Question

I have some code that changes a value of some data within my database while within a loop. I’m just wondering what is the most efficient way of filtering my data first? I’ll give an example:-

With the class:-

public class myObj 
{
    int id {get;set;}
    string product {get; set;}
    string parent{get;set;}
    bool received {get;set;}
}

And the DbContext:-

public class myCont:DbContext
{
    public DbSet<myObj> myObjs {get;set;}
}

Is it better to do this:-

int[] list;
/* Populate list with a bunch of id numbers found in myOBjs */
myCont data = new myCont();
myObj ob = data.myObjs.Where(o => o.parent == "number1");
foreach(int i in list)
{
    ob.First(o => o.id == i && o.received != true).received = true;
}

Or:-

int[] list;
/* Populate list with a bunch of id numbers found in myOBjs */
myCont data = new myCont();
foreach(int i in list)
{
    data.myObjs.First(o => o.parent == "number1" && o.id == i && o.received != true).received = true;
}

Or is there no difference?

Answer 1

Not sure how you get to compile your code example above.

In your myObj object, the received property is an int, yet you are evaluating it against a bool which should cause this line o.received != true to results in an error Cannot apply operator '!=' to operands of type 'int' and 'bool'.

To Check the SQL
Once the code compiles use SQL Profiler to see what SQL is generated.

That will show you the constructed SQLs

Benchmarking
The below is a very crude description of only one possible way you can benchmark your code execution.

Wrap your code into a method, for example:

public void TestingOperationOneWay()
{
    int[] list;
    /* Populate list with a bunch of id numbers found in myOBjs */
    myCont data = new myCont();
    myObj ob = data.myObjs.Where(o => o.parent == "number1");
    foreach(int i in list)
    {
        ob.First(o => o.id == i && o.received != true).received = true;
    }
}

And:

public void TestingOperationAnotherWay()
{
    int[] list;
    /* Populate list with a bunch of id numbers found in myOBjs */
    myCont data = new myCont();
    foreach(int i in list)
    {
        data.myObjs.First(o => o.parent == "number1" && o.id == i && o.received != true).received = true;
    }
}

Crate a method which iterates x amount of times over each method using the Stopwatch similar to this:

private static TimeSpan ExecuteOneWayTest(int iterations)
{
    var stopwatch = Stopwatch.StartNew();

    for (var i = 1; i < iterations; i++)
    {
        TestingOperationOneWay();
    }

    stopwatch.Stop();

    return stopwatch.Elapsed;
}

Evaluate the results similar to this:

static void RunTests()
{
    const int iterations = 100000000;

    var timespanRun1 = ExecuteOneWayTest(iterations);
    var timespanRun2 = ExecuteAnotherWayTest(iterations);

    // Evaluate Results....
}