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Type:
Bug
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Resolution: Done
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Priority:
Minor - P4
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None
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Affects Version/s: 3.0.5
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Component/s: Aggregation Framework
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Labels:None
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ALL
The following behavior seems like a bug to me:
> db.test.insert({ "_id" : ObjectId("55d386eeb4a9494cd24e94fc"), "name" : "test", "myarray" : [ ] });
WriteResult({ "nInserted" : 1 })
> db.test.aggregate([{'$group' : {'_id' : '$name', 'thing' : {'$first' : '$myarray.made_up_field'}}}]);
{ "_id" : "test", "thing" : [ ] }
Why does "thing" get set to an empty array? It should be null?
I ran into this problem while doing a $push like the following during a $group phase
'inventory' => ['$push' => [ warehouse' => '$sku.inventory.warehouse', at_once' => '$sku.inventory.at_once' ]]
and getting an empty array for warehouse often times instead of a string when sku.inventory was an empty array.