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  • Is having functionality in DB a road block to scalability?

    - by Estefany Velez
    I may not be able to give the right title to the question. But here it is, We are developing financial portal for wealth management. We are expecting over 10000 clients to use the application. The portal calculates various performance analytics based on the the technical analysis of the stock market. We developed lot of the functionality through Stored procedures, user defined functions, triggers etc. through Database. We thought we can gain huge performance boost doing stuff directly in database than through C# code. And we actually did get a huge performance boost. When I tried to brag about the achievement to our CTO, he counter questioned my decision of having functionality implemented in database rather than code. According to him such applications suffer scalability problems. In his words "These days things are kept in memory/cache. Clustered data is hard to manage over time. Facebook, Google have nothing in database. It is the era of thin servers and thick clients. DB is used only to store plain data and functionality should be completely decoupled from the database." Can you guys please give me some suggestions as to whether what he says is right. How to go about architect such an application?

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  • Clustering and custom applications

    - by Ahmed ilyas
    I was not entirely sure what tags to put but hope this is ok. This is just a general question in regards to clustering and applications: so lets say we have a clustered environment setup. We cluster SQL Server (I dont know exactly how its done but lets just say its been done for the sake of argument). Now if a website or application is trying to access that database for read/write (say an ASP.NET app or a C# Winforms app) and during that time SQL goes down - it takes a couple of minutes for the clustering failover to take affect to switch to another node. What happens during this time? I think it will time out/unable to connect. BUT is there a way for it to place the request in some pipeline so when the cluster node is back up/switched over it will continue as normal? as you can see, I know nothing much about clustering! what about your own custom .NET apps? Would there be a special way to develop them? I know that you can say create a simple Hello world app, and cluster that but they wouldnt be something you could see interms of the UI or anything, so they would effectively need to be developed as a Windows Service perhaps or even as a standard Console app which runs and not wait for user input but you wouldnt see any output from it (unless you redirect output to somewhere else) What im getting at here is... for those who have experience or developed a cluster application in .NET, how did you do it and what are the things to be aware of? For example we have the cloud service - fundamentally its built on clustering - if there is an outage, another node takes place and service is resumed as normal but we dont really see much of that downtime.

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  • Running multiple box2D world objects on a server

    - by CharbelAbdo
    I'm creating a multiplayer game using LibGdx (with Box2d) and Kryonet. Since this is the first time I work on multiplayer games, I read a bit about server - client implementations, and it turns out that the server should handle important tasks like collision detection, hits, characters dying etc... Based on some articles (like the excellent Gabriel Gambetta Fast paced multiplayer series), I also know that the client should work in parallel to avoid the lag while the server responds to commands. Physics wise, each game will have 2 players, and any projectiles fired. What I'm thinking of doing is the following: Create a physics world on the client When the game is signaled to start, I create the same physics world on the server (without any rendering obviously). Whenever the player issues a command (move or fire), I send the command to the server and immediately start processing it on the client. When the server receives the command, it applies it on the server's world (set velocity etc...) Each 100ms, the server sends the new state to the client which corrects what was calculated locally. Any critical action (hit, death, level up) is calculated only on the server and sent to the client. Essentially, I would have a Box2d World object running on the server for each game in progress, in sync with the worlds running on the clients. The alternative would be to do my own calculations on the server instead of relying on Box2D to do them for me, but I'm trying to avoid that. My question is: Is it wise to have, for example, 1000 instances of the World object running and executing steps on the server? Tomcat used around 750 MBytes of memory when trying it without any object added to the world. Anybody tried that before? If not, is there any alternative? Google did not help me, are there any guidelines to use when you want to have physics on both the client and the server? Thanks for any help.

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  • REST - Tradeoffs between content negotiation via Accept header versus extensions

    - by Brandon Linton
    I'm working through designing a RESTful API. We know we want to return JSON and XML for any given resource. I had been thinking we would do something like this: GET /api/something?param1=value1 Accept: application/xml (or application/json) However, someone tossed out using extensions for this, like so: GET /api/something.xml?parm1=value1 (or /api/something.json?param1=value1) What are the tradeoffs with these approaches? Is it best to rely on the accept header when an extension isn't specified, but honor extensions when specified? Is there a drawback to that approach?

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  • Where to store shaders

    - by Mark Ingram
    I have an OpenGL renderer which has a Scene member variable. The Scene object can contain N SceneObjects. I use these SceneObjects for storing the vertex position and any transforms. My question is, where should shaders be stored in this arrangement? I guess they need to be in a central location because multiple objects can use the same shader. But then each object needs access to the shader because it needs to set attributes into the shader. Does anyone have any advice?

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  • How do I cleanly design a central render/animation loop?

