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  1. Core Server
  2. SERVER-100949

$elemMatch object form should simplify to a trivially false expression if possible

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    • Type: Icon: Improvement Improvement
    • Resolution: Unresolved
    • Priority: Icon: Major - P3 Major - P3
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    • Affects Version/s: None
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    • Query Optimization
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    • 3
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      We already simplify the $element value form to a trivially false expression.

      Compare:

      db.test.find({"a.m":{$elemMatch:{$in:[]}}}).explain(true)
...
winningPlan: { isCached: false, stage: 'EOF', type: 'predicateEvalsToFalse' },

      db.test.find({a:{$elemMatch:{m:{$in:[]}}}}).explain(true)
...
    winningPlan: {
      isCached: false,
      stage: 'COLLSCAN',
      filter: { a: { '$elemMatch': { '$alwaysFalse': 1 } } },
      direction: 'forward'
    },

            Assignee:
            Unassigned Unassigned
            Reporter:
            jess.balint@mongodb.com Jess Balint
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              Created:
              Updated: