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Type:
Improvement
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Resolution: Unresolved
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: Aggregation Framework
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Query Optimization
$concat expression tests if all arguments passed to it are of type String and then calls coerceToString before concatenating them.
All other expressions that expect a string just call coerceToString on the argument(s) and rely on that to throw an error if the conversion is impossible.
I think all string-expecting expressions should be consistent - if the passed in value can be coerced to string then do that.
db.foo.aggregate({$project:{dateToString:{$substr:["$d",0,4]},_id:0}})
{ "dateToString" : "2017" }
db.foo.aggregate({$project:{dateToString:{$toUpper:"$d"},_id:0}})
{ "dateToString" : "2017-08-01T17:29:05" }
db.foo.aggregate({$project:{dateToString:{$toLower:"$d"},_id:0}})
{ "dateToString" : "2017-08-01t17:29:05" }
db.foo.aggregate({$project:{dateToString:{$concat:["$d","_"]},_id:0}})
assert: command failed: {
"ok" : 0,
"errmsg" : "$concat only supports strings, not date",
"code" : 16702,
"codeName" : "Location16702",
"$clusterTime" : {
"clusterTime" : Timestamp(1501608545, 1),
"signature" : {
"hash" : BinData(0,"y9mqIQNK2OhW40Hm2VIctAxrgcQ="),
"keyId" : NumberLong("6448521287567409154")
}
},
"operationTime" : Timestamp(1501608545, 1)
} : aggregate failed
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:16:14
assert.commandWorked@src/mongo/shell/assert.js:403:5
DB.prototype._runAggregate@src/mongo/shell/db.js:250:9
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1269:12
@(shell):1:1
2017-08-01T10:48:52.841-0700 E QUERY [thread1] Error: command failed: {
"ok" : 0,
"errmsg" : "$concat only supports strings, not date",
"code" : 16702,
"codeName" : "Location16702",
"$clusterTime" : {
"clusterTime" : Timestamp(1501608545, 1),
"signature" : {
"hash" : BinData(0,"y9mqIQNK2OhW40Hm2VIctAxrgcQ="),
"keyId" : NumberLong("6448521287567409154")
}
},
"operationTime" : Timestamp(1501608545, 1)
} : aggregate failed :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:16:14
assert.commandWorked@src/mongo/shell/assert.js:403:5
DB.prototype._runAggregate@src/mongo/shell/db.js:250:9
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1269:12
@(shell):1:1
I can work-around by wrapping what's passed to $concat in {{$substr:[ <expr>, 0, 99999]]] but it seems silly and inconsistent.
- is related to
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SERVER-85081 Standardize behavior of non-string inputs to string expressions
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- Closed
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- Backlog
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- related to
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SERVER-8239 $concat should fail on non-string types
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- Closed
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SERVER-6195 consider $concat to concatenate strings instead of overloading $add
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- Closed
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