What is LINQ? Learn it by solving problems.


Introduction

LINQ (Language INtegrated Query) fills the gap between programming languages and database.

According to Anders Hejlsberg (C# Chief Architect):-

“Microsoft’s original motivation behind LINQ was to address the impedance mismatch between programming languages and database.”

If we compare LINQ to SQL, LINQ is simpler, tidier and very handy to use. It’s rather like comparing C# to C/C++ Programming, the time is gone when C/C++ was best but now coder needs something special like LINQ and it’s a big win. SQL is a very old language that was invented about 1974. Since then it's been extended endlessly, but never redesigned. This has made the language messy. You might have become so accustomed to this that you can't see anything wrong.

I think my above lines will increase your concrete knowledge about Microsoft LINQ, so let’s look at some problems and we will solve this using LINQ and non-LINQ.

Question: We have a collection of Student objects and we want to find out three students who have minimum age.

Look at the non-LINQ Solution:-

using System;
using System.Collections.Generic;
 
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            // create the object of the class and assigning values
            Student[] std = {
                                  new Student { Name = "Abhimanyu", Age = 21 },
                                  new Student { Name = "Deepak", Age = 10 },
                                  new Student { Name = "Mahtab", Age = 15 },
                                  new Student { Name = "Ravi", Age = 12 },
                                  new Student { Name = "Avnish", Age = 13 }
                              };
 
            // define the array to hold the results
            Student[] results = new Student[3];
 
            // short the contents of the array
            Array.Sort(std, (student1, student2) => {
                return Comparer<decimal>.Default.Compare(student1.Age, student2.Age);
            });
 
            // get the first three students in the array as the results
            Array.Copy(std, results, 3);
 
            // print out the name
            foreach (Student s in results)
            {
                Console.WriteLine("Name: {0}, Age: {1}", s.Name, s.Age);
            }
 
            Console.ReadKey();
        }
    }
 
    //class
    class Student
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }
}
 
Now by using LINQ we can significantly simplify the querying process, look at example below.

using System;
using System.Linq;
 
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            // create the object of the class and assigning values
            Student[] std = {
                                  new Student { Name = "Abhimanyu", Age = 21 },
                                  new Student { Name = "Deepak", Age = 10 },
                                  new Student { Name = "Mahtab", Age = 15 },
                                  new Student { Name = "Ravi", Age = 12 },
                                  new Student { Name = "Avnish", Age = 13 }
                              };
 
            // using LINQ
            var results = from s in std
                          orderby s.Age ascending
                          select new
                          {
                              s.Name, s.Age
                          };
 
            int count = 0;
            // print the name
            foreach (var a in results)
            {
                Console.WriteLine("Name: {0}, Age: {1}", a.Name, a.Age);
                if (++count == 3)
                {
                    break;
                }
            }
            Console.ReadKey();
        }
    }
 
    //class
    class Student
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }
}
 
Remember to add a namespace using System.Linq.

This is lot neater. You can see SQL like query is used that is LINQ. We order the student objects in ascending and descending order and use the select keyword to return an anonymous type that contains just the properties we want. This style of LINQ is known as query syntax and it is the kind most developers familiar with.

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