I like Linq more every time I use is. I've posted about XLinq and using linq to sort and filter lists. You can also use Linq to join two objects and select properties from each to create a new collection of objects (somewhat like SQL), run ForEach clauses, and do simple functions like Distinct, Sum, and Count. Here's a code sample (I prefer to do minimalist samples with a unit test syntax for easy demos):
using System;
using System.Text;
using System.Collections.Generic;
using System.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace LinqDemo
{
/// <summary>
/// Summary description for UnitTest1
/// </summary>
[TestClass]
public class UnitTest1
{
private Employee[] GetEmployees()
{
return new Employee[]
{
new Employee(){ FirstName = "Homer", LastName ="Simpson", FavoriteNumber=7, DeptId=1},
new Employee(){ FirstName = "Marge", LastName ="Simpson", FavoriteNumber=18, DeptId=0},
new Employee(){ FirstName = "Bart", LastName ="Simpson", FavoriteNumber=99, DeptId=0},
new Employee(){ FirstName = "Monty", LastName ="Burns", FavoriteNumber=23, DeptId=9},
new Employee(){ FirstName = "Ned", LastName ="Flanders", FavoriteNumber=5, DeptId=0}
};
}
private Department[] GetDepartments()
{
return new Department[]
{
new Department(){ DeptId=1, DeptName="Safety Operator"},
new Department(){ DeptId=2, DeptName="Customer Service"},
new Department(){ DeptId=9, DeptName="Executive"},
};
}
[TestMethod]
public void SelectProperties()
{
//create data
Employee[] emps = GetEmployees();
//Use linq to get a distinct list from some property
List<string> lastNames = emps
.Where(n => n.FavoriteNumber > 10) //Some filter
.OrderBy(n => n.LastName)
.Select(n => n.LastName) //Select specific fields
.Distinct() //Get only distict elements
.ToList();
Assert.AreEqual("Burns", lastNames[0]);
Assert.AreEqual("Simpson", lastNames[1]);
}
[TestMethod]
public void JoinAndCreateAnotherObject()
{
//Join "Employee" and Department to create "Worker"
Employee[] emps = GetEmployees();
Department[] depts = GetDepartments();
//This could be useful is emps and depts came from
// different sources, or depts was cached
Worker[] workers =
(
from emp in emps
from dept in depts
where emp.DeptId == dept.DeptId
&& emp.DeptId > 0
select new Worker()
{
FirstName = emp.FirstName,
DeptName = dept.DeptName
}
).ToArray();
Assert.AreEqual("Homer", workers[0].FirstName);
Assert.AreEqual("Safety Operator", workers[0].DeptName);
}
[TestMethod]
public void ForEach()
{
//Use a single line to update a property
List<Employee> emps = GetEmployees().ToList();
Assert.AreEqual(7, emps[0].FavoriteNumber);
//Double everyone's favorte number
//Easier than writing a for-each loop
emps.ForEach(n => n.FavoriteNumber = n.FavoriteNumber * 2);
Assert.AreEqual(14, emps[0].FavoriteNumber);
}
[TestMethod]
public void Do_Aggregates()
{
//Get the sum of all numbers where the number is already > 10.
List<Employee> emps = GetEmployees().ToList();
int intSum = emps
.Where(n => n.FavoriteNumber > 10)
.Sum(n => n.FavoriteNumber);
Assert.AreEqual(140, intSum);
}
}
public class Employee
{
public int FavoriteNumber { get; set; }
public int DeptId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public override string ToString()
{
return string.Format("{0} {1} - {2}", this.FirstName, this.LastName, this.FavoriteNumber);
}
}
public class Department
{
public int DeptId { get; set; }
public string DeptName { get; set; }
}
public class Worker
{
public string FirstName { get; set; }
public string DeptName { get; set; }
}
}