    - by mtoast
    I'm learning some graphics programming, and am in the midst of my first such project of any substance. But, I am really struggling at the moment with how to architect it cleanly. Let me explain. To display complicated graphics in my current language of choice (JavaScript -- have you heard of it?), you have to draw graphical content onto a <canvas> element. And to do animation, you must clear the <canvas> after every frame (unless you want previous graphics to remain). Thus, most canvas-related JavaScript demos I've seen have a function like this: function render() { clearCanvas(); // draw stuff here requestAnimationFrame(render); } render, as you may surmise, encapsulates the drawing of a single frame. What a single frame contains at a specific point in time, well... that is determined by the program state. So, in order for my program to do its thing, I just need to look at the state, and decide what to render. Right? Right. But that is more complicated than it seems. My program is called "Critter Clicker". In my program, you see several cute critters bouncing around the screen. Clicking on one of them agitates it, making it bounce around even more. There is also a start screen, which says "Click to start!" prior to the critters being displayed. Here are a few of the objects I'm working with in my program: StartScreenView // represents the start screen CritterTubView // represents the area in which the critters live CritterList // a collection of all the critters Critter // a single critter model CritterView // view of a single critter Nothing too egregious with this, I think. Yet, when I set out to flesh out my render function, I get stuck, because everything I write seems utterly ugly and reminiscent of a certain popular Italian dish. Here are a couple of approaches I've attempted, with my internal thought process included, and unrelated bits excluded for clarity. Approach 1: "It's conditions all the way down" // "I'll just write the program as I think it, one frame at a time." if (assetsLoaded) { if (userClickedToStart) { if (critterTubDisplayed) { if (crittersDisplayed) { forEach(crittersList, function(c) { if (c.wasClickedRecently) { c.getAgitated(); } }); } else { displayCritters(); } } else { displayCritterTub(); } } else { displayStartScreen(); } } That's a very much simplified example. Yet even with only a fraction of all the rendering conditions visible, render is already starting to get out of hand. So, I dispense with that and try another idea: Approach 2: Under the Rug // "Each view object shall be responsible for its own rendering. // "I'll pass each object the program state, and each can render itself." startScreen.render(state); critterTub.render(state); critterList.render(state); In this setup, I've essentially just pushed those crazy nested conditions to a deeper level in the code, hiding them from view. In other words, startScreen.render would check state to see if it needed actually to be drawn or not, and take the correct action. But this seems more like it only solves a code-aesthetic problem. The third and final approach I'm considering that I'll share is the idea that I could invent my own "wheel" to take care of this. I'm envisioning a function that takes a data structure that defines what should happen at any given point in the render call -- revealing the conditions and dependencies as a kind of tree. Approach 3: Mad Scientist renderTree({ phases: ['startScreen', 'critterTub', 'endCredits'], dependencies: { startScreen: ['assetsLoaded'], critterTub: ['startScreenClicked'], critterList ['critterTubDisplayed'] // etc. }, exclusions: { startScreen: ['startScreenClicked'], // etc. } }); That seems kind of cool. I'm not exactly sure how it would actually work, but I can see it being a rather nifty way to express things, especially if I flex some of JavaScript's events. In any case, I'm a little bit stumped because I don't see an obvious way to do this. If you couldn't tell, I'm coming to this from the web development world, and finding that doing animation is a bit more exotic than arranging an MVC application for handling simple requests - responses. What is the clean, established solution to this common-I-would-think problem?

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  • Correct order of tasks in each frame for a Physics simulation

    - by Johny
    I'm playing a bit around with 2D physics. I created now some physic blocks which should collide with each other. This works fine "mostly" but sometimes one of the blocks does not react to a collision and i think that's because of my order of tasks done in each frame. At the moment it looks something like this: function GameFrame(){ foreach physicObject do AddVelocityToPosition(); DoCollisionStuff(); // Only for this object not to forget! AddGravitationToVelocity(); end RedrawScene(); } Is this the correct order of tasks in each frame?

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  • Decorator not calling the decorated instance - alternative design needed

    - by Daniel Hilgarth
    Assume I have a simple interface for translating text (sample code in C#): public interface ITranslationService { string GetTranslation(string key, CultureInfo targetLanguage); // some other methods... } A first simple implementation of this interface already exists and simply goes to the database for every method call. Assuming a UI that is being translated at start up this results in one database call per control. To improve this, I want to add the following behavior: As soon as a request for one language comes in, fetch all translations from this language and cache them. All translation requests are served from the cache. I thought about implementing this new behavior as a decorator, because all other methods of that interface implemented by the decorater would simple delegate to the decorated instance. However, the implementation of GetTranslation wouldn't use GetTranslation of the decorated instance at all to get all translations of a certain language. It would fire its own query against the database. This breaks the decorator pattern, because every functionality provided by the decorated instance is simply skipped. This becomes a real problem if there are other decorators involved. My understanding is that a Decorator should be additive. In this case however, the decorator is replacing the behavior of the decorated instance. I can't really think of a nice solution for this - how would you solve it? Everything is allowed, even a complete re-design of ITranslationService itself.

