How to save data in C# ASP.NET MVC without using database?

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C#

ASP.NET

repository

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 BD.
I'm trying to store data in memory without using db. I don't now how to add new item?
This is my Clas DataBase (repository)

What I have tried:

<pre><pre lang="c#">public class DataBase : IDataBase
{
    private List<Proveedor> proveedors;
    private List<Factura> facturas;
    private List<FacturadeArticulo> facturadeArticulos;

    public  DataBase()
    {
        this.proveedors= new List<Proveedor>();
        this.facturas= new List<Factura>();
        this.facturadeArticulos= new List<FacturadeArticulo>();
    }
    public Proveedor AddProveedor(Proveedor item)
    {
        // acces db
            if (item == null)  
            {  
                throw new ArgumentNullException("item");  
            }  
  
            users.Add(item);  
            return item; 

    }
}

My interface IDataBase

public interface IDatabase
    {
        Proveedor Add(Proveedor item);

    }

Is that possible in this way save data in memory..Tnx