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Type:
Improvement
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Resolution: Fixed
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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:
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Fully Compatible
When executing a $merge with a whenMatched: fail option specified, the error message can be misleading. See the following example:
> db.source.find()
{ "_id" : 1, "a" : 2, "b" : 3, "c" : 4 }
{ "_id" : 2, "a" : 3, "b" : 4, "c" : 5 }
{ "_id" : 3, "a" : 4, "b" : 5, "c" : 6 }
> db.target.find()
{ "_id" : 1, "a" : 2, "black" : "sheep" }
> db.source.aggregate([
... {
... $merge: {
... into: "target",
... on: "a",
... whenMatched: "fail",
... whenNotMatched: "insert"
... }
... }
... ])
uncaught exception: Error: command failed: {
"ok" : 0,
"errmsg" : "E11000 duplicate key error collection: playground.target index: _id_ dup key: { _id: 1.0 }",
"code" : 11000,
"codeName" : "DuplicateKey",
"keyPattern" : {
"_id" : 1
},
"keyValue" : {
"_id" : 1
}
} : aggregate failed :
_getErrorWithCode@src/mongo/shell/utils.js:25:13
doassert@src/mongo/shell/assert.js:18:14
_assertCommandWorked@src/mongo/shell/assert.js:618:17
assert.commandWorked@src/mongo/shell/assert.js:708:16
DB.prototype._runAggregate@src/mongo/shell/db.js:266:5
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:1046:12
@(shell):1:1
Instead of elucidating that the operation failed because a document in the source matched one in the target collection, a duplicate key error is returned.
The error message should be updated to indicate that this is expected due to the documents matching in this case.