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  • What common interface would be appropriate for these game object classes?

    - by Jefffrey
    Question A component based system's goal is to solve the problems that derives from inheritance: for example the fact that some parts of the code (that are called components) are reused by very different classes that, hypothetically, would lie in a very different branch of the inheritance tree. That's a very nice concept, but I've found out that CBS is often hard to accomplish without using ugly hacks. Implementations of this system are often far from clean. But I don't want to discuss this any further. My question is: how can I solve the same problems a CBS try to solve with a very clean interface? (possibly with examples, there are a lot of abstract talks about the "perfect" design already). Context Here's an example I was going for before realizing I was just reinventing inheritance again: class Human { public: Position position; Movement movement; Sprite sprite; // other human specific components }; class Zombie { Position position; Movement movement; Sprite sprite; // other zombie specific components }; After writing that I realized I needed an interface, otherwise I would have needed N containers for N different types of objects (or to use boost::variant to gather them all together). So I've thought of polymorphism (move what systems do in a CBS design into class specific functions): class Entity { public: virtual void on_event(Event) {} // not pure virtual on purpose virtual void on_update(World) {} virtual void on_draw(Window) {} }; class Human : public Entity { private: Position position; Movement movement; Sprite sprite; public: virtual void on_event(Event) { ... } virtual void on_update(World) { ... } virtual void on_draw(Window) { ... } }; class Zombie : public Entity { private: Position position; Movement movement; Sprite sprite; public: virtual void on_event(Event) { ... } virtual void on_update(World) { ... } virtual void on_draw(Window) { ... } }; Which was nice, except for the fact that now the outside world would not even be able to know where a Human is positioned (it does not have access to its position member). That would be useful to track the player position for collision detection or if on_update the Zombie would want to track down its nearest human to move towards him. So I added const Position& get_position() const; to both the Zombie and Human classes. And then I realized that both functionality were shared, so it should have gone to the common base class: Entity. Do you notice anything? Yes, with that methodology I would have a god Entity class full of common functionality (which is the thing I was trying to avoid in the first place). Meaning of "hacks" in the implementation I'm referring to I'm talking about the implementations that defines Entities as simple IDs to which components are dynamically attached. Their implementation can vary from C-stylish: int last_id; Position* positions[MAX_ENTITIES]; Movement* movements[MAX_ENTITIES]; Where positions[i], movements[i], component[i], ... make up the entity. Or to more C++-style: int last_id; std::map<int, Position> positions; std::map<int, Movement> movements; From which systems can detect if an entity/id can have attached components.

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  • Framework for Everything - Where to begin? [Longer post]

    - by SquaredSoft
    Back story of this question, feel free to skip down for the specific question Hello, I've been very interested in the idea of abstract programming the last few years. I've made about 30 attempts at creating a piece of software that is capable of almost anything you throw at it. I've undertook some attempts at this that have taken upwards of a year, while getting close, never releasing it beyond my compiler. This has been something I've always tried wrapping my head around, and something is always missing. With the title, I'm sure you're assuming, "Yes of course you noob! You can't account for everything!" To which I have to reply, "Why not?" To give you some background into what I'm talking about, this all started with doing maybe a shade of gray hat SEO software. I found myself constantly having to create similar, but slightly different sets of code. I've gone through as many iterations of way to communicate on http as the universe has particles. "How many times am I going to have to write this multi-threaded class?" is something I found myself asking a lot. Sure, I could create a class library, and just work with that, but I always felt I could optimize what I had, which often was a large undertaking and typically involved frequent use of the CRTL+A keyboard shortcut, mixed with the delete button. It dawned on me that it was time to invest in a plugin system. This would allow me to simply add snippets of code. as time went on, and I could subversion stuff out, and distribute small chunks of code, rather than something that encompasses only a specific function or design. This comes with its own complexity, of course, and by the time I had finished the software scope for this addition, it hit me that I would want to add to everything in the software, not just a new http method, or automation code for a specific website. Great, we're getting more abstract. However, the software that I have in my mind comes down to a quite a few questions regarding its execution. I have to have some parameters to what I am going to do. After writing what the perfect software would do in my mind, I came up with this as a list of requirements: Should be able to use networking A "Macro" or "Expression system" which would allow people to do something like : =First(=ParseToList(=GetUrl("http://www.google.com?q=helloworld!"), Template.Google)) Multithreaded Able to add UI elements through some type of XML -- People can make their own addons etc. Can use third party API through the plugins, such as Microsoft CRM, Exchange, etc. This would allow the software to essentially be used for everything. Really, any task you wish to automate, in a simple way. Making the UI was as also extremely hard. How do you do all of this? Its very difficult. So my question: With so many attempts at this, I'm out of ideas how to successfully complete this. I have a very specific idea in my mind, but I keep failing to execute it. I'm a self taught programmer. I've been doing it for years, and work professionally in it, but I've never encountered something that would be as complex and in-depth as a system which essentially does everything. Where would you start? What are the best practices for design? How can I avoid constantly having to go back and optimize my software. What can I do to generalize this and draw everything out to completion. These are things I struggle with. P.s., I'm using c# as my main language. I feel like in this example, I might be hitting the outer limit of the language, although, I don't know if that is the case, or if I'm just a bad programmer. Thanks for your time.

