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• Optimal Database design regarding functionality of letting user share posts by other users

  - by codecool

  I want to implement functionality which let user share posts by other users similar to what Facebook and Google+ share button and twitter retweet. There are 2 choices: 1) I create duplicate copy of the post and have a column which keeps track of the original post id and makes clear this is a shared post. 2) I have a separate table shared post where I save the post id which is a foreign key to post id in post table. Talking in terms of programming basically I keep pointer to the original post in a separate table and when need to get post posted by user and also shared ones I do a left join on post and shared post table Post(post_id(PK), post_content, posted_by) SharedPost(post_id(FK to Post.post_id), sharing_user, sharedfrom(in case someone shares from non owners profile)) I am in favour of second choice but wanted to know the advice of experts out there? One thing more posts on my webapp will be more on the lines of facebook size not tweet size.

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• Design patterns for effects between actors and technology

  - by changelog

  I'm working on my first game, and taking the opportunity to brush up my C++ (I want to make as much of it as portable as I can.) Whilst working on the technology tree and how it affects actors (spaceships, planets, crew, buildings, etc) I can't find a pattern that decouples these entities enough to feel like a clean approach. Just as an idea, here's the type of effects these actors can have on one another (and techs too) An engineer inside a spaceship boosts its shield A hero in a spaceship in a fleet increases morale A technology improves spaceships' travel distance A building in a planet improves its production The best I can come up with is the Observer pattern, and basically manage it more or less manually (when a crew member enters a spaceship, fire the event; when a new building is built in a planet, fire the event, etc etc.) but it seems to be too tightly coupled to me. I would love to get some ideas about how to approach this better.

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• Should we consider code language upon design?

  - by Codex73

  Summary This question aims to conclude if an applications usage will be a consideration when deciding upon development language. What factors if any could be considered upon language writing could be taken into context. Application Type: Web Question Of the following popular languages, when should we use one or the other? What factors if any could be considered upon language writing could be taken into context. Languages PHP Ruby Python My initial thought is that language shouldn't be considered as much as framework. Things to consider on framework are scalability, usage, load, portability, modularity and many more. Things to consider on Code Writing maybe cost, framework stability, community, etc.

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• Need advice on framework design: how to make extending easy

  - by beginner_

  I'm creating a framework/library for a rather specific use-case (data type). It uses diverse spring components, including spring-data. The library has a set of entity classes properly set up and according service and dao layers. The main work or main benefit of the framework lies in the dao and service layer. Developers using the framework should be able to extend my entity classes to add additional fields they require. Therefore I made dao and service layer generic so it can be used by such extended entity classes. I now face an issue in the IO part of the framework. It must be able to import the according "special data type" into the database. In this part I need to create a new entity instance and hence need the actual class used. My current solution is to configure in spring a bean of the actual class used. The problem with this is that an application using the framework could only use 1 implementation of the entity (the original one from me or exactly 1 subclass but not 2 different classes of the same hierarchy. I'm looking for suggestions / desgins for solving this issue. Any ideas?

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• Android From Local DB (DAO) to Server sync (JSON) - Design issue

  - by Taiko

  I sync data between my local DB and a Server. I'm looking for the cleanest way to modelise all of this. I have a com.something.db package That contains a Data Helper and couple of DAO classes that represents objects stored in the db (I didn't write that part) com.something.db --public DataHelper --public Employee @DatabaseField e.g. "name" will be an actual column name in the DB -name @DatabaseField -salary etc... (all in all 50 fields) I have a com.something.sync package That contains all the implementation detail on how to send data to the server. It boils down to a ConnectionManager that is fed by different classes that implements a 'Request' interface com.something.sync --public interface ConnectionManager --package ConnectionManagerImpl --public interface Request --package LoginRequest --package GetEmployeesRequest My issue is, at some point in the sync process, I have to JSONise and de-JSONise my data (E.g. the Employee class). But I really don't feel like having the same Employee class be responsible for both his JSONisation and his actual representation inside the local database. It really doesn't feel right, because I carefully decoupled the rest, I am only stuck on this JSON thing. What should I do ? Should I write 3 Employee classes ? EmployeeDB @DatabaseField e.g. "name" will be an actual column name in the DB -name @DatabaseField -salary -etc... 50 fields EmployeeInterface -getName -getSalary -etc... 50 fields EmployeeJSON -JSON_KEY_NAME = "name" The JSON key happens to be the same as the table name, but it isn't requirement -name -JSON_KEY_SALARY = "salary" -salary -etc... 50 fields It feels like a lot of duplicates. Is there a common pattern I can use there ?