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  • Structure of a correctly implemented JTable with TableModel and Listeners?

    - by bamboocha
    I am pretty new to Java and its JTables and this is where I am struggling at the moment. I need to create a GUI which shows me results of a sql query like SELECT * FROM tblPeople WHERE name='Doe'. My idea was to create a a JFrame which displays a JTable with all found records. Besides this, I need to also implement some code to handle when a user is double clicking a record or selecting it by using his arrow keys (additional feature: pressing 12(e.g.) should select the 12th record). What is the best way to structure my program (what classes do I need and especially where do I store my logic)? I came up with structuring it the following way: Main.java ("view") SQLConnection.java PeopleTableModel.java (only stores and returns data given by the passed ResultSet, "model" inherits from DefaultTableModel) PeopleTable.java (stores basically all my logic including KeyListener and MouseListener, "controller", inherits from JTable) Are there better ways to achieve my goals? If so, what are they?

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  • BPM Process Accelerator Packs - Update

    - by Pat Shepherd
    There are 3 BPM Process Accelerator Packs available now (Accelerator Packs Available ) as discssed in my earlier post: https://blogs.oracle.com/enterprisearchitecture/entry/bpm_process_accelerator_packs There is a new and very useful white paper on BPM/Accelerator best practices at: http://www.oracle.com/technetwork/middleware/bpm/learnmore/processaccelbestpracticeswhitepaper-1708910.pdf Thought I'd post that as the topic is getting more and more attention in various discussions I have been having.

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  • Questions about identifying the components in MVC

    - by luiscubal
    I'm currently developing an client-server application in node.js, Express, mustache and MySQL. However, I believe this question should be mostly language and framework agnostic. This is the first time I'm doing a real MVC application and I'm having trouble deciding exactly what means each component. (I've done web applications that could perhaps be called MVC before, but I wouldn't confidently refer to them as such) I have a server.js that ties the whole application together. It does initialization of all other components (including the database connection, and what I think are the "models" and the "views"), receiving HTTP requests and deciding which "views" to use. Does this mean that my server.js file is the controller? Or am I mixing code that doesn't belong there? What components should I break the server.js file into? Some examples of code that's in the server.js file: var connection = mysql.createConnection({ host : 'localhost', user : 'root', password : 'sqlrevenge', database : 'blog' }); //... app.get("/login", function (req, res) { //Function handles a GET request for login forms if (process.env.NODE_ENV == 'DEVELOPMENT') { mu.clearCache(); } session.session_from_request(connection, req, function (err, session) { if (err) { console.log('index.js session error', err); session = null; } login_view.html(res, user_model, post_model, session, mu); //I named my view functions "html" for the case I might want to add other output types (such as a JSON API), or should I opt for completely separate views then? }); }); I have another file that belongs named session.js. It receives a cookies object, reads the stored data to decide if it's a valid user session or not. It also includes a function named login that does change the value of cookies. First, I thought it would be part of the controller, since it kind of dealt with user input and supplied data to the models. Then, I thought that maybe it was a model since it dealt with the application data/database and the data it supplies is used by views. Now, I'm even wondering if it could be considered a View, since it outputs data (cookies are part of HTTP headers, which are output)

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  • Velocity collision detection (2D)

    - by ultifinitus
    Alright, so I have made a simple game engine (see youtube) And my current implementation of collision resolution has a slight problem, involving the velocity of a platform. Basically I run through all of the objects necessary to detect collisions on and resolve those collisions as I find them. Part of that resolution is setting the player's velocity = the platform's velocity. Which works great! Unless I have a row of platforms moving at different velocities or a platform between a stack of tiles.... (current system) bool player::handle_collisions() { collisions tcol; bool did_handle = false; bool thisObjectHandle = false; for (int temp = 0; temp < collideQueue.size(); temp++) { thisObjectHandle = false; tcol = get_collision(prevPos.x,y,get_img()->get_width(),get_img()->get_height(), collideQueue[temp]->get_position().x,collideQueue[temp]->get_position().y, collideQueue[temp]->get_img()->get_width(),collideQueue[temp]->get_img()->get_height()); if (prevPos.y >= collideQueue[temp]->get_prev_pos().y + collideQueue[temp]->get_img()->get_height()) if (tcol.top > 0) { add_pos(0,tcol.top); set_vel(get_vel().x,collideQueue[temp]->get_vel().y); thisObjectHandle = did_handle = true; } if (prevPos.y + get_img()->get_height() <= collideQueue[temp]->get_prev_pos().y) if (tcol.bottom > 0) { add_pos(collideQueue[temp]->get_vel().x,-tcol.bottom); set_vel(get_vel().x/*collideQueue[temp]->get_vel().x*/,collideQueue[temp]->get_vel().y); ableToJump = true; jumpTimes = maxjumpable; thisObjectHandle = did_handle = true; } /// /// ADD CODE FROM NEXT CODE BLOCK HERE (on forum, not in code) /// } for (int temp = 0; temp < collideQueue.size(); temp++) { thisObjectHandle = false; tcol = get_collision(x,y,get_img()->get_width(),get_img()->get_height(), collideQueue[temp]->get_position().x,collideQueue[temp]->get_position().y, collideQueue[temp]->get_img()->get_width(),collideQueue[temp]->get_img()->get_height()); if (prevPos.x + get_img()->get_width() <= collideQueue[temp]->get_prev_pos().x) if (tcol.left > 0) { add_pos(-tcol.left,0); set_vel(collideQueue[temp]->get_vel().x,get_vel().y); thisObjectHandle = did_handle = true; } if (prevPos.x >= collideQueue[temp]->get_prev_pos().x + collideQueue[temp]->get_img()->get_width()) if (tcol.right > 0) { add_pos(tcol.right,0); set_vel(collideQueue[temp]->get_vel().x,get_vel().y); thisObjectHandle = did_handle = true; } } return did_handle; } (if I add the following code {where the comment to do so is}, which is glitchy, the above problem doesn't happen, though it brings others) if (!thisObjectHandle) { if (tcol.bottom > tcol.top) { add_pos(collideQueue[temp]->get_vel().x,-tcol.bottom); set_vel(get_vel().x,collideQueue[temp]->get_vel().y); } else if (tcol.top > tcol.bottom) { add_pos(0,tcol.top); set_vel(get_vel().x,collideQueue[temp]->get_vel().y); } } How would you change my system to prevent this?