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  • When things go awry

    - by Phil Factor
    The moment the Entrepreneur opened his mouth on prime-time national TV, spelled out the URL and waxed big on how exciting ‘his’ new website was, I knew I was in for a busy night. I’d designed and built it. All at once, half a million people tried to log into the website. Although all my stress-testing paid off, I have to admit that the network locked up tight long before there was any danger of a database or website problem. Soon afterwards, the Entrepreneur and the Big Boss were there in the autopsy meeting. We picked through all our systems in detail to see how they’d borne the unexpected strain. Mercifully, in view of the sour mood of the Big Boss, it turned out that the only thing we could have done better was buy a bigger pipe to and from the internet. We’d specified that ‘big pipe’ when designing the system. The Big Boss had then railed at the cost and so we’d subsequently compromised. I felt that my design decisions were vindicated. The Big Boss brooded for a while. Then he made the significant comment: “What really ****** me off is the fact that, for ten minutes, we couldn’t take people’s money.” At that point I stopped feeling smug. Had the internet connection been better, the system would have reached its limit and failed rather precipitously, and that wasn’t what he wanted. Then it occurred to me that what had gummed up the connection was all those images on the site, that had made it so impressive for the visitors. If there had been a way to automatically pare down the site to the bare essentials under stress… Hmm. I began to consider disaster-recovery in the broadest sense – maintaining a service in spite of unusual or unexpected events. What he said makes a lot of sense: sacrifice whatever isn’t essential to keep the core service running when we approach the capacity limits. Maybe in IT we should borrow (or revive) the business concept of the ‘Skeleton service’, maintaining only the priority parts under stress, using a process that is well-prepared and carefully rehearsed. How might this work? Whatever the event we have to prepare for, it is all about understanding the priorities; knowing what one can dispense with when the going gets tough. In the event of database disaster, it’s much faster to deploy a skeletal system with only the essential data than to restore the entire system, though there would have to be a reconciliation process to update the revived database retrospectively, once the emergency was over. It isn’t just the database that could be designed for resilience. One could prepare for unusually high traffic in a website by designing a system that degraded gradually to a ‘skeletal’ site, one that maintained the commercial essentials without fat images, JavaScript libraries and razzmatazz. This is all what the Big Boss scathingly called ‘a mere technicality’. It seems to me that what is needed first is a culture of application and database design which acknowledges that we live in a very imperfect world, and react accordingly when things go awry.

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  • Customer Loyalty vs. Customer Engagement: Who Cares?

    - by Jeb Dasteel-Oracle
    Have you read the recent Forbes OracleVoice blog titled Customer Loyalty is Dead. Long Live Engagement!? If you haven’t, take a look. This article prompted lots of conversation in the social realm. Many who read the article voiced their reactions to the headline and now I’m jumping in to add my view. Normal 0 false false false EN-US X-NONE X-NONE Customer loyalty is still key. It’s the effect and engagement is the cause. We at least know that to be true for our customers. We are in an age where customers are demanding to be heard. We need them to be actively involved – or engaged – as well. Greater levels of customer engagement, properly targeted, positively correlate with satisfaction. Our data has shown us this over and over. Satisfied customers are more loyal and more willing to vocalize their satisfaction through referencing, and are more likely to purchase again, all of which in turn drives incremental revenue – from the customer doing the referencing AND the customer on the receiving end of that reference. Turning this around completely, if we begin to see the level of a customer’s engagement start to wane, this is an indicator that their satisfaction, loyalty, and future revenue are likely at risk. At Oracle, we’ve put in place many programs to target, encourage, and then track engagement, allowing us to measure engagement as a determinant of loyalty. Some of these programs include our Key Accounts, solution design and architectural, Executive Sponsorship, as well as executive advisory boards. Specific programs allow us to engage specific contacts within specific customer organizations (based on role) and then systematically track their engagement activities over time, along side of tracking customer satisfaction, loyalty, referenceability, and incremental revenue contribution. Continuous measurement of engagement allows us to better understand customer views of what it means to partner with a provider and adjust program participation to better meet the needs of the partnership. We can also track across customer segments, and design new programs that are even more effective than the ones we have in place today. In case you missed any of my previous Forbes articles, I’ve included links below for easy access. Award-Winning Companies Put Customers First The Power of Peer Networks: 5 Reasons to Get (and Stay) Involved Technology At Work: Traveling In Style Customer Central: 8 Strategies for Putting Customers at the Core of Your Business Technology at Work: Five Companies Doing IT Right /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}

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  • XamlParseException using Silverlight Toolkit control in Expression Blend

