如何按MongoDB中数组内容的差异排序？
要按差异排序，请在MongoDB中使用aggregate()。让我们创建一个包含文档的集合-
> db.demo155.insertOne({"Scores":[{"Value":45},{"Value":50}]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e354584fdf09dd6d08539e3")
}
> db.demo155.insertOne({"Scores":[{"Value":60},{"Value":10}]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e35458efdf09dd6d08539e4")
}
> db.demo155.insertOne({"Scores":[{"Value":100},{"Value":95}]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e354599fdf09dd6d08539e5")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo155.find();
这将产生以下输出-
{ "_id" : ObjectId("5e354584fdf09dd6d08539e3"), "Scores" : [ { "Value" : 45 }, { "Value" : 50 } ] }
{ "_id" : ObjectId("5e35458efdf09dd6d08539e4"), "Scores" : [ { "Value" : 60 }, { "Value" : 10 } ] }
{ "_id" : ObjectId("5e354599fdf09dd6d08539e5"), "Scores" : [ { "Value" : 100 }, { "Value" : 95 } ] }以下是使用MongoDB按数组内容的差异进行排序的查询-
> db.demo155.aggregate([
... { "$match": { "Scores.1": { "$exists": true } } },
... { "$project": {
... "Scores": "$Scores",
... "sub": {
... "$let": {
... "vars": {
... "f": { "$arrayElemAt": [ "$Scores", -2 ] },
... "l": { "$arrayElemAt": [ "$Scores", -1 ] }
... },
... "in": { "$subtract": [ "$$l.Value", "$$f.Value" ] }
... }
... }
... }},
... { "$sort": { "sub": -1 } }
... ])这将产生以下输出-
{ "_id" : ObjectId("5e354584fdf09dd6d08539e3"), "Scores" : [ { "Value" : 45 }, { "Value" : 50 } ], "sub" : 5 }
{ "_id" : ObjectId("5e354599fdf09dd6d08539e5"), "Scores" : [ { "Value" : 100 }, { "Value" : 95 } ], "sub" : -5 }
{ "_id" : ObjectId("5e35458efdf09dd6d08539e4"), "Scores" : [ { "Value" : 60 }, { "Value" : 10 } ], "sub" : -50 }