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Type:
Bug
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Resolution: Duplicate
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Priority:
Major - P3
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Affects Version/s: 3.6.23, 4.2.17
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Component/s: None
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The $regex operation accepts invalid expressions when used inside an aggregate command. For example, the regular expression ^+somestring is not valid. However, Mongo executes the following command without any error:
{
"aggregate": "PayeeReputationByPayeeAndLegalEntity",
"pipeline": [
{
"$match": {
"_id": {
"$regex": "^+somestring",
"$options": ""
}
}
}
],
"explain": true
}
The problem is that the query plan for the above aggregation is the following:
{
"waitedMS": NumberLong(0),
"stages": [
{
"$cursor": {
"query": {
"_id": {
"$regex": "^+somestring",
"$options": ""
}
},
"queryPlanner": {
"plannerVersion": 1,
"namespace": "db.some-collection"
"indexFilterSet": false,
"parsedQuery": {
"_id": /^+somestring/
},
"winningPlan": {
"stage": "FETCH",
"inputStage": {
"stage": "IXSCAN",
"filter": {
"_id": /^+somestring/
},
"keyPattern": {
"_id": 1
},
"indexName": "_id_",
"isMultiKey": false,
"isUnique": true,
"isSparse": false,
"isPartial": false,
"indexVersion": 1,
"direction": "forward",
"indexBounds": {
"_id": [
"[\"\", {})",
"[/^+somestring/, /^+somestring/]"
]
}
}
},
"rejectedPlans": []
}
}
}
],
"ok": 1.0
}
As we can notice, the indexBounds information is completely nonsense:
"indexBounds": { "_id": [ "[\"\", {})", "[/^+somestring/, /^+somestring/]" ] }
The above bound makes the database perform a full index-scan. Adding an escape character in front of the + character doesn't change the situation. So, the expression ^+somestring produces the same effects.
The real problem is that the above command is the command generated by Spring Data MongoDB. In this case, there is no workaround 
I didn't try to reproduce it on version 5.x of Mongo, but I'm quite sure that the bug persists.
- duplicates
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SERVER-39698 Make $regexFind, $regexFindAll, and $regexMatch error if the regex is invalid
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- Closed
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