Info
If a regex query contains an escaped pipe symbol it is not handled as an escaped | but as an OR. Only if the pipe is double escaped ( \ \ | ) it is being handle as an escaped |.
Steps to Reproduce
Setup test data:
for(var i=0; i < 100; i++) { db.regexTest.insertOne({name:"test|"+i})}
The follwoing query should only return a single document, but instead it returns all:
db.regexTest.find({name: { $regex: "^test\|18"}})
If a double escape is being used, then it matches only a single document:
db.regexTest.find({name: { $regex: "^test\\|18"}})
The results are the same if an index is being used.
However because of the related bug SERVER-16622 in the classification of the regex, the regex is classified as complex and the wrong index bounds are being used:
db.regexTest.createIndex({name:1})
db.regexTest.find({name: { $regex: "^test\\|18"}}).explain()
{
"queryPlanner": {
"plannerVersion": 1,
"namespace": "test.regexTest",
"indexFilterSet": false,
"parsedQuery": {
"name": /^test\|18/
},
"winningPlan": {
"stage": "FETCH",
"inputStage": {
"stage": "IXSCAN",
"filter": {
"name": /^test\|18/
},
"keyPattern": {
"name": 1
},
"indexName": "name_1",
"isMultiKey": false,
"multiKeyPaths": {
"name": [ ]
},
"isUnique": false,
"isSparse": false,
"isPartial": false,
"indexVersion": 2,
"direction": "forward",
"indexBounds": {
"name": [
"[\"\", {})",
"[/^test\\|18/, /^test\\|18/]"
]
}
}
},
"rejectedPlans": [ ]
},
