Re: Generic question - C# Discussion Boards

Re: Handling with multiple SQL-DataReader

softwarejaeger10-Aug-09 19:38

10-Aug-09 19:38

Well a lot of answers from you thanks =)

So to the question, "why doesn't get every thread a db-connection?", the answer is, that i make a server-application and for each user-connection i have on thread, but i don't have a huge amount of requests from each user, so it doesn't make sense to give each user a own db-connection, and the second is i don't know how many users will use the server.

So the idea with this RequestManager. I make maybe 5 or 10 (or how many i need) instances from it, stored in a List<requestmanager>. Each RequestManager has an own DB-Connection and handles the Reader for itself. If a user now makes a request, the class of the User-Connection starts the Method "GetData()" (give the baby a name Wink | ;)

) from one of this RequestManagers. So i can make a few requests parallel and if i need more i can easily put even more RequestManager in this List<>.

How does my application get the information to put more RequestManager-instances into this list? Well that's easy, over a configuration-file. I let my application reload them every 5 minutes and it checks how many RequestManager i need and so i'm able to configure them while my system is running.

Your examples, had the nearly the same idea as mine. But i only handle with the "RequestManager" and not with Reader and Connections seperately. I can only make failures on one place (the RequestManager).

Thanks for your help, you gave me a lot of inspiration for this problem. Thumbs Up | :thumbsup:

Re: Handling with multiple SQL-DataReader

senguptaamlan10-Aug-09 22:54

senguptaamlan

10-Aug-09 22:54

MARS (Multiple Active Result Set) can give you a quick solution in this respect (if you are using ADO.NET 2.0 and SQL Server 2005).

Re: Handling with multiple SQL-DataReader

softwarejaeger11-Aug-09 2:19

softwarejaeger

11-Aug-09 2:19

Thanks,

but i don't use SQL Server 2005, but i read the Article about MARS on MSDN, this is not exactly that, what i want, because i want the possibility to have more parallel running transactions.

But many thanks to you all for your answers, but i have now the solution (or at least the ideas for my solution)

Generic question

Peter Todd10-Aug-09 5:50

Peter Todd

10-Aug-09 5:50

Suppose I have a generic class A with a method Xyz.

public class A<t> : where T : class
{
// lots of stuff omitted...

public int Xyz()
{ // details omitted
}
}

Elsewhere I have an object reference. I want to test if the reference refers to an instance of A (don't care about what <t> is), and if it is an instance of A, invoke method Xyz and get the return value. Something like

if (ref is A)
{
int returnValue = ((A)ref).Xyz();
}

except that this code doesn't work when A is a generic type. Can this be done?

Thanks

Peter

Re: Generic question

J4amieC10-Aug-09 6:03

J4amieC

10-Aug-09 6:03

the problem you have is that A does not exist, but A<T> does. So you cant cast to A.

However, seeing as method Xyz() does not rely on Generic type T at all, I would structure your code to include non-generic type A and then inherit for the generic stuff:

public class A 
{
// non-generic implementation ommited

public int Xyz()
{ // details omitted
}
}

public class A<T> : A where T : class
{
  // generic implementation ommited
}

now, this will work:

if (ref is A)
{
int returnValue = ((A)ref).Xyz();
}

Re: Generic question

Luc Pattyn10-Aug-09 6:14

Luc Pattyn

10-Aug-09 6:14

Yes, however IMO that would fail if Xyz() depends on T.

Smile | :)

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Re: Generic question

J4amieC10-Aug-09 6:59

J4amieC

10-Aug-09 6:59

True, but the information provided did not appear to indicate that Xyz relied on T. I can only answe on info provided Wink | ;)

Re: Generic question

Luc Pattyn10-Aug-09 6:03

Luc Pattyn

10-Aug-09 6:03

Hi,

this generates "1":

public class A<T> where T : class {

    public int Xyz() { return 1; }
}

public class CPTest_Generic : CPTest {

    public override void Test(int arg) {
        test2(new A<Form>());
    }

    public int test2(object rf) {
        A<Form> aa=rf as A<Form>;
        int result=0;
        if (aa!=null) result=aa.Xyz();
        log("result="+result);
        return result;
    }
}

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Re: Generic question

PIEBALDconsult10-Aug-09 6:17

PIEBALDconsult

10-Aug-09 6:17

You could write an interface that specifies Xyz, have A<T> implement it, then test for the interface rather than A.

Re: Generic question

Luc Pattyn10-Aug-09 6:22

Luc Pattyn

10-Aug-09 6:22

Yes, this:

public interface Abase {
    int Xyz();
}

public class A<T> : Abase where T : class {
    public int Xyz() { return 1; }
}

public class CPTest_Generic : CPTest {

    public override void Test(int arg) {
        test2(new A<Form>());
    }

    public int test2(object rf) {
        Abase aa=rf as Abase;
        int result=0;
        if (aa!=null) result=aa.Xyz();
        log("result="+result);
        return result;
    }
}

works however it forces Xyz() to be T-agnostic, so what is generic about it?

