MongoDB中如何查询聚合嵌套数组
要在MongoDB中聚合嵌套数组，请使用aggregate()。让我们创建一个包含文档的集合-
> db.demo441.insertOne(
... {
...
... "Name" : "David",
... "Age" : 21,
...
... "details" : [
... {
... "id" : 1,
... "CountryName" : "US",
... "details1" : [
... {
... "SubjectName" : "MySQL",
... "Score":56
... },
... {
... "SubjectName" : "MongoDB",
... "Score":78
... }
... ]
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5e78cc05bbc41e36cc3caeb7")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo441.find();
这将产生以下输出-
{ "_id" : ObjectId("5e78cc05bbc41e36cc3caeb7"), "Name" : "David", "Age" : 21, "details" : [ { "id" : 1, "CountryName" : "US", "details1" : [ { "SubjectName" : "MySQL", "Score" : 56 }, { "SubjectName" : "MongoDB", "Score" : 78 } ] } ] }以下是聚合嵌套数组的查询-
> db.demo441.aggregate([{
... $addFields: {
... ResultOfDetails: {
... $map: {
... input: "$details",
... as: "output",
... in: {
... id: "$$output.id",
... CountryName: "$$output.CountryName",
... details1: {
... $let: {
... vars: {
... last: {
... $arrayElemAt: ["$$output.details1", -1]
... }
... },
... in: {
... $cond: [{
... $eq: ["$$last.Score", 78]
... },
... ["$$last"],
... []
...
... }
... }
... }
... }
... }
... }
... }
... }]).pretty();这将产生以下输出-
{
"_id" : ObjectId("5e78cc05bbc41e36cc3caeb7"),
"Name" : "David",
"Age" : 21,
"details" : [
{
"id" : 1,
"CountryName" : "US",
"details1" : [
{
"SubjectName" : "MySQL",
"Score" : 56
},
{
"SubjectName" : "MongoDB",
"Score" : 78
}
]
}
],
"ResultOfDetails" : [
{
"id" : 1,
"CountryName" : "US",
"details1" : [
{
"SubjectName" : "MongoDB",
"Score" : 78
}
]
}
]
}