class Person
{
	public string FirstName { get; set; }
	public string LastName { get; set; }
	public string Position { get; set; }
}

static List<Person> _persons = new List<Person>() {
	new Person() { FirstName = "Ivan", LastName="Ivanov", Position="Manager" },
	new Person() { FirstName = "Maxim", LastName="Ivanov", Position="Employee" },
	new Person() { FirstName = "Maxim", LastName="Petrov", Position="Employee" }
};

static Dictionary<string, Func<object, Expression<Func<Person, bool>>>> expressions = 
	new Dictionary<string, Func<object, Expression<Func<Person, bool>>>>() 
{
	{"first", (p) => ((a) => a.FirstName == p.ToString())},
	{"last", (p) => ((a) => a.LastName == p.ToString())},
	{"position", (p) => ((a) => a.Position == p.ToString())}
};

static void TestExpressions()
{

	var conditions = new[] {
		new { Field = "first", Value = "Maxim" },
		new { Field = "position", Value = "Employee" }
	};

	var q = _persons.AsQueryable();
	foreach (var cond in conditions)
	{
		q = q.Where(expressions[cond.Field](cond.Value));
	}
	foreach (var res in q)
	{
		Console.WriteLine("{0} {1} - {2}", res.FirstName, res.LastName, res.Position);
	}
	Console.ReadKey();
}