关于mongodb:MongoDB聚合aggregate常用操作及示例

简介

MongoDB 中聚合(aggregate)次要用于解决数据(诸如统计平均值，求和等)，并返回计算后的数据后果。

有点相似 SQL 语句中的 count(*)。

罕用操作

示例

$match

//查问条件 以某个分组查问 （能够多个查问条件累加到match外面）
db.getCollection('doc_views').aggregate([
    {
        $match: { "orgName" : "前端技术部" }
    }
])
//查问后果如下
/* 1 */
{
    "_id" : ObjectId("5fcb2c6cdfebd2682b2ae01b"),
    "__v" : 0,
    "time" : "2020-11-11",
    "docName" : "testPublishAll",
    "orgGroup" : "汽车事业群",
    "orgName" : "前端技术部",
    "count" : 3
}
...

$project

//删减字段
db.getCollection('doc_views').aggregate([
    {
        $match: { "orgName" : "前端技术部" }
    },
    {
        $project: {
            docName: true,
            orgName: true
        }
    }
])
//查问后果如下 只显示设置为true的字段
/* 1 */
{
    "_id" : ObjectId("5fcb2c6cdfebd2682b2ae01b"),
    "docName" : "testPublishAll",
    "orgName" : "前端技术部"
}
...
//定义别名 把orgGroup指定指定成count字段
db.getCollection('doc_views').aggregate([
    {
        $match: { "orgName" : "前端技术部" }
    },
    {
        $project: {
            docName: true,
            orgName: true,
            orgGroup: "$count"
        }
    }
])
//查问后果orgGroup字段展现count的值
/* 1 */
{
    "_id" : ObjectId("5fcb2c6cdfebd2682b2ae01b"),
    "docName" : "testPublishAll",
    "orgName" : "前端技术部",
    "orgGroup" : 3
}

$group

//聚合条件 _id ：强制必须存在。 
db.getCollection('doc_views').aggregate([
    {
        $group: { 
            _id: { name: "$docName", orgName: "$orgName" },
           total: { $sum: "$count" } 
        }
    }
    
])
//1、_id: null  _id为null的查问后果
/* 1 */
{
    "_id" : null,
    "total" : 474
}
//2、_id: "$docName" _id为某字段
/* 1 */
{
    "_id" : "gch-gitbook",
    "total" : 8
}
...
//3、_id: { name: "$docName", orgName: "$orgName" } _id查问条件并为字段定义别名
/* 1 */
{
    "_id" : {
        "name" : "vuepress-hjw-test",
        "orgName" : "前端技术部"
    },
    "total" : 2
}

$sort、$skip、$limit

//列表分页的时候个别三个联结应用来做数据分页
//sort列表排序 skip指定跳过多少条 limit每次查问条数
//skip的计算形式：(以后页码-1)*每页大小 如：(pageIndex - 1) * pageSize
db.getCollection('doc_views').aggregate([
    {$sort: {_id: -1}},
    {$skip:Number(100)},
    {$limit:Number(10)} 
])
//查问后果如下
/* 1 */
{
    "_id" : ObjectId("604ecc57b3b65a411b5600de"),
    "__v" : 0,
    "time" : "2021-02-25",
    "docName" : "abgFeedback",
    "docType" : "vuepress",
    "orgGroup" : "汽车事业群",
    "orgName" : "前端技术部",
    "count" : 1
}

/* 2 */
{
    "_id" : ObjectId("604ecc57b3b65a411b5600dd"),
    "__v" : 0,
    "time" : "2021-02-24",
    "docName" : "testtestdocs",
    "docType" : "docsify",
    "orgGroup" : "汽车事业群",
    "orgName" : "前端技术部",
    "count" : 1
}

$lookup

//联表查问
db.getCollection('doc_views').aggregate([
    {$sort: {_id: -1}},
    {$skip:Number(100)},
    {$limit:Number(10)},
    {$lookup:{
        from: "docs",
        localField: "docName",
        foreignField: "name",
        as: "child"
    }}
])
//查问后果
/* 1 */
{
    "_id" : ObjectId("604ecc57b3b65a411b5600de"),
    "__v" : 0,
    "time" : "2021-02-25",
    "docName" : "abgFeedback",
    "docType" : "vuepress",
    "orgGroup" : "汽车事业群",
    "orgName" : "前端技术部",
    "count" : 1,
    "child" : [ 
        {
            "_id" : ObjectId("5f6da851a18a783210da7a16"),
            "docType" : "vuepress",
            "name" : "abgFeedback",
            "description" : "二手车问题反馈收集问题",
            "owner" : "gongchenghui",
            "orgGroup" : "汽车事业群",
            "orgName" : "前端技术部",
            "newGit" : false,
            "toTop" : ISODate("2020-11-20T02:41:33.742Z"),
            "realName" : "龚成辉",
            "dest" : "abgFeedback",
            "opendFiles" : [],
            "createTime" : ISODate("2020-09-25T08:20:33.373Z")
        }
    ]
}

$facet 分类查问

//依据条件 分类一次查问出想要的数据和数据的总数
db.getCollection('doc_views').aggregate([
    {$match: {"orgName" : "前端技术部"}},
    {
        $facet: {
            respData: [
                {$sort: {_id: -1}},
                {$skip:Number(100)},
                {$limit:Number(1)},
            ],
            total: [
                {
                    $count: "total"
                }
            ]
        }
    }
//查问后果如下
  /* 1 */
{
    "respData" : [ 
        {
            "_id" : ObjectId("604ecc57b3b65a411b5600de"),
            "__v" : 0,
            "time" : "2021-02-25",
            "docName" : "abgFeedback",
            "docType" : "vuepress",
            "orgGroup" : "汽车事业群",
            "orgName" : "前端技术部",
            "count" : 1
        }
    ],
    "total" : [ 
        {
            "total" : 284
        }
    ]
}

留神：此办法只能在3.4以上版本的数据库中应用，低版本的话还是做两次查问