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How to: Store the Results of a Query in Memory (C# Programming Guide)

A query is basically a set of instructions for how to retrieve and organize data. To execute the query requires a call to its GetEnumerator method. This call is made when you use a foreach loop to iterate over the elements. To store the results at any time before or after you execute the foreach loop, just call one of the following methods on the query variable:

We recommend that when you store the query results, you assign the returned collection object to a new variable as shown in the following example:

class StoreQueryResults
{
    static List<int> numbers = new List<int>() { 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 };
    static void Main()
    {

        IEnumerable<int> queryFactorsOfFour =
            from num in numbers
            where num % 4 == 0
            select num;

        // Store the results in a new variable 
        // without executing a foreach loop.
        List<int> factorsofFourList = queryFactorsOfFour.ToList();

        // Iterate the list just to prove it holds data. 
        foreach (int n in factorsofFourList)
        {
            Console.WriteLine(n);
        }

        // Keep the console window open in debug mode.
        Console.WriteLine("Press any key");
        Console.ReadKey();
    }
}
  • Create a Visual Studio project that targets the .NET Framework version 3.5. By default, the project has a reference to System.Core.dll and a using directive for the System.Linq namespace.

  • Copy the code into your project.

  • Press F5 to compile and run the program.

  • Press any key to exit the console window.

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