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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 clear the the activity stack in android.

  - by Sam

  Hi, im having following application flow in my android app, Login-Home-screen1-screen2-screen3-screen4- logout In the screen4 i've a log out button,which allow user to logout from the application and re login.when i re-logn to the app previous data still be shown,is there way to start the application in fresh when user log out from the app NOTE: all the above activities launch mode set to "single task", regards, Sam.

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• CSS Multi-Column Forms in HTML/ASP.NET

  - by Caveatrob

  I've researched for hours and still haven't found a robust, non-absolute-positioning solution for displaying multiple-column forms and values without using TABLE tags. Can someone point me to a resource specifically oriented towards reproducing table-based, multiple-column forms (like name and address forms) in CSS to standards? Most of the forms I see only have a single column with field/value.

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• Why would an error get thrown inside my try-catch?

  - by George Johnston

  Why would my try-catch block still be throwing an error when it's handled? Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. Try Here >> : _MemoryStream.Seek(6 * StartOffset, 0) _MemoryStream.Read(_Buffer, 0, 6) Catch ex As IOException // Handle Error End Try Edit: Cleaned the question up to remove the extraneous information.

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• How to do both ways integrations across different perfoce depots?

  - by Sorin Sbarnea

  I would like to know how we are supposed to do integration between different perforce servers/depots. I'm looking for a solution that would allow us to do both-ways integrations. Currently I found some information on Using Remote Depots article where they say how to map the remote depot as read only. Is there the only solution to do mappings on both servers? - this means that I could not use a single branch spec to do both ways integrations.

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• How does one escape backslashes and forward slashes in VIM find/search?

  - by stormist

  For instance, if I wanted to a find and replace with strings containing backward or forward slashes, how would this be accomplished in vim? Thank you! Examples Find & Replace is : :%s/foo/bar/g what if I wanted to find all occurences of <dog/> and replace it with <cat\>

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• Mixing two wav music files of different size

  - by iphoneDev

  Hi, I want to mix audio files of different size into a one single .wav file. There is a sample through which we can mix files of same size [(http://www.modejong.com/iOS/#ex4 )(Example 4)]. I modified the code to get the mixed file as a .wav file. But I am not able to understand that how to modify this code for unequal sized files. If someone can help me out with some code snippet,i'll be really thankful.

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• Binding JBoss to IP Address

  - by Anand

  Hi, I am running a JBoss instance on a linux server I am using the ./run.sh -b This is not working what could be the reason. I am unable to share the error message details as of now will post it when I can, till then any alternatives or solutions ?

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• How to lock files in a tomcat web application?

  - by yankee

  The Java manual says: The locks held on a particular file by a single Java virtual machine do not overlap. The overlaps method may be used to test whether a candidate lock range overlaps an existing lock. I guess that if I lock a file in a tomcat web application I can't be sure that every call to this application is done by a different JVM, can I? So how can I lock files within my tomcat application in a reliable way?

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• What is the proper backlog for an asynchronous server socket?

  - by The.Anti.9

  If you're working with an Asynchronous server socket in C#, what is the proper backlog to put on the socket? For instance: server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); IPEndPoint iep = new IPEndPoint(IPAddress.Any, port); server.Bind(iep); server.Listen(10);

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• Can nunit be configured to drop the app domain per fixture (or per test)

  - by Ralph Shillington

  In testing singleton classes we need the single instance to "go away" after each test. Is there a way to configure nunit to recreate the test app domain after each test, or at least after each fixture?

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• Automatically connect to a DB in a swing application

  - by Oussama

  Hello, I m working on a single user swing application that access an hsqldb database. How can i Automatically run the DB server when a user run the application.? for example, after i finish development i will put the application into an exe file. If the exe file is distributed to multiple users. How can the DB server run and the DB be created when the user run the exe file? Thanks

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• Create normal zip file programmatically

  - by j-t-s

  Hi All I have seen many tutorials on how to compress a single file in c#. But I need to be able to create a normal *.zip file out of more than just one file. Is there anything in .NET that can do this? What would you suggest (baring in mind I'm under strict rules and cannot use other libraries) Thank you

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• How can I write an installer for 32 and 64 bit

  - by tom greene

  I have a .NET app which works in 32 and 64 bit. I would like to write one single installer that installs to c:\program files, not c:\program files(x86) regardless of the platform. From this link: http://msdn.microsoft.com/en-us/library/w1behyzx(v=VS.90).aspx it doesn't look possible. Is it the case?

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• Learning to read GCC assembler output

  - by porgarmingduod

  I'm considering picking up some very rudimentary understanding of assembly. My current goal is simple: VERY BASIC understanding of GCC assembler output when compiling C/C++ with the -S switch. Just enough to do simple things such as looking at a single function and verifying whether GCC optimizes away things I expect to disappear. Does anyone have/know of a truly concise introduction to assembly, relevant to GCC and specifically for the purpose of reading, and a list of the most important instructions anyone casually reading assembly should know?

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• Which programming languages that can generate self contained windows .exes?

  - by Zubair

  I want to make an easy to deploy Windows application and was was wondering which programming systems can create totally self contained Windows .exe files? As a plus, if the same can be done with MacOSX and Linux from the same source this would be a bonus. I took a look at Realbasic but they have since abandoned the single .exe concept.

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• Question about factory classes

  - by devoured elysium

  Currently I have created a ABCFactory class that has a single method creating ABC objects. Now that I think of it, maybe instead of having a factory, I could just make a static method in my ABC Method. What are the pro's and con's on making this change? Will it not lead to the same? I don't foresee having other classes inherit ABC, but one never knows! Thanks

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• Deleting Multiple rows from a TableView

  - by Sid

  hi Frnz, i want to delete multiple rows from a table view based on users selection.obviously i cant use didSelectRowAtIndexPath method coz it will be called for every row selected. i want to allow user to select multiple rows for deletion and then delete them in one go...Is it possible if yes then how to go about it.Also i am using a single view based project and i want the header of table view changed to "Delete" on the same view when the user want to delete the rows from the view. Thx

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• Linq to SQL - Returning two values with one query

  - by Sir Psycho

  Hi, Is it possible to return a single value and an enumerable collection using LINQ to SQL? The problem is, I'm trying to do paging across a large recordset. I only want to return 10 rows at a time so I'm using .Skip(20).Take(10) approach. However I need to know the total number of records so I can show an appropriate page x of y. Trying to avoid two separate queries. Thanks

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• Handling multiple HTTP requests from one source (e.g.a hacker)

  - by Haraldo

  Hi there, I have a script to handle http requests. I'm trying to think of some of the security issues I might have with it. My biggest concern at the moment is how I can manage multiple requests from the same source over and over. For instance someone trying to shut down my system. Do I need to be concerned or will Apache handling this issue. If not what is the best approach to take using php? Thanks,

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• Using AMQP to collect events

  - by synapse

  Does AMQP has any advantages over an ad-hoc implementation for a simple stats gathering scenario? It works like this - clients send events (more than we care to put into persistent storage) to (several) web workers, the workers aggrregate them and write to a single database. I don't think I should consider using AMQP for this because I'll still need web workers to receive events from clients through HTTP and to publish them. Am I missing something?

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• How to create a windows service from java app

  - by ideasculptor

  I've just inherited a java application that needs to be installed as a service on XP and vista. It's been about 8 years since I've used windows in any form and I've never had to create a service, let alone from something like a java app (I've got a jar for the app and a single dependency jar - log4j). What is the magic necessary to make this run as a service? I've got the source, so code modifications, though preferably avoided, are possible.

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• Explain this C++ operator definition

  - by David Johnstone

  I have the following operator defined in a C++ class called StringProxy: operator std::string&() { return m_string; } a) What is this and how does this work? I understand the idea of operator overloading, but they normally look like X operator+(double i). b) Given an instance of StringProxy, how can I use this operator to get the m_string?

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• using a Singleton to pass credentials in a multi-tenant application a code smell?

  - by Hans Gruber

  Currently working on a multi-tenant application that employs Shared DB/Shared Schema approach. IOW, we enforce tenant data segregation by defining a TenantID column on all tables. By convention, all SQL reads/writes must include a Where TenantID = '?' clause. Not an ideal solution, but hindsight is 20/20. Anyway, since virtually every page/workflow in our app must display tenant specific data, I made the (poor) decision at the project's outset to employ a Singleton to encapsulate the current user credentials (i.e. TenantID and UserID). My thinking at the time was that I didn't want to add a TenantID parameter to each and every method signature in my Data layer. Here's what the basic pseudo-code looks like: public class UserIdentity { public UserIdentity(int tenantID, int userID) { TenantID = tenantID; UserID = userID; } public int TenantID { get; private set; } public int UserID { get; private set; } } public class AuthenticationModule : IHttpModule { public void Init(HttpApplication context) { context.AuthenticateRequest += new EventHandler(context_AuthenticateRequest); } private void context_AuthenticateRequest(object sender, EventArgs e) { var userIdentity = _authenticationService.AuthenticateUser(sender); if (userIdentity == null) { //authentication failed, so redirect to login page, etc } else { //put the userIdentity into the HttpContext object so that //its only valid for the lifetime of a single request HttpContext.Current.Items["UserIdentity"] = userIdentity; } } } public static class CurrentUser { public static UserIdentity Instance { get { return HttpContext.Current.Items["UserIdentity"]; } } } public class WidgetRepository: IWidgetRepository{ public IEnumerable<Widget> ListWidgets(){ var tenantId = CurrentUser.Instance.TenantID; //call sproc with tenantId parameter } } As you can see, there are several code smells here. This is a singleton, so it's already not unit test friendly. On top of that you have a very tight-coupling between CurrentUser and the HttpContext object. By extension, this also means that I have a reference to System.Web in my Data layer (shudder). I want to pay down some technical debt this sprint by getting rid of this singleton for the reasons mentioned above. I have a few thoughts on what an better implementation might be, but if anyone has any guidance or lessons learned they could share, I would be much obliged.

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• runModalForWindow throttles http requests

  - by Nikita Rybak

  I have url connection, which normally works fine NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:delegate]; But when I create a modal window, no request ever receives response: [NSApp runModalForWindow:window]; If I comment this line out, thus creating a 'standard' window, everything works. I tried implementing all methods from NSURLConnectionDelegate, not a single of them called. I suspect this is something about 'run loops', but have little experience in this area. Does anybody have experience in this? Thank you

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