MongoDB聚合框架中的字段之间是否匹配？
您可以为此使用$cmp运算符。为了理解这个概念，让我们用文档创建一个集合。使用文档创建集合的查询如下-
> db.matchBetweenFieldsDemo.insertOne({"FirstValue":40,"SecondValue":70});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c92c9625259fcd19549980d")
}
> db.matchBetweenFieldsDemo.insertOne({"FirstValue":20,"SecondValue":5});
{
"acknowledged" : true,
"insertedId" : ObjectId("5c92c96b5259fcd19549980e")
}在find()method的帮助下显示集合中的所有文档。查询如下-
> db.matchBetweenFieldsDemo.find().pretty();
以下是输出-
{
"_id" : ObjectId("5c92c9625259fcd19549980d"),
"FirstValue" : 40,
"SecondValue" : 70
}
{
"_id" : ObjectId("5c92c96b5259fcd19549980e"),
"FirstValue" : 20,
"SecondValue" : 5
}这是聚合框架中字段之间$match的查询-
> db.matchBetweenFieldsDemo.aggregate([
... {$project: {
...
... firstGreaterThanOrNot: {$cmp: ['$FirstValue', '$SecondValue']}
... }},
... {$match: {firstGreaterThanOrNot:{$gt: 0}}}
... ]);以下是输出-
{ "_id" : ObjectId("5c92c96b5259fcd19549980e"), "firstGreaterThanOrNot" : 1 }