Question

I have a method which compares two objects and returns a list of all the property names which are different.

public static IList<string> GetDifferingProperties(object source, object target)
{
    var sourceType = source.GetType();
    var sourceProperties = sourceType.GetProperties();
    var targetType = target.GetType();
    var targetProperties = targetType.GetProperties();

    var properties = (from s in sourceProperties
                      from t in targetProperties
                      where s.Name == t.Name &&
                            s.PropertyType == t.PropertyType &&
                            s.GetValue(source,null) != t.GetValue(target,null)
                      select s.Name).ToList();
    return properties;
}

For example if I have two classes as follows:

public class Address
    {
        public string AddressLine1 { get; set; }
        public string AddressLine2 { get; set; }
        public string City { get; set; }
        public string State { get; set; }
        public string Zip { get; set; }
    }

       public class Employee
        {
            public string FirstName { get; set; }
            public string MiddleName { get; set; }
            public string LastName { get; set; }
            public Address EmployeeAddress { get; set; }
        }

I am trying to compare the following two employee instances:

var emp1Address = new Address();
        emp1Address.AddressLine1 = "Microsoft Corporation";
        emp1Address.AddressLine2 = "One Microsoft Way";
        emp1Address.City = "Redmond";
        emp1Address.State = "WA";
        emp1Address.Zip = "98052-6399";

        var emp1 = new Employee();
        emp1.FirstName = "Bill";
        emp1.LastName = "Gates";
        emp1.EmployeeAddress = emp1Address;


        var emp2Address = new Address();
        emp2Address.AddressLine1 = "Gates Foundation";
        emp2Address.AddressLine2 = "One Microsoft Way";
        emp2Address.City = "Redmond";
        emp2Address.State = "WA";
        emp2Address.Zip = "98052-6399";

        var emp2 = new Employee();
        emp2.FirstName = "Melinda";
        emp2.LastName = "Gates";
        emp2.EmployeeAddress = emp2Address;

So when I pass these two employee objects to my GetDifferingProperties method currently it returns FirstName and EmployeeAddress, but it does not tell me which exact property (which in this case is Address1) in the EmployeeAddress has changed. How can I tweak this method to get something like EmployeeAddress.Address1?

Answer 1

It’s because you are using != which, for objects, tests the identity of an object rather than its value. The key is to use recursion to generate the list of properties of properties. This will go as deep as you want…

public static IList<string> GetDifferingProperties(object source, object target)
{
  var sourceType = source.GetType();
  var sourceProperties = sourceType.GetProperties();
  var targetType = target.GetType();
  var targetProperties = targetType.GetProperties();

  var result = new List<string>();

  foreach (var property in
      (from s in sourceProperties
       from t in targetProperties
       where s.Name == t.Name &&
       s.PropertyType == t.PropertyType &&
       !Equals(s.GetValue(source, null), t.GetValue(target, null))
       select new { Source = s, Target = t }))
  {
    // it's up to you to decide how primitive is primitive enough
    if (IsPrimitive(property.Source.PropertyType))
    {
      result.Add(property.Source.Name);
    }
    else
    {
      foreach (var subProperty in GetDifferingProperties(
          property.Source.GetValue(source, null),
          property.Target.GetValue(target, null)))
      {
        result.Add(property.Source.Name + "." + subProperty);
      }
    }
  }

  return result;
}

private static bool IsPrimitive(Type type)
{
  return type == typeof(string) || type == typeof(int);
}