[SERVER-78800] Umlauts are not converted to lower or upper case letters Created: 10/Jul/23  Updated: 27/Oct/23  Resolved: 10/Jul/23

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: 6.0.5
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Felix Pries Assignee: Yuan Fang
Resolution: Works as Designed Votes: 0
Labels: Bug
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Operating System: ALL
Steps To Reproduce:
  1. Create a new document in which a field contains umlauts.
    Example: `{"a": "äÄöÖüÜ"}`
  2. Create a new aggregation pipeline
  3. Add a project stage that contains the operation `$toLower` and/or `$toUpper`.
    Example: `{$project: {"upper": {$toUpper: "$a"}, "lower": {$toLower: "$a"}}`
Participants:

 Description   

Umlauts (äÄ,öÖ,üÜ) are not converted to their lower or upper case with the aggregation pipeline operations `$toLower` or `$toUpper`.



 Comments   
Comment by Yuan Fang [ 10/Jul/23 ]

Hi felix.pries@icloud.com

Thank you for your report. I understand that  $toLower and $toUpper are not working with äüö(and upper-case umlauts). This is expected behavior because MongoDB aggregation pipeline operator $toUpper only has a well-defined behavior for strings of ASCII characters, and the same applies to $toLower.

I can see how this behavior would be valuable for supporting non-ASCII characters. However, this JIRA project is for bug reports, but you can help get this on the radar by submitting a feature request to our MongoDB Feedback Engine.

You may also want to search and post on the MongoDB Developer Community Forums, as it's possible there are others who have guidance on how to satisfy your use case.

Regards,
Yuan

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