可以在MongoDB中使用regex查找不同的_id.field值

Question

我有一个MongoDB集合，其_id由键、值和度量建立。我想找到特定键值对的所有不同度量。如何最好地实现这一点？即，对于以下数据

> db.schedule.find()
{ "_id" : { "key" : "source", "value" : "a", "metric" : "index.references.added.all" }, "nextCheck" : ISODate("2016-07-07T14:36:27.760Z") },
{ "_id" : { "key" : "source", "value" : "a", "metric" : "index.references.added.some" }, "nextCheck" : ISODate("2016-07-07T14:36:27.761Z") },
{ "_id" : { "key" : "source", "value" : "b", "metric" : "index.references.added.all" }, "nextCheck" : ISODate("2016-07-07T14:36:27.760Z") },
{ "_id" : { "key" : "source", "value" : "b", "metric" : "index.references.added.some" }, "nextCheck" : ISODate("2016-07-07T14:36:27.759Z") }

我想按照的思路取得一些成就

db.schedule.distinct("_id.metric", {_id : {"key" : "source", "value" : "a", "metric" : {$regex : "all"}}})
["index.references.added.all", "index.references.added.some"]

目前，这不会返回任何内容。我已经确认

db.schedule.distinct("_id.metric")
["index.references.added.all", "index.references.added.some"]

工作。我做错了什么？

Answer 1

您需要使用点表示法来访问嵌入的字段。

db.schedule.distinct(
    "_id.metric", 
    { "_id.key": "source", "_id.value" : "a", "_id.metric": /all/ }
)