    - by Dan Auclair
    I am having a strange issue opening up my UserControl in Expression Blend when using a Silverlight Toolkit control. My UserControl uses the toolkit's ListBoxDragDropTarget as follows: <controlsToolkit:ListBoxDragDropTarget mswindows:DragDrop.AllowDrop="True" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch"> <ListBox ItemsSource="{Binding MyItemControls}" ScrollViewer.HorizontalScrollBarVisibility="Disabled"> <ListBox.ItemsPanel> <ItemsPanelTemplate> <controlsToolkit:WrapPanel/> </ItemsPanelTemplate> </ListBox.ItemsPanel> </ListBox> </controlsToolkit:ListBoxDragDropTarget> Everything works as expected at runtime and looks fine in Visual Studio 2008. However, when I try to open my UserControl in Blend I get XamlParseException: [Line: 0 Position: 0] and I can not see anything in the design view. More specifically Blend complains: The element "ListBoxDragDropTarget" could not be displayed because of a problem with System.Windows.Controls.ListBoxDragDropTarget: TargetType mismatch. My silverlight application is referencing System.Windows.Controls.Toolkit from the Nov. 2009 toolkit release, and I've made sure to include these namespace declarations for the ListBoxDragDropTarget: xmlns:controlsToolkit="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Toolkit" xmlns:mswindows="clr-namespace:Microsoft.Windows;assembly=System.Windows.Controls.Toolkit" If I comment out the ListBoxDragDropTarget control wrapper and just leave the ListBox I can see everything fine in the design view without errors. Furthermore, I realized this is happening with a variety of Silverlight Toolkit controls because if I comment out ListBoxDragDropTarget and replace it with <controlsToolkit:BusyIndicator /> the same exact error occurs in Blend. What is even weirder is that if I start a brand new silverlight application in blend I can add these toolkit elements without any kind of error, so it seems like something dumb that is happening with my project references to the toolkit assemblies. I'm pretty sure this has something to do with loading the default styles for the toolkit controls from its generic.xaml, since the error has to do with the TargetType and Blend is probably trying to load up the default styles. Has anyone encountered this issue before or have any ideas as to what may be my problem?

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  • How to properly test for constraint violation in hibernate?

    - by Cesar
    I'm trying to test Hibernate mappings, specifically a unique constraint. My POJO is mapped as follows: <property name="name" type="string" unique="true" not-null="true" /> What I want to do is to test that I can't persist two entities with the same name: @Test(expected=ConstraintViolationException.class) public void testPersistTwoExpertiseAreasWithTheSameNameIsNotAllowed(){ ExpertiseArea ea = new ExpertiseArea("Design"); ExpertiseArea otherEA = new ExpertiseArea("Design"); ead.setSession(getSessionFactory().getCurrentSession()); ead.getSession().beginTransaction(); ead.makePersistent(ea); ead.makePersistent(otherEA); ead.getSession().getTransaction().commit(); } On commiting the current transaction, I can see in the logs that a ConstraintViolationException is thrown: 16:08:47,571 DEBUG SQL:111 - insert into ExpertiseArea (VERSION, name, id) values (?, ?, ?) Hibernate: insert into ExpertiseArea (VERSION, name, id) values (?, ?, ?) 16:08:47,571 DEBUG SQL:111 - insert into ExpertiseArea (VERSION, name, id) values (?, ?, ?) Hibernate: insert into ExpertiseArea (VERSION, name, id) values (?, ?, ?) 16:08:47,572 WARN JDBCExceptionReporter:100 - SQL Error: -104, SQLState: 23505 16:08:47,572 ERROR JDBCExceptionReporter:101 - integrity constraint violation: unique constraint or index violation; SYS_CT_10036 table: EXPERTISEAREA 16:08:47,573 ERROR AbstractFlushingEventListener:324 - Could not synchronize database state with session org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update So I would expect the test to pass, since the expected ConstraintViolationException is thrown. However, the test never completes (neither pass nor fails) and I have to manually kill the test runner. What's the correct way to test this?

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  • How to achieve "Blendability" when using DataServiceCollection in my ViewModel

