MongoDB查询如何限制字段的返回值
> db.demo594.insertOne(
... {
... id:1,
... details:[
... {Name:"Chris",Age:21},
... {Name:"Bob",Age:20},
... {Name:"David",Age:23},
... {Name:"Sam",Age:22}
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e933459fd2d90c177b5bcdd")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo594.find();
这将产生以下输出-
{ "_id" : ObjectId("5e933459fd2d90c177b5bcdd"), "id" : 1, "details" : [
{ "Name" : "Chris", "Age" : 21 },
{ "Name" : "Bob", "Age" : 20 },
{ "Name" : "David", "Age" : 23 },
{ "Name" : "Sam", "Age" : 22 }
] }以下是查询以限制字段的返回值-
> db.demo594.find({}, {"Name": 1, "details": { "$slice": 1}});这将产生以下输出-
{ "_id" : ObjectId("5e933459fd2d90c177b5bcdd"), "details" : [
{ "Name" : "Chris", "Age" : 21 }
] }