Showing how to use expressions with constructors to drive strongly typed validation.

FieldValidationAfter.cs

    public class FieldValidation
    {
        public FieldValidation(string fieldName, string message)
        {
            FieldName = fieldName;
            Message = message;
        }

        public string FieldName { get; set; }
        public string Message { get; set; }
    }

    public class FieldValidation<T> : FieldValidation where T : class
    {
        public FieldValidation(
            Expression<Func<T, object>> expression,
            string message)
        {
            //Will work for reference types
            var body = expression.Body as MemberExpression;

            if (body == null)
            {
                //Will work for value types
                var uBody = (UnaryExpression)expression.Body;
                body = uBody.Operand as MemberExpression;
            }


            if (body == null)
                throw new ArgumentException("Invalid property expression");

            FieldName = body.Member.Name;
            Message = message;
        }
    }

FieldValidationBefore.cs

    public class FieldValidation
    {
        public FieldValidation(string fieldName, string message)
        {
            FieldName = fieldName;
            Message = message;
        }

        public string FieldName { get; set; }
        public string Message { get; set; }
    }

HowItIsUsed.cs

//#1 Specify field name up front - how we currently use this
var oldSchoolValidation = new FieldValidation(
  "WithAProperty", "Message of some kind...");

//#2 Field name driven directly by property - how we want to use this
var newSchoolValidation = new FieldValidation<AnObject>(
  x => x.WithAProperty, "Message of some kind...");

/// <summary>
/// Example class for demo
/// </summary>
public class AnObject
{
  public bool WithAProperty { get; set; }
}