using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Drawing.Drawing2D;
using System.Windows.Forms.DataVisualization.Charting;
using System.Linq.Expressions;

namespace Test_2
{
    public partial class Form1 : Form
    {
        private List<Expression<Func<Personnel, bool>>> personnelFilter = new List<Expression<Func<Personnel,bool>>>();

        public Form1()
        {
            InitializeComponent();

            AddFilter(a => a.FirstName == "Test");
            AddFilter(a => a.FirstName == "More");

            // Or adding something stupid like:
            AddFilter(a => a.Id == 1);
        }

        public void AddFilter(Expression<Func<Personnel, bool>> filter)
        {
            this.personnelFilter.Add(filter);
        }

        public static Expression<Func<T, bool>> Combine_Or<T>(Expression<Func<T, bool>> expr1,
                                                    Expression<Func<T, bool>> expr2)
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
        }

        private Expression<Func<Personnel, bool>> JoinFilter()
        {
            var result = personnelFilter[0];
            for (int i = 1; i < personnelFilter.Count; i++)
                result = Combine_Or<Personnel>(result, personnelFilter[i]);

            return result;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            List<Personnel> personnel = new List<Personnel> {
                new Personnel { Id=3, FirstName="walter" },
                new Personnel { Id=1, FirstName="More" },
                new Personnel { Id=1, FirstName="More" },
                new Personnel { Id=1, FirstName="john" },
                new Personnel { Id=2, FirstName="michael" },
                new Personnel { Id=2, FirstName="Test" },
                new Personnel { Id=1, FirstName="Raj" }
            };

            Func<Personnel, bool> filter = JoinFilter().Compile();
            var filtered = personnel.Where(filter);

            foreach (var item in filtered)
                System.Console.WriteLine(item.FirstName);

            /* Prints:
                More
                More
                john
                Test
                Raj
             */
        }
    }

    public class Personnel
    {
        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public int OrganizationalUnitId { get; set; }
        public int RoleId { get; set; }
    }
}