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• Flexible forms and supporting database structure

  - by sunwukung

  I have been tasked with creating an application that allows administrators to alter the content of the user input form (i.e. add arbitrary fields) - the contents of which get stored in a database. Think Modx/Wordpress/Expression Engine template variables. The approach I've been looking at is implementing concrete tables where the specification is consistent (i.e. user profiles, user content etc) and some generic field data tables (i.e. text, boolean) to store non-specific values. Forms (and model fields) would be generated by first querying the tables and retrieving the relevant columns - although I've yet to think about how I would setup validation. I've taken a look at this problem, and it seems to be indicating an EAV type approach - which, from my brief research - looks like it could be a greater burden than the blessings it's flexibility would bring. I've read a couple of posts here, however, which suggest this is a dangerous route: How to design a generic database whose layout may change over time? Dynamic Database Schema I'd appreciate some advice on this matter if anyone has some to give regards SWK

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• UIImageView is clipping a pixel of the bottom of my UIImage...?

  - by akaii

  I'm not sure what might be causing this, but UIImageView occasionally clips off about a pixel or 2 from the bottom of some square/rectangular UIImages I'm using as subviews for UITableViewCells. These UIImageViews are well within the borders of the cell, so it shouldn't be due to cliptobounds. There seems to be no consistency or pattern to which images are being clipped, nor when they're clipped, other than that it only happens to (or is only noticable in) square/rectangular icons, and only ones that are parented to UITableViewCells (or their subclasses). I'm having trouble reproducing the problem consistently, which is why I haven't posted any code this time. Has anyone encountered something similar to this before? I've encountered a similar bug that involved floating point values for origin/size being interpreted weirdly... but that doesn't seem to be the cause of this particular problem. I don't need a specific solution at this point, I'm just making sure I haven't missed any well-known bugs or documented problems that involve UIImageView.

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• What is the fastest way to scrape HTML webpage in Android?

  - by kunjaan

  I need to extract information from an unstructured web page in Android. The information I want is embedded in a table that doesn't have an id. <table> <tr><td>Description</td><td></td><td>I want this field next to the description cell</td></tr> </table> Should I use Pattern Matching? Use BufferedReader to extract the information? Or are there faster way to get that information?

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• How do i set the Transaction Isolation in EJB?

  - by Nitesh Panchal

  Hello, I am not able to find a way to set TransactionIsolation in ejb. Can anybody tell me how do i set it? I am using persistence. I have looked the following classes : EntityManager , EntityManagerFactory, UserTransaction. None of them seems to have any method like setTransactionIsolation or such. Do we need to change persistence.xml? I just read a book named Mastering EJB 3.0 4th edition. They gave a full 10 page theory about Isolation level that this problems occur and that occurs and such things but at the end they gave this paragraph :- "As we now know, the EJB standard does not deal with isolation levels directly, and rightly so. EJB is a component specification. It defines the behavior and contracts of a business component with clients and middleware infrastructure (containers) such that the component can be rendered as various middleware services properly. EJBs therefore are transactional components that interact with resource managers, such as the JDBC resource manager or JMS resource manager, via JTS, as part of a transaction. They are not, hence, resource components in themselves. Since isolation levels are very specific to the behavior and capabilities of the underlying resources, they should therefore be specified at the resource API levels. " What exactly does it mean? What is meant by resource level APIs? Please help me. If persistence has no way to set Isolation Level then why do they give such huge theory in an EJB book and make it heavy in weight unnecessarily :(

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• How do you tell that your unit tests are correct?

  - by Jacob Adams

  I've only done minor unit testing at various points in my career. Whenever I start diving into it again, it always troubles me how to prove that my tests are correct. How can I tell that there isn't a bug in my unit test? Usually I end up running the app, proving it works, then using the unit test as a sort of regression test. What is the recommended approach and/or what is the approach you take to this problem? Edit: I also realize that you could write small, granular unit tests that would be easy to understand. However, if you assume that small, granular code is flawless and bulletproof, you could just write small, granular programs and not need unit testing. Edit2: For the arguments "unit testing is for making sure your changes don't break anything" and "this will only happen if the test has the exact same flaw as the code", what if the test overfits? It's possible to pass both good and bad code with a bad test. My main question is what good is unit testing since if your tests can be flawed you can't really improve your confidence in your code, can't really prove your refactoring worked, and can't really prove that you met the specification?

