MongoDB中实现具有多个键的聚合
要实现具有多个键的聚合，请使用aggregate()和$group。让我们创建一个包含文档的集合-
> db.demo190.insertOne(
... {
...
... "DueDate" : ISODate("2020-01-01"),
... "Value" : 10,
... "Name" : "Chris"
... }
...);
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3ad76403d395bdc21346bf")
}
>
> db.demo190.insertOne(
... {
...
... "DueDate" : ISODate("2020-02-05"),
... "Value" : 30,
... "Name" : "David"
... }
...);
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3ad76403d395bdc21346c0")
}
> db.demo190.insertOne(
... {
...
... "DueDate" : ISODate("2020-01-01"),
... "Value" : 40,
... "Name" : "Chris"
... }
...);
{
"acknowledged" : true,
"insertedId" : ObjectId("5e3ad7f003d395bdc21346c1")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo190.find();
这将产生以下输出-
{ "_id" : ObjectId("5e3ad76403d395bdc21346bf"), "DueDate" : ISODate("2020-01-01T00:00:00Z"), "Value" : 10, "Name" : "Chris" }
{ "_id" : ObjectId("5e3ad76403d395bdc21346c0"), "DueDate" : ISODate("2020-02-05T00:00:00Z"), "Value" : 30, "Name" : "David" }
{ "_id" : ObjectId("5e3ad7f003d395bdc21346c1"), "DueDate" : ISODate("2020-01-01T00:00:00Z"), "Value" : 40, "Name" : "Chris" }以下是使用多个键实现MongoDB聚合的查询-
> db.demo190.aggregate( [ { "$group": { "_id": { "Name": "$Name", "DueDate": { "$year": "$DueDate" } }, "Value": { "$sum": "$Value" } } } ], function(err,results) { console.log(results); } );这将产生以下输出-
{ "_id" : { "Name" : "David", "DueDate" : 2020 }, "Value" : 30 }
{ "_id" : { "Name" : "Chris", "DueDate" : 2020 }, "Value" : 50 }