Question

What is the best way to compare two arbitrary dynamic objects for equality? For example these two objects.

I.e.

dynamic obj1 = new ExpandoObject();
obj1.Name = "Marcus";
obj1.Age = 39;
obj1.LengthInMeters = 1.96;

dynamic obj2 = AMethodReturningADynamic();
obj2.Name = "Marcus";
obj2.Age = 39;
obj2.LengthInMeters = 1.96;

Assert.AreEqual(obj1, obj2); // ?

Or is there a way to get the actual properties and their values as lists? To create an ExpandoObject from a dynamic type for example?

Answer 1

The Microsoft API’s for dynamically invoking methods and propertys on arbitrary dynamic objects (IDynamicMetaObjectProvider) are not easy to use when you don’t have the compiler’s help. You can use Dynamitey (via nuget) to simplify this completely. It has a static function Dynamic.InvokeGet to call property’s getters with just a target and a property name.

To get a list of properties of the dynamic object, there is a bit of a gotcha, as the dynamic object has to support it (if it’s a DynamicObject that means implementing GetDynamicMemberNames, Expando supports it, but random IDynamicMetaObjectProvider may not and just return an empty list). Dynamitey has a method to simplifying getting those names as well, Dynamic.GetMemberNames.

Both of those two functions give you the basic tools necessary to compare many arbitrary dynamic objects via properties.

//using System.Dynamic;
//using Dynamitey;
//using System.Linq;

IEnumerable<string> list1 =Dynamic.GetMemberNames(obj1);
list1 = list1.OrderBy(m=>m);
IEnumerable<string> list2 =Dynamic.GetMemberNames(obj2);
list2 = list2.OrderBy(m=>m);

if(!list1.SequenceEqual(list2))
 return false;

foreach(var memberName in list1){
 if(!Dynamic.InvokeGet(obj1, memberName).Equals(Dynamic.InvokeGet(obj2,memberName))){
    return false;
 }
}
return true;

However, if they are just your own DynamicObject subclass then it’d be easier to just follow the typical rules for implementing Equals, there really is no difference from non-dynamic objects, and just compare what you are internally using for state.