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• ASP.NET design not SOLID

  - by w0051977

  SOLID principles are described here: http://en.wikipedia.org/wiki/SOLID_%28object-oriented_design%29 I am developing a large ASP.NET app. The previous developer created a few very large classes each with lots of different purposes. It is very difficult to maintain and extend. The classes are deployed to the web server along with the code behind files etc. I want to share a small amount of the app with another application. I am considering moving all of the classes of the ASP.NET web app to a DLL, so the small subset of functionality can be shared. I realise it would be better to only share the classes which contain code to be shared but because of the dependencies this is proving to be very difficult e.g. class A contains code that should be shared, however class A contains references to classes B, C, D, E, F, G etc, so class A cannot be shared on its own. I am planning to refactor the code in the future. As a temporary solution I am planning to convert all the classes into a single class library. Is this a bad idea and if so, is there an alternative? as I don't have time to refactor at the moment.

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• PyQt design issues

  - by Falmarri

  I've been working on a my first real project using PyQt lately. I've done just a little bit of work in Qt for C++ but nothing more than just messing around. I've found that the Qt python bindings are essentially just a straight port of C++ classes into python, which makes sense. The issue is that this creates a lot of messy, unpythonic code. For example if you look at QAbstractItemModel, there's a lot of hoops you have to go through that forces you to hide the actual python. I was just wondering if there's any intention of writing a python implementation of Qt that isn't necessarily just a wrapper? Either by Nokia or anyone else? I really like Qt but I would love to be able to write more pythonic code. I hope this is OK to ask here. I'm not trying to start a GUI war or anything.

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• How Would You Design This Table?

  - by sooprise

  I have to create a table where each row needs to store 50 number values. Each row will always need to store 50 number values. If this was a smaller number of values, I would just make fields for each of the values, but because there are 50, this approach seems a bit cumbersome (but since it will always be 50 values, maybe this is the correct approach?). Is there a way to store an array of values in a field? This seems like a nice solution, but the concept is almost identical to creating a relational database.

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• How to design brain games [on hold]

  - by samesky

  I will wonder if anybody has some information about designing games for brain improvement. Recently lumosity is into a gear. I guess they research a lot or have experts. But is there any other research paper that is publicly available for designing the brain games ? Any equation or data that can help? Or what characteristics a brain game should have ? I am getting interested on this and search internet a lot, but unfortunately I could not find the core structure of it. It will really a helpful for me if somebody can give some information. Thank you.

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• Client-server application design issue

  - by user2547823

  I have a collection of clients on server's side. And there are some objects that need to work with that collection - adding and removing clients, sending message to them, updating connection settings and so on. They should perform these actions simultaneously, so mutex or another synchronization primitive is required. I want to share one instance of collection between these objects, but all of them require access to private fields of collection. I hope that code sample makes it more clear[C++]: class Collection { std::vector< Client* > clients; Mutex mLock; ... } class ClientNotifier { void sendMessage() { mLock.lock(); // loop over clients and send message to each of them } } class ConnectionSettingsUpdater { void changeSettings( const std::string& name ) { mLock.lock(); // if client with this name is inside collection, change its settings } } As you can see, all these classes require direct access to Collection's private fields. Can you give me an advice about how to implement such behaviour correctly, i.e. keeping Collection's interface simple without it knowing about its users?

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• Layering Design Pattern in Java clean code style

  - by zeraDev

  As a Java developer, I am developing trying to use the clean code rules. But in my team we are facing a concrete problem: We have a business layer offering a service called "createObject", this service makes a lot of operation which can result to problem. E.g: parentObjectDontExist, objectAlreadyExist, dontHaveAuthorizationToCreate, operationFailed... and we want the UI using this service to display different information messages depending which error occurred. In old java dev, we should have create all signed exception type and throw it in createObject. As Clean code says, it is forbidden to use Exception for business logic AND signed exceptions are evil... Why not...But i don't know how to solved this problem and i don't want to use return code. How do you do? Thanks for youre experience return.

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• What OO Design to use ( is there a Design Pattern )?

  - by Blundell

  I have two objects that represent a 'Bar/Club' ( a place where you drink/socialise). In one scenario I need the bar name, address, distance, slogon In another scenario I need the bar name, address, website url, logo So I've got two objects representing the same thing but with different fields. I like to use immutable objects, so all the fields are set from the constructor. One option is to have two constructors and null the other fields i.e: class Bar { private final String name; private final Distance distance; private final Url url; public Bar(String name, Distance distance){ this.name = name; this.distance = distance; this.url = null; } public Bar(String name, Url url){ this.name = name; this.distance = null; this.url = url; } // getters } I don't like this as you would have to null check when you use the getters In my real example the first scenario has 3 fields and the second scenario has about 10, so it would be a real pain having two constructors, the amount of fields I would have to declare null and then when the object are in use you wouldn't know which Bar you where using and so what fields would be null and what wouldn't. What other options do I have? Two classes called BarPreview and Bar? Some type of inheritance / interface? Something else that is awesome?

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• How can I design multi-threaded application for larger user base

  - by rokonoid

  Here's my scenario, I need to develop a scalable application. My user base may be over 100K, every user has 10 or more small tasks. Tasks check every minute with a third party application through web services, retrieving data which is written in the database, then the data is forwarded to it's original destination. So here's the processing of a small task: while(true){ Boolean isNewInformationAvailable = checkWhetherInformationIsAvailableOrNot(); If(isNewInformationAvailable ==true){ fetchTheData(); writeToDatabase(); findTheDestination(); deliverTheData(); isAvailable =false; } } As the application is large, how should I approach designing this? I'm going to use Java to write it. Should I use concurrency, and how would you manage the concurrency?

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• invoking a system call at remote system in an application running on my system

  - by Ajay Pandey

  hiii all! I am working on an application which requires my iPhone to connect to mac via bluetooth and once connected my aplication will cause vnc aplication to run on the remote PC(mac). now that my iPhone is connected to mac.....via bluetooth.....i want to know as how can i make vnc run on tht mac expecting a quick reply...... thanks

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• Introducing Oracle System Assistant

  - by B.Koch

  by Josh Rosen One of the challenges with today's servers is getting the server up and running and understanding what all of the steps are once you plug the server in for the first time. So many different pieces come into play: installing drivers, updating firmware, configuring RAID, and provisioning the operating system. All of these steps must be done before you can even start using the server. Finding the latest firmware and drivers, making sure you have the right versions, and knowing that all the different software and firmware components work together properly can be a real challenge. If not done correctly, such as if you separately downloading disk firmware or controller firmware that doesn't match the existing OS drivers, you could experience bugs, performance problems, and incompatibilities. Gone are the days of having to locate the tools and drivers media that shipped with the server only to find out that newer versions of software and firmware are available on the web. Oracle has solved these challenges in the new X3-2 family of servers by introducing Oracle System Assistant. Oracle System Assistant is an innovative tool that is built-in to every new x86 server. It provides step-by-step assistance with configuring the server, updating firmware and drivers, and provisioning the operating system. Once you have completed all of the steps in the Oracle System Assistant tool, the server is ready to use. Oracle System Assistant was designed to be easy and straightforward. Starting it is as simple as pressing F9 when the server is booting. You'll need a keyboard, monitor, and mouse or you can use the remote console feature of Oracle ILOM (Integrated Lights Out Manager) to access a virtual KVM to the server from any machine. From there Oracle System Assistant will walk you through each of the steps necessary to set up your server. After configuring the network settings for Oracle System Assistant, the next step is to check for any new software or firmware for the server. Oracle System Assistant connects back to Oracle using your My Oracle Support account and downloads any updates that were made available to you for this specific server. This is where you really start to see the innovation that went into Oracle System Assistant. Firmware for Oracle ILOM and BIOS, operating system drivers, and other system firmware (including for option cards and disk drivers) come as a single bundle, downloading as a single unit, that has been engineered and tested to work together by Oracle. Oracle System Assistant figures out the right combination for your server, so you don't have to. Now that the server has the latest firmware, Oracle System Assistant will next walk you through configuring the hardware. From Oracle System Assistant, you can configure many Oracle ILOM settings, including the network settings and initial user accounts. This ensures that ILOM is accessible and ready to use. Oracle System Assistant is where all parts of the server come together. In addition to communicating with Oracle ILOM and interacting with BIOS, Oracle System Assistant understands and can configure the storage subsystem. Before installing the operating system, Oracle System Assistant can detect the storage configuration and configure RAID for all disks in the system. At this point, the server is ready to be provisioned with the host operating system. You can use Oracle System Assistant to provision a supported OS, including Oracle Linux, Oracle VM, RHEL, SuSe Linux, and Windows. And by using Oracle System Assistant, you can be sure that the proper OS drivers are installed for each of the installed hardware components. With Oracle System Assistant, initial setup of the server has never been easier. If we can innovate around problems and find solutions to make our servers easier to manage, this reduces IT costs and makes managing servers simpler. I think with Oracle System Assistant we have done just that. Josh Rosen is a Principal Product Manager at Oracle and previously spent more than a decade as a developer and architect of system management software. Josh has worked on system management for many of Oracle's hardware products ranging from the earliest blade systems to the latest Oracle x86 servers.

