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Asked: 2026-05-30T20:14:10+00:00

I have a table called devicesegments , each row of which contains a large

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I have a table called devicesegments, each row of which contains a large array called devices. Owing to the size of the device array, I’ve been asked not to include it in my query for a page that lists all devicesegments, but only include their count. Is this possible?
What I was doing before :
A simple db.devicesegments.find()

What I’m doing now :
db.devicesegments.find({}, { devices : 0 })

What I want to achieve :
db.devicesegments.find({}, { devices : 0, devices.length : 1 })

Something like a COUNT(devices) AS device_count!

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1 Answer

  1. Editorial Team

    Ashkay, there’s no way to do this with Mongo currently. As @rompetroll says, your application should keep a “count” field on each document, and carefully $inc it whenever you change the number of entries in the array. Then when you query for the document, exclude the array like:

    db.collection.find({}, {devices:0})

    If you’re willing to run MongoDB 2.1, which is a development release, the aggregation framework provides a means to calculate the array size within a query:

    http://www.mongodb.org/display/DOCS/Aggregation+Framework

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