }
                    }
                }, { $project: { name: 1, _id: 0 } }
            ],
            as: "salesman"
        }
    }])

查询1的结果

/* 1 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32eb"),
    "name" : "Mango",
    "salesman" : [ 
        {
            "name" : "abc"
        }, 
        {
            "name" : "zxc"
        }
    ]
}

/* 2 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32ec"),
    "name" : "Pears",
    "salesman" : [ 
        {
            "name" : "def"
        }, 
        {
            "name" : "zxc"
        }
    ]
}

/* 3 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32de"),
    "name" : "apple",
    "salesman" : [ 
        {
            "name" : "abc"
        }, 
        {
            "name" : "zxc"
        }
    ]
}

/* 4 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32fe"),
    "name" : "guava",
    "salesman" : []
}

或者如果您希望这些名称位于数组中：

查询2：

db.fruit.aggregate([
    {
        $lookup:
        {
            from: "salesman",
            let: { fruitName: { $toString: '$_id' } },
            pipeline: [
                {
                    $match:
                    {
                        $expr:
                            { $in: ["$$fruitName", "$fruits"] }
                    }
                }, { $project: { name: 1, _id: 0 } }
            ],
            as: "salesmanList"
        }
    }, {
        $project: {
            name: 1, salesman: {
                $map:
                {
                    input: "$salesmanList",
                    as: "each",
                    in: '$$each.name'
                }
            }
        }
    }])

查询2的结果

/* 1 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32eb"),
    "name" : "Mango",
    "salesman" : [ 
        "abc", 
        "zxc"
    ]
}

/* 2 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32ec"),
    "name" : "Pears",
    "salesman" : [ 
        "def", 
        "zxc"
    ]
}

/* 3 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32de"),
    "name" : "apple",
    "salesman" : [ 
        "abc", 
        "zxc"
    ]
}

/* 4 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32fe"),
    "name" : "guava",
    "salesman" : []
}

水果收藏：

/* 1 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32eb"),
    "name" : "Mango"
}

/* 2 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32ec"),
    "name" : "Pears"
}

/* 3 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32de"),
    "name" : "apple"
}

/* 4 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba32fe"),
    "name" : "guava"
}

推销员收藏：

/* 1 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba3258"),
    "name" : "abc",
    "fruits" : [ 
        "5b101caddcab7850a4ba32eb", 
        "5b101caddcab7850a4ba32de"
    ]
}

/* 2 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba3259"),
    "name" : "def",
    "fruits" : [ 
        "5b101caddcab7850a4ba32ec"
    ]
}

/* 3 */
{
    "_id" : ObjectId("5b101caddcab7850a4ba3260"),
    "name" : "zxc",
    "fruits" : [ 
        "5b101caddcab7850a4ba32ec", 
        "5b101caddcab7850a4ba32de", 
        "5b101caddcab7850a4ba32eb"
    ]
}

如果要从salesman中删除整个对象，则可以从{ $project: { name: 1, _id: 0 } }中删除$lookup。

参考： $lookup，$map

当外来字段是ID数组时的MongoDB查找

2 个答案: