Demo does not have an access modifier, and the default classes are internal , so it is less accessible than the DbSet Demo , which is public . In addition, you should probably call DbSet Demos so as not to confuse them, and since it semantically contains a set of demos.
Since the kit is publicly available:
public DbSet<Demo> Demo { get; set; }
You also need to make the Demo class public:
public class Demo { .... }
As already mentioned, I also suggest changing the set:
public DbSet<Demo> Demos { get; set; }
so that you do not confuse the set with the class type.
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