How to diff two versions of same object ?

Question

I want to compare two objects of different versions and display their differences in UI.

First I call a method to know if there is any difference between the two objects

The method is:

public bool AreEqual(object object1,object object2, Type comparisionType)

If the above method returns true, I call the GetDifferences method to get the differences which is:

public ObjectDifference[] GetObjectDifferences(object object1, object object2, Type comparisionType)
{
  ArrayList memberList = new ArrayList();
  ArrayList differences = new ArrayList();

  memberList.AddRange(comparisionType.GetProperties());
  memberList.AddRange(comparisionType.GetFields());

  for (int loopCount = 0; loopCount < memberList.Count; loopCount++)
  {
    object objVal1 = null;
    object objVal2 = null;
    MemberInfo member = ((MemberInfo)memberList[loopCount]);
    switch (((MemberInfo)memberList[loopCount]).MemberType)
    {
      case MemberTypes.Field:
        objVal1 = object1 != null ? ((FieldInfo)memberList[loopCount]).GetValue(object1) : null;
        objVal2 = object2 != null ? ((FieldInfo)memberList[loopCount]).GetValue(object2) : null;
        break;
      case MemberTypes.Property:

        objVal1 = object1 != null ? ((PropertyInfo)memberList[loopCount]).GetValue(object1, null) : null;
        objVal2 = object2 != null ? ((PropertyInfo)memberList[loopCount]).GetValue(object2, null) : null;
        break;
      default:
        break;
    }

    if (AreValuesDifferentForNull(objVal1, objVal2))
    {
      ObjectDifference obj = new ObjectDifference(objVal1, objVal2, member, member.Name);
      differences.Add(obj);
    }
    else if (AreValuesDifferentForPrimitives(objVal1, objVal2))
    {
      ObjectDifference obj = new ObjectDifference(objVal1, objVal2, member, member.Name);
      differences.Add(obj);
    }
    else if (AreValuesDifferentForList(objVal1, objVal2))
    {
      ObjectDifference[] listDifference = GetListDifferences((ICollection)objVal1, (ICollection)objVal2, member);
      differences.AddRange(listDifference);
    }
    else if ((!AreValuesEqual(objVal1, objVal2)) && (objVal1 != null || objVal2 != null))
    {
      ObjectDifference obj = new ObjectDifference(objVal1, objVal2, member, member.Name);
      differences.Add(obj);
    }
  }
  return (ObjectDifference[])differences.ToArray(typeof(ObjectDifference));
}


public class ObjectDifference
{
  private readonly object objectValue1;
  private readonly object objectValue2;
  private readonly System.Reflection.MemberInfo member;
  private readonly string description;

  public object ObjectValue1
  {
    get { return objectValue1; }
  }
  public object ObjectValue2
  {
    get { return objectValue2; }
  }
  public System.Reflection.MemberInfo Member
  {
    get { return member; }
  }
  public string Description
  {
    get { return description; }
  }

  public ObjectDifference(object objVal1, object objVal2, System.Reflection.MemberInfo member, string description)
  {
    this.objectValue1 = objVal1;
    this.objectValue2 = objVal2;
    this.member = member;
    this.description = description;
  }
}

For each difference I create an object of type ObjectDifference and add it to the array. The highlighted portion is the one where I am stuck! If the object contains another complex object, My program does give me the differences but I dont know which type it belonged to

For example, I have two objects of type Name

class Name
{
  string firstName, LastName;
  List phNumber;
}

class PhoneNumber
{
  string officeNo, MobileNo, HomeNo;
}

while comparing two objects the output I get is plain -

• firstname - John Mary
• LastName - cooper Lor
• officeNo - 22222 44444
• MobileNo - 989898 089089
• HomeNo - 4242 43535

The Hierarchy that officeNo is of type PhoneNumber is lost, which is important for me to display.

How should I maintain this type of tree while creating differences? Hope I am able to make my problem understood.

Answer 1

What you are trying to do and display is inherently complex. I've done this in the past (for diffgram/delta-based processes), and even trying to display nested changes in a simple and friendly way is tricky.

If it fits your user-base, one option might be to simply serialize the two graphs as xml, and use something like xml diff.