    - by andlju
    I'm looking at using oData endpoints in my Silverlight client. Naturally, I'm doing MVVM and I want the project to be nice and "Blendable" (i.e. I must be able to cleanly use static data instead of the oData endpoints when in design mode.) Now to the problem. I'd like to use the DataServiceCollection in my ViewModels, since it allows for nice bindable collections without having to worry too much with BeginExecute/EndExecute etc. Now, let's look at some code. My Model interface looks like this: public interface ITasksModel { IQueryable<Task> Tasks { get; } } The oData endpoint implementation of that interface: public class TasksModel : ITasksModel { Uri svcUri = new Uri("http://localhost:2404/Services/TasksDataService.svc"); TaskModelContainer _container; public TasksModel() { _container = new TaskModelContainer(svcUri); } public IQueryable<Task> Tasks { get { return _container.TaskSet; } } } And the "Blendable" design-time implementation: public class DesignModeTasksModel : ITasksModel { private List<Task> _taskCollection = new List<Task>(); public DesignModeTasksModel() { _taskCollection.Add(new Task() { Id = 1, Title = "Task 1" }); _taskCollection.Add(new Task() { Id = 2, Title = "Task 2" }); _taskCollection.Add(new Task() { Id = 3, Title = "Task 3" }); } public IQueryable<Task> Tasks { get { return _taskCollection.AsQueryable(); } } } However, when I try to use this last one in my ViewModel constructor: public TaskListViewModel(ITasksModel tasksModel) { _tasksModel = tasksModel; _tasks = new DataServiceCollection<Task>(); _tasks.LoadAsync(_tasksModel.Tasks); } I get an exception: Only a typed DataServiceQuery object can be supplied when calling the LoadAsync method on DataServiceCollection. First of all, if this is the case, why not make the input parameter of LoadAsync be typed as DataServiceQuery? Second, what is the "proper" way of doing what I'm trying to accomplish?

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  • "cloud architecture" concepts in a system architecture diagrams

    - by markus
    If you design a distributed application for easy scale-out, or you just want to make use of any of the new “cloud computing” offerings by Amazon, Google or Microsoft, there are some typical concepts or components you usually end up using: distributed blob storage (aka S3) asynchronous, durable message queues (aka SQS) non-Relational-/non-transactional databases (like SimpleDB, Google BigTable, Azure SQL Services) distributed background worker pool load-balanced, edge-service processes handling user requests (often virtualized) distributed caches (like memcached) CDN (content delivery network like Akamai) Now when it comes to design and sketch an architecture that makes use of such patterns, are there any commonly used symbols I could use? Or even a download with some cool Visio stencils? :) It doesn’t have to be a formal system like UML but I think it would be great if there were symbols that everyone knows and understands, like we have commonly used shapes for databases or a documents, for example. I think it would be important to not mix it up with traditional concepts like a normal file system (local or network server/SAN), or a relational database. Simply speaking, I want to be able to draw some conclusions about an application’s scalability or data consistency issues by just looking at the system architecture overview diagram. Update: Thank you very much for your answers. I like the idea of putting a small "cloud symbol" on the traditional symbols. However I leave this thread open just in case someone will find specific symbols (maybe in a book or so) - or uploaded some pimped up Visio stencils ;)

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  • Thread-safe data structures

    - by Inso Reiges
    Hello, I have to design a data structure that is to be used in a multi-threaded environment. The basic API is simple: insert element, remove element, retrieve element, check that element exists. The structure's implementation uses implicit locking to guarantee the atomicity of a single API call. After i implemented this it became apparent, that what i really need is atomicity across several API calls. For example if a caller needs to check the existence of an element before trying to insert it he can't do that atomically even if each single API call is atomic: if(!data_structure.exists(element)) { data_structure.insert(element); } The example is somewhat awkward, but the basic point is that we can't trust the result of exists call anymore after we return from atomic context (the generated assembly clearly shows a minor chance of context switch between the two calls). What i currently have in mind to solve this is exposing the lock through the data structure's public API. This way clients will have to explicitly lock things, but at least they won't have to create their own locks. Is there a better commonly-known solution to these kinds of problems? And as long as we're at it, can you advise some good literature on thread-safe design? Thank you.

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  • WCF Manual SOAP POST using HttpWebRequest over https with Usertoken

    - by VonBlender
    Hi, I'm writing a client that calls a number of WCF webservices (written externallyt to my company) that are very similar in structure. The design I was hoping to use is to manually build the SOAP message from XML chunks that are stored in a database and then processed through a generic web service handler class. I have access to the WSDL's for each webservice and example working XML. The design approach is such that we can easily add to the message dynamically, hence the reason for not using the auto generated proxy classes I am basically at the last part now with the entire SOAP message constructed but am getting a SOAP fault security error returned. I have used fiddler to compare the message I'm sending with one that is sent using the normal (far simpler...) WCF generated proxy classes and can't see any difference apart from the id attribute of the Usertoken element in the SOAP header. This is where my lack of experience in this area isn't helping. I think this is because the id is generated automatically (presumably because we're using https). My question is how do I generate this programatically? I have searched for hours online but the majority of solutions are either using the proxy classes or not over https. I have briefly looked at WCE but aware this is replaced by WCF now so don't want to waste time looking into this if it's not the solution. Any help with this would be greatly appreciated. I can post some code examples when I'm back in work if it will help but the method I'm using is very straightforward and only using XElements and such like at the moment (as we're using linq to sql). thanks, Andy

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  • Exporting from SSRS 2008 ReportViewer to Excel Causes Duplicate Columns

