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  • MySQL - Calculating fields on the fly vs storing calculated data

    - by Christian Varga
    Hi Everyone, I apologise if this has been asked before, but I can't seem to find an answer to a question that I have about calculating on the fly vs storing fields in a database. I read a few articles that suggested it was preferable to calculate when you can, but I would just like to know if that still applies to the following 2 examples. Example 1. Say you are storing data relating to a car. You store the fuel tank size in litres, and how many litres it uses per 100km. You also want to know how many KMs it can travel, which can be calculated from the tank size and economy. I see 2 ways of doing this: When a car is added or updated, calculate the amount of KMs and store this as a static field in the database. Every time a car is accessed, calculate the amount of KMs on the fly. Because the cars economy/tank size doesn't change (although it could be edited), the KMs is a pretty static value. I don't see why we would calculate it every single time the car is accessed. Wouldn't this waste cpu time as opposed to simply storing it in a separate field in the database and calculating only when a car is added or updated? My next example, which is almost an entirely different question (but on the same topic), relates to counting children. Let's say we have a app which has categories and items. We have a view where we display all the categories, and a count of all the items inside each category. Again, I'm wondering what's better. To perform a MySQL query to count all the items in each category every single time the page is accessed? Or store the count in a field in the categories table and update when an item is added / deleted? I know it is redundant to store anything that can be calculated, but I worry that calculating fields or counting records might be slow as opposed to storing the data in a field. If it's not then please let me know, I just want to learn about when to use either method. On a small scale I guess it wouldn't matter either way, but apps like Facebook, would they really count the amount of friends you have every time someone views your profile or would they just store it as a field? I'd appreciate any responses to both of these scenarios, and any resource that might explain the benefits of calculating vs storing. Thanks in advance, Christian

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  • How to navigate to another html page?

    - by newbie
    In my application there's a usual login page sending username and password to the server script, where it needs to be authenticated, and in case of an authentic user, the server should redirect to a page student.html. This is my code var ports = 3000; var portt = 3001; var express = require('express'); var student = require('express')(); var teacher = require('express')(); var server_s = require('http').createServer(student); var server_t = require('http').createServer(teacher); var ios = require('socket.io').listen(server_s); var iot = require('socket.io').listen(server_t); var path = require('path'); server_s.listen(ports); server_t.listen(portt); student.use(express.static(path.join(__dirname, 'public'))); student.get('/', function(req,res){ res.sendfile(__dirname + '/login.html'); }); teacher.use(express.static(path.join(__dirname, 'public'))); teacher.get('/', function(req,res){ res.sendfile(__dirname + '/mytry.html'); }); ios.sockets.on('connection', function(socket){ var username, password; socket.on('check',function(data){ username = data[0]; password = data[1]; //************* Database connection and query ************* var mysql = require('mysql'); var connection = mysql.createConnection({ host : 'localhost', user : 'user', password: '*******', database: 'my_db' }); connection.connect(); var qstring = 'SELECT s_id FROM login_student WHERE username='+username+'AND password='+password; connection.query(qstring, function(err, rows, fields) { if (err) { console.log('ERROR: ' + err); socket.emit('login_failure','DB error'); return; } console.log('The solution is: ', rows[0].solution); if (rows>0) //***** Here i want redirection to another page ****** else socket.emit('login_failure','Invalid Username or password'); }); connection.end(); }); }); iot.sockets.on('connection', function(socket){ ; }); }); Can anyone suggest what should I do?

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  • c++ object sizes

    - by anon
    Suppose I have: struct Foo: public Bar { .... } Foo introduces no new member varaibles. Foo only introduces a bunch of member functions & static functions. Does any part of the C++ standard now guarantee me that: sizeof(Foo) == sizeof(Bar) ? Thanks!

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  • 2 roles, admin and user. Is using anything other than basic http auth overkill?

    - by juststarting
    I'm building my first website with rails,it consists of a blog, a few static pages and a photo gallery. The admin section has namespaced controllers. I also want to create a mailing list, collecting contact info, (maybe a spree store in the future too.) Should I just use basic http authentication and check if the user is admin? Or is a plugin like authlogic better, then define user roles even though there would only be two; admin and user?

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  • Access XAMPP Localhost from Internet

    - by coool
    Hi, I have XAMPP installed in local laptop. And I have a almost static ip. I would like to give the ip to other to run it from thier browser. I configured apache httpd-vhosts.conf to listen my ip address:80 and added the virtual server with the ip address and domain root to local httdocs directory and the servername as localhost. Apache doesn't start. what should I do to access my website from external computer. THnks

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  • How to remove index from url in asp.net mvc?

    - by Pandiya Chendur
    I am doing a return RedirectToAction("Index", "Clients"); from my home controller.... It is fine but my url looks like http://localhost:1115/Clients/Index... How to remove index from url in asp.net mvc? Any suggestion.... My routes, public static void RegisterRoutes(RouteCollection routes) { routes.IgnoreRoute("{resource}.axd/{*pathInfo}"); routes.MapRoute( "Registrations", "{controller}/{action}/{id}", new { controller = "Registration", action = "Create", id = "" } ); }

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  • functional, bind1st and mem_fun

    - by Neil G
    Why won't this compile? #include <functional> #include <boost/function.hpp> class A { A() { typedef boost::function<void ()> FunctionCall; FunctionCall f = std::bind1st(std::mem_fun(&A::process), this); } void process() {} }; Errors: In file included from /opt/local/include/gcc44/c++/bits/stl_function.h:712, from /opt/local/include/gcc44/c++/functional:50, from a.cc:1: /opt/local/include/gcc44/c++/backward/binders.h: In instantiation of 'std::binder1st<std::mem_fun_t<void, A> >': a.cc:7: instantiated from here /opt/local/include/gcc44/c++/backward/binders.h:100: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:103: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:106: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:111: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h:117: error: no type named 'second_argument_type' in 'class std::mem_fun_t<void, A>' /opt/local/include/gcc44/c++/backward/binders.h: In function 'std::binder1st<_Operation> std::bind1st(const _Operation&, const _Tp&) [with _Operation = std::mem_fun_t<void, A>, _Tp = A*]': a.cc:7: instantiated from here /opt/local/include/gcc44/c++/backward/binders.h:126: error: no type named 'first_argument_type' in 'class std::mem_fun_t<void, A>' In file included from /opt/local/include/boost/function/detail/maybe_include.hpp:13, from /opt/local/include/boost/function/detail/function_iterate.hpp:14, from /opt/local/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:47, from /opt/local/include/boost/function.hpp:64, from a.cc:2: /opt/local/include/boost/function/function_template.hpp: In static member function 'static void boost::detail::function::void_function_obj_invoker0<FunctionObj, R>::invoke(boost::detail::function::function_buffer&) [with FunctionObj = std::binder1st<std::mem_fun_t<void, A> >, R = void]': /opt/local/include/boost/function/function_template.hpp:913: instantiated from 'void boost::function0<R>::assign_to(Functor) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' /opt/local/include/boost/function/function_template.hpp:722: instantiated from 'boost::function0<R>::function0(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' /opt/local/include/boost/function/function_template.hpp:1064: instantiated from 'boost::function<R()>::function(Functor, typename boost::enable_if_c<boost::type_traits::ice_not::value, int>::type) [with Functor = std::binder1st<std::mem_fun_t<void, A> >, R = void]' a.cc:7: instantiated from here /opt/local/include/boost/function/function_template.hpp:153: error: no match for call to '(std::binder1st<std::mem_fun_t<void, A> >) ()'

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  • TimeOuts with HttpWebRequest when running Selenium concurrently in .NET

    - by domsom
    I have a download worker that uses ThreadPool-threads to download files. After enhancing these to apply some Selenium tests to the downloaded files, I am constantly experiencing TimeOut-exceptions with the file downloaders and delays running the Selenium tests. More precisely: When the program starts, the download threads start downloading and a couple of pages are seamlessly processed via Selenium Shortly after, the first download threads start throwing TimeOut exceptions from HttpWebRequest. At the same time, commands stop flowing to Selenium (as observed in the SeleniumRC log), but the thread running Selenium is not getting any exception This situation holds as long as there are entries in the download list: new download threads are being started and terminate after receiving TimeOuts (without trying to lock Selenium) As soon as no more download threads are being started, Selenium starts receiving commands again and the threads waiting for the lock are processed sequentially as designed Now here's the download code: HttpWebRequest request = null; WebResponse response = null; Stream stream = null; StreamReader sr = null; try { request = (HttpWebRequest) WebRequest.Create(uri); request.ServicePoint.ConnectionLimit = MAX_CONNECTIONS_PER_HOST; response = request.GetResponse(); stream = response.GetResponseStream(); // Read the stream... } finally { if (request != null) request.Abort(); if (response != null) response.Close(); if (stream != null) { stream.Close(); stream.Dispose(); } if (sr != null) { sr.Close(); sr.Dispose(); } } And this is how Selenium is used afterwards in the same thread: lock(SeleniumLock) { selenium.Open(url); // Run some Selenium commands, but no selenium.stop() } Where selenium is a static variable that is initialized in the static constructor of the class (via selenium.start()). I assume I am running into the CLR connection limit, so I added these lines during initalization: ThreadPool.GetMaxThreads (out maxWorkerThreads, out maxCompletionPortThreads); HttpUtility.MAX_CONNECTIONS_PER_HOST = maxWorkerThreads; System.Net.ServicePointManager.DefaultConnectionLimit = maxWorkerThreads + 1; The + 1 is for the connection to the SeleniumRC, due to my guess that the Selenium client code also uses HttpWebRequest. It seems like I'm still running into some kind of deadlock - although the threads waiting for the Selenium lock do not hold any resources. Any ideas on how to get this working?

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  • .NET Reflection: How to call method of interface without creating instance?

    - by jitm
    I have situation where I have to call method of interface using reflection, like this object x = null; MethodInfo method = interfaceExists.GetMethod("ShutDown"); method.Invoke(x, new object[] { 4 }) As you can see I do not create instance of object! And, as I can supposed, I receive exception Non-static method requires a target And Question, Can I call method of interface using reflection without creating instance of interface and if YES, How I can do it ?

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  • How to List Some Table Records in Windows Application? - C#.NET

    - by user327387
    Which control should i use? I don't want the records to be displayed on the Windows Application list in the same way records displayed in database as this: I want the records to be displayed statically and a user when right click a record, he/she gets Edit and Remove choices. Of course there has to be static headers at the top. I hope my request is clear. I'm using C#.NET - VS 2008

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  • C# Generics - Strange Interview Question

    - by udana
    An interviewer argued me "Genrics are not completely Genrics", He provided the example (Parameters int k,int d are not generic) public static void PrintThis<T>(T a, T b, T c, int k,int d) { } He asked me if i prove still it is generics , i will be allowed to take up the next round. I did not know what he is expecting from me,and what he really means by showing such example. Guide me how to smartly face such a strange interview ?. Thanks in advance.

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  • Different ways of accessing configuration parameters from a JAX-WS service

    - by ecerulm
    As far as I know I can access the web.xml <context-param>s by making my class implement ServletContextListener and use the ServletContext.getInitParam(String) to read them, but it´s cumbersome as only one instance of the class will receive the contextInitialized(ServletContextEvent sce) call, so I need to make the ServletContext an static member of the class. What other ways exist of setting conf params at deployment time and what are the recommended ones?

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  • iphone :- i have one webservice in that Authentication require

    - by Heart PAL
    hello, i have one webservice given by my client ... problem is this webservise require Authentication...without username and password no one get data from this url...so how can i do authentication this webservice . this is same like u r gling to login to facebook or twitter then first we enter username and password for authenticate . how can i do this same. i have username and password for this webservise can i pass this static data in code ?

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  • Did Visual Studio 2010 break "Project Dependencies" between C++ projects?

    - by Roger Lipscombe
    In Visual Studio 2008, if I had a solution containing multiple C++ projects, I could make them depend on each-other and correctly link by using the "Project Dependencies" option. This fixed up the build order and also made (e.g.) the main application project link against the static library outputs. In Visual Studio 2010, this doesn't seem to work. Did Visual Studio 2010 change the way this works?

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  • read length of string from stdin

    - by teoz
    I want to take a string from stdin but I don't want a static array of fixed size I know that scanf need something where save the stdin input, but I can't do something like this: char string[10] scanf("%s",string); becouse I need to know before how long will be the string in order to allocate the right memory space. Can you help me to resolve this problem?

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  • Multipage forms for joomla (looking outside the box)

    - by John Snow
    I have created a number of forms using various Joomla components which have more or less worked successfully. Recently I have attempted to create mult-page forms - the forms work...but they are slow as molasses. Having spent a couple of weeks trying to resolve this and not seeing any signs of improvement ...... I wonder if anyone has experience of using hosted forms services in Joomla either using a wrapper or as a static page within a Joomla site. Any pointers or recommendations would be appreciated.

