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I previously wrote this article in my blog, Think Big!.
The following example shows how query execution is deferred until the results is enumerated (requested in other words.)
static void TryLinq() { int i = 0; int[] numbers = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }; // fake values for the query only (10 values) var result = from n in numbers select Increment(ref i); Console.WriteLine("After query i = {0}", i); // i still 0 Console.WriteLine(); Console.WriteLine("Enumerating results:"); foreach (var v in result) { Console.WriteLine("v = {0},ti = {1}", v, i); // i is incremented every loop } Console.WriteLine("Press any key to continue . . ."); Console.ReadKey(true); // Result:- // After query i = 0 // Enumerating results: // v = 1, i = 1 // v = 2, i = 2 // ............. // v = 9, i = 9 // v = 10, i = 10 // What you get? // Deferred-Execution / Lazy-Execution // - Query doesn't execute until you // begin retrieving it's results. // - Every time you try get a value // the query executes on this value only. } static int Increment(ref int i) { return ++i; }
Next is an example shows how you can immediate-execute the query.
static void TryLinq() { int i = 0; int[] numbers = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }; // fake values for the query only (10 values) var result = (from n in numbers select Increment(ref i)).ToList(); // The last call tries to get the value immediately. Console.WriteLine("After query i = {0}", i); // i is 10 Console.WriteLine(); Console.WriteLine("Enumerating results:"); foreach (var v in result) { Console.WriteLine("v = {0},ti = {1}", v, i); // i still 10 every loop } Console.WriteLine("Press any key to continue . . ."); Console.ReadKey(true); // Result:- // After query i = 10 // Enumerating results: // v = 1, i = 10 // v = 2, i = 10 // ............. // v = 9, i = 10 // v = 10, i = 10 // What you get? // Deferred-Execution / Lazy-Execution // - Query doesn't execute until you // begin retrieving it's results. // - Every time you try get a value the // query executes on this value only. // - You can immediate-execute the query by // calling some conversation methods like // ToList or ToQuery. } static int Increment(ref int i) { return ++i; }
What you get?
Deferred-Execution / Lazy-Execution
- Query doesn't execute until you begin retrieving it's results.
- Every time you try get a value the query executes on this value only.
- You can immediate-execute the query by calling some conversation methods like ToList or ToQuery.
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Mohammad Elsheimy
I am a MCP, MCTS, and MCPD independent software developer, trainer, and author. I was born in 1991 in Banha, KB Egypt. Yet, I am a student of the 8-years Holy Quran Science Institute, KB Egypt, where we study the Holy Quran sciences and Islamic legislations.
I write about various technologies and products including C, C++, and .NET Framework in many places specially my sites, Just Like a Magic (http://JustLikeAMagic.net.tc) where I write in English, and With .NET (http://With.NET.tc) where I write in Arabic.
In addition, I write articles about Islam and Islamic sciences in my site: http://Islamtecture.net.tc
You can reach me at Geming.Leader@Hotmail.com, or you can call me directly on +2 018 577 1171. I'm also available for IM at Geming.Leader@Yahoo.com. Do not forget to follow me on Twitter: http://www.Twitter.com/Elsheimy. I'm in Facebook too: http://www.Facebook.com/Elsheimy.
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