    - by Daniel Coffman
    I have a report that groups months by quarters, so each quarter has three months and the display of the months under the quarter is toggled by the quarter header. It looks just fine in the ReportViewer, but when exporting to Excel the first month in the quarter with data is duplicated and appended to the end of the quarter group. Here is what it looks like in the ReportViewer (with Quarters 2 and 4 expanded, note May and June do not have any data and show blank columns by design): http://i.imgur.com/MykZE.png This is how it looks when exported to Excel: http://i.imgur.com/zfLuk.png The collapsed Quarter should only show the LAST month in the quarter. You can see that in the Excel export July is inserted in Q1 even though it should be hidden entirely since that quarter is collapsed, December is appended to Q2, January is inserted into Q3, and April is duplicated and appended to Q4. Exporting the any format OTHER than Excel works correctly and does not insert these columns. A similar bug for rows was filed and marked as "by design": http://connect.microsoft.com/SQLServer/feedback/details/508823/reporting-services-2008-group-by-export-to-excel-duplicate-rows-csv-ok-pdf-ok How do I stop the export to Excel feature from inserting these duplicate columns?

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  • Problem using Flash Components in multiple SWC files

    - by Ken Dunnington
    [Edit: Short version - how do you properly handle namespace collisions in SWC files if one SWC has fewer classes from that namespace than another?] I have a rather large Flash application which I'm building in Flash Builder (because coding/debugging in the Flash IDE is... not good) and I've got a ton of external SWC files which I'm linking in to my application. This has worked well so far - the file size is on the large side, but it's a lot simpler than loading in SWFs, especially since I am extending most of the classes in each SWC and adding custom code that way (it's a very design-heavy app.) The problem I'm having is when I have Flash Components, like ComboBox or TextInput, in more than one SWC. Whichever SWC was compiled last will work fine, but the others will fail with errors like the following: TypeError: Error #1034: Type Coercion failed: cannot convert flash.display::MovieClip@1f21adc1 to fl.controls.TextInput. at flash.display::Sprite/constructChildren() at flash.display::Sprite() at flash.display::MovieClip() at com.company.design.login::LoginForm() at com.company.view::Login()[/Users/ken/Workspace/src/com/company/view/Login.as:22] at com.company.view::Main/showLogin()[/Users/ken/Workspace/src/com/company/view/Main.as:209] at flash.events::EventDispatcher/dispatchEventFunction() at flash.events::EventDispatcher/dispatchEvent() at com.company.view::Navigation/handleUIClick()[/Users/ken/Workspace/src/com/company/view/Navigation.as:88] I've been researching components, ComponentShim, etc. but I'm running up against a brick wall. I thought it might be the fact that some of the components had their skins modified in the source FLA, so I tried replacing them with the default skins, but that didn't seem to help. How can I ensure that I have the components imported and available to all my classes, yet still be able to skin them and include them in my various FLAs? (I am never creating new instances of them, they are all laid out by my designer.)

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  • General Web Programming/designing Question: ?

    - by Prasad
    hi, I have been in web programming for 2 years (Self taught - a biology researcher by profession). I designed a small wiki with needed functionalities and a scientific RTE - ofcourse lot is expected. I used mootools framework and AJAX extensively. I was always curious when ever I saw the query strings passed from URL. Long encrypted query string directly getting passed to the server. Especially Google's design is such. I think this is the start of providing a Web Service to a client - I guess. Now, my question is : is this a special, highly professional, efficient / advanced web design technique to communicate queries via the URL ? I always felt that direct URL based communication is faster. I tried my bit and could send a query through the URL directly. here is the link: http://sgwiki.sdsc.edu/getSGMPage.php?8 By this , the client can directly link to the desired page instead of searching and / or can automate. There are many possibilities. The next request: Can I be pointed to such technique of web programming? oops: I am sorry, If I have not been able to convey my request clearly. Prasad.

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  • UML class diagram vs ER database diagram

    - by salva84
    Hi, I'm a little confused, I'm developing a program, the program consist in two parts, the server and the clients, there are groups, places, messages... stored in the server, and the clients has to connect with it. I've design the use cases diagram, the activity diagrams, and I have design the class diagram too. The thing is that I want to implement the server in a mysql tables for storing the users, groups, places... users in groups... so I've designed a E-R diagram consisting in 6 tables, but the problem is that I think that my class diagram and my ER diagram looks too similar, I mean, I think I'm not doing things right because I have a class for each table practically, and when I have to extract all the users on my system, do I have to convert all the rows into objects at first and write in the database for each object modified? The easy choice for me would be to base my whole application only in the database, and making a class to extract and insert data in it, but I have to follow the UML specification and I'm a little confused what to do with the class diagram, because the books I have read say that I have to create a class for each "entity" of my program. Sorry for my bad English. Thank you.

