SQL Connection in AutoCAD 2025
Which version of Microsoft.EntityFrameworkCore Nuget package did you add to your project? You should not add latest version of 9.x.x, because it is for .NET 9 or later, while AutoCAD 2025/6 uses .NET 8. That is, the if you use EntityFrameworkCore in your Acad plugin, it should ne version 8.x.x or older.
However, EntityFrameworkCore is meant for building enterprise business entities and being accessed via service apps for data consuming user apps (AutoCAD, in this case). At this stage of technology progress, it would be better (and a trend) to avoid direct access to the database server from an user app. The data from a data source should be exposed as a services, typically, a HTTP service, and your Acad plugin uses HTTP client to reach the data.
If you really want to directly get data from database server, say, your data needs are very simple and want to save the effort of building an extra service layer, and the database admin does allow you to have access directly (this kind of DB admin would hard to find these days), you want to consider use much light technologies for database server access, say, considering to use Dapper (do a online search, there are a plenty of links, samples about how easy/simple Dapper would make the database server access be).
