Deferred Execution and Immediate Execution in LINQ

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By  Dhananjay Kumar   On  15 Jan 2011 05:01:15
Tag : LINQ , General
Deferred Execution executes the query only when Loop starts. What I mean here is that, we iterate through the query variable to get the result.
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Introduction

Deferred Execution executes the query only when Loop starts. What I mean here is that, we iterate through the query variable to get the result. 

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Here the result variable does not contain the actual result. To get the result, we may iterate through the result (query) variable in loop as many time as we want. We do deferred execution mainly when multiple values is being returned from the query.

Example

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication3
{
 class Program
 {
 static void Main(string[] args)
 {
 DataClasses1DataContext context = new DataClasses1DataContext();
 var result = from r in context.Persons select r;
 foreach (var a in result)
 {
 Console.WriteLine(a.FirstName + "" + a.LastName);
 }
 Console.ReadKey(true);

 }
 }
}

Output 

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Immediate Execution happens when LINQ query returns a single value.

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Above query is returning a single value so it can be executed immediately.

Example

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication3
{
 class Program
 {
 static void Main(string[] args)
 {
 DataClasses1DataContext context = new DataClasses1DataContext();
 var numberOfRecords = (from r in context.Persons select r).Count();
 Console.WriteLine(numberOfRecords);
 Console.ReadKey(true);

}
 }
}

Output 

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If we want to make a query returning multiple values or sequence of values as immediate then we need to explicitly convert the result in ToList().

 

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So above query is returning multiple values and would be executed immediately.

Example

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;namespace ConsoleApplication3
{
 class Program
 {
 static void Main(string[] args)
 {
 DataClasses1DataContext context = new DataClasses1DataContext();
 var result1 = (from r in context.Persons select r).ToList();
 foreach (var a in result1)
 {
 Console.WriteLine(a.FirstName + "" + a.LastName);
 }
 Console.ReadKey(true);
 }
 }
}

Output

Image Loading

That's all. happy coding.

 
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About Author
 
Dhananjay Kumar
Occupation-Software Engineer
Company-Infosys Technolgies,Pune
Member Type-Gold
Location-India
Joined date-20 Jul 2009
Home Page-http://dhananjaykumar.net/
Blog Page-http://dhananjaykumar.net/
Dhananjay Kumar is Microsoft MVP on connected system. He blogs at http://dhananjaykumar.net/ . You can follow him http://twitter.com/debugmode_/ and reach him at dhananjay.25july@gmail.com
 
 
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