allow $expr with $in expression to use indexes

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    • Query Optimization
    • Fully Compatible
    • v8.0, v7.0, v6.0
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      Similarly to SERVER-31760 it's possible to rewrite $expr with $in expression to an indexable MatchExpression.

      Semantically 

       {$expr:{$in:[ "$value", [ "v1", "v2", "v3" ]] } }

      is exactly equivalent to 

       {"value":{$in:[ "v1", "v2", "v3"]}}

      if value is not an array.

      If we restrict using an index for $expr $in expressions to non-multikey indexes/paths, then we will only get back matches from the index that are guaranteed to be correct semantically to the aggregation meaning of $in.

      This is also exactly equivalent query that can use any index and return only agg semantics:

      db.reviews.find({product_id:{$in:["hat","shirt"],$not:{$elemMatch:{$exists:true}}}})

      The second part prevents reaching into arrays for comparison.

            Assignee:
            Lynne Wang
            Reporter:
            Asya Kamsky
            Votes:
            28 Vote for this issue
            Watchers:
            51 Start watching this issue

              Created:
              Updated:
              Resolved: