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• Looking for a good course/book/resource on modern databases

  - by spanky

  This is slightly embarrassing. I'm a professional developer working at one of the big tech companies and I've never used a database. I've got an idea for a website I want to build as a learning experience and possibly as a business, but I don't have the faintest idea what database to use, let alone how to fix/debug the database when I run into problems. I'm looking for a course, a website, a book, etc., that will give me an overview of modern database technology (SQL vs. NOSQL vs. relational vs. non-relational (I only have a vague idea what these even mean)). I'm starting by googling/wikipediaing all of these terms, but if there are better, comprehensive resources available that I should be aware of, I'd love to hear about them.

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• Index out of range, but why?

  - by Stuart

  I have a gridview, and i have a SelectedIndexChanged event on it... protected void GridView1_SelectedIndexChanged(object sender, EventArgs e) { GridViewRow Row = GridView1.SelectedRow; //do some stuff } Then i get an error... Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index I dont understand why, the Gridview is being binded in pageload. but not in post back... if (!IsPostBack) { GridView1.DataSource = UserAccounts; GridView1.DataBind(); }

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• I want to be able to derive from a class internally, but disallow class in other assemblies to derive from the class

  - by Rokke

  Hej I have the following setup: Assembly 1 public abstract class XX<T> : XX where T: YY { } public abstract class XX {} Assembly 2 public class ZZ : YY {} public class ZZFriend : XX<ZZ> {} I use this feature in reflection when in YY: public class YY { public Type FindFriend { return GetType().Assembly.GetTypes().FirstOrDefault( t => t.BaseType != null && t.BaseType.IsGenericType && typeof(XX).IsAssignableFrom(t) && t.BaseType.GetGenericArguments().FirstOrDefault() == GetType()); } } I would like do disallow inheritance of the non generic class XX like: public class ZZFriend: XX {} Alternatively, I need a method like (that can be used in the reflection in YY.FindFrind()): public Type F(Type t) { return GetTypeThatIsGeneric(XX, Type genericTypeParameter); } That can be used in YY as: Typeof(XX<ZZ) == F(typeof(GetType()) Hope that makes sense... Thanks in advance Søren Rokkedal

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• Identifying control characters in Perl

  - by sganesh

  Actually, I am doing one project. In that I want to implement the command line features as like in linux terminal. And I saw this in ftp command also. If I press tab I need to list the commands. If I press control characters I need to get that characters based on that I will do some action. And If I give any commands it should execute. For this I tried with Term::ReadKey that is non canonical mode. But here I am facing more problems like, If I press any control character or arrow I got three characters. Ex: for up arrow I got ascii as 279165. Can anyone help me out of this problem? And I feel that there will be a better solution for this. Thanks in Advance.

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• Sorting and displaying a custom QVariant type.

  - by Kranar

  Hello, I have a custom type I'd like to use with QVariant but I don't know how to get the QVariant to display in a table or have it sort in a QSortFilterProxyModel. I register the type with Q_DECLARE_METATYPE and wrote streaming operators registered via qRegisterMetaTypeStreamOperators but for whatever reason when I use the type with a table model, it doesn't display anything and it doesn't sort. I should specify that this custom type can not be modified. It has a copy and default constructor, but I can not go in and modify the source code to get it to work with QVariant. Is there a way of non-intrusively getting the behaviour I'd like?

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• How to identify deadlock conditions in a third-party application?

  - by Imhotep is Invisible

  I am using a third-party application to handle batch CD audio extraction via multiple FireWire attached devices, but the application frequently (though non-deterministically) hangs during the extraction. I suspect that the multithreaded application is deadlocking over some shared resource. The developer, however, suspects the problem lies elsewhere but is not addressing the problem at this time. I would like to be able to do some legwork on my end to a) prove the condition exists and b) ideally point him in the right direction. The problems: while I used to be a programmer, it's been awhile and I need to shake off the dust (last work I did was back in '99 and it was under Solaris, while the application runs under XP). Rather than there being a dearth of information online, there's almost too much to digest. Are there any suggested guides or tutorials that might help me get back up to speed sufficient enough to help identify and/or diagnose the deadlock, or are there tools or approaches that I should study up on to aid me in my task? Many thanks for all suggestions!

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• Detect when home button is pressed iOS

  - by nick

  I have several iOS apps that all use the same port to listen for a network beacon. On the main view I use viewWillDisappear to close the port when another view is opened, which was working great. Then I noticed if I pressed the home button from the main view controller without opening another view to close the port, then the port stays open and non of my other apps can listen on that port any more. I then tried using viewWillUnload, but that doesn't seem to get called when I press the home button. -(void)viewWillUnload { //[super viewWillUnload]; NSLog(@"View will unload"); [udpSocket close]; udpSocket = nil; } View will unload is never displayed in the console, which leads me to believe that the method is never getting called. Is there a way to detect when the home button is pressed so I can close my port?

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• fastest in objC: IsEqualToString:@"" or length > 0?

  - by Cœur

  I'd like to know which one is fastest for testing a non-empty NSString for iOS 4.0+ (iPhone 3G). Note: the strings to test will be 99% of the time from 2 to 100 chars length. if ([foo length] > 0) or if ([foo isEqualToString:@""] == NO && foo != nil) I think it depends if isEqualToString: compares the length first (and in that case first way is faster) or if isEqualToString: compares first character of strings first (and in that case second way might be faster). ps: I already know isEqualToString: is faster than isEqual: which is itself faster than compare:.

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• Aside from performance concerns, is Java still chosen over Groovy/JRuby etc.?

  - by yar

  [This is an empirical question about the state-of-the-art: I am NOT asking if Java is cooler or less cool than the dynamic languages that work in the JVM.] Aside from cases where performance is a main decision factor, do companies/developers still willingly chose Java over Groovy, JRuby or JPython? Personal Note: The reason I am asking is that, while I do some subset of my professional work in Ruby (not JRuby, for now), in my personal projects I use Java. While I have written non-trivial apps in Groovy, I prefer Java, but I wonder if I should just get over it and do everything in Groovy. I like Java because I feel that static typing saves me time and aids refactoring. (No, I am not familiar with Scala.) However, I feel that this very empirical, on-topic programming question may inform my decision.

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• Visual Studio Snippets: How to reference an assembly that is not in the GAC

  - by user334220

  Hi, I have a 3rd party non-signed assembly that I want to reference in several projects. So I created a snippet to add the reference and the relative imports I tried the following, and several variations with full paths, without file:// etc, to no avail. Any ideas? ... <Snippet> <References> <Reference> <Assembly>MyAssemly.dll</Assembly> <Url>file://C:\Program Files\MyProduct</Url> </Reference> </References> <Imports> <Import> ...

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• How big can a SQL Server row be before it's a problem?

  - by John Leidegren

  Occasionally I run into this limitation using SQL Server 2000 that a row size can not exceed 8K bytes. SQL Server 2000 isn't really state of the art, but it's still in production code and because some tables are denormalized that's a problem. However, this seems to be a non issue with SQL Server 2005. At least, it won't complain that row sizes are bigger than 8K, but what happens instead and why was this a problem in SQL Server 2000? Do I need to care about my rows growing? Should I try and avoid large rows? Are varchar(max) and varbinary(max) a solution or expensive, in terms of size in database and/or CPU time? Why do I care at all about specifying the length of a particular column, when it seems like it's just a matter of time before someones going to hit that upper limit?

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• Java ServerSocketChannel SocketChannel (Callback)

  - by ikurtz

  I am trying to learn Java. I would like to implement a simple networked connect 4 game as well as a chat feature. I want my network logic to be non blocking so after much study I found that SocketChannel is what I am after regrading my needs. What has not made sense still is the lack of CallBack functions in SocketChannels.. Like one finds in C#. My query for this time is: How do I deliver the data received to the Chat or Game form (JFrame)? Some guidance is most welcome.

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• Why isn't the compiler smarter in this const function overloading problem?

