如何使用MongoDB聚合计算特定文档的总和？
总而言之，请使用$sum并获取特定文档的总和，您需要在MongoDB中使用$group对其进行分组。
首先让我们创建一个包含文档的集合-
>db.calculateSumOfDocument.insertOne({"ListOfUsers":["Carol","Bob"],"UsersDetails":[{"FirstUser":"Carol","TotalLikes":20},{"FirstUser":"Bob","TotalLikes":45}]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e084e9125ddae1f53b6220c")
}
>db.calculateSumOfDocument.insertOne({"ListOfUsers":["Carol","Bob"],"UsersDetails":[{"FirstUser":"Carol","TotalLikes":60},{"FirstUser":"Bob","TotalLikes":50}]});
{
"acknowledged" : true,
"insertedId" : ObjectId("5e084f6125ddae1f53b6220d")
}以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.calculateSumOfDocument.find().pretty();
这将产生以下输出-
{
"_id" : ObjectId("5e084e9125ddae1f53b6220c"),
"ListOfUsers" : [
"Carol",
"Bob"
],
"UsersDetails" : [
{
"FirstUser" : "Carol",
"TotalLikes" : 20
},
{
"FirstUser" : "Bob",
"TotalLikes" : 45
}
]
}
{
"_id" : ObjectId("5e084f6125ddae1f53b6220d"),
"ListOfUsers" : [
"Carol",
"Bob"
],
"UsersDetails" : [
{
"FirstUser" : "Carol",
"TotalLikes" : 60
},
{
"FirstUser" : "Bob",
"TotalLikes" : 50
}
]
}以下是查询以使用聚合计算特定文档的总和-
> db.calculateSumOfDocument.aggregate([
... {
... "$match": { "UsersDetails.FirstUser": "Carol" }
... },
... { "$unwind" : "$UsersDetails" },
... {
... "$match": { "UsersDetails.FirstUser": "Carol" }
... },
... {
... "$group": {
... "_id": null,
... "total": { "$sum": "$UsersDetails.TotalLikes" }
... }
... }
... ]);这将产生以下输出-
{ "_id" : null, "total" : 80 }