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  1. Core Server
  2. SERVER-25717

Allow for negative $push indexes.

    • Type: Icon: Improvement Improvement
    • Resolution: Done
    • Priority: Icon: Major - P3 Major - P3
    • 3.5.6
    • Affects Version/s: 3.3.11
    • Component/s: Write Ops
    • Fully Compatible
    • Query 2017-03-27, Query 2017-04-17

      Requiring a query to determine the length of a document's array and calculate the appropriate positive integer index introduces a race condition. By allowing negative indexes (indicating distance from the end) on the $position modifier, this race condition could be avoided.

      This would match Python semantics for list manipulation. An example, given the following document:

      {
        acl: [
            {grant: True, user: "amcgregor"},
            {grant: True, user: "bdole"},
            {grant: False}
          ]
      }
      

      And the following update operation:

      {
        $push: {
          acl: {
             $each: [ { grant: True, user: "algore" } ],
             $position: -1
          }
        }
      }
      

      The resulting document should be:

      {
        acl: [
            {grant: True, user: "amcgregor"},
            {grant: True, user: "bdole"},
            {grant: True, user: "algore"},
            {grant: False}
          ]
      }
      

      The default insert location, the end (when $position is omitted or exceeds the length of the array), is unaffected.

      Thank you for your consideration!

            Assignee:
            tess.avitabile@mongodb.com Tess Avitabile (Inactive)
            Reporter:
            alice@gothcandy.com Dissatisfied Former User
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              Created:
              Updated:
              Resolved: