使用MongoDB聚合按多个字段进行计数
要按多个字段计数，请在MongoDB中使用$facet。在$facet处理在同一组输入文档的单级中的多个聚集的管道。让我们创建一个包含文档的集合-
> db.demo721.insertOne(
... {
...
... "details1": {
... "id":101
...
... },
... "details2": {
... "id":101
... },
... "details3": {
... "id":101
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eaaebdd43417811278f5887")
}
>
>
> db.demo721.insertOne(
... {
...
... "details1": {
... "id":101
...
... },
... "details2": {
... "id":102
... },
... "details3": {
... "id":102
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eaaebe943417811278f5888")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo721.find();
这将产生以下输出-
{ "_id" : ObjectId("5eaaebdd43417811278f5887"), "details1" : { "id" : 101 }, "details2" : { "id" : 101 }, "details3" : { "id" : 101 } }
{ "_id" : ObjectId("5eaaebe943417811278f5888"), "details1" : { "id" : 101 }, "details2" : { "id" : 102 }, "details3" : { "id" : 102 } }以下是要按多个字段计数的查询-
> db.demo721.aggregate([
... {$facet:{
... ids:[
... {$group:{ _id:null,
... d3:{$addToSet: "$details3.id"},
... d2:{$addToSet:"$details2.id"},
... d1:{$addToSet:"$details1.id"}}},
... {$project:{ _id:0,
... listofall:{$setUnion:["$d1","$d2","$d3"]}}}],
... d:[{$project:{ _id:0,
... a1:"$details1.id",
... a2:"$details2.id",
... a3:"$details3.id"}}]}},
... {$unwind:"$d"},
... {$unwind:"$ids"},
... {$unwind:"$ids.listofall"},
... {$group:{ _id:"$ids.listofall",
... details1id:{$sum:{$cond:[{$eq:["$d.a1","$ids.listofall"]},1,0]}},
... details2id:{$sum:{$cond:[{$eq:["$d.a2","$ids.listofall"]},1,0]}},
... details3id:{$sum:{$cond:[{$eq:["$d.a3","$ids.listofall"]},1,0]}}}}])这将产生以下输出-
{ "_id" : 102, "details1id" : 0, "details2id" : 1, "details3id" : 1 }
{ "_id" : 101, "details1id" : 2, "details2id" : 1, "details3id" : 1 }