Create a class that simulates the DB in ASP.NET MVC

I am developing an application with ASP.NET MVC using Visual Studio 2017 applying the Code First approach. I have three classes (tables) in the model and I am trying to create a class that simulates the BBDD.

 

With class DataBase I'm trying to make simulated Data Base. Is it possible to do the following? 

 

public class DataBase { 

private static List<Proveedor> proveedors= new ArrayList();

private static List<Factura> facturas= new ArrayList();

private static List<FacturadeArticulo> facturadeArticulos= new ArrayList(); 

public static getProveedor() { return proveedors; } 

public static getFactura() {

 return facturas; } 

public static getFacturadeArticulo() 

{ return facturadeArticulos; } 

}

I need to do this and save data in memory without using database. Thank you.