C# Extend a class dynamically to include more fields during execution

Question

I have a class

 Class account {
    Int id ;
 }

I want change it on the run to

 Class account {
     Int id;
     String Name;
 }

And I want to make a object of newly modified class

Is this possible, it would be really helpful

You can't just dynamically change a class at execution time. You could *derive* a new class, if you want... — Jon Skeet, Jun 05 '16 at 16:43
You could possibly do this using castle dynamic proxy [http://kozmic.net/dynamic-proxy-tutorial/](http://kozmic.net/dynamic-proxy-tutorial/) has a good tutorial — pquest, Jun 05 '16 at 16:57
try the `dynamic` type: https://msdn.microsoft.com/en-us/library/dd264736.aspx — Stefan, Jun 05 '16 at 17:05

LuqJensen · Answer 1 · 2016-06-05T17:15:37.170

Im not to say that it is impossible, but i would think it is not. Instead you can use Entity Composition like so

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            Account a = new Account();
            a.Add("My name is John");
            a.Add(10);

            Console.WriteLine(a.Get<int>(typeof(int)));
            Console.WriteLine(a.Get<string>(typeof(string)));
            Console.ReadLine();
        }
    }

    class Account
    {
        private Dictionary<Type, object> _fields = new Dictionary<Type, object>();

        public void Add(object data)
        {
            _fields.Add(data.GetType(), data);
        }

        public void Remove(Type type)
        {
            _fields.Remove(type);
        }

        public T Get<T>(Type type)
        {
            object data = null;
            if (_fields.TryGetValue(type, out data))
            {
                return (T)data;
            }

            return default(T);
        }
    }
}

You can add any class and retrieve it again. I recommend using a wrapper class even for the simplest fields, otherwise you may prevent yourself from adding more fields of type string. For example you cannot add both a name and a surname, you will have to wrap them in a Name and Surname class. Now if you want to do this during runtime, you will have to also look into using a component framework such as MEF

We have used this very approach above to develop a component based game in Java using the Netbeans Platform. So yes it is indeed possible. Although you should be aware that patterns like this do add some overhead. — LuqJensen, Jun 05 '16 at 17:19

score 1 · Answer 2 · edited May 23 '17 at 12:34

1

It seems like it's not possible. However, you could use a different approach:

 var account = new Dictionary<string, object>();
 account["id"] = 42;
 account["name"] = "my name";

Which will probably be more performance-friendly rather than trying to add another field.

Edit

Following @LuqJensen answer, who would have issues if adding, for example, two strings, you could as well do:

class Account
{
    private Dictionary<string, object> _fields = new Dictionary<Type, object>();

    public void Set(string name, object data)
    {
        _fields[name] = data;
    }

    public T Get<T>(string name)
    {
        object data = null;
        if (_fields.TryGetValue(type, out data))
            return (T)data;

        return default(T);
    }
}

edited May 23 '17 at 12:34

Community

1
1

answered Jun 05 '16 at 16:48

Lonami

5,945
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Wow, missed that dynamic thing... Thanks – Jun 05 '16 at 16:55
Sorry @ArunprasadesEdathadan I couldn't test it. It isn't working, but I've updated my answer – Lonami Jun 05 '16 at 17:00
Not only looks, but **is** impossible. The above just doesn't work (you get runtime exception). – Ivan Stoev Jun 05 '16 at 17:01
There must be some way to achieve this – Jun 05 '16 at 17:03
You must add the key/values before accessing. – Stefan Jun 05 '16 at 17:06
@Stefan actually, you don't need to use .Add(...) before! – Lonami Jun 05 '16 at 17:07
My requirement is actually with the entity framework classes, I have a class, if any changes are made, i need to add few more details like who,time,etc to the object and save it as a another object... – Jun 05 '16 at 17:08
Your better approach is to use a dictionary in my opinion. It's easy to serialize as well. – Lonami Jun 05 '16 at 17:12
You missed the text below. I advise to use wrappers for each part. Ie. if Name and Surname could be different classes containing a single string field. Or a single class could have both Name and Surname. The issue is only apparant if you use primitives or non custom classes. I prefer my approach because it has strong type-safety :) – LuqJensen Jun 05 '16 at 17:23

score 0 · Answer 3 · answered Jun 05 '16 at 17:08

0

If you really need to do this, and I'll always advise against it, you could use the System.Dynamic namespace like so:

dynamic obj = new System.Dynamic.ExpandoObject();
obj.id = 100;
obj.Name = "Something";

Keeping in mind of course that everything that the compiler does on your behalf to keep your code functional, now has to be done at run time.

answered Jun 05 '16 at 17:08

theB

6,450
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But I want to add few extra fields dynamically to already written class – Jun 05 '16 at 17:13
1

In that case to quote Mr. Skeet: "You can't just dynamically change a class at execution time. You could derive a new class, if you want..." – theB Jun 05 '16 at 17:20
Can you give a sample or a link to this , derive dynamically – Jun 06 '16 at 05:10

C# Extend a class dynamically to include more fields during execution

3 Answers3

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