MongoDB subdocument query to limit elements

Question

Here's what my document looks like.

{
    ID: "XYZ",
    messages: [
        {
            ID: "AAA",
            text: "this is a message"
        },
        {
            ID: "BBB",
            text: "this is a message"
        },
        {
            ID: "CCC",
            text: "this is a message"
        },
        {
            ID: "DDD",
            text: "this is a message"
        },
        {
            ID: "EEE",
            text: "this is a message"
        },
        {
            ID: "FFF",
            text: "this is a message"
        },
        {
            ID: "GGG",
            text: "this is a message"
        }
    ]
}

And I want to aggregate and get messages for example from CCC to FFF

{
    ID: "XYZ",
    messages: [
        {
            ID: "CCC",
            text: "this is a message"
        },
        {
            ID: "DDD",
            text: "this is a message"
        },
        {
            ID: "EEE",
            text: "this is a message"
        },
        {
            ID: "FFF",
            text: "this is a message"
        }

    ]
}

So how is this possible?

Try using $unwind, $match, and then $group in your pipeline. — JohnnyHK
– JohnnyHK, Commented Apr 14, 2013 at 0:44

asaf am · Accepted Answer · 2015-05-20 12:06:11Z

2

This can be achieved by using the $slice operator. Check out the mongodb documentation on $slice. Run your query to get the document and use the slice operator with the query:

query.slice('messages', [numOfElementsToSkip, numOfElementsToReturn]);

Or more specific to your request:

query.slice('messages', [2, 4]); // Return 4 elements after skipping 2

answered May 20, 2015 at 12:06

asaf am

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