Question

我对MongoDb聚合的$group参数有疑问。我的数据结构如下：

我的“Event”集合包含以下单个文档：

{
   "_id": ObjectId("mongodbobjectid..."),
   "name": "Some Event",
   "attendeeContainer": {
       "min": 0,
       "max": 10,
       "attendees": [
            {
               "type": 1,
               "status": 2,
               "contact": ObjectId("mongodbobjectidHEX1")
            },
            {
               "type": 7,
               "status": 4,
               "contact": ObjectId("mongodbobjectidHEX2")
            }
        ]
    }
}

我的“联系人”集合包含以下文档：

{
    "_id": ObjectId("mongodbobjectidHEX1"),
    "name": "John Doe",
    "age": 35
},
{
    "_id": ObjectId("mongodbobjectidHEX2"),
    "name": "Peter Pan",
    "age": 60
}

我想要做的是在“事件”集合上执行aggregate查询，并使用完整的“联系”数据获得以下结果：

{
   "_id": ObjectId("mongodbobjectid..."),
   "name": "Some Event",
   "attendeeContainer": {
       "min": 0, 
       "max": 10,
       "attendees": [
             {
                "type": 1,
                "status": 2,
                "contact": {
                   "_id": ObjectId("mongodbobjectidHEX1"),
                   "name": "John Doe",
                   "age": 35
                }
             },
             {
                "type": 7,
                "status": 4,
                "contact": {
                   "_id": ObjectId("mongodbobjectidHEX2"),
                   "name": "Peter Pan",
                   "age": 60
                }
             }
         ]
     }
}

我现在使用的参数如下（缩短版本）：

"$unwind" : "$attendeeContainer.attendees",
"$lookup" : { "from" : "contactinfo", "localField" : "attendeeContainer.attendees.contact","foreignField" : "_id", "as" : "contactInfo" },
"$unwind" : "$contactInfo",
"$group"  : { "_id": "$_id", 
              "name": { "$first" : "$name" }, 
              ...
              "contact": { "$push": { "contact": "$contactInfo"} }
            }

然而，这导致“联系”数组处于“事件”级别（因为分组），而不是每个“attendeeContainer.attendees”处的数组的一个文档。 如何将“联系”数组推送到“attendeeContainer.attendees”？（如上面所需的输出所示）

我尝试过这样的事情：

"attendeeContainer.attendees.contact": { "$push": { "contact": "$contactInfo"} }

但是mongodb显然不允许“。”在$group阶段。

Answer 1

尝试运行以下聚合管道，关键是使用最终的 $project 管道来创建attendeeContainer子文档：

db.event.aggregate([
    { "$unwind": "$attendeeContainer.attendees" },
    {
        "$lookup" : { 
            "from" : "contactinfo", 
            "localField" : "attendeeContainer.attendees.contact",
            "foreignField" : "_id", 
            "as" : "attendeeContainer.attendees.contactInfo" 
        }
    },
    { "$unwind": "$attendeeContainer.attendees.contactInfo" },
    {
        "$group": {
            "_id" : "$_id",
            "name": { "$first": "$name" },   
            "min" : { "$first": "$attendeeContainer.min" },
            "max" : { "$first": "$attendeeContainer.max" },
            "attendees": { "$push": "$attendeeContainer.attendees" }            
        }
    },
    {
        "$project": {
            "name": 1,
            "attendeeContainer.min": "$min",
            "attendeeContainer.max": "$min",
            "attendeeContainer.attendees": "$attendees"
        }
    }
])

调试提示

在第4阶段调试管道，你会得到结果

db.event.aggregate([
    { "$unwind": "$attendeeContainer.attendees" },
    {
        "$lookup" : { 
            "from" : "contactinfo", 
            "localField" : "attendeeContainer.attendees.contact",
            "foreignField" : "_id", 
            "as" : "attendeeContainer.attendees.contactInfo" 
        }
    },
    { "$unwind": "$attendeeContainer.attendees.contactInfo" },
    {
        "$group": {
            "_id": "$_id",
            "name": { "$first": "$name" },   
            "min" : { "$first": "$attendeeContainer.min" },
            "max" : { "$first": "$attendeeContainer.max" },
            "attendees": { "$push": "$attendeeContainer.attendees" }            
        }
    }/*,
    {
        "$project": {
            "name": 1,
            "attendeeContainer.min": "$min",
            "attendeeContainer.max": "$min",
            "attendeeContainer.attendees": "$attendees"
        }
    }*/
])

管道结果

{
    "_id" : ObjectId("582c789282a9183adc0b53f5"),
    "name" : "Some Event",
    "min" : 0,
    "max" : 10,
    "attendees" : [ 
        {
            "type" : 1,
            "status" : 2,
            "contact" : ObjectId("582c787682a9183adc0b53f3"),
            "contactInfo" : {
                "_id" : ObjectId("582c787682a9183adc0b53f3"),
                "name" : "John Doe",
                "age" : 35
            }
        }, 
        {
            "type" : 7,
            "status" : 4,
            "contact" : ObjectId("582c787682a9183adc0b53f4"),
            "contactInfo" : {
                "_id" : ObjectId("582c787682a9183adc0b53f4"),
                "name" : "Peter Pan",
                "age" : 60
            }
        }
    ]
}

并且最终的 $project 管道将为您提供所需的结果：

db.event.aggregate([
    { "$unwind": "$attendeeContainer.attendees" },
    {
        "$lookup" : { 
            "from" : "contactinfo", 
            "localField" : "attendeeContainer.attendees.contact",
            "foreignField" : "_id", 
            "as" : "attendeeContainer.attendees.contactInfo" 
        }
    },
    { "$unwind": "$attendeeContainer.attendees.contactInfo" },
    {
        "$group": {
            "_id": "$_id",
            "name": { "$first": "$name" },   
            "min" : { "$first": "$attendeeContainer.min" },
            "max" : { "$first": "$attendeeContainer.max" },
            "attendees": { "$push": "$attendeeContainer.attendees" }            
        }
    },
    {
        "$project": {
            "name": 1,
            "attendeeContainer.min": "$min",
            "attendeeContainer.max": "$min",
            "attendeeContainer.attendees": "$attendees"
        }
    }/**/
])

期望/实际输出

{
    "_id" : ObjectId("582c789282a9183adc0b53f5"),
    "name" : "Some Event",
    "attendeeContainer" : {
        "min" : 0,
        "max" : 10,
        "attendees" : [ 
            {
                "type" : 1,
                "status" : 2,
                "contact" : ObjectId("582c787682a9183adc0b53f3"),
                "contactInfo" : {
                    "_id" : ObjectId("582c787682a9183adc0b53f3"),
                    "name" : "John Doe",
                    "age" : 35
                }
            }, 
            {
                "type" : 7,
                "status" : 4,
                "contact" : ObjectId("582c787682a9183adc0b53f4"),
                "contactInfo" : {
                    "_id" : ObjectId("582c787682a9183adc0b53f4"),
                    "name" : "Peter Pan",
                    "age" : 60
                }
            }
        ]
    }
}

使用$ group和$ push进入子文档的MongoDb聚合查询

1 个答案: