shell should raise a useful error on mixed usage of $query document with .explain()

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    • Type: Bug
    • Resolution: Duplicate
    • Priority: Major - P3
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    • Affects Version/s: 2.4.12
    • Component/s: Shell
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    • Hide 
      db.test.find():
{
    "_id" : ObjectId("54c158402f512862b58738c4"),
    "a" : 8,
    "b" : 3
}

/* 1 */
{
    "_id" : ObjectId("54c158402f512862b58738c5"),
    "a" : 8,
    "b" : 9
}

/* 2 */
{
    "_id" : ObjectId("54c158402f512862b58738c6"),
    "a" : 7,
    "b" : 4
}
...

db.test.getIndexes():
{
    "0" : {
        "v" : 1,
        "name" : "_id_",
        "key" : {
            "_id" : 1
        },
        "ns" : "test.test"
    },
    "1" : {
        "v" : 1,
        "name" : "b_1",
        "key" : {
            "b" : 1
        },
        "ns" : "test.test"
    },
    "2" : {
        "v" : 1,
        "name" : "a_1",
        "key" : {
            "a" : 1
        },
        "ns" : "test.test"
    }
}
      Show
      db.test.find(): { "_id" : ObjectId( "54c158402f512862b58738c4" ), "a" : 8, "b" : 3 } /* 1 */ { "_id" : ObjectId( "54c158402f512862b58738c5" ), "a" : 8, "b" : 9 } /* 2 */ { "_id" : ObjectId( "54c158402f512862b58738c6" ), "a" : 7, "b" : 4 } ... db.test.getIndexes(): { "0" : { "v" : 1, "name" : "_id_" , "key" : { "_id" : 1 }, "ns" : "test.test" }, "1" : { "v" : 1, "name" : "b_1" , "key" : { "b" : 1 }, "ns" : "test.test" }, "2" : { "v" : 1, "name" : "a_1" , "key" : { "a" : 1 }, "ns" : "test.test" } }
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      Consider the following code:

      t = db.t;
t.drop();
t.ensureIndex({a: 1});
t.ensureIndex({b: 1});
t.find({$query: {a: 1}, $orderby: {b: -1}}).explain()

      This should error with a useful message. a 2.4 server does not raise an error, whereas a 2.6 server raises an unhelpful error message. Instead, the shell could raise a useful error before sending the query to the server.

      Original Description

      I don't know if this is a bug, but the following two queries result in completely different outputs. The first output shows a full table scan whereas the second one claims to make use of the index. Which one is correct?

      query 1:

      db.java.find({ "$query" : { "a" : 1} , "$orderby" : { "b" : -1}}).explain()
{
    "cursor" : "BasicCursor",
    "isMultiKey" : false,
    "n" : 0,
    "nscannedObjects" : 100,
    "nscanned" : 100,
    "nscannedObjectsAllPlans" : 100,
    "nscannedAllPlans" : 100,
    "scanAndOrder" : false,
    "indexOnly" : false,
    "nYields" : 0,
    "nChunkSkips" : 0,
    "millis" : 0,
    "indexBounds" : {},
    "server" : "XXXX"
}

      query 2:

      db.java.find({ "$query" : { "a" : 1} , "$orderby" : { "b" : -1}, "$explain" : true})
/* 0 */
{
    "cursor" : "BtreeCursor a_1",
    "isMultiKey" : false,
    "n" : 6,
    "nscannedObjects" : 6,
    "nscanned" : 6,
    "nscannedObjectsAllPlans" : 19,
    "nscannedAllPlans" : 19,
    "scanAndOrder" : true,
    "indexOnly" : false,
    "nYields" : 0,
    "nChunkSkips" : 0,
    "millis" : 0,
    "indexBounds" : {
        "a" : [ 
            [ 
                1, 
                1
            ]
        ]
    },
    "allPlans" : [ 
        {
            "cursor" : "BtreeCursor b_1 reverse",
            "n" : 0,
            "nscannedObjects" : 7,
            "nscanned" : 7,
            "indexBounds" : {
                "b" : [ 
                    [ 
                        {
                            "$maxElement" : 1
                        }, 
                        {
                            "$minElement" : 1
                        }
                    ]
                ]
            }
        }, 
        {
            "cursor" : "BtreeCursor a_1",
            "n" : 6,
            "nscannedObjects" : 6,
            "nscanned" : 6,
            "indexBounds" : {
                "a" : [ 
                    [ 
                        1, 
                        1
                    ]
                ]
            }
        }, 
        {
            "cursor" : "BasicCursor",
            "n" : 0,
            "nscannedObjects" : 6,
            "nscanned" : 6,
            "indexBounds" : {}
        }
    ],
    "oldPlan" : {
        "cursor" : "BtreeCursor a_1",
        "indexBounds" : {
            "a" : [ 
                [ 
                    1, 
                    1
                ]
            ]
        }
    },
    "server" : "nbwinviemg:27017"
}

            Assignee:
            Matt Kangas (Inactive)
            Reporter:
            Musti
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            Watchers:
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              Created:
              Updated:
              Resolved: