$expr operators are not implicitly ANDed in compound queries

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    • Type: Bug
    • Resolution: Duplicate
    • Priority: Major - P3
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    • Affects Version/s: None
    • Component/s: Querying
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      If I move both $expr condition into one $expr with an explicit $and, the query performs correctly, I don't understand why the implicit AND doesn't work in this case.

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      If I move both $expr condition into one $expr with an explicit $and, the query performs correctly, I don't understand why the implicit AND doesn't work in this case.
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      The documentation for queries states that,

      Implicitly, a logical AND conjunction connects the clauses of a compound query so that the query selects the documents in the collection that match all the conditions.

      Therefore, I expect this query with two $expr fields to find documents with an array where field foo is the same at indexes 0 and 1, and field bar is different:

      db.collection.find({
  $expr: {
    $eq: [
      { $arrayElemAt: ['$arrO.foo', 0] },
      { $arrayElemAt: ['$arrO.foo', 1] }
    ]
  },
  $expr: {
    $ne: [
      { $arrayElemAt: ['$arrO.bar', 0] },
      { $arrayElemAt: ['$arrO.bar', 1] }
    ]
  }
});

      What happens is that other documents are returned as well, where foo is different between arrO[0] and arrO[1].

      Collection:

      [
  {
    arrO: [
      {
        foo: 1,
        bar: "bar diff..."
      },
      {
        foo: 2,
        bar: "bar ...erent",
        
      }
    ]
  },
  {
    arrO: [
      {
        foo: 3,
        bar: "bar diff..."
      },
      {
        foo: 3,
        bar: "bar ...erent"
      }
    ]
  }
]

            Assignee:
            Eric Sedor
            Reporter:
            Dan Dascalescu
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              Created:
              Updated:
              Resolved: