MongoDB聚合到数组内部的切片数组
为此，请aggregate()在MongoDB中使用。在那，使用$slice在array内对array进行切片。让我们创建一个包含文档的集合-
> db.demo111.insertOne(
... {
... "_id" : 101,
... "Name" : "Chris",
... "Details" : [
... {
... "_id" : 101,
... "Score" : 78,
... "Subjects" : [
... {
... "_id" : "10001",
... "SubjectName" : "MySQL"
... },
... {
... "_id" : "10003",
... "SubjectName" : "MongoDB"
... }
... ]
... },
... {
... "_id" : 102,
... "Score" : 87,
... "Subjects" : [
... {
... "_id" : "10004",
... "SubjectName" : "Java"
... }
... ]
... }
... ]
... }
... );
{ "acknowledged" : true, "insertedId" : 101 }在find()方法的帮助下显示集合中的所有文档-
> db.demo111.find();
这将产生以下输出-
{
"_id" : 101, "Name" : "Chris", "Details" : [
{ "_id" : 101, "Score" : 78, "Subjects" : [ { "_id" : "10001", "SubjectName" : "MySQL" },
{ "_id" : "10003", "SubjectName" : "MongoDB" } ] },
{ "_id" : 102, "Score" : 87, "Subjects" : [ { "_id" : "10004", "SubjectName" : "Java" } ] }
]
}以下是在数组内部切片数组的查询-
> db.demo111.aggregate([
... { "$addFields": {
... "Details": {
... "$map": {
... "input": "$Details",
... "as": "out",
... "in": {
... "_id": "$$out._id",
... "Score": "$$out.Score",
... "Subjects": { "$slice": [ "$$out.Subjects", 1 ] }
... }
... }
... }
... }}
... ])这将产生以下输出-
{
"_id" : 101, "Name" : "Chris", "Details" : [
{ "_id" : 101, "Score" : 78, "Subjects" : [ { "_id" : "10001", "SubjectName" : "MySQL" } ] },
{ "_id" : 102, "Score" : 87, "Subjects" : [ { "_id" : "10004", "SubjectName" : "Java" } ] }
]
}