查询以在MongoDB中检索数组中的多个项目？
要检索数组中的多个项目，请使用聚合框架。首先让我们创建一个包含文档的集合-
> db.retrieveMultipleDemo.insertOne(
... {
... "UserDetails":
... [
... { "_id": "101", "UserName":"John", "UserAge": 23 },
... { "_id": "102", "UserName":"Carol", "UserAge": 21 },
... { "_id": "103", "UserName":"David", "UserAge": 23},
... { "_id": "104", "UserName":"Sam", "UserAge": 25}
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd40c85edc6604c74817cf0")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.retrieveMultipleDemo.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5cd40c85edc6604c74817cf0"),
"UserDetails" : [
{
"_id" : "101",
"UserName" : "John",
"UserAge" : 23
},
{
"_id" : "102",
"UserName" : "Carol",
"UserAge" : 21
},
{
"_id" : "103",
"UserName" : "David",
"UserAge" : 23
},
{
"_id" : "104",
"UserName" : "Sam",
"UserAge" : 25
}
]
}以下是检索数组中多个项目的查询-
> db.retrieveMultipleDemo.aggregate([
... {$unwind:"$UserDetails"},
... {$match:{"UserDetails._id":{$in:myIds},"UserDetails.UserAge":23}},
... {$group:{"_id":"_id","UserDetails":{$push:"$UserDetails"}}},
... {$project:{"_id":0,"UserDetails":1}}
... ]);这将产生以下输出-
{ "UserDetails" : [ { "_id" : "101", "UserName" : "John", "UserAge" : 23 }, { "_id" : "103", "UserName" : "David", "UserAge" : 23 } ] }