  - by Frank

  The following code does not compile: #include <iostream> class Foo { std::string s; public: const std::string& GetString() const { return s; } std::string* GetString() { return &s; } }; int main(int argc, char** argv){ Foo foo; const std::string& s = foo.GetString(); // error return 0; } I get the following error: const1.cc:11: error: invalid initialization of reference of type 'const std::string&' from expression of type 'std::string* It does make some sense because foo is not of type const Foo, but just Foo, so the compiler wants to use the non-const function. But still, why can't it recognize that I want to call the const GetString function, by looking at the (type of) variable I assign it to? I found this kind of surprising.

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• Is catching NumberFormatException a bad practice?

  - by integeruser

  I have to parse a String that can assume hex values or other non-hex values 0xff, 0x31 or A, PC, label, and so on. I use this code to divide the two cases: String input = readInput(); try { int hex = Integer.decode(input); // use hex ... } catch (NumberFormatException e) { // input is not a hex, continue parsing } Can this code be considered "ugly" or difficult to read? Are there other (maybe more elegant) solutions? EDIT : I want to clarify that (in my case) a wrong input doesn't exist: i just need to distinguish if it is a hex number, or not. And just for completeness, i'm making a simple assebler for DCPU-16.

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• Extract elements from list based on object property type

  - by Dustin Digmann

  Often, I have a list of objects. Each object has properties. I want to extract a subset of the list where a specific property has a predefined value. Example: I have a list of User objects. A User has a homeTown. I want to extract all users from my list with "Springfield" as their homeTown. I normally see this accomplished as follows: List users = getTheUsers(); List returnList = new ArrayList(); for (User user: users) { if ("springfield".equalsIgnoreCase(user.getHomeTown()) returnList.add(user); } I am not particularly satisfied with this solution. Yes, it works, but it seems so slow. There must be a non-linear solution. Suggestions?

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• C Newbie, ascii control function

  - by user570607

  Hey there, I have written a program that works well in C that converts non-readable ASCII to their character values. I would appreciate if a C master? would show me a better way of doing it that I have currently done, mainly this section: if (isascii(ch)) { switch (ch) { case 0: printControl("NUL"); break; case 1: printControl("SOH"); break; .. etc (32 in total) case default: putchar(ch); break; } } Is it normal to make a switch that big? Or should I be using some other method (input from an ascii table?)

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• Best way to use the same HTML on static web-pages

  - by John

  If you use dynamic pages like JSP or asp.net, you can have your page template included, and then content added. But what if you have no server-side component and all pages are just HTML/JS? You can of course create a template then copy it for each page, but then if you want to change something you risk having to modify every page, even if you put most styling in CSS properly. Are there any non-awful ways to do this? I could see that an iframe could be used to load the content into the central page but that sounds nasty. Does HTML provide any way to include a base file and add to it?

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• Why does Ruby 1.9.2 remove "." from LOAD_PATH, and what's the alternative?

  - by John Feminella

  The latest changesets to Ruby 1.9.2 no longer make the current directory . part of your LOAD_PATH. I have a non-trivial number of Rakefiles that assume that . is part of the LOAD_PATH, so this broke them. Was there a particular justification for doing this? As for a fix, adding $: << "." everywhere works, but seems incredibly hacky and I don't want to do that. What's the preferred way to make my Rakefiles 1.9.2+ compatible?

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• Most optimal way to detect if black (or any color pixels) exist in an image file?

  - by Zando

  What's the best and most flexible algorithm to detect any black (or colored pixel) in a given image file? Say I'm given an image file that could, say, have a blue background. And any non blue pixel, including a white pixel, is counted as a "mark". The function returns true if there are X number of pixels that deviate from each other at a certain threshold. I thought it'd be fastest to just simply iterate through every pixel and see if its color matches the last. But if it's the case that pixel (0,0) is deviant, and every other pixel is the same color (and I want to allow at least a couple deviated pixels before considering an image to be "marked), this won't work or be terribly efficient.

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• iOS - Losing in-app subscription?

