How to create a group of methods/properties within a class?

Here is another solution using explicit interfaces:

public interface ICustomMethods {    string FullName {get;}}public partial class Employee: Entity, ICustomMethods {    public ICustomMethods CustomMethods {       get {return (ICustomMethods)this;}    }    //explicitly implemented    string ICustomMethods.FullName {       get { return this.FirstName + " " + this.LastName; }    }}

Usage:

string fullName;fullName = employee.FullName; //Compiler error    fullName = employee.CustomMethods.FullName; //OK

public class CustomMethods{    Employee _employee;    public CustomMethods(Employee employee)    {        _employee = employee;    }    public string FullName     {        get         {            return string.Format("{0} {1}",                 _employee.FirstName, _employee.LastName);         }    }}public partial class Employee : Entity{    CustomMethods _customMethods;    public CustomMethods CustomMethods    {        get         {            if (_customMethods == null)                _customMethods = new CustomMethods(this);            return _customMethods;        }    }}

typically I would put Properties like FullName right on the Partial class but I can see why you might want separation.