MongoDB使用聚合管道将嵌入文档的数组上移到父级并更改键/值
在MongoDB聚合中使用$replaceRoot。$replaceRoot用指定的文档替换输入文档。该操作将替换输入文档中的所有现有字段，包括_id字段。让我们用文档创建一个集合–
> db.demo733.insertOne(
... {
... "SubjectDetails":
... [
... {
... SubjectName:"MongoDB",
... "Marks":85
... },
... {
... SubjectName:"MySQL",
... "Marks":90
... },
... {
... SubjectName:"PL/SQL",
... "Marks":98
... }
... ]
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eac6e6156e85a39df5f6342")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo733.find();
这将生成以下输出−
{ "_id" : ObjectId("5eac6e6156e85a39df5f6342"), "SubjectDetails" : [ { "SubjectName" : "MongoDB", "Marks" : 85 }, { "SubjectName" : "MySQL", "Marks" : 90 }, { "SubjectName" : "PL/SQL", "Marks" : 98 } ] }下面是一个查询，用于将嵌入的文档数组上移到父级并使用聚合管道-更改键/值
> db.demo733.aggregate([
... {
... $replaceRoot: {
... newRoot: {
... $mergeObjects: [
.. . { _id: "$_id" },
... { $arrayToObject: { $map: { input: "$SubjectDetails", in: [ "$$this.SubjectName", "$$this.Marks" ] } } }
... ]
... }
... }
... }
... ]).pretty()这将产生以下输出−
{
"_id" : ObjectId("5eac6e6156e85a39df5f6342"),
"MongoDB" : 85,
"MySQL" : 90,
"PL/SQL" : 98
}