MongoDB查询以确定是否存在特定值？

要确定特定值是否不存在，请在MongoDB中使用$ne。让我们创建一个包含文档的集合-

> db.demo206.insertOne( ... { ... "ClientDetails": ... [ ... { ... "Name":"Chris", ... "Age":28, ... "CountryName":"US" ... } ... ] ... } ...); { "acknowledged" : true, "insertedId" : ObjectId("5e3d8bd403d395bdc21346ee") } > db.demo206.insertOne( ... { ... "ClientDetails": ... [ ... { ... "Name":"David", ... "Age":29, ... "CountryName":"UK" ... } ... ] ... } ...); { "acknowledged" : true, "insertedId" : ObjectId("5e3d8bd403d395bdc21346ef") } > > db.demo206.insertOne( ... { ... "ClientDetails": ... [ ... { ... "Name":"Bob", ... "Age":31, ... "CountryName":"US" ... } ... ] ... } ...); { "acknowledged" : true, "insertedId" : ObjectId("5e3d8bd503d395bdc21346f0") }

在find()方法的帮助下显示集合中的所有文档-

> db.demo206.find();

这将产生以下输出-

{ "_id" : ObjectId("5e3d8bd403d395bdc21346ee"), "ClientDetails" : [ { "Name" : "Chris", "Age" : 28, "CountryName" : "US" } ] } { "_id" : ObjectId("5e3d8bd403d395bdc21346ef"), "ClientDetails" : [ { "Name" : "David", "Age" : 29, "CountryName" : "UK" } ] } { "_id" : ObjectId("5e3d8bd503d395bdc21346f0"), "ClientDetails" : [ { "Name" : "Bob", "Age" : 31, "CountryName" : "US" } ] }

以下是确定特定值是否不存在的查询-

> db.demo206.find({"ClientDetails.CountryName": {"$ne": "US"}});

这将产生以下输出-

{ "_id" : ObjectId("5e3d8bd403d395bdc21346ef"), "ClientDetails" : [ { "Name" : "David", "Age" : 29, "CountryName" : "UK" } ] }