What is the best way to instance of base class to instance of derived class in C# 4.0?

Question

Now, I am working on ASP.NET MVC 2. I just found some serious problem about View Model class that derives from base class in Model project. Every time when I fetch data from database, I have to cast it to View Model instance that is not possible in most OOP language.

Base class

public class MyBaseClass
{
    public string ID { get;set; }
    public string Value { get;set; }
}

Derived class

public class MyDerivedClass : MyBaseClass, ISomeInterface
{
    // logic for My Derived Class
}

However, I try to create some method that copy all readable property from instance of base class to instance of derived class like the following code.

public static TDerived CastObject<TBase, TDerived>(TBase baseObj)
{
    Type baseType = typeof(TBase);
    Type derivedType = typeof(TDerived);

    if (!baseType.IsAssignableFrom(derivedType))
    {
        throw new Exception("TBase must be a parent of TDerived.");
    }

    TDerived derivedObj = Activator.CreateInstance<TDerived>();

    foreach (PropertyInfo pi in baseType.GetProperties())
    {
        if (pi.CanRead)
        {
            PropertyInfo derivedProperty = derivedType.GetProperty(pi.Name);

            if (derivedProperty.CanWrite)
            {
                derivedProperty.SetValue(derivedObj, pi.GetValue(baseObj, null), null);
            }
        }
    }

    return derivedObj;
}

But I do not sure about the above code that will work great on large-scale website and there are a lot of feature in DLR of C# 4.0 that I do not know.

Do you have any idea for converting item by using C# 4.0?

Thanks,

Answer 1

Is there any reason why the base type couldn't have a constructor which took an instance to copy data from?

public class MyBaseClass
{
    public string ID { get;set; }
    public string Value { get;set; }

    public MyBaseClass() {}

    public MyBaseClass(MyBaseClass other)
    {
        ID = other.ID;
        Value = other.Value;
    }
}


public class MyDerivedClass : MyBaseClass, ISomeInterface
{
    public MyDerivedClass(MyBaseClass other) : base(other)
    {           
    }
}

Alternatively, could you do this with composition instead of inheritance? Could your derived class keep a reference to the instance of MyBaseClass to get its value and ID from?

Finally, could you change the data access layer so that it could create an instance of the right class to start with?