MongoDB中获取特定值的计数

要获取MongoDB中特定值的计数，请使用aggregate()。让我们创建一个包含文档的集合-

> db.demo210.insertOne( ... { ... details: [ ... { ... ClientName: "Robert" ... }, ... { ... ... lientName: "John Doe" ... }, ... { ... ... ClientName: "Robert" ... }, ... { ... ... ClientName: "Robert" ... }, ... { ... ... ClientName: "David Miller" ... } ... ] ... } ...); { "acknowledged" : true, "insertedId" : ObjectId("5e3d99ab03d395bdc21346f9") }

在find()方法的帮助下显示集合中的所有文档-

> db.demo210.find();

这将产生以下输出-

{ "_id" : ObjectId("5e3d99ab03d395bdc21346f9"), "details" : [ { "ClientName" : "Robert" }, { "ClientName" : "John Doe" }, { "ClientName" : "Robert" }, { "ClientName" : "Robert" }, { "ClientName" : "David Miller" } ] }

以下是获取特定值的计数的查询-

> db.demo210.aggregate([ ... { "$match" : { "details.ClientName" : "Robert" } }, ... { "$unwind" : "$details" }, ... { "$match" : { "details.ClientName" : "Robert" } }, ... { "$group" : { "_id" : "$_id", "Size" : { "$sum" : 1 } } }, ... { "$match" : { "Size" : { "$gte" : 2 } } } ...]);

这将产生以下输出-

{ "_id" : ObjectId("5e3d99ab03d395bdc21346f9"), "Size" : 3 }