计算MongoDB集合中的行数
要计算文档数，请在MongoDB中使用count()。让我们创建一个包含文档的集合-
> db.demo664.insertOne({_id:1,ClientName:"Chris"});
{ "acknowledged" : true, "insertedId" : 1 }
> db.demo664.insertOne({_id:2,ClientName:"Bob"});
{ "acknowledged" : true, "insertedId" : 2 }
> db.demo664.insertOne({_id:3,ClientName:"Sam"});
{ "acknowledged" : true, "insertedId" : 3 }
> db.demo664.insertOne({_id:4,ClientName:"David"});
{ "acknowledged" : true, "insertedId" : 4 }在find()方法的帮助下显示集合中的所有文档-
> db.demo664.find();
这将产生以下输出-
{ "_id" : 1, "ClientName" : "Chris" }
{ "_id" : 2, "ClientName" : "Bob" }
{ "_id" : 3, "ClientName" : "Sam" }
{ "_id" : 4, "ClientName" : "David" }以下是计算行数的查询-
> var numberOfRows=db.demo664.count();
> print ("Number Of Rows="+numberOfRows);这将产生以下输出-
Number Of Rows=4