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Type:
Improvement
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Resolution: Done
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: Aggregation Framework
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Labels:None
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Fully Compatible
Currently when a document has nested array based documents, $unwind only shows records where parent documents contain the $unwind field. It would be useful in certain scenarios to have an $unwind stage with some other optional configuration, which will produce an output document for a document that does not contain the $unwind field.
In a collection with the following documents:
{
"FirstName" : "John",
"LastName" : "Doe",
"Notes" : [
{
"CustomerId" : DBRef("Customer", 1002),
"PostDate" : ISODate("2014-02-05T00:04:45Z"),
"Comment" : "Rocks"
},
{
"CustomerId" : DBRef("Customer", 1002),
"PostDate" : ISODate("2014-02-05T04:06:45Z"),
"Comment" : "Sucks"
}
],
"_id" : 1002
}
{
"FirstName" : "Jane",
"LastName" : "Smith",
"_id" : 1001
}
When you run this pipeline:
db.coll.aggregate([{$unwind: '$Notes'}])
You get the following results:
{
"FirstName" : "John",
"LastName" : "Doe",
"Notes" :
{
"CustomerId" : DBRef("Customer", 1002),
"PostDate" : ISODate("2014-02-05T00:04:45Z"),
"Comment" : "Rocks"
},
"_id" : 1002
}
{
"FirstName" : "John",
"LastName" : "Doe",
"Notes" :
{
"CustomerId" : DBRef("Customer", 1002),
"PostDate" : ISODate("2014-02-05T04:06:45Z"),
"Comment" : "Sucks"
}
],
"_id" : 1002
}
It would be nice if it also returned the following result:
{ "_id" : 1001,
"FirstName" : "Jane",
"LastName" : "Smith"
}
Here is user groups discussion on this topic
https://groups.google.com/forum/#!topic/mongodb-user/UKYPddRN37E
There is workaround exists using the $IFNULL, see the above link.
- is depended on by
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SERVER-19095 $lookup
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- Closed
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- related to
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SERVER-8088 $unwind of non-array should be allowed
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- Closed
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- Closed
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