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  • How to create an Orthographic display in OpenGL (ES) that handles different screen sizes and orientations?

    - by Piku
    I'm trying to create an iPad/iPhone game using GLES2.0 that contains a 3D scene with a heads-up-display/GUI overlaid on the top. However, this problem would also apply if I were to port my game to a computer and run the game in a resizable window, or allow the user to change screen resolutions... When trying to make the 2D GUI/HUD work I've made the assumption that all I'm really doing is drawing a load of 2D textured 'quads' on the screen and am trying to treat the orthographic projection as an old-style 2D display with 0,0 in the upper left and screenWidth,ScreenHeight in the lower right. This causes me all sorts of confusion when I rotate my ipad into Landscape mode since I can't work out what to put into my projection and modelview matrices to turn everything around the right way. It also gets messy if I want to support the iPad's large screen, an iPhone or a Retina display since I have to then draw three sets of textures for everything and work out which ones to use. Should I be trying to map the 2D OpenGL co-ords 1:1 with the screen? While typing out this question it occurs to me that I could keep my origin in the centre, still running -1/+1 along the axes. This would let me scale my 2D content appropriately on the different screen sizes, but wouldn't I end up with the textures being scaled and possibly losing quality? I'm using OpenGLES 2.0 and have a matrix library that has equivalents to the GLES1.1 glOrthof() and glFrustrum() calls.

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  • Where should you put constants and why?

    - by Tim Meyer
    In our mostly large applications, we usually have a only few locations for constants: One class for GUI and internal contstants (Tab Page titles, Group Box titles, calculation factors, enumerations) One class for database tables and columns (this part is generated code) plus readable names for them (manually assigned) One class for application messages (logging, message boxes etc) The constants are usually separated into different structs in those classes. In our C++ applications, the constants are only defined in the .h file and the values are assigned in the .cpp file. One of the advantages is that all strings etc are in one central place and everybody knows where to find them when something must be changed. This is especially something project managers seem to like as people come and go and this way everybody can change such trivial things without having to dig into the application's structure. Also, you can easily change the title of similar Group Boxes / Tab Pages etc at once. Another aspect is that you can just print that class and give it to a non-programmer who can check if the captions are intuitive, and if messages to the user are too detailed or too confusing etc. However, I see certain disadvantages: Every single class is tightly coupled to the constants classes Adding/Removing/Renaming/Moving a constant requires recompilation of at least 90% of the application (Note: Changing the value doesn't, at least for C++). In one of our C++ projects with 1500 classes, this means around 7 minutes of compilation time (using precompiled headers; without them it's around 50 minutes) plus around 10 minutes of linking against certain static libraries. Building a speed optimized release through the Visual Studio Compiler takes up to 3 hours. I don't know if the huge amount of class relations is the source but it might as well be. You get driven into temporarily hard-coding strings straight into code because you want to test something very quickly and don't want to wait 15 minutes just for that test (and probably every subsequent one). Everybody knows what happens to the "I will fix that later"-thoughts. Reusing a class in another project isn't always that easy (mainly due to other tight couplings, but the constants handling doesn't make it easier.) Where would you store constants like that? Also what arguments would you bring in order to convince your project manager that there are better concepts which also comply with the advantages listed above? Feel free to give a C++-specific or independent answer. PS: I know this question is kind of subjective but I honestly don't know of any better place than this site for this kind of question. Update on this project I have news on the compile time thing: Following Caleb's and gbjbaanb's posts, I split my constants file into several other files when I had time. I also eventually split my project into several libraries which was now possible much easier. Compiling this in release mode showed that the auto-generated file which contains the database definitions (table, column names and more - more than 8000 symbols) and builds up certain hashes caused the huge compile times in release mode. Deactivating MSVC's optimizer for the library which contains the DB constants now allowed us to reduce the total compile time of your Project (several applications) in release mode from up to 8 hours to less than one hour! We have yet to find out why MSVC has such a hard time optimizing these files, but for now this change relieves a lot of pressure as we no longer have to rely on nightly builds only. That fact - and other benefits, such as less tight coupling, better reuseability etc - also showed that spending time splitting up the "constants" wasn't such a bad idea after all ;-)

