Allow $slice operator in $project

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    • Type: New Feature
    • Resolution: Done
    • Priority: Major - P3
    • 3.1.6
    • Affects Version/s: 2.1.1
    • Component/s: Aggregation Framework
    • None
    • Minor Change
    • Quint Iteration 4, Quint Iteration 5, Quint Iteration 6
    • None
    • 3
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      Aggregation $project stage should support $slice operator on array fields similar to $slice in projection and syntax similar to aggregation $substr operator:

      { "$project" : { "newArray" : { "$slice" : [ "$oldarray" , 10, 4 ] } } }

      The above would take 4 elements from oldarray starting at position 10 (akin to "skipping first ten elements, as position is 0 based).

      Original description:

      If I have a document with an array of values in it, I would like to be able to project a slice of those values while aggregating.

      { title: "A doc",
  intervals: [
    { value: 1, foo: true, bar: false },
    { value: 2, foo: false, bar: true },
    { value: 3, foo: true, bar: false}
  ]
}

      $project with a $slice should work as expected:

      { $project : {
    title: 1,
    fewerIntervals: {intervals:{$slice:2}}
  }
}

      results in a pipelined document =>

      { title: "A doc",
  fewerIntervals: [
    { value: 1, foo: true, bar: false },
    { value: 2, foo: false, bar: true }
  ]
}

      Similarly, the remainder of the existing $slice syntax should work as expected.

      { $project : {
    title: 1,
    fewerIntervals: {intervals:{$slice:[1,1]}}
  }
}

      should produce

      { title: "A doc",
  fewerIntervals: [
    { value: 2, foo: false, bar: true }
  ]
}

            Assignee:
            Charlie Swanson
            Reporter:
            Matt Weyant
            Votes:
            58 Vote for this issue
            Watchers:
            47 Start watching this issue

              Created:
              Updated:
              Resolved: