JSON Entity Converter

json_entity_converter.cs

void Main()
{
	var co = new Company { Id = 1, Name = "Moof Inc." };
	var clarus = new Contact { Id = 1, Name = "Clarus" };
	var mark = new Contact { Id = 2, Name = "Mark" };
	co.AddContact(clarus);
	co.AddContact(mark);
	co.MainContact = clarus;

	// Attempt #1: Straight up, no converter
	// var serializer1 = new JavaScriptSerializer();
	// serializer1.Serialize(co).Dump(); 
	// => InvalidOperationException: A circular reference was detected while serializing an object of type 'UserQuery+Company'. 
	
	// Attempt #2: Converter handles all Entities
	var converter2 = new EntityConverter();
	var serializer2 = new JavaScriptSerializer();
	serializer2.RegisterConverters(new[] { converter2 });
	serializer2.Serialize(co).Dump(); 
	// => {"Name":"Moof Inc.","Contacts":[{"Name":"Clarus","WorksFor":1,"Id":1},{"Name":"Mark","WorksFor":1,"Id":2}],"MainContact":1,"Id":1}
	
	// Attempt #3: Converter handles only contacts
	var converter3 = new EntityConverter(new[] { typeof(Contact) });
	var serializer3 = new JavaScriptSerializer();
	serializer3.RegisterConverters(new[] { converter3 });
	serializer3.Serialize(co).Dump(); 
	// => {"Name":"Moof Inc.","Contacts":[{"Name":"Clarus","WorksFor":1,"Id":1},{"Name":"Mark","WorksFor":1,"Id":2}],"MainContact":{"Name":"Clarus","WorksFor":1,"Id":1},"Id":1}

	// Attempt #4: Converter with custom output for entities.
	var converter4 = new EntityConverter(new[] { typeof(Contact) }, en => new ReducedEntity(en));
	var serializer4 = new JavaScriptSerializer();
	serializer4.RegisterConverters(new[] { converter4 });
	serializer4.Serialize(co).Dump(); 
	// => {"Name":"Moof Inc.","Contacts":[{"Name":"Clarus","WorksFor":{"TypeName":"Company","Id":1},"Id":1},{"Name":"Mark","WorksFor":{"TypeName":"Company","Id":1},"Id":2}],"MainContact":{"Name":"Clarus","WorksFor":{"TypeName":"Company","Id":1},"Id":1},"Id":1}



}

// Define other methods and classes here
public class Entity {
	public int Id { get; set; }
}

public class Company : Entity { 
	public string Name { get; set; }
	public IEnumerable<Contact> Contacts { get { return _contacts; } }
	public Contact MainContact { get; set; }
	
	public void AddContact(Contact aContact) {
		if (_contacts.Contains(aContact)) throw new ArgumentException("Contact already exists in the list.");
		aContact.WorksFor = this;
		_contacts.Add(aContact);
	}
	private List<Contact> _contacts = new List<Contact>();
}

public class Contact : Entity {
	public string Name { get; set; }
	// public string Address { get; set; }
	public Company WorksFor { get; set; }
}

public class EntityConverter : JavaScriptConverter {
	private IEnumerable<Type> _supportedTypes;
	private Func<Entity, object> _reducer;
	public EntityConverter() : this(new[] { typeof(Entity) }) {}
	public EntityConverter(IEnumerable<Type> supportedTypes, Func<Entity, object> reducer = null) {
		_supportedTypes = supportedTypes.DefaultIfEmpty(typeof(Entity));
		_reducer = reducer ?? (en => en.Id);
	}
	
	public override IEnumerable<Type> SupportedTypes { get { return _supportedTypes; } } 
	
	public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer) {
		var ret = new Dictionary<string, object>();
		if (obj == null) return ret;
		
		string name; object value;
		var props = obj.GetType().GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.GetProperty);
		foreach (PropertyInfo prop in props) {
			name = prop.Name;
			value = prop.GetValue(obj, null);
			if (value != null && typeof(Entity).IsAssignableFrom(prop.PropertyType))
				ret.Add(name, _reducer((Entity) value));
			else
				ret.Add(name, value);
		}

		return ret;
	}
	public override object Deserialize(IDictionary<string, object> obj, Type type, JavaScriptSerializer serializer) {
		throw new NotImplementedException();
	}
}

	
public class ReducedEntity {
	public ReducedEntity(Entity anEntity) {
		TypeName = anEntity.GetType().Name;
		Id = anEntity.Id;
	}
	public string TypeName { get; private set; }
	public int Id { get; private set; }
}