Facade a class without writing lots of boilerplate code?

Question

Let's say I have a class from a 3rd-party, which is a data-model. It has perhaps 100 properties (some with public setters and getters, others with public getters but private setters). Let's call this class ContosoEmployeeModel

I want to facade this class with an interface (INavigationItem, which has Name and DBID properties) to allow it to be used in my application (it's a PowerShell provider, but that's not important right now). However, it also needs to be usable as a ContosoEmployeeModel.

My initial implementation looked like this:

public class ContosoEmployeeModel
{
    // Note this class is not under my control. I'm supplied
    // an instance of it that I have to work with.

    public DateTime EmployeeDateOfBirth { get; set; }
    // and 99 other properties.
}

public class FacadedEmployeeModel : ContosoEmployeeModel, INavigationItem
{
    private ContosoEmployeeModel model;
    public FacadedEmployeeModel(ContosoEmployeeModel model)
    {
        this.model = model;
    }

    // INavigationItem properties
    string INavigationItem.Name { get; set;}

    int INavigationItem.DBID { get; set;}

    // ContosoEmployeeModel properties
    public DateTime EmployeeDateOfBirth
    {
        get { return this.model.EmployeeDateOfBirth; }
        set { this.model.EmployeeDateOfBirth = value; }
    }
    // And now write 99 more properties that look like this :-(
}

However, it's clear that this will involve writing a huge amount of boilerplate code to expose all the properties , and I'd rather avoid this if I can. I can T4 code-generate this code in a partial class, and will do if there aren't any better ideas, but I though I'd ask here to see if anyone had any better ideas using some super wizzy bit of C# magic

Please note - the API I use to obtain the ContosoEmployeeModel can only return a ContosoEmployeeModel - I can't extend it to return a FacededEmployeeModel, so wrapping the model is the only solution I can think of - I'm happy to be corrected though :)

Answer 1

The other approach may be suitable for you is to use AutoMapper to map base class to your facade here is sample code:

class Program
    {
        static void Main(string[] args)
        {
            var model = new Model { Count = 123, Date = DateTime.Now, Name = "Some name" };

            Mapper.CreateMap<Model, FacadeForModel>();
            var mappedObject = AutoMapper.Mapper.Map<FacadeForModel>(model);

            Console.WriteLine(mappedObject);

            Console.ReadLine();
        }

        class Model
        {
            public string Name { get; set; }

            public DateTime Date { get; set; }

            public int Count { get; set; }
        }

        interface INavigationItem
        {
            int Id { get; set; }

            string OtherProp { get; set; }
        }

        class FacadeForModel : Model, INavigationItem
        {
            public int Id { get; set; }

            public string OtherProp { get; set; }
        }
    }

Answer 2

Resharper allows the creation of "delegating members", which copies the interface of a contained object onto the containing object and tunnels the method calls/property access through to the contained object.

http://www.jetbrains.com/resharper/webhelp/Code_Generation__Delegating_Members.html

Once you've done that, you can then extract an interface on your proxy class.