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• Are today's young programmers getting wrapped around the axle with patterns and practices?

  - by Robert Harvey

  Recently I have noticed a number of questions on SO that look something like this: I am writing a small program to keep a list of the songs that I keep on my ipod. I'm thinking about writing it as a 3-tier MVC Ruby on Rails web application with TDD, DDD and IOC, using a factory pattern to create the classes and a singleton to store my application settings. Do you think I'm taking the right approach? Do you think that we're handing novice programmers a very sharp knife and telling them, "Don't cut yourself with this"? NOTE: Despite the humorous tone, this is a serious (and programming-related) question.

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• javascript singleton question

  - by Shawn

  I just read a few threads on the discussion of singleton design in javascript. I'm 100% new to the Design Pattern stuff but as I see since a Singleton by definition won't have the need to be instantiated, conceptually if it's not to be instantiated, in my opinion it doesn't have to be treated like conventional objects which are created from a blueprint(classes). So my wonder is why not just think of a singleton just as something statically available that is wrapped in some sort of scope and that should be all. From the threads I saw, most of them make a singleton though traditional javascript new function(){} followed by making a pseudo constructor. Well I just think an object literal is enough enough: var singleton = { dothis: function(){}, dothat: function(){} } right? Or anybody got better insights? [update] : Again my point is why don't people just use a simpler way to make singletons in javascript as I showed in the second snippet, if there's an absolute reason please tell me. I'm usually afraid of this kind of situation that I simplify things to much :D

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• Routing Error in Chapter 7.1.2 of the Ruby on Rails Tutorial

  - by user2985910

  I've been working through the tutorial for the past few days, and finally hit a snag in chapter 7. It is in this step where the line in routes.rb: get "users/new" is replaced with resource :users After I do this, I get a routing error when visiting http://localhost:3000/users/1 - No route matches [GET] "/users/1" instead of the other "Unknown Action" error shown here. Per the instructions, my routes.db file looks like this: SampleApp::Application.routes.draw do resource :users root "static_pages#home" match '/signup', to: 'users#new', via: 'get' match '/help', to: 'static_pages#help', via: 'get' match '/about', to: 'static_pages#about', via: 'get' match '/contact', to: 'static_pages#contact', via: 'get' end Output from 'rake routes' shows: Prefix Verb URI Pattern Controller#Action users POST /users(.:format) users#create new_users GET /users/new(.:format) users#new edit_users GET /users/edit(.:format) users#edit GET /users(.:format) users#show PATCH /users(.:format) users#update PUT /users(.:format) users#update DELETE /users(.:format) users#destroy root GET / static_pages#home signup GET /signup(.:format) users#new help GET /help(.:format) static_pages#help about GET /about(.:format) static_pages#about contact GET /contact(.:format) static_pages#contact Does anyone have any insight to get past this? Many thanks.

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• SELECT with a Replace()

  - by andyjohnson

  I have a table of names and addresses, which includes a postcode column. I want to strip the spaces from the postcodes and select any that match a particular pattern. I'm trying this (simplified a bit) in T-SQL on SQL Server 2005: SELECT Replace(Postcode, ' ', '') AS P FROM Contacts WHERE P LIKE 'NW101%' But I get the following error; Msg 207, Level 16, State 1, Line 3 Invalid column name 'P'. If I remove the WHERE clause I get a list of postcodes without spaces, which is what I want to search. How should I approach this? What am I doing wrong?

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• Avoiding configSections in .NET app.config files

  - by Chris Clark

  I'm looking for a way to avoid declaring my configuration section in the configSections inside the App.config file. Basically, I want to specify my configuration information just like I do for built-in .NET systems. For instance, when configuring WCF, I just put stuff in the <system.serviceModel>, I don't have to declare a section in the configSections up top. The same thing applies for <system.diagnostics> and many other namespaces. I know I could just load it up as an XML file and parse through it, but I'd prefer to stick with the pattern if possible. Moreover, looking at the WCF configuration with Reflector, I notice that it uses the same configuration subsystem (defined in System.Configuration). If you're wondering why this is important, it's because it's confusing our IT people. If it were self contained in one place, it would be much easier on them. I also realize I'll lose the ability to have multiple of the same section type, but that's not important in our case.

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• Asynchrous calls cause StaleObjectStateException

  - by Mulone

  Hi all, I'm struggling with a Grails service. The service gets AJAX calls from the clients and behaves like a simple local cache for remote objects: void **someCallFromClient**() { // extract params def results = remoteService.queryService(params) results.each{ // try to fetch result object from local DB def obj = SomeClass.findBySomeField(result.someField) if (!obj){ obj = new Result(params) obj.save() } // do stuff on obj } } The service works fine when only one client is connected, but as soon as 2 or more clients start bombing the server with requests, I start getting: 2010-05-24 13:09:49,764 [30893094@qtp-26315919-2] ERROR errors.GrailsExceptionResolver - Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [ some object #892901] org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [ some object #892901] // very long stactrace It probably happens when 2 calls are trying to create the same object concurrently. I suppose this is a rather typical situation to end up in. Could you recommend any pattern/good practice to fix this issue? For example, is there a way to say to one of the service instances to hang on and wait for the other to finish its stuff and try again? Cheers!

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• Cancelling Two Way Data Binding In Silverlight

  - by DaveB

  I have an ObervableCollection of data items. This collection is bound to a ListBox. When the user selects a item from the listbox and clicks the Edit button a UserControl with the details of that item is displayed with the various properties bound to text boxes. Each binding mode is set for TwoWay. On this details UserControl, I would like to implement 2 buttons, OK and Cancel. This would be consistent with UIs in Windows. This application is using the Model-View_ViewModel pattern. Here is my question: 1) How can I implement the Cancel button when all the changes have already been committed?

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• Beginner SQL section: avoiding repeated expression

  - by polygenelubricants

  I'm entirely new at SQL, but let's say that on the StackExchange Data Explorer, I just want to list the top 15 users by reputation, and I wrote something like this: SELECT TOP 15 DisplayName, Id, Reputation, Reputation/1000 As RepInK FROM Users WHERE RepInK > 10 ORDER BY Reputation DESC Currently this gives an Error: Invalid column name 'RepInK', which makes sense, I think, because RepInK is not a column in Users. I can easily fix this by saying WHERE Reputation/1000 > 10, essentially repeating the formula. So the questions are: Can I actually use the RepInK "column" in the WHERE clause? Do I perhaps need to create a virtual table/view with this column, and then do a SELECT/WHERE query on it? Can I name an expression, e.g. Reputation/1000, so I only have to repeat the names in a few places instead of the formula? What do you call this? A substitution macro? A function? A stored procedure? Is there an SQL quicksheet, glossary of terms, language specification, anything I can use to quickly pick up the syntax and semantics of the language? I understand that there are different "flavors"?

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• Setting up Matcher for String phrase match in file

  - by randomCoder

  Having trouble figuring out how to match a phrase string to a phrase in file stream. The file I'm dealing with contains random words such as: 3 little pigs built houses and 1 little pig went to the market etc. for many lines Using "little pig" as my pattern and matcher.find() I can locate 2 matches: "little pig" and "little pigs". However, I only want it to match "little pig". What can I do? I thought about using matcher.lookingAt() but I wouldn't know how to set a proper region when I can't rely on the file string phrases I'm matching being on separate lines.

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• In c++ is there any Events/delegates/interfaces/notifications! anything?