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  • Low-level game engine renderer design

    - by Mark Ingram
    I'm piecing together the beginnings of an extremely basic engine which will let me draw arbitrary objects (SceneObject). I've got to the point where I'm creating a few sensible sounding classes, but as this is my first outing into game engines, I've got the feeling I'm overlooking things. I'm familiar with compartmentalising larger portions of the code so that individual sub-systems don't overly interact with each other, but I'm thinking more of the low-level stuff, starting from vertices working up. So if I have a Vertex class, I can combine that with a list of indices to make a Mesh class. How does the engine determine identical meshes for objects? Or is that left to the level designer? Once we have a Mesh, that can be contained in the SceneObject class. And a list of SceneObject can be placed into the Scene to be drawn. Right now I'm only using OpenGL, but I'm aware that I don't want to be tying OpenGL calls right in to base classes (such as updating the vertices in the Mesh, I don't want to be calling glBufferData etc). Are there any good resources that discuss these issues? Are there any "common" heirachies which should be used?

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  • Recommened design pattern to handle multiple compression algorithms for a class hierarchy

    - by sgorozco
    For all you OOD experts. What would be the recommended way to model the following scenario? I have a certain class hierarchy similar to the following one: class Base { ... } class Derived1 : Base { ... } class Derived2 : Base { ... } ... Next, I would like to implement different compression/decompression engines for this hierarchy. (I already have code for several strategies that best handle different cases, like file compression, network stream compression, legacy system compression, etc.) I would like the compression strategy to be pluggable and chosen at runtime, however I'm not sure how to handle the class hierarchy. Currently I have a tighly-coupled design that looks like this: interface ICompressor { byte[] Compress(Base instance); } class Strategy1Compressor : ICompressor { byte[] Compress(Base instance) { // Common compression guts for Base class ... // if( instance is Derived1 ) { // Compression guts for Derived1 class } if( instance is Derived2 ) { // Compression guts for Derived2 class } // Additional compression logic to handle other class derivations ... } } As it is, whenever I add a new derived class inheriting from Base, I would have to modify all compression strategies to take into account this new class. Is there a design pattern that allows me to decouple this, and allow me to easily introduce more classes to the Base hierarchy and/or additional compression strategies?

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  • Best approach to designing multi-client applications

    - by Tomh
    Hi, I was wondering how you guys start out if you need to design a multi-client project where multiple clients can interact with a server. In specific how do you go about dealing with different states and message handling, how do you start designing and considering all these cases? For example a video webchat application where it is possible that you call another client, while that client is already in a call, or is stuck in a modal dialog such that the calling dialog does not come through.

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  • Digital "Post It" notes for organizing content of sites/pages

    - by Alex
    We're restructuring our old intranet into a new one and are going through each site to find content and use our new standard structure/look-and-feel. Do you recommend a tool where you can do "digital Post-It" notes? It would provide a way to type some items on a "card" and be able to move it around and organize it quickly. Also, if you know of tools in general for this kind of task, please advise. Thank you.

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  • Why should I adopt MVC?

    - by Andrew
    I decided to get my hands wet and got the YII framework for PHP. I created my first application, then created new controller, model and view. Connected to database, got my record passed from controller to the view and printed the hello world. I am confused now. If I have to do the same thing for each page, this seems like a nightmare to me. In each controller I have to do a lot of same operations - declare variables, and pass them to views. I also need to create models for each page and this is all confusing to me. In my idea the main goal of development is to avoid duplication, but what I see here is lots and lots of duplicated code. Please advise and clarify. Maybe you could suggest a good reading about MVC and coding patterns and best practices in MVC. Because so far, it takes much more time to create a small site using MVC than using my own programming schema.

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  • Is this project Structure Valid?

