MongoDB在数学计算上过滤文档
答
假设我有以下格式的集合 “数据” - 下面的示例文件:
{ "_id" : ObjectId("533e46e99710181b60737702"), "a" : 65, "b" : 25.3 }
{ "_id" : ObjectId("533e46e99710181b60737703"), "a" : 39.1, "b" : 66 }
{ "_id" : ObjectId("533e46e99710181b60737704"), "a" : 31.7, "b" : 96.3 }
{ "_id" : ObjectId("533e46e99710181b60737705"), "a" : 48.6, "b" : 75.1 }
{ "_id" : ObjectId("533e46e99710181b60737706"), "a" : 20.8, "b" : 97.3 }
下面是该查询:
> db.data.aggregate([ { $project: { t: { $divide: [ "$a", "$b" ] } } },
{ $match: { t: { $gt: 20} } } ])
{
"result" : [
{
"_id" : ObjectId("533e46e99710181b6073770d"),
"t" : 40.75
},
],
"ok" : 1
}