MongoDB Query Join Query

Question

User will enter a input name and broadband Speed like below
Name: shankar
Speed:10Mbps
Then i need to display
Name:Shankar
Speed : 10Mbps
Data Used : 500MB

from below given sample mongodb document structure how to query in mongoDB?
Parent Record is :
{
subscriber_id : 001
name: shankar
total_data_used: 1000MB
Timestamp: 2016-Aug-01 00:03:00
}
{
subscriber_id : 002
name: John
total_data_used: 2000MB
Timestamp: 2016-Aug-01 00:10:00
}

Detail or child record as follows:
{
subscriber_id: 001
service:10Mbps
Timestamp: 2016-Aug-01 00:01:00
total_data_usage: 500MB
}

{
subscriber_id: 001
service:10Mbps
total_data_usage: 500MB
Timestamp: 2016-Aug-01 00:02:00
}

{
subscriber_id: 002
service:10Mbps
Timestamp: 2016-Aug-01 00:07:00
total_data_usage: 1000MB
}

{
subscriber_id: 002
service:10Mbps
total_data_usage: 1000MB
Timestamp: 2016-Aug-01 00:08:00
}

Anyone tell me in mongodb query how to retrieve

Regards,
Shankar

Not so sure about your question, if you wanna query the parent documents and children documents , and then join them in one document , mongodb don't support that. Maybe $aggregate can help but it's not how mongodb work. You have to make it in two query, one for parent, one for child — John Zeng
– John Zeng, Commented Aug 25, 2016 at 8:37
Looks like it may fit your requirement , but I am not sure about the performance . You'd better use an explain() to check the performance before you decide to use it. — John Zeng
– John Zeng, Commented Aug 25, 2016 at 10:22

Anirudh Srinivas Madhavan · Accepted Answer · 2016-10-05 17:12:37Z

This query should work. The first 'lookup' stage joins the child collection with the parent collection based on the subscriber_id field. It appends all documents in parent collection which match in the subscriber_details array of the child document.

In your case, this will be the output after the first stage.

{ subscriber_id: 001, service:10Mbps, Timestamp: 2016-Aug-01 00:01:00, total_data_usage: 500MB, subscriber_details:[{ subscriber_id : 001, name: shankar, total_data_used: 1000MB, Timestamp: 2016-Aug-01 00:03:00 }] }

{ subscriber_id: 001, service:10Mbps, total_data_usage: 500MB, Timestamp: 2016-Aug-01 00:02:00, subscriber_details:[{ subscriber_id : 001, name: shankar, total_data_used: 1000MB, Timestamp: 2016-Aug-01 00:03:00, }] }

After this stage, I am using a 'match' to filter out against your input conditions and then a 'project' stage to obtain the output in the form you desire.

db.child.aggregate([
{
   $lookup:
     {
       "from": "parent",
       "localField": "subscriber_id",
       "foreignField": "subscriber_id",
       "as": "subscriber_details"
     }
}, 
{
   $match:
     {
       "service":"<input_speed>",
       "subscriber_details.name":"<input_name>"
     }
},
{
   $project:
     {
       "_id":0
       "Name":"$subscriber_details.0.name"
       "Speed":"$service"
       "Data Used":"$total_data_usage"
     }
}])

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