    - by rafuru
    I have a dilemma: In the university we learn to create modular software (on java), but this modularity is explained using a single project with packages (a package for business, another one for DAOS and another one for the model, oh and a last package for frontend). But in my work we use the next structure: I will try to explain: First we create a java library project where the model (entities classes) are created in a package. Next we create an EJB named DAOS and using the netbeans wizard we store the DAOS interfaces in the library project in another package , these interfaces are implemented in the DAOS bean. So the next part is the business logic, we create a business EJB for each group of functions , again using the wizard we store the interface in the java library project in another package then is implemented on the business bean. The final part (for the backend) is a bean that I have suggested: a Facade bean who will gather every method of the business beans in a single bean and this has an interface too that is created in our library project and implemented in the bean. So the next part is call the facade module on the web project. But I don't know how valid or viable is this, maybe I'm doing everything wrong and I don't even know! so I want to ask your opinion about this.

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  • How can I gather client's data on Google App Engine without using Datastore/Backend Instances too much?

    - by ruslan
    One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting?

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  • Snake Game Help

    - by MuhammadA
    I am making a snake game and learning XNA at the same time. I have 3 classes : Game.cs, Snake.cs and Apple.cs My problem is more of a conceptual problem, I want to know which class is really responsible for ... detecting collision of snake head on apple/itself/wall? which class should increase the snakes speed, size? It seems to me that however much I try and put the snake stuff into snake.cs that game.cs has to know a lot about the snake, like : -- I want to increase the score depending on size of snake, the score variable is inside game.cs, which means now I have to ask the snake its size on every hit of the apple... seems a bit unclean all this highly coupled code. or -- I DO NOT want to place the apple under the snake... now the apple suddenly has to know about all the snake parts, my head hurts when I think of that. Maybe there should be some sort of AppleLayer.cs class that should know about the snake... Whats the best approach in such a simple scenario? Any tips welcome. Game.cs : using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; using Microsoft.Xna.Framework.Design; namespace Snakez { public enum CurrentGameState { Playing, Paused, NotPlaying } public class Game1 : Microsoft.Xna.Framework.Game { private GraphicsDeviceManager _graphics; private SpriteBatch _spriteBatch; private readonly Color _niceGreenColour = new Color(167, 255, 124); private KeyboardState _oldKeyboardState; private SpriteFont _scoreFont; private SoundEffect _biteSound, _crashSound; private Vector2 _scoreLocation = new Vector2(10, 10); private Apple _apple; private Snake _snake; private int _score = 0; private int _speed = 1; public Game1() { _graphics = new GraphicsDeviceManager(this); Content.RootDirectory = "Content"; } /// <summary> /// Allows the game to perform any initialization it needs to before starting to run. /// This is where it can query for any required services and load any non-graphic /// related content. Calling base.Initialize will enumerate through any components /// and initialize them as well. /// </summary> protected override void Initialize() { base.Initialize(); } /// <summary> /// LoadContent will be called once per game and is the place to load /// all of your content. /// </summary> protected override void LoadContent() { _spriteBatch = new SpriteBatch(GraphicsDevice); _scoreFont = Content.Load<SpriteFont>("Score"); _apple = new Apple(800, 480, Content.Load<Texture2D>("Apple")); _snake = new Snake(Content.Load<Texture2D>("BodyBlock")); _biteSound = Content.Load<SoundEffect>("Bite"); _crashSound = Content.Load<SoundEffect>("Crash"); } /// <summary> /// UnloadContent will be called once per game and is the place to unload /// all content. /// </summary> protected override void UnloadContent() { Content.Unload(); } /// <summary> /// Allows the game to run logic such as updating the world, /// checking for collisions, gathering input, and playing audio. