Question

what seemed a simple task, came to be a challenge for me.

I have the following mongodb structure:

{
(...)
"services": {
    "TCP80": {
      "data": [{
          "status": 1,
          "delay": 3.87,
          "ts": 1308056460
        },{
          "status": 1,
          "delay": 2.83,
          "ts": 1308058080
        },{
          "status": 1,
          "delay": 5.77,
          "ts": 1308060720
        }]
    }
}}

Now, the following query returns whole document:

{ 'services.TCP80.data.ts':{$gt:1308067020} }

I wonder – is it possible for me to receive only those “data” array entries matching $gt criteria (kind of shrinked doc)?

I was considering MapReduce, but could not locate even a single example on how to pass external arguments (timestamp) to Map() function. (This feature was added in 1.1.4 https://jira.mongodb.org/browse/SERVER-401)

Also, there’s always an alternative to write storedJs function, but since we speak of large quantities of data, db-locks can’t be tolerated here.

Most likely I’ll have to redesign the structure to something 1-level deep, like:

{
   status:1,delay:3.87,ts:138056460,service:TCP80
},{
   status:1,delay:2.83,ts:1308058080,service:TCP80
},{
   status:1,delay:5.77,ts:1308060720,service:TCP80
}

but DB will grow dramatically, since “service” is only one of many options which will append each document.

please advice!

thanks in advance

Answer 1

This is not currently supported. By default you will always receive the whole document/array unless you use field restrictions or the $slice operator. Currently these tools do not allow filtering the array elements based on the search criteria.

You should watch this request for a way to do this: https://jira.mongodb.org/browse/SERVER-828