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  1. Core Server
  2. SERVER-90869

Disallow dotted full-path renames for '$elemMatch' expressions

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    • Query Execution
    • Fully Compatible
    • ALL
    • v8.0, v7.3, v7.0
    • QE 2024-05-27, QE 2024-06-10, QE 2024-06-24
    • 0

       The following pipeline returns different results with optimisations disabled via the "disablePipelineOptimization" failpoint:

      // Collection contains only the document: {outer: [{inner: 0}]}
[
    {
        $project: {
            flattened: {
                $map: {input: '$outer', as: "iter", in : "$$iter.inner"},
            },
        },
    },
    {
        $match: {flattened: {$elemMatch: {$eq: 0}},
    }
];
      • With the optimisation it returns []
      • Without the optimisation it returns [{flattened: [0]}]

      The rewrite turns the match expression into {$match: {"outer.inner": {$elemMatch: {$eq: 0}}}} which is not exactly the same in this context due to implicit dotted array traversal. [Mongo docs.

            Assignee:
            catalin.sumanaru@mongodb.com Catalin Sumanaru
            Reporter:
            catalin.sumanaru@mongodb.com Catalin Sumanaru
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              Created:
              Updated:
              Resolved: