In your EntityTypeConfiguration you can do something like this:
Property(m => m.CompanyId)
.HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute("IX_YourUniqueIndexName", 1) { IsUnique = true }));
Property(m => m.Code)
.HasColumnAnnotation("Index", new IndexAnnotation(new IndexAttribute("IX_YourUniqueIndexName", 2) { IsUnique = true }));
This will create a unique index on those 2 columns.
Make sure you use the same name for the unique index. Both need to be name “IX_YourUniqueIndex”. If one is called “IX_Index1” and the other “IX_Index2” then it will create a unique index on each, which is not what you want
solved how can create Unique Constraint with multi column with entityframework