Search key in Mongodb document - mongodb

Question

following is my json which i have inserted in mongodb. I need to find record where cardholders value is 200
{
"_id": "11",
"cardholders": {
"100": [
{
"message": "message1",
"time": "timestamp"
},
{
"message": "message2",
"time": "timestamp"
}
],
"200": [
{
"message": "message1",
"time": "timestamp"
},
{
"message": "message2",
"time": "timestamp"
},
{
"message": "message3",
"time": "timestamp"
}
],
"300": [
{
"message": "message1",
"time": "timestamp"
},
{
"message": "message2",
"time": "timestamp"
}
]
}
}
Please advice. I have following
db.test3.find({"message1":{$eq:true}})
> db.test3.find({"100":{$eq:true}})
> db.test3.find({cardholders:{$eq:'100'}})
> db.test3.find({cardholders:{$eq:100}})

Answer 1

You essentially want to include a projection argument in your find() query which matches documents containing only the projection field and the _id field. In this case since "200" is the key, you can project it and use the map() cursor to get the values as follows:
db.test3.find(
{},
{"cardholders.200": 1}
).map(function(doc){ return doc["cardholders"]["200"]})
Output:
/* 0 */
{
"0" : [
{
"message" : "message1",
"time" : "timestamp"
},
{
"message" : "message2",
"time" : "timestamp"
},
{
"message" : "message3",
"time" : "timestamp"
}
]
}
UPDATE
To make querying easier, I would recommend changing your schema to change the cardholders key into an array that holds embedded documents. These embedded documents would have a key and value fields; the key field holds the previous dynamic keys and the value field holds the array values:
{
"_id": "11",
"cardholders": [
{
"key": "100",
"values": [
{
"message": "message1",
"time": "timestamp"
},
{
"message": "message2",
"time": "timestamp"
}
]
},
{
"key": "200",
"values": [
{
"message": "message1",
"time": "timestamp"
},
{
"message": "message2",
"time": "timestamp"
}
]
},
{
"key": "300",
"values": [
{
"message": "message1",
"time": "timestamp"
},
{
"message": "message2",
"time": "timestamp"
}
]
}
]
}
You can then query the embedded documents using a combination of the dot notation and the $elemMatch projection as follows:
db.test3.find(
{"cardholders.key": "200"},
{
"cardholders": {
"$elemMatch": { "key": "200" }
}
}
);