Smile | :)

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Re: Generic question [modified]

PIEBALDconsult10-Aug-09 9:35

PIEBALDconsult

10-Aug-09 9:35

Make the interface generic?

public interface Abase<T>
{
    T Xyz() ;
}

(Not tested.)

modified on Monday, August 10, 2009 6:57 PM

Re: Generic question

DaveyM6910-Aug-09 7:00

DaveyM69

10-Aug-09 7:00

I agree with PIEBALDconsult, an interface is probably the cleanest way to do this:

public class A<T> : IA where T : class
{
    public int Xyz()
    {
        return 1;
    }
}
public interface IA
{
    int Xyz();
}

// where a is an instance of A<T>
if (a is IA)
    int returnValue = (a as IA).Xyz();

Dave
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Visual Basic is not used by normal people so we're not covering it here. (Uncyclopedia)
Why are you using VB6? Do you hate yourself? (Christian Graus)

Re: Generic question

PIEBALDconsult10-Aug-09 12:59

PIEBALDconsult

10-Aug-09 12:59

Why use is and as? Pick one.

Re: Generic question

DaveyM6910-Aug-09 21:25

DaveyM69

10-Aug-09 21:25

Force of habit. Say a was passed as a parameter (object o). Without the is, you would have to catch the NullReferenceException at the as if it wasn't an A<T> instance, and without the as (or some other cast/conversion), there would be no way to access the Xyz method.

Re: Generic question

PIEBALDconsult10-Aug-09 22:02

PIEBALDconsult

10-Aug-09 22:02

A<T> a = o as A<T> ;
if ( a != null ) a.Xyz() ;

if ( a is A<T> ) ((A<T>) o).Xyz() ;

Aw crap, how'd it get to be 01:00? I'd better get to bed.

Lock(This)

jpk42010-Aug-09 5:06

jpk420

10-Aug-09 5:06

Hello All ,

I was readinf the lock concept and find that there is problem with lock(this) or lock(public type).
what is the problem doing like that ?

Please explain me with an example

Re: Lock(This)

Ennis Ray Lynch, Jr.10-Aug-09 5:30

Ennis Ray Lynch, Jr.

10-Aug-09 5:30

A good starting point for research is the documentation[^]. I think you would be surprised at the information available in MSDN.

Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting.

A man said to the universe:
"Sir I exist!"
"However," replied the universe,
"The fact has not created in me
A sense of obligation."
--Stephen Crane

Re: Lock(This)

Luc Pattyn10-Aug-09 5:52

Luc Pattyn

10-Aug-09 5:52

Nah. MSDN documentation is like holiday brochures without pictures, nothing interesting there. Laugh | :laugh:

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Re: Lock(This)

Ennis Ray Lynch, Jr.10-Aug-09 5:55

Ennis Ray Lynch, Jr.

10-Aug-09 5:55

Actually, the particular article I referenced while sparse does indicate the common problems and a common solution in the remarks section. Although, most MSDN is total crap.

Re: Lock(This)

jpk42010-Aug-09 5:57

jpk420

10-Aug-09 5:57

I check the documentation . I did not get that what was the problem .

any way we are making lock on that object . So what matters if that is private or public?

Please help me out

Re: Lock(This)

Luc Pattyn10-Aug-09 6:06

Luc Pattyn

10-Aug-09 6:06

you could as well ask why private and protected members exist at all. Why not make everything public?

it is a matter of encapsulation, separation of concern, improving reliability, etc.

Smile | :)

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Re: Lock(This)

jpk42010-Aug-09 6:28

jpk420

10-Aug-09 6:28

No That i not mean at all . what i got confused is anyhow i am locking that object . So untill i done with my work no body can tamper it with .

So even if i declare private or public i am holding a lock on that . So how that acces specifier will affect that .

Sorry to trouble u .. bUt a good example will clear my doubt .. my brain is not able to leav this doubt unanswered.

Re: Lock(This)

Luc Pattyn10-Aug-09 6:38

Luc Pattyn

10-Aug-09 6:38

when your locker object is public I can lock it without your code being aware of it; so all your code would break right away. Don't make public what doesn't have to be public, that is one of the OO principles.

Smile | :)

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Re: Lock(This)

PIEBALDconsult10-Aug-09 7:04

PIEBALDconsult

10-Aug-09 7:04

Yet with Reflection I can see your privates. Cool | :cool:

Re: Lock(This)

Luc Pattyn10-Aug-09 7:10

Luc Pattyn

10-Aug-09 7:10

You'd better think twice before applying reflection on me... $Shucks | :-\$

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