setting onelake security column level security programmatically

Hi kjetil_hamre, 

Welcome to the fun of preview features - don't try and push this into production until it becomes GA. 

This is interesting, the error message you are getting states that lakehouses with schemas (also in preview and should not be in use in production) aren't supported, but the documentation seems to say otherwise: 

https://learn.microsoft.com/en-us/rest/api/fabric/core/onelake-data-access-security/create-or-update-data-access-roles?tabs=HTTP#columnconstraint

Are you able to do this via the UI at all? 
https://learn.microsoft.com/en-us/fabric/onelake/security/get-started-onelake-security

If you can, there might be a bug with the API. 

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