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Update(GameTime gameTime) { KeyboardState newKeyboardState = Keyboard.GetState(); if (newKeyboardState.IsKeyDown(Keys.Escape)) { this.Exit(); // Allows the game to exit } else if (newKeyboardState.IsKeyDown(Keys.Up) && !_oldKeyboardState.IsKeyDown(Keys.Up)) { _snake.SetDirection(Direction.Up); } else if (newKeyboardState.IsKeyDown(Keys.Down) && !_oldKeyboardState.IsKeyDown(Keys.Down)) { _snake.SetDirection(Direction.Down); } else if (newKeyboardState.IsKeyDown(Keys.Left) && !_oldKeyboardState.IsKeyDown(Keys.Left)) { _snake.SetDirection(Direction.Left); } else if (newKeyboardState.IsKeyDown(Keys.Right) && !_oldKeyboardState.IsKeyDown(Keys.Right)) { _snake.SetDirection(Direction.Right); } _oldKeyboardState = newKeyboardState; _snake.Update(); if (_snake.IsEating(_apple)) { _biteSound.Play(); _score += 10; _apple.Place(); } base.Update(gameTime); } /// <summary> /// This is called when the game should draw itself. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(_niceGreenColour); float frameRate = 1 / (float)gameTime.ElapsedGameTime.TotalSeconds; _spriteBatch.Begin(); _spriteBatch.DrawString(_scoreFont, "Score : " + _score, _scoreLocation, Color.Red); _apple.Draw(_spriteBatch); _snake.Draw(_spriteBatch); _spriteBatch.End(); base.Draw(gameTime); } } } Snake.cs : using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework; namespace Snakez { public enum Direction { Up, Down, Left, Right } public class Snake { private List<Rectangle> _parts; private readonly Texture2D _bodyBlock; private readonly int _startX = 160; private readonly int _startY = 120; private int _moveDelay = 100; private DateTime _lastUpdatedAt; private Direction _direction; private Rectangle _lastTail; public Snake(Texture2D bodyBlock) { _bodyBlock = bodyBlock; _parts = new List<Rectangle>(); _parts.Add(new Rectangle(_startX, _startY, _bodyBlock.Width, _bodyBlock.Height)); _parts.Add(new Rectangle(_startX + bodyBlock.Width, _startY, _bodyBlock.Width, _bodyBlock.Height)); _parts.Add(new Rectangle(_startX + (bodyBlock.Width) * 2, _startY, _bodyBlock.Width, _bodyBlock.Height)); _parts.Add(new Rectangle(_startX + (bodyBlock.Width) * 3, _startY, _bodyBlock.Width, _bodyBlock.Height)); _direction = Direction.Right; _lastUpdatedAt = DateTime.Now; } public void Draw(SpriteBatch spriteBatch) { foreach (var p in _parts) { spriteBatch.Draw(_bodyBlock, new Vector2(p.X, p.Y), Color.White); } } public void Update() { if (DateTime.Now.Subtract(_lastUpdatedAt).TotalMilliseconds > _moveDelay) { //DateTime.Now.Ticks _lastTail = _parts.First(); _parts.Remove(_lastTail); /* add new head in right direction */ var lastHead = _parts.Last(); var newHead = new Rectangle(0, 0, _bodyBlock.Width, _bodyBlock.Height); switch (_direction) { case Direction.Up: newHead.X = lastHead.X; newHead.Y = lastHead.Y - _bodyBlock.Width; break; case Direction.Down: newHead.X = lastHead.X; newHead.Y = lastHead.Y + _bodyBlock.Width; break; case Direction.Left: newHead.X = lastHead.X - _bodyBlock.Width; newHead.Y = lastHead.Y; break; case Direction.Right: newHead.X = lastHead.X + _bodyBlock.Width; newHead.Y = lastHead.Y; break; } _parts.Add(newHead); _lastUpdatedAt = DateTime.Now; } } public void SetDirection(Direction newDirection) { if (_direction == Direction.Up && newDirection == Direction.Down) { return; } else if (_direction == Direction.Down && newDirection == Direction.Up) { return; } else if (_direction == Direction.Left && newDirection == Direction.Right) { return; } else if (_direction == Direction.Right && newDirection == Direction.Left) { return; } _direction = newDirection; } public bool IsEating(Apple apple) { if (_parts.Last().Intersects(apple.Location)) { GrowBiggerAndFaster(); return true; } return false; } private void GrowBiggerAndFaster() { _parts.Insert(0, _lastTail); _moveDelay -= (_moveDelay / 100)*2; } } } Apple.cs : using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework; namespace Snakez { public class Apple { private readonly int _maxWidth, _maxHeight; private readonly Texture2D _texture; private readonly Random random = new Random(); public Rectangle Location { get; private set; } public Apple(int screenWidth, int screenHeight, Texture2D texture) { _maxWidth = (screenWidth + 1) - texture.Width; _maxHeight = (screenHeight + 1) - texture.Height; _texture = texture; Place(); } public void Place() { Location = GetRandomLocation(_maxWidth, _maxHeight); } private Rectangle GetRandomLocation(int maxWidth, int maxHeight) { // x and y -- multiple of 20 int x = random.Next(1, maxWidth); var leftOver = x % 20; x = x - leftOver; int y = random.Next(1, maxHeight); leftOver = y % 20; y = y - leftOver; return new Rectangle(x, y, _texture.Width, _texture.Height); } public void Draw(SpriteBatch spriteBatch) { spriteBatch.Draw(_texture, Location, Color.White); } } }

