Introduction
Imagine a scenario in which we have a collection of objects and want to allow the user to filter the collection by filtering on combination of properties. To make the scenario concrete, let's assume that our object is declared as follows:
namespace SampleLinq
{
public class Genericuselinq
{
public int Id { get; set; }
public string Name { get; set; }
}
}
Now suppose we have a collection of
Genericuselinq like this (this is just for explanation purposes, in real life you would get a much bigger collection from database):
List<Genericuselinq> objGL = new List<Genericuselinq>();
Genericuselinq obj = new Genericuselinq();
obj.Id = 1;
obj.Name = "sriram";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 1;
obj.Name = "sri";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 1;
obj.Name = "sree";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 1;
obj.Name = "srithar";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 1;
obj.Name = "sridevi";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 6;
obj.Name = "arun";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 5;
obj.Name = "malar";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 14;
obj.Name = "peter";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 13;
obj.Name = "kumar";
objGL.Add(obj);
obj = new Genericuselinq();
obj.Id = 123;
obj.Name = "John";
objGL.Add(obj);
Suppose we want to allow the user to filter the collection on any property or any combination of properties (on our UI form). One way would be to have a function for each property and each combination of properties, something like:
Ex 1:
List<Genericuselinq> objGL = GenericValues();
var output = (from t in objGL
where t.Name == "sriram"
select t).FirstOrDefault();
Console.WriteLine("Id "+output.Id+" Name
"+ output.Name);
FirstOrDefault is almost the same as First. The difference is how it handles empty
collections. If a collection is empty, it returns the default value for the
type. This method simplifies code.
Ex 2:
List<Genericuselinq> objGL = GenericValues();
var output = (from t in objGL
where t.Name.StartsWith("s")
select t).ToList();
foreach (var w in output)
{
Console.WriteLine("Id : " + w.Id + " Name :
" + w.Name);
}
Console.Read();
ToList converts collections to List instances. It
is a fast and easy-to-remember method. It returns a List instance with the
appropriate elements. It creates a new List internally, with the List
constructor
