单个MongoDB查询以按日期排序并按用户分组
为此，只需aggregate()在MongoDB中使用。让我们创建一个包含文档的集合-
> db.demo243.insertOne({"userId":1,dueDate:new ISODate("2019-01-10")});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e4575f81627c0c63e7dba5f")
}
> db.demo243.insertOne({"userId":2,dueDate:new ISODate("2019-11-10")});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e4576011627c0c63e7dba60")
}
> db.demo243.insertOne({"userId":2,dueDate:new ISODate("2020-01-31")});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e4576151627c0c63e7dba61")
}
> db.demo243.insertOne({"userId":1,dueDate:new ISODate("2010-01-10")});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e45761b1627c0c63e7dba62")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo243.find();
这将产生以下输出-
{ "_id" : ObjectId("5e4575f81627c0c63e7dba5f"), "userId" : 1, "dueDate" : ISODate("2019-01-10T00:00:00Z") }
{ "_id" : ObjectId("5e4576011627c0c63e7dba60"), "userId" : 2, "dueDate" : ISODate("2019-11-10T00:00:00Z") }
{ "_id" : ObjectId("5e4576151627c0c63e7dba61"), "userId" : 2, "dueDate" : ISODate("2020-01-31T00:00:00Z") }
{ "_id" : ObjectId("5e45761b1627c0c63e7dba62"), "userId" : 1, "dueDate" : ISODate("2010-01-10T00:00:00Z") }以下是查询排序日期和按用户分组-
> db.demo243.aggregate({
... $group: {
... _id : '$userId',
... dueDate: { $max: '$dueDate'}
... }
...})这将产生以下输出-
{ "_id" : 2, "dueDate" : ISODate("2020-01-31T00:00:00Z") }
{ "_id" : 1, "dueDate" : ISODate("2019-01-10T00:00:00Z") }