CSharp - Query Results Changing Between Enumerations

Introduction

Queries returning IEnumerable<T> are deferred.

You can define the query once but use it multiple times by enumerating it multiple times.

Each time you enumerate the results, you will get different results if the data changes.

The following code shows an example of a deferred query where the query results are not cached and can change from one enumeration to the next.

Demo

using System;
using System.Collections.Generic;
using System.Linq;
class Program//from  w  w  w. j a va  2  s  . c o m
{
    static void Main(string[] args)
    {

        //  Create an array of ints.  
        int[] intArray = new int[] { 1, 2, 3 };

        IEnumerable<int> ints = intArray.Select(i => i);

        //  Display the results.  
        foreach (int i in ints)
            Console.WriteLine(i);

        // Change an element in the source data.  
        intArray[0] = 5;


        //  Display the results again.  
        foreach (int i in ints)
            Console.WriteLine(i);

    }
}

Result

Related Topic

• Query Expressions
• Create Anonymous Types
• Collection Initialization on List
• Returning IEnumerable<T>, Yielding, and Deferred Queries
• Returning a List So the Query Is Executed Immediately and the Results Are Cached
• Using One of the Func Delegate Declarations
• Query with Intentional Exception Deferred Until Enumeration
• Use the var Keyword When Confused
• XML Query Using LINQ to XML
• Database Query Using LINQ to SQL
• Converting an Array of Strings to Integers and Sorting It
• Get SQL query via DataContext Log
• Create extension for string to convert string to double and bool
• LINQ to Objects Query

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