It is ASP.Net Core architecture utilizing EntityFramework Core at time 34:05 in the video I'm watching. They are demonstrating an extension method.
It gives the following problem when I try this in my code: No available extension method taking a first parameter of type "ModelBuilder" and no definition for "ApplyAllConfigurations" in the class "ModelBuilder" could be located. (Are you missing a using directive or an assembly reference?
Do I need another reference? Otherwise, how can I include this into my project?