Hi @Ralph Foster ,
You could create provider-hosted add-in for sharepoint: https://learn.microsoft.com/en-us/sharepoint/dev/sp-add-ins/get-started-creating-provider-hosted-sharepoint-add-ins
Then use Entity Framework in it.
You could refer to this article: https://www.c-sharpcorner.com/uploadfile/a30324/provider-hosted-sharepoint-add-in-with-sql-database-in-azure/
Here is a similar question: https://social.technet.microsoft.com/Forums/en-US/41f96a3e-5ff3-4316-a3b5-8d6a689a66ec/entity-framework-for-sharepoint-online-list?forum=onlineservicessharepoint
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