Details
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Type:
Bug
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Status: Closed
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Priority:
Major - P3
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Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: 4.3.1
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Component/s: Aggregation Framework
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Labels:
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Backwards Compatibility:Minor Change
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Operating System:ALL
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Sprint:Query 2019-09-23, Query 2019-10-07
Description
> db.foo.find()
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{ "_id" : 2 }
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{ "_id" : 1, "x" : null }
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{ "_id" : 3, "y" : null }
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{ "_id" : 4, "x" : null, "y" : null }
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> db.foo.aggregate([{$group: {_id: ["$x", "$y"]}}])
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{ "_id" : [ "$x", "$y" ] }
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> db.foo.aggregate([{$group: {_id: {z: ["$x", "$y"]}}}])
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{ "_id" : { "z" : [ null, null ] } }
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I would contend that the middle one should result in
{_id: [null, null]}
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Looks like this is the offending line.