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  • Rule of thumb for cost vs. savings for code re-use

    - by Styler
    Is it a good rule of thumb to always write code for the intent of re-using it somewhere down the road? Or, depending on the size of the component you are writing, is it better practice to design it for re-use when it makes sense with regards to time spent on it. What is a good rule of thumb for spending extra time on analysis and design on project components that have "some probability" of being needed later down the road for other things that may or may need this part. For example, if I have the need for project X to do things A, and B. A definitely needs to be written for re-use because it just makes sense to do so. B is very project specific at the moment, and I can hack it all together in a couple days to finish the project on time and give everyone kudos for being a great team, etc. Or if we say, lets spend a whole friggin' 2 weeks figuring out what project Y/Z might need this thing for and spend a load of extra time on on part B because someday we might need to use it on project Y/Z (where the savings will be realized). I'd imagine a perfect world situation would be a nicely crafted combination of project specific vs. re-use architected components given the project. However some code shops might feel it would be a great idea to write everything for the intention of using it at some point down the road.

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  • Hiring New IT Employees versus Promoting Internally for IT Positions

    Recently I was asked my opinion regarding the hiring of IT professionals in regards to the option of hiring new IT employees versus promoting internally for IT positions. After thinking a little more about this question regarding staffing, specifically pertaining to promoting internally verses new employees; I think my answer to this question is that it truly depends on the situation. However, in most cases I would side with promoting internally. The key factors in this decision should be based on a company/department’s current values, culture, attitude, and existing priorities.  For example if a company values retaining all of its hard earned business knowledge then they would tend to promote existing employees internal over hiring a new employee. Moreover, the company will have to pay to train an existing employee to learn a new technology and the learning curve for some technologies can be very steep. Conversely, if a company values new technologies and technical proficiency over business knowledge then a company would tend to hire new employees because they may already have experience with a technology that the company is planning on using. In this scenario, the company would have to take on the additional overhead of allowing a new employee to learn how the business operates prior to them being fully effective. To illustrate my points above let us look at contractor that builds in ground pools for example.  He has the option to hire employees that are very strong but use small shovels to dig, or employees weak in physical strength but use large shovels to dig. Which employee should the contractor use to dig a hole for a new in ground pool? If we compare the possible candidates for this job we will find that they are very similar to hiring someone internally verses a new hire. The first example represents the existing workers that are very strong regarding the understanding how the business operates and the reasons why in a specific manner. However this employee could be potentially weaker than an outsider pertaining to specific technologies and would need some time to build their technical prowess for a new position much like the strong worker upgrading their shovels in order to remove more dirt at once when digging. The other employee is very similar to hiring a new person that may already have the large shovel but will need to increase their strength in order to use the shovel properly and efficiently so that they can move a maximum amount of dirt in a minimal amount of time. This can be compared to new employ learning how a business operates before they can be fully functional and integrated in the company/department. Another key factor in this dilemma pertains to existing employee and their passion for their work, their ability to accept new responsibility when given, and the willingness to take on responsibilities when they see a need in the business. As much as possible should be considered in this decision down to the mood of the team, the quality of existing staff, learning cure for both technology and business, and the potential side effects of the existing staff.  In addition, there are many more consideration based on the current team/department/companies culture and mood. There are several factors that need to be considered when promoting an individual or hiring new blood for a team. They both can provide great benefits as well as create controversy to a group. Personally, staffing especially in the IT world is like building a large scale system in that all of the components and modules must fit together and preform as one cohesive system in the same way a team must come together using their individually acquired skills so that they can work as one team.  If a module is out of place or is nonexistent then the rest of the team will suffer until the all of its issues are addressed and resolved. Benefits of Promoting Internally Internal promotions give employees a reason to constantly upgrade their technology, business, and communication skills if they want to further their career Employees can control their own destiny based on personal desires Employee already knows how the business operates Companies can save money by promoting internally because the initial overhead of allowing new hires to learn how a company operates is very expensive Newly promoted employees can assist in training their replacements while transitioning to their new role within a company. Existing employees already have a proven track record in regards fitting in with the business culture; this is always an unknown with all new hires Benefits of a New Hire New employees can energize and excite existing employees New employees can bring new ideas and advancements in technology New employees can offer a different perspective on existing issues based on their past experience. As you can see the decision to promote an existing employee from within a company verses hiring a new person should be based on several factors that should ultimately place the business in the best possible situation for the immediate and long term future. How would you handle this situation? Would you hire a new employee or promote from within?

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  • About shared (static) Members and its behavior

    - by Allende
    I just realized that I can access shared members from instances of classes (probably this is not correct, but compile and run), and also learn/discover that, I can modify shared members, then create a new instance and access the new value of the shared member. My question is, what happens to the shared members, when it comes back to the "default" value (class declaration), how dangerous is it do this ? is it totally bad ? is it valid in some cases ?. If you want to test my point here is the code (console project vb.net) that I used to test shared members, as you can see/compile/run, the shared member "x" of the class "Hello" has default value string "Default", but at runtime it changes it, and after creating a new object of that class, this object has the new value of the shared member. Module Module1 Public Class hello Public Shared x As String = "Default" Public Sub New() End Sub End Class Sub Main() Console.WriteLine("hello.x=" & hello.x) Dim obj As New hello() Console.WriteLine("obj.x=" & obj.x) obj.x = "Default shared memeber, modified in object" Console.WriteLine("obj.x=" & obj.x) hello.x = "Defaul shared member, modified in class" Console.WriteLine("hello.x=" & hello.x) Dim obj2 As New hello() Console.WriteLine("obj2.x=" & obj2.x) Console.ReadLine() End Sub End Module UPDATE: First at all, thanks to everyone, each answer give feedback, I suppose, by respect I should choose one as "the answer", I don't want to be offensive to anyone, so please don't take it so bad if I didn't choose you answer.

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