Mongoose - 嵌套查询

示例数据：

{"_id" : ObjectId("5ca560896208983d3c55b87e"),"createdBy" : {"kind" : "admin","item" : ObjectId("5c9d84c98a007636043f1fe6")}
}

完全匹配嵌套数据进行查询：

db.getCollection('xxxx').find({ "createdBy": { "kind": "admin", "item": ObjectId("5c9d84c98a007636043f1fe6")}})

部分匹配嵌套数据进行查询：

db.getCollection('trainingEntries').find({"createdBy.kind": "admin"})