如何在MongoDB中排序，选择和查询子文档？
要进行排序，请在MongoDB中使用$sort。让我们创建一个包含文档的集合-
> db.demo236.insertOne({"details":{"Name":"Chris","Age":21}});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e419015f4cebbeaebec514c")
}
> db.demo236.insertOne({"details":{"Name":"David","Age":23}});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e41901cf4cebbeaebec514d")
}
> db.demo236.insertOne({"details":{"Name":"Bob","Age":24}});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e419023f4cebbeaebec514e")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo236.find();
这将产生以下输出-
{ "_id" : ObjectId("5e419015f4cebbeaebec514c"), "details" : { "Name" : "Chris", "Age" : 21 } }
{ "_id" : ObjectId("5e41901cf4cebbeaebec514d"), "details" : { "Name" : "David", "Age" : 23 } }
{ "_id" : ObjectId("5e419023f4cebbeaebec514e"), "details" : { "Name" : "Bob", "Age" : 24 } }以下是对MongoDB中的子文档进行排序，选择和查询的查询-
> db.demo236.aggregate(
... [
... { $unwind: "$details" },
... { $project: {
... Name: '$details.Name',
... Age: '$details.Age'
...
... }},
... { $sort: {Name: -1}}
...]
...);这将产生以下输出-
{ "_id" : ObjectId("5e41901cf4cebbeaebec514d"), "Name" : "David", "Age" : 23 }
{ "_id" : ObjectId("5e419015f4cebbeaebec514c"), "Name" : "Chris", "Age" : 21 }
{ "_id" : ObjectId("5e419023f4cebbeaebec514e"), "Name" : "Bob", "Age" : 24 }