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  • Static factory pattern with EJB3/JBoss

    - by purecharger
    I'm fairly new to EJBs and full blown application servers like JBoss, having written and worked with special purpose standalone Java applications for most of my career, with limited use of JEE. I'm wondering about the best way to adapt a commonly used design pattern to EJB3 and JBoss: the static factory pattern. In fact this is Item #1 in Joshua Bloch's Effective Java book (2nd edition) I'm currently working with the following factory: public class CredentialsProcessorFactory { private static final Log log = LogFactory.getLog(CredentialsProcessorFactory.class); private static Map<CredentialsType, CredentialsProcessor> PROCESSORS = new HashMap<CredentialsType, CredentialsProcessor>(); static { PROCESSORS.put(CredentialsType.CSV, new CSVCredentialsProcessor()); } private CredentialsProcessorFactory() {} public static CredentialsProcessor getProcessor(CredentialsType type) { CredentialsProcessor p = PROCESSORS.get(type); if(p == null) throw new IllegalArgumentException("No CredentialsProcessor registered for type " + type.toString()); return p; } However, in the implementation classes of CredentialsProcessor, I require injected resources such as a PersistenceContext, so I have made the CredentialsProcessor interface a @Local interface, and each of the impl's marked with @Stateless. Now I can look them up in JNDI and use the injected resources. But now I have a disconnect because I am not using the factory anymore. My first thought was to change the getProcessor(CredentialsType) method to do a JNDI lookup and return the SLSB instance that is required, but then I need to configure and pass the proper qualified JNDI name. Before I go down that path, I wanted to do more research on accepted practices. How is this design pattern treated in EJB3 / JEE?

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  • People not respecting good practices at workplace

    - by VexXtreme
    Hi There are some major issues in my company regarding practices, procedures and methodologies. First of all, we're a small firm and there are only 3-4 developers, one of which is our boss who isn't really a programmer, he just chimes in now and then and tries to do code some simple things. The biggest problems are: Major cowboy coding and lack of methodologies. I've tried explaining to everyone the benefits of TDD and unit testing, but I only got weird looks as if I'm talking nonsense. Even the boss gave me the reaction along the lines of "why do we need that? it's just unnecessary overhead and a waste of time". Nobody uses design patterns. I have to tell people not to write business logic in code behind, I have to remind them not to hardcode concrete implementations and dependencies into classes and cetera. I often feel like a nazi because of this and people think I'm enforcing unnecessary policies and use of design patterns. The biggest problem of all is that people don't even respect common sense security policies. I've noticed that college students who work on tech support use our continuous integration and source control server as a dump to store their music, videos, series they download from torrents and so on. You can imagine the horror when I realized that most of the partition reserved for source control backups was used by entire seasons of TV series and movies. Our development server isn't even connected to an UPS and surge protection. It's just plugged straight into the wall outlet. I asked the boss to buy surge protection, but he said it's unnecessary. All in all, I like working here because the atmosphere is very relaxed, money is good and we're all like a family (so don't advise me to quit), but I simply don't know how to explain to people that they need to stick to some standards and good practices in IT industry and that they can't behave so irresponsibly. Thanks for the advice

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  • Core Data Migration - "Can't add source store" error

    - by Tofrizer
    Hi, In my iPhone app I'm using Core Data and I've made changes to my data model that cannot be automatically migrated over (i.e. added new relationships). I added the data model version (Design - Data Model - Add Model Version) and applied my new data model changes to the new version 2. I then created a mapping object model and set the Source and Destination models to their correct data models (old and new respectively). When I run the app and call the persistentStoreCoordinator, my app barfs with the following: 2010-02-27 02:40:30.922 XXXX[73578:20b] Unresolved error Error Domain=NSCocoaErrorDomain Code=134110 UserInfo=0xfc2240 "Operation could not be completed. (Cocoa error 134110.)", { NSUnderlyingError = Error Domain=NSCocoaErrorDomain Code=134130 UserInfo=0xfbb3a0 "Operation could not be completed. (Cocoa error 134130.)"; reason = "Can't add source store"; } FWIW (not much i think) I've also made the usual code changes in persistentStoreCoordinator to use the NSMigratePersistentStoresAutomaticallyOption and NSInferMappingModelAutomaticallyOption (for future data model changes that can be automatically migrated). More relevantly, my managedObjectModel is created by calling initWithContentsOfURL where the file/resource type is "momd". I've tried updating both the source and destination model in the mapping model (Design - Mapping Model - Update XXX Model) as well as deleted the mapping model and recreated it. I've cleaned and re-built but all to no avail. I still get the above error message. Any pointers/thoughts on how I can further debug or resolve this problem please? I haven't posted any code snippets because this feels much more like a build environment issue (and my code is very standard - just the usual core data code to handle migrations using a mapping model but I'm happy to show the code if it helps). Appreciate any help. Thanks

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  • Custom Event - invokation list implementation considerations

