Need help regarding generics, interfaces, and base classes

Question

Suppose I have these two objects:

public class Object1
{
  string prop1;
  string prop2;
}

public class Object2
{
  string prop1;
  int prop2;
  int prop3;
}

and the following classes & methods:

public class Object1Service
{
  public Object1 GetObject(Object1 o) { return o; }
  public void SaveProperty2(Object1 o, string s) { o.prop2 = s; }
}

public class Object2Service
{
  public Object2 GetObject(Object2 o) { return o; }
  public void SaveProperty2(Object2 o, int i) { o.prop2 = i; }
}

How do I turn this into a generic?
I preferably need something so that the services implement an interface and just call some generic base class if possible.
Would it help if the two objects share a common parent class? If so, how will they be structured?

---

Addendum:

It's the return that is my real problem.

public T GetObjectByKey<T>(string key)
{
    using (DBEntities db = new DBEntities())
    {
        try
        {
            T returnedEntity = default(T);

            switch (EntityDictionary[typeof (T)])
            // I have a dictionary setup like this dictionary<type, string>
            {
                case "Object1" :
                    returnedEntity = ( from r in db.ObjectONESets
                                        where r.prop1 == key
                                        select new T
                                        {
                                            prop1 = r.prop1,
                                            prop2 = r.prop2
                                        }).FirstOrDefault();
                    break ;
                case "Object2" :
                    returnedEntity = ( from r in db.ObjectTWOSets
                                        where r.prop1 == key
                                        select new T
                                        {
                                            prop1 = r.prop1,
                                            prop2 = r.prop2,
                                            prop3 = r.prop3
                                        }).FirstOrDefault();
                    break ;
            }
            return returnedEntity;
        }
        catch (NullReferenceException )
        {
            return default(T);
        }
    }
}

Without putting ALL my object properties in the base object, it has no way of knowing that prop1-3 is a property of T.
If I do put all properties (common or not) in the base object, and if I need Object1, it then has a prop3 attached to it which I do not need.
I'm not sure if I'm making much sense at this point, or if what I'm asking is even doable with Generics.

Answer 1

Justin is correct, without modifying the OP's objects, there is no way to make this "neatly" generic.

Here is a messy solution:

interface IObject<T>
{
    T prop2 {get;set;}
}

class ObjectService<T, Z> where T : IObject<Z>
{
    public T GetObject(T o)
    {
        return o;
    }

    public void SetValue(T o, Z val)
    {
        o.prop2 = val;
    }
}

Answer 2

Here is a solution which should do what you're after:

public interface IPropertyProvider<T>
{
    T Prop2 { get; set; }
}

public class ObjectService<T, TProp> where T : IPropertyProvider<TProp>
{
    public void SaveProperty(T o, TProp i)
    {
        o.Prop2 = i;
    }
}

public class Object1 : IPropertyProvider<string>
{
    public string Prop1 { get; set; }
    public string Prop2 { get; set; }
}

public class Object2 : IPropertyProvider<int>
{
    public string Prop1 { get; set; }
    public int Prop2 { get; set; }
    public int Prop3 { get; set; }
}

public class Object1Service : ObjectService<Object1, string>
{
}

public class Object2Service : ObjectService<Object2, int>
{
}

Answer 3

I believe that you will not gain a benefit with generics here. The reason is because prop2 is a different type in each of these classes. If they were the same, then you could put the common properties into a base class and do something like this

public class BaseObject
{
    string prop1;
    string prop2
}

public class Object1 : BaseObject
{

}

public class Object2 : BaseObject
{
    int prop3;
}

public class ObjectService<T> where T is BaseObject
{
    public T GetObject(T o) { return o; }
    public void SaveProperty2(T o, string i) { o.prop2 = i; }
}

You could at least make the GetObject a generic using your current example...however that entire method really seems pointless:

public class ObjectService
{
  public T GetObject<T>(T o) { return o; }
  public void SaveObject2Property2(Object2 o, int i) { o.prop2 = i; }
  public void SaveObject1Property2(Object1 o, string s) { o.prop2 = s; }
}