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Type:
Task
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Resolution: Done
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: None
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Labels:None
I try the same query in the mongo shell and the explain shows index only:
db.merchants.find({st:{"$regex" : "cr", "$options": "i"}}, {n:1, _id:1})
{ "n" : "Crab shack", "_id" : ObjectId("51c908cc1925f3ca51000001") }
{ "n" : "Tacos R Us", "_id" : ObjectId("51c16f201925f3df4300001b") }
db.merchants.find({st:{"$regex" : "cr", "$options": "i"}}, {n:1, _id:1}).explain()
{
"cursor" : "BtreeCursor st_1_n_1__id_1 multi",
"isMultiKey" : false,
"n" : 2,
"nscannedObjects" : 2,
"nscanned" : 2,
"nscannedObjectsAllPlans" : 2,
"nscannedAllPlans" : 2,
"scanAndOrder" : false,
"indexOnly" : true,
"nYields" : 0,
"nChunkSkips" : 0,
"millis" : 0,
"indexBounds" : {
"st" : [
[
"",
{
}
],
[
/cr/i,
/cr/i
]
],
"n" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
],
"_id" : [
[
{
"$minElement" : 1
},
{
"$maxElement" : 1
}
]
]
},
"server" : "Arvinds-MacBook-Pro.local:27017"
}
But the same query run from the rails console gives me:
Merchant.where({:st => { '$regex'=> "cr", '$options' => 'i' } }).only(:_id, :n).explain
=> {"cursor"=>"BtreeCursor st_1_n_1__id_1 multi", "isMultiKey"=>false, "n"=>2, "nscannedObjects"=>2, "nscanned"=>2, "nscannedObjectsAllPlans"=>2, "nscannedAllPlans"=>2, "sca
nAndOrder"=>false, "indexOnly"=>false, "nYields"=>0, "nChunkSkips"=>0, "millis"=>0, "indexBounds"=>{"st"=>[["", {}], [/cr/i, /cr/i]], "n"=>[[{"$minElement"=>1}, {"$maxElemen
t"=>1}]], "_id"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]]}, "allPlans"=>[{"cursor"=>"BtreeCursor st_1_n_1__id_1 multi", "n"=>2, "nscannedObjects"=>2, "nscanned"=>2, "index
Bounds"=>{"st"=>[["", {}], [/cr/i, /cr/i]], "n"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]], "_id"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]]}}], "oldPlan"=>{"cursor"=>"Btr
eeCursor st_1_n_1__id_1 multi", "indexBounds"=>{"st"=>[["", {}], [/cr/i, /cr/i]], "n"=>[[{"$minElement"=>1}, {"$maxElement"=>1}]], "_id"=>[[{"$minElement"=>1}, {"$maxElement
"=>1}]]}}, "server"=>"Arvinds-MacBook-Pro.local:27017"}
I suspect this is because of the only() modifier. Or is this a bug?