  - by user3280451

  I've just built an iOS app that uses a non-reoccuring subscription model. You hit "buy" and then when the client device receives the receipt from the Apple server it whizzes it off to my server to validate it and add the subscription to my user database. If the connection fails before my server has responded then the request is cached, ready to be resent the next time the client comes online. My problem is, what happens if the connection fails between when the user hits the buy button and the receipt is received by the client from Apple? Theres no way for it to know that the purchase has been made? Presumably I should add a "restore purchases" button that sends all of the users receipts to my server which checks if they've already been validated and their respective subscriptions added to the database? Is there a less intrusive way of doing this?

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• Using Rails, how can I set my primary key to not be an integer-typed column?

  - by Rudd Zwolinski

  I'm using Rails migrations to manage a database schema, and I'm creating a simple table where I'd like to use a non-integer value as the primary key (in particular, a string). To abstract away from my problem, let's say there's a table employees where employees are identified by an alphanumeric string, e.g. "134SNW". I've tried creating the table in a migration like this: create_table :employees, {:primary_key => :emp_id} do |t| t.string :emp_id t.string :first_name t.string :last_name end What this gives me is what seems like it completely ignored the line t.string :emp_id and went ahead and made it an integer column. Is there some other way to have rails generate the PRIMARY_KEY constraint (I'm using PostgreSQL) for me, without having to write the SQL in an execute call? NOTE: I know it's not best to use string columns as primary keys, so please no answers just saying to add an integer primary key. I may add one anyway, but this question is still valid.

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• For what purposes have YOU used T4?

  - by Chris Melinn

  T4 has existed for several years in Visual Studio, but doesn't get a lot of attention. However, for those that know it, there seems to be some very creative and useful purposes. I am researching some different ways that T4 is used, and I would appreciate to hear how YOU may have used it for real life scenarios. I am primarily interested in non-standard and creative uses. Some interesting examples: Phil Haack uses T4 to create static CSS files from .less To Generate WPF and Silverlight Dependency Properties using T4 Templates Note: I realize this is a discussion-oriented question, but the answers could be helpful to others. I have tagged it as subjective and also marked as "community wiki", so please allow the question to remain open. Thanks!

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• How does HTTP Analyzer works?

  - by Rampage

  Halo, i am interest in methods, which http analyzer uses to capture data. I would like to write program which saves emails sent via web based clients. The problem is https and HTTP Analyzer solves it, but i dont know how. I got one interesting answer on my question before, but it doesnt reveal as much as i would like to know. Programs like HTTP Analyzer can catch the HTTPS data because they insert themselves in the HTTPS stack. As a result, they get the data after it's generated but before it's being encrypted and put in IP packets. This is highly non-trivial. How it is possible to make? If you have any interesting articles solving this issue, please let me know.

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• Why are Objective-C instance variables declared in an interface?

  - by Chase

  I'm just getting into Objective-C (Java is my primary OO language). Defining an object's instance variables in the interface instead of the class seems strange. I'm used to an interface being a public API definition with nothing besides method signatures (not counting constants here). Is there some reason that state is defined in an interface (even if it is private) and behaviour is defined in a class. It just seems odd that since objects are state+behavior that the definition would be split into two separate places. Is it a design benefit is some way? A pain in the rear issue that you are just forced to deal with in Objective-C? A non-issue, just different? Any background on why it's done this way? Or can you put object state in a class and I just haven't hit that part in my book yet?

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• What's the advantage of an Adobe AIR app over a traditional desktop app?

  - by John

  I'm pretty familiar with using Adobe Flex & AS3, and compared with writing apps in JS/HTML I think it's very cool. However, since AIR is essentially a non-browser version of Flex with benefits like local storage, it seems to be competing as a cross-platform desktop application platform... and in that space it's much less mature than more established desktop technologies. So what's the advantage of creating a desktop application using AIR compared to something like Java (or C++ using a cross-platform GUI library like wxWidgets)? Java's equally capable of communicating with the server for instance, I'm not quite sure what AIR adds when competing head-to-head in the desktop development world?

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