    - by M.A. Hanin
    I'm looking for some pointers on implementing Custom Events in VB.NET (Visual Studio 2008, .NET 3.5). I know that "regular" (non-custom) Events are actually Delegates, so I was thinking of using Delegates when implementing a Custom Event. On the other hand, Andrew Troelsen's "Pro VB 2008 and the .NET 3.5 Platform" book uses Collection types in all his Custom Events examples, and Microsoft's sample codes match that line of thought. So my question is: what considerations should I have when choosing one design over the other? What are the pros and cons for each design? Which of these resembles the inner-implementation of "regular" events? Below is a sample code demonstrating the two designs. Public Class SomeClass Private _SomeEventListeners As EventHandler Public Custom Event SomeEvent As EventHandler AddHandler(ByVal value As EventHandler) _SomeEventListeners = [Delegate].Combine(_SomeEventListeners, value) End AddHandler RemoveHandler(ByVal value As EventHandler) _SomeEventListeners = [Delegate].Remove(_SomeEventListeners, value) End RemoveHandler RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs) _SomeEventListeners.Invoke(sender, e) End RaiseEvent End Event Private _OtherEventListeners As New List(Of EventHandler) Public Custom Event OtherEvent As EventHandler AddHandler(ByVal value As EventHandler) _OtherEventListeners.Add(value) End AddHandler RemoveHandler(ByVal value As EventHandler) _OtherEventListeners.Remove(value) End RemoveHandler RaiseEvent(ByVal sender As Object, ByVal e As System.EventArgs) For Each handler In _OtherEventListeners handler(sender, e) Next End RaiseEvent End Event End Class

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  • Why is "Fixup" needed for Persistence Ignorant POCO's in EF 4?

    - by Eric J.
    One of the much-anticipated features of Entity Framework 4 is the ability to use POCO (Plain Old CLR Objects) in a Persistence Ignorant manner (i.e. they don't "know" that they are being persisted with Entity Framework vs. some other mechanism). I'm trying to wrap my head around why it's necessary to perform association fixups and use FixupCollection in my "plain" business object. That requirement seems to imply that the business object can't be completely ignorant of the persistence mechanism after all (in fact the word "fixup" sounds like something needs to be fixed/altered to work with the chosen persistence mechanism). Specifically I'm referring to the Association Fixup region that's generated by the ADO.NET POCO Entity Generator, e.g.: #region Association Fixup private void FixupImportFile(ImportFile previousValue) { if (previousValue != null && previousValue.Participants.Contains(this)) { previousValue.Participants.Remove(this); } if (ImportFile != null) { if (!ImportFile.Participants.Contains(this)) { ImportFile.Participants.Add(this); } if (ImportFileId != ImportFile.Id) { ImportFileId = ImportFile.Id; } } } #endregion as well as the use of FixupCollection. Other common persistence-ignorant ORMs don't have similar restrictions. Is this due to fundamental design decisions in EF? Is some level of non-ignorance here to stay even in later versions of EF? Is there a clever way to hide this persistence dependency from the POCO developer? How does this work out in practice, end-to-end? For example, I understand support was only recently added for ObservableCollection (which is needed for Silverlight and WPF). Are there gotchas in other software layers from the design requirements of EF-compatible POCO objects?

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  • Which Computer Organization & Architecture book is good for me?

    - by claws
    I'm always interested in learning the inner working of things. I started with C programming and then learnt Operating systems (from stallings) and then linkers & loaders and then assembly language after reading these now I want to go into little more depth. Computer Architecture. I feel that makes everything clear. As per SO archives these are the two good books: Computer Architecture: A Quantitative Approach, 4th Edition Computer Organization and Design, Fourth Edition, ~ David A. Patterson, John L. Hennessy But I've browsed through the contents of these books and found that they don't exactly meet my needs. I want to learn more about caches, Memory Management Unit , mapping b/w virtual memory & physical memory I'm no way interested in other ISAs like MIPS etc.. I'm IA32 and X86-64 fan and I want to stick to it. I'm not a hardware developer I don't want to details like circuit diagrams or How is L1, L2 & L3 caches are implemented? I want to know the parallel processing technologies like HyperThreading at the architecture level but again I don't want to design them. I liked the table of Contents of - Computer Architecture: A Quantitative Approach, 4th Edition but Quantitave Approach? Seriously?? I want to know the details of current technologies and I dont want to spend reading 200 pages of outdated old technologies ( I experienced this while learning ASM}

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  • How should I handle persistence in a Java MUD? OptimisticLockException handling

    - by Chase
    I'm re-implementing a old BBS MUD game in Java with permission from the original developers. Currently I'm using Java EE 6 with EJB Session facades for the game logic and JPA for the persistence. A big reason I picked session beans is JTA. I'm more experienced with web apps in which if you get an OptimisticLockException you just catch it and tell the user their data is stale and they need to re-apply/re-submit. Responding with "try again" all the time in a multi-user game would make for a horrible experience. Given that I'd expect several people to be targeting a single monster during a fight I think the chance of an OptimisticLockException would be high. My view code, the part presenting a telnet CLI, is the EJB client. Should I be catching the PersistenceExceptions and TransactionRolledbackLocalExceptions and just retrying? How do you decide when to stop? Should I switch to pessimistic locking? Is persisting after every user command overkill? Should I be loading the entire world in RAM and dumping the state every couple of minutes? Do I make my session facade a EJB 3.1 singleton which would function as a choke point and therefore eliminating the need to do any type of JPA locking? EJB 3.1 singletons function as a multiple reader/single writer design (you annotate the methods as readers and writers). Basically, what is the best design and java persistence API for highly concurrent data changes in an application where it is not acceptable to present resubmit/retry prompts to the user?