  - by Bach

  Say i have these classes ViewA and ViewB In objective C using the delegate pattern I could do @protocol ViewBDelegate{ - (void) doSomething(); } then in ViewB interface: id<ViewBDelegate> delegate; then in ViewA implementation i set the delegate: viewB.delegate = self; and now I can call in doSomething from viewB onto any that unknown type delegate. [delegate doSomething]; "C++ How to Program" has been the worse read an can't find simple examples that demonstrates basic design patterns. What i'm looking for in C++ is: events ActionScript and java either delegates or notifications in Objective C anything that allows class A, Class B and Class C to know that ClassX didSomething()!!! thanks

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• friend declaration in C++

  - by Happy Mittal

  In Thinking in C++ by Bruce eckel, there is an example given regarding friend functions as // Declaration (incomplete type specification): struct X; struct Y { void f(X*); }; struct X { // Definition private: int i; public: friend void Y::f(X*); // Struct member friend }; void Y::f(X* x) { x->i = 47; } Now he explained this: Notice that Y::f(X*) takes the address of an X object. This is critical because the compiler always knows how to pass an address, which is of a fixed size regardless of the object being passed, even if it doesn’t have full information about the size of the type. If you try to pass the whole object, however, the compiler must see the entire structure definition of X, to know the size and how to pass it, before it allows you to declare a function such as Y::g(X). But when I tried void f(X); as declaration in struct Y, it shows no error. Please explain why?

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• Behavior with primitive data types' value out of range & C99's PRI* macros

  - by Yktula

  Say we have an 8-bit unsigned integer n (UINT8_MAX=255); what is the behavior of the compiler for n=256? Where can I find a table of default behavior when the value of a data type is out of range for different data types? Is there a pattern to how they behave when set out of range? #include <stdio.h> #include <inttypes.h> uint8_t n = UINT8_MAX; int main() { printf("%hhu ",n++); printf("%hhu",n); return 0; } Compiling with gcc -std=c99 -Wall *.c, this prints: 255 0 Also, is it acceptable to use C99's PRI* macros? How are they named?

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• Is it possible to create nested classes in PHP as it is in C#?

  - by Edward Tanguay

  In C# you can have nested classes like this, which are useful if you have classes which do not have meaning outside the scope of one particular class, e.g. in a factory pattern: public abstract class BankAccount { private BankAccount() {} private sealed class SavingsAccount : BankAccount { ... } private sealed class CheckingAccount : BankAccount { ... } public BankAccount MakeSavingAccount() { ... } public BankAccount MakeCheckingAccount() { ... } } Is this possible in PHP? I've read that it was planned for PHP 5, then cancelled, then planned again, but can't find definitive info. Does anyone know how to create nested classes (classes within the scope of another class) as in the above C# example using PHP 5.3?

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• How, in general, can web framework support REST style?

  - by juro

  I would like to know, what are the ways a web framework may be suitable for designing a RESTful app, in general. One goal is for example to provide http request routing, so they are automatically sent to appropriate controllers. From architectural point of view, web framework based on MVC pattern are more suitable for REST. What other features of web frameworks are helpful by building apps satisfying the REST constraints? Is there any reason why you consider certain languages(python/java) or web frameworks(django/turbogears/jersey/restlets/...) as the most applicable ones?

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• Strict pointer aliasing: is access through a 'volatile' pointer/reference a solution?

  - by doublep

  On the heels of a specific problem, a self-answer and comments to it, I'd like to understand if it is a proper solution, workaround/hack or just plain wrong. Specifically, I rewrote code: T x = ...; if (*reinterpret_cast <int*> (&x) == 0) ... As: T x = ...; if (*reinterpret_cast <volatile int*> (&x) == 0) ... with a volatile qualifier to the pointer. Let's just assume that treating T as int in my situation makes sense. Does this accessing through a volatile reference solve pointer aliasing problem? For a reference, from specification: [ Note: volatile is a hint to the implementation to avoid aggressive optimization involving the object because the value of the object might be changed by means undetectable by an implementation. See 1.9 for detailed semantics. In general, the semantics of volatile are intended to be the same in C++ as they are in C. — end note ] EDIT: The above code did solve my problem at least on GCC 4.5.

