Inherited C# Class Losing "Reference"

Question

I have a partial class using an interface because I can’t inherit what was an original abstract class due to the other partial class being auto-generated from Entity Framework 4 and therefore already inheriting ObjectContext.

I have the following for my partial class:

namespace Model
{
    using Microsoft.Practices.EnterpriseLibrary.Validation;
    using Microsoft.Practices.EnterpriseLibrary.Validation.Validators;
    using Utilities.BusinessRules;
    using Utilities.BusinessRules.Rules;

    [HasSelfValidation]
    public partial class MyObject : IBusinessObject
    {
        private readonly IBusinessObject businessObject = new BusinessObject();

        private IBusinessObject BusinessObject
        {
            get
            {
                return businessObject;
            }
        }

        public Comment()
        {
            AddRule(new ValidateRequired("Title"));
        }

        public void AddRule(BusinessRule rule)
        {
            BusinessObject.AddRule(rule);
        }

        [SelfValidation]
        public void Validate(ValidationResults results)
        {
            BusinessObject.Validate(results);
        }
    }
}

Here’s the interface:

namespace Utilities.BusinessRules
{
    using Microsoft.Practices.EnterpriseLibrary.Validation;

    public interface IBusinessObject
    {
        void AddRule(BusinessRule rule);

        void Validate(ValidationResults results);
    }
}

And the implementation:

namespace Utilities.BusinessRules
{
    using System.Collections.Generic;
    using System.Linq;
    using Microsoft.Practices.EnterpriseLibrary.Validation;
    using Microsoft.Practices.EnterpriseLibrary.Validation.Validators;

    public class BusinessObject : IBusinessObject
    {
        private readonly IList<BusinessRule> businessRules = new List<BusinessRule>();

        public void AddRule(BusinessRule rule)
        {
            this.businessRules.Add(rule);
        }

        [SelfValidation]
        public void Validate(ValidationResults results)
        {
            foreach (var rule in this.businessRules)
            {
                if (!rule.Validate(this))
                {
                     results.AddResult(new ValidationResult(rule.ErrorMessage, this, rule.Key, rule.Tag, null));
                }
            }
        }
    }
}

Don’t worry about the rules, they work. The problem is if I use an abstract class in a test project, the Validate() method in BusinessObject will correctly identity (this) as whatever class inherited the abstract class (in this example, I would expect that to be MyObject). Unfortunately, switching to an Interface, (this) loses the inheriting class and instead identifies this as BusinessObject.

How can I make it so the inheriting class is properly identified?

Here’s the calling console class:

namespace ModelConsumer
{
    using Model;
    using System;
    using Microsoft.Practices.EnterpriseLibrary.Validation;

    class Program
    {
        static void Main(string[] args)
        {
            using (var myEntities = new MyEntities())
            {
                var myObject= new MyObject();

                myObject.Title = "Credo";

                var validationResults = Validation.Validate(myObject);

                if (validationResults.IsValid)
                {
                    myEntities.MyObjects.AddObject(myObject);
                    //myEntities.SaveChanges();

                    Console.WriteLine("Valid.");
                }
                else
                {
                    foreach (var validationResult in validationResults)
                    {
                        Console.WriteLine(validationResult.Message);
                    }
                }

                Console.Read();
            }
        }
    }
}

This should be valid but will instead be invalid because (this) is identified as being type BusinessObject instead of MyObject.

Argh! I'm so close, it's pretty vexing.

Richard

Answer 1

I believe that your implementation of BusinessObject is written assuming that it would be inherited. However, now that you r using it as a composed object, you need to make few changes:

public interface IBusinessObjectValidator
{
  void AddRule(BusinessRule rule);

  void Validate(IBusinessObject target, ValidationResults results);
}


Public class BusinessObject: IBusinessObjectValidator
{
...

  public void Validate(IBusinssObject target, ValidationResults results)
  {
      foreach (var rule in this.businessRules)
      {
          if (!rule.Validate(target))
          {
             results.AddResult(new ValidationResult(rule.ErrorMessage, target, rule.Key, rule.Tag, null));
          }
      }
  }
}

And you will use it as follows:

[HasSelfValidation]
    public partial class MyObject : IBusinessObject
    {
        private readonly IBusinessObjectValidator validator = new BusinessObject();

        private IBusinessObjectValidator BusinessObjectValidator
        {
            get
            {
                return validator ;
            }
        }
    public Comment()
    {
        AddRule(new ValidateRequired("Title"));
    }

    public void AddRule(BusinessRule rule)
    {
        validator .AddRule(rule);
    }

    [SelfValidation]
    public void Validate(ValidationResults results)
    {
        validator.Validate(this, results);
    }
}

Essentially, we are saying that we will have an implementation of validator externally and hence, we need to have target object (that is being validated) passed to the validate method. I would also suggest to rename BusinessObject as BusinessObjectValidtor.