Is there an easy way to merge C# anonymous objects

Question

Let's say I have two anonymous objects like this:

var objA = new { test = "test", blah = "blah" };
var objB = new { foo = "foo", bar = "bar" };

I want to combine them to get:

new { test = "test", blah = "blah", foo = "foo", bar = "bar" };

I won't know what the properties are for both objA and objB at compile time. I want this to be like jquery's extend method.

Anybody know of a library or a .net framework class that can help me do this?

Answer 1

If you truly do mean dynamic in the C# 4.0 sense, then you can do something like:

static dynamic Combine(dynamic item1, dynamic item2)
{
    var dictionary1 = (IDictionary<string, object>)item1;
    var dictionary2 = (IDictionary<string, object>)item2;
    var result = new ExpandoObject();
    var d = result as IDictionary<string, object>; //work with the Expando as a Dictionary

    foreach (var pair in dictionary1.Concat(dictionary2))
    {
        d[pair.Key] = pair.Value;
    }

    return result;
}

You could even write a version using reflection which takes two objects (not dynamic) and returns a dynamic.

Answer 2

Using TypeDescriptor

As mentioned in comments, Luke Foust solution does not work with anonymous types. The cast to Dictionary does not work, I propose to construct the Dictionaries using the TypeDescriptor.GetProperties method:

public static dynamic CombineDynamics(object object1, object object2)
{
  IDictionary<string, object> dictionary1 = GetKeyValueMap(object1);
  IDictionary<string, object> dictionary2 = GetKeyValueMap(object2);

  var result = new ExpandoObject();

  var d = result as IDictionary<string, object>;
  foreach (var pair in dictionary1.Concat(dictionary2))
  {
    d[pair.Key] = pair.Value;
  }

  return result;
}

private static IDictionary<string, object> GetKeyValueMap(object values)
{
  if (values == null)
  {
    return new Dictionary<string, object>();
  }

  var map = values as IDictionary<string, object>;
  if (map == null)
  {
    return map;
  }

  map = new Dictionary<string, object>();
  foreach (PropertyDescriptor descriptor in TypeDescriptor.GetProperties(values))
  {
    map.Add(descriptor.Name, descriptor.GetValue(values));
  }

  return map;
}

It's now working with anonymous types:

var a = new {foo = "foo"};
var b = new {bar = "bar"};

var c = CombineDynamics(a, b);

string foobar = c.foo + c.bar;

---

Notes:

My GetKeyValueMap method is based on the RouteValueDictionary class (System.Web.Routing). I've rewritten it (using ILSpy to disassemble it) because I think that a System.Web class has nothing to do with object merging.