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  • Postback event not firing on FIRST button click..

    - by ClarkeyBoy
    Hi, I have a form which accepts two arguments. The first one is mode - this is either view, new or edit. If it is new then the second argument is type - this is either range, collection or design. When set to new, and the type is valid, a new instance of that type is created and the data from the form is added to it. The item (range, collection or design) then validates the data. If any of the data is invalid then it throws an error, and this error is displayed at the top of the form telling the user why it is invalid. A variable, _Databind, is set to false so that it does not change the data input by the user (in the form fields). The button used to submit the button is called btnSave, and is created in the html source. The click event is wired up in the form Protected Sub Blah(sender, e) Handles btnSave.Click. Strangely, whenever I edit an item that already exists the form submits fine the first time - the click event is fired. However when in "new" mode I have to click the button twice to fire the event. It also blanks all the form fields out on first click. I have even put a Response.Write("Hello World") line at the start of the click event - this is not being output on first click when adding a new item either. It is on first load when the mode is set to edit however. Does anyone have any ideas as to what is causing it to behave this way? Thanks in advance for any help. Regards, Richard

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  • API Wrapper Architecture Best Practice

    - by Adam Taylor
    Hi, So I'm writing a Perl wrapper module around a REST webservice and I'm hoping to have some advice on how best to architect the module. I've been looking at a couple of different Perl modules for inspiration. Flickr::Simple2 - so this is basically one big file with methods wrapping around the different methods in the Flickr API, e.g. getPhotos() etc. Flickr::API - this is a sub-class of another module (LWP) for making HTTP requests. So basically it just allows you to make calls through the module, using LWP, that go to the correct API method/URL without defining any wrapper methods itself. (That's explained pretty poorly - but basically it has a method that takes an argument (a API method name) and constructs the correct API call). e.g request() / response(). An alternative design would be like the first described, but less monolithic, with separate classes for separate "areas" of the API. I'd like to follow modern/best practice Perl methods so I'm using Dist::Zilla to build the module and Moose for the OO stuff but I'd appreciate some input on how to actually design/architect my wrapper. Guides/tutorials or pointers to other well designed modules would be appreciated. Cheers

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  • How to switch users in a smooth way in a Point-Of-Sale system?

    - by Sanoj
    I am designing a Point-Of-Sale system for a small shop. The shop just have one Point-Of-Sale but often they are one to three users (sellers) in the shop. Each user have their own user account in the system so they login and logout very often. How should I design the login/logout system in a good way? For the moment the users don't use passwords, because it takes so long time to type the password each time they login. The Platform is Windows Vista but I would like to support Windows 7 too. We use Active Directory on the Network. The system is developed in Java/Swing for the moment, but I'm thinking about to change to C#.NET/WPF. I am thinking about an SmartCard solution, but I don't know if that fits my situation. It would be more secure (which I like) but I don't know if it will be easy to implement and smooth to use, i.e. can I have the POS-system running in the background or started very quickly when the users switch? Are SmartCard solutions very expensive? (My customers are small shops) Is it preferred to use .NET or Java in a SmartCard solution? What other solutions do I have other than passwords/no passwords/smartcards? How should I design the login/logout system in a good way? Is there any good solution using SmartCards for this purpose? I would like suggested solutions both for C#.NET/WPF and Java/Swing platforms. I would like suggested solutions both for Active Directory solutions and solutions that only use one user profile in Windows. How is this problem solved in similar products? I have only seen password-solutions, but they are clumsy.

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  • Limit the number of service calls in a RESTful application

    - by Slavo
    Imagine some kind of a banking application, with a screen to create accounts. Each Account has a Currency and a Bank as a property, Currency being a separate class, as well as Bank. The code might look something like this: public class Account { public Currency Currency { get; set; } public Bank Bank { get; set; } } public class Currency { public string Code { get; set; } public string Name { get; set; } } public class Bank { public string Name { get; set; } public string Country { get; set; } } According to the REST design principles, each resource in the application should have its own service, and each service should have methods that map nicely to the HTTP verbs. So in our case, we have an AccountService, CurrencyService and BankService. In the screen for creating an account, we have some UI to select the bank from a list of banks, and to select a currency from a list of currencies. Imagine it is a web application, and those lists are dropdowns. This means that one dropdown is populated from the CurrencyService and one from the BankService. What this means is that when we open the screen for creating an account, we need to make two service calls to two different services. If that screen is not by itself on a page, there might be more service calls from the same page, impacting the performance. Is this normal in such an application? If not, how can it be avoided? How can the design be modified without going away from REST?

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