如何在MongoDB中将分组投影到对象中并仅显示标记字段
> var document= [
... { "SubjectName" : "MySQL", "Marks" : 78 },
... { "SubjectName" : "MongoDB", "Marks" : 89 },
... { "SubjectName" : "Java", "Marks" : 71 },
... ];以下是显示文档的查询-
> printjson(document);
这将产生以下输出-
[
{
"SubjectName" : "MySQL",
"Marks" : 78
},
{
"SubjectName" : "MongoDB",
"Marks" : 89
},
{
"SubjectName" : "Java",
"Marks" : 71
}
]以下是将项目分组到MongoDB中的对象的查询-
> var makeObject= {};
> document.forEach(function (d){
... makeObject[d.SubjectName] = d.Marks;
... });
> printjson(makeObject);这将产生以下输出-
{ "MySQL" : 78, "MongoDB" : 89, "Java" : 71 }