在MongoDB中执行聚合排序？
您可以将aggregate()method和$sort()运算符一起使用。为了理解这个概念，让我们用文档创建一个集合。使用文档创建集合的查询如下-
> db.aggregationSortDemo.insertOne({"StudentId":98,"StudentFirstName":"John","StudentLastName":"Smith"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90140c5705caea966c5587")
}
> db.aggregationSortDemo.insertOne({"StudentId":128,"StudentFirstName":"Carol","StudentLastName":"Taylor"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90141b5705caea966c5588")
}
> db.aggregationSortDemo.insertOne({"StudentId":110,"StudentFirstName":"David","StudentLastName":"Miller"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90142f5705caea966c5589")
}
> db.aggregationSortDemo.insertOne({"StudentId":139,"StudentFirstName":"Chris","StudentLastName":"Brown"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90146a5705caea966c558a")
}
> db.aggregationSortDemo.insertOne({"StudentId":125,"StudentFirstName":"Sam","StudentLastName":"Williams"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c9015695705caea966c558b")
}
> db.aggregationSortDemo.insertOne({"StudentId":139,"StudentFirstName":"Mike","StudentLastName":"Wilson"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c90158e5705caea966c558c")
}在find()method的帮助下显示集合中的所有文档。查询如下-
> db.aggregationSortDemo.find().pretty();
以下是输出-
{
"_id" : ObjectId("5c90140c5705caea966c5587"),
"StudentId" : 98,
"StudentFirstName" : "John",
"StudentLastName" : "Smith"
}
{
"_id" : ObjectId("5c90141b5705caea966c5588"),
"StudentId" : 128,
"StudentFirstName" : "Carol",
"StudentLastName" : "Taylor"
}
{
"_id" : ObjectId("5c90142f5705caea966c5589"),
"StudentId" : 110,
"StudentFirstName" : "David",
"StudentLastName" : "Miller"
}
{
"_id" : ObjectId("5c90146a5705caea966c558a"),
"StudentId" : 139,
"StudentFirstName" : "Chris",
"StudentLastName" : "Brown"
}
{
"_id" : ObjectId("5c9015695705caea966c558b"),
"StudentId" : 125,
"StudentFirstName" : "Sam",
"StudentLastName" : "Williams"
}
{
"_id" : ObjectId("5c90158e5705caea966c558c"),
"StudentId" : 139,
"StudentFirstName" : "Mike",
"StudentLastName" : "Wilson"
}这是对MongoDB聚合排序的查询。
情况1-每当您希望结果按降序排列时。查询如下-
> db.aggregationSortDemo.aggregate( {$group: {_id: '$StudentId',"TotalOccurrences": {$sum: 1}}}, {$sort: {_id: -1}} ).pretty();以下是输出：
{ "_id" : 139, "TotalOccurrences" : 2 }
{ "_id" : 128, "TotalOccurrences" : 1 }
{ "_id" : 125, "TotalOccurrences" : 1 }
{ "_id" : 110, "TotalOccurrences" : 1 }
{ "_id" : 98, "TotalOccurrences" : 1 }情况2-只要您希望结果按升序排列。查询如下-
> db.aggregationSortDemo.aggregate( {$group: {_id: '$StudentId', "TotalOccurrences": {$sum: 1}}}, {$sort: {_id: 1}} ).pretty();以下是输出-
{ "_id" : 98, "TotalOccurrences" : 1 }
{ "_id" : 110, "TotalOccurrences" : 1 }
{ "_id" : 125, "TotalOccurrences" : 1 }
{ "_id" : 128, "TotalOccurrences" : 1 }
{ "_id" : 139, "TotalOccurrences" : 2 }