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  • jms unresolved message-destination-ref

    - by portoalet
    hi, I am using netbeans 6.8, and glassfish v3, and making a simple jms application to work. I got this: com.sun.enterprise.container.common.spi.util.InjectionException: Exception attempting to inject Unresolved Message-Destination-Ref jms/[email protected]@null into class enterpriseapplication4.Main Code: public class Main { @Resource(name = "jms/myQueue") private static Topic myQueue; @Resource(name = "jms/myFactory") private static ConnectionFactory myFactory; ... // the rest is just boiler plate created by netbeans } In my Glassfish v3 admin console, I have jms/myFactory as my ConnectionFactory and jms/myQueue as my Destination Resources. What am I missing? Full stack: WARNING: enterprise.deployment.backend.invalidDescriptorMappingFailure com.sun.enterprise.container.common.spi.util.InjectionException: Exception attempting to inject Unresolved Message-Destination-Ref jms/[email protected]@null into class enterpriseapplication4.Main at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl._inject(InjectionManagerImpl.java:614) at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl.inject(InjectionManagerImpl.java:384) at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl.injectClass(InjectionManagerImpl.java:210) at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl.injectClass(InjectionManagerImpl.java:202) at org.glassfish.appclient.client.acc.AppClientContainer$ClientMainClassSetting.getClientMainClass(AppClientContainer.java:599) at org.glassfish.appclient.client.acc.AppClientContainer.getMainMethod(AppClientContainer.java:498) at org.glassfish.appclient.client.acc.AppClientContainer.completePreparation(AppClientContainer.java:397) at org.glassfish.appclient.client.acc.AppClientContainer.prepare(AppClientContainer.java:311) at org.glassfish.appclient.client.AppClientFacade.prepareACC(AppClientFacade.java:264) at org.glassfish.appclient.client.acc.agent.AppClientContainerAgent.premain(AppClientContainerAgent.java:75) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at sun.instrument.InstrumentationImpl.loadClassAndStartAgent(InstrumentationImpl.java:323) at sun.instrument.InstrumentationImpl.loadClassAndCallPremain(InstrumentationImpl.java:338) Caused by: javax.naming.NamingException: Lookup failed for 'java:comp/env/jms/myQueue' in SerialContext targetHost=localhost,targetPort=3700 [Root exception is javax.naming.NameNotFoundException: No object bound for java:comp/env/jms/myQueue [Root exception is java.lang.NullPointerException]] at com.sun.enterprise.naming.impl.SerialContext.lookup(SerialContext.java:442) at javax.naming.InitialContext.lookup(InitialContext.java:392) at com.sun.enterprise.container.common.impl.util.InjectionManagerImpl._inject(InjectionManagerImpl.java:513) ... 15 more Caused by: javax.naming.NameNotFoundException: No object bound for java:comp/env/jms/myQueue [Root exception is java.lang.NullPointerException] at com.sun.enterprise.naming.impl.JavaURLContext.lookup(JavaURLContext.java:218) at com.sun.enterprise.naming.impl.SerialContext.lookup(SerialContext.java:428) ... 17 more Caused by: java.lang.NullPointerException at javax.naming.InitialContext.getURLScheme(InitialContext.java:269) at javax.naming.InitialContext.getURLOrDefaultInitCtx(InitialContext.java:318) at javax.naming.InitialContext.lookup(InitialContext.java:392) at com.sun.enterprise.naming.util.JndiNamingObjectFactory.create(JndiNamingObjectFactory.java:75) at com.sun.enterprise.naming.impl.GlassfishNamingManagerImpl.lookup(GlassfishNamingManagerImpl.java:688) at com.sun.enterprise.naming.impl.GlassfishNamingManagerImpl.lookup(GlassfishNamingManagerImpl.java:657) at com.sun.enterprise.naming.impl.JavaURLContext.lookup(JavaURLContext.java:148) ... 18 more Regards

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  • Multitenant NHibernate application with with separate SQL Server schema for each tenant

    - by Branko
    I am writing a new multi-tenant WCF RIA application. I plan to have a shared database with separate SQL Server schema for each tenant. I would like to use NHibernate for object-ralational mapping. Configuration of SQL Server schema in mapping classes doesn't help because it is static and would need one set of mapping classes for each tenant. Is it possible to dynamically configure ISession which SQL Server schema should be used for mapping objects to tables?

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  • quartz 2d multiple UIViews

    - by coure06
    I want to create two UIViews in quartz 2D application. First UIView for static text, it will redraw automatically after each one second. Second UIView for animated text, it will be redrawn automatically after each .1 second. How can i create multiple Views/Layers? Is there drawRect methods will be different?

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