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    Type:Bug 
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    Resolution: Fixed
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    Priority:Major - P3 
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    Affects Version/s: 4.0.0, 4.2.0, 4.4.0, 5.0.0, 6.0.0, 6.3.0-rc3
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    Component/s: Write Ops
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        Query Optimization
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        Minor Change
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        ALL
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        v7.0, v6.3, v6.0, v5.0, v4.4, v4.2
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        QO 2023-05-15, QO 2023-05-29
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        None
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The update subsystem lacks the equivalent of all of these lines from fixDocumentForInsert() to check the document doesn't have multiple _id fields when inserted by an update sent with upsert=true.
- is related to
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                    SERVER-4830 Reject upsert if would create duplicate field names -         
- Closed
 
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                    SERVER-19361 Insert of document with duplicate _id fields should be forbidden -         
- Closed
 
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- related to
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                    SERVER-77858 Collection validation and dbCheck should error if document has an invalid _id -         
- Open
 
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                    SERVER-78093 Investigate and add test cases to validate query behavior in the presence of duplicate fields -         
- Backlog
 
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