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• Boost singleton and undefined reference

  - by Ockonal

  Hello, I globally use singleton pattern in my project. To make it easier - boost::singleton. Current project uses Ogre3d library for rendering. Here is some class: class GraphicSystem : public singleton<GraphicSystem> { private: Ogre::RenderWindow *mWindow; public: Ogre::RenderWindow *getWindow() const { return mWindow; } }; In GraphicSystem constructor I fill the mWindow value: mWindow = mRoot->createRenderWindow(...); I cheked it, everything makes normally. So, now I have to use handler for the window in input system (to get window handle). Somewhere else in another class: Ogre::RenderWindow *temp = GraphicSystem::get_mutable_instance().getWindow(); GraphicSystem::get_mutable_instance().getWindow()->getCustomAttribute("WINDOW", &mWindowHandle); temp is 0x00, and there is segfault at last line (getting custon attribute). I can't understand, why does singleton returns undefined pointer for the window. All another singleton-based classes work well.

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• Why is 'using' improving C# performances

  - by Wernight

  It seems that in most cases the C# compiler could call Dispose() automatically. Like most cases of the using pattern look like: public void SomeMethod() { ... using (var foo = new Foo()) { ... } // Foo isn't use after here (obviously). ... } Since foo isn't used (that's a very simple detection) and since its not provided as argument to another method (that's a supposition that applies to many use cases and can be extended), the compiler could automatically call Dispose() without the developper requiring to do it. This means that in most cases the using is pretty useless if the compiler does some smart job. IDisposable seem low level enough to me to be taken in account by a compiler. Now why isn't this done? Wouldn't that improve the performances (if the developpers are... dirty).

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• silverlight vs ASP.NET MVC

  - by magellings

  I'm debating whether to use Silverlight 2.0 vs ASP.NET MVC for a web application. The web application will be a subscription free service marketing all age groups. It's important the source is highly testable, but also with the Web 2.0 movement a graphical web application is important as well for competitive reasons. I'm assuming silverlight is better than the ajax helpers/MVC graphically, but foundation-wise testing is better/easier with MVC. Possibly an MVP pattern with Silverlight could increase the testability of the source. Could anyone elaborate on the pros/cons of each technology and recommend one or the other based on the above? (addition 9/22/08) In regards to allowing search engines to index the site, using either technology it will utilize a backend database whereas a lot of the content will be dynamically generated. Based on some of the comments, when we talk of the searchable content would the home page of the application if written in silverlight be searchable? Would I be able to get the site to appear in a google search?

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• Recommendations with hierarchical data on non-relational databases?

  - by Luki

  I'm developing an web application that uses a non-relational database as a backend (django-nonrel + AppEngine). I need to store some hierarchical data (projects/subproject_1/subproject_N/tasks), and I'm wondering which pattern should I use. For now I thought of: Adjacency List (store the item's parent id) Nested sets (store left and right values for the item) In my case, the depth of nesting for a normal user will not exceed 4-5 levels. Also, on the UI, I would like to have a pagination for the items on the first level, to avoid to load too many items at the first page load. From what I understand so far, nested sets are great when the hierarchy is used more for displaying. Adjacency lists are great when editing on the tree is done often. In my case I guess I need the displaying more than the editing (when using nested sets, even if the display would work great, the above pagination could complicate things on editing). Do you have any thoughts and advice, based on your experience with the non-relational databases?

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• Django - Static content display based on URL

  - by Steven Potter

  I'm working on a Django site with a basic three column design. Left column navigation, center column content and right column URL specific content blocks. My question is about the best method of controlling the URL specific content blocks in the right column. I am thinking of something along the lines of the Flatpages app that will make the content available to the template context if the URL matches a pre-determined pattern (perhaps regex?). Does anyone know if such an app already exists? If not, I am looking for some advice about the best way to implement it. Particularly in relation to the matching of patterns to the current URL. Is there any good way to re-use parts of the Django URL dispatcher for this use?

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