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• Would Using a PHP Framework Be Beneficial in My Context?

  - by Fractal

  I've just started work at a small start-up company who mainly uses PHP to develop their front-end apps. I had no prior PHP experience before joining, and this has led to my apps becoming large pieces of spaghetti code. I essentially started by adding code to implement an initial feature, and then continued to hack in more code to implement further features – without much thought for the overall design. The apps themselves output XML to render on small mobile devices. I recently started looking into frameworks that I could use. I reckon an advantage would be that they seem to force developers to modularise their programs using good-practice design patterns. This seems great for someone in my position. The extra functions they provide, for example: interfacing with databases in such a way as to make SQL injection impossible, would be very useful too. The downside I can see is that there will be a lot of overhead for me in terms of the time taken to learn the framework itself (while still getting to grips with PHP itself). I'm also worried that it will be overkill for the scale of the apps we develop. They tend to be programs that interface with a fairly simple back-end DB, and will generate about 5 different XML screens. Probably around 1 or 2 thousand lines of code. The time it takes just to configure the frameworks may not be worth it. The final problem I can see is that developers in the company – who have to go over my code, and who do not know the PHP framework I may use – will have a much harder time understanding it. Given those pros and cons, I'm still not sure on what the best course of action will be; so any advice will be greatly appreciated.

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• Checking preconditions or not

  - by Robert Dailey

  I've been wanting to find a solid answer to the question of whether or not to have runtime checks to validate input for the purposes of ensuring a client has stuck to their end of the agreement in design by contract. For example, consider a simple class constructor: class Foo { public: Foo( BarHandle bar ) { FooHandle handle = GetFooHandle( bar ); if( handle == NULL ) { throw std::exception( "invalid FooHandle" ); } } }; I would argue in this case that a user should not attempt to construct a Foo without a valid BarHandle. It doesn't seem right to verify that bar is valid inside of Foo's constructor. If I simply document that Foo's constructor requires a valid BarHandle, isn't that enough? Is this a proper way to enforce my precondition in design by contract? So far, everything I've read has mixed opinions on this. It seems like 50% of people would say to verify that bar is valid, the other 50% would say that I shouldn't do it, for example consider a case where the user verifies their BarHandle is correct, but a second (and unnecessary) check is also being done inside of Foo's constructor.

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• Confused about implementing Single Responsibility Principle

  - by HichemSeeSharp

  Please bear with me if the question looks not well structured. To put you in the context of my issue: I am building an application that invoices vehicles stay duration in a parking. In addition to the stay service there are some other services. Each service has its own calculation logic. Here is an illustration (please correct me if the design is wrong): public abstract class Service { public int Id { get; set; } public bool IsActivated { get; set; } public string Name { get; set } public decimal Price { get; set; } } public class VehicleService : Service { //MTM : many to many public virtual ICollection<MTMVehicleService> Vehicles { get; set; } } public class StayService : VehicleService { } public class Vehicle { public int Id { get; set; } public string ChassisNumber { get; set; } public DateTime? EntryDate { get; set; } public DateTime? DeliveryDate { get; set; } //... public virtual ICollection<MTMVehicleService> Services{ get; set; } } Now, I am focusing on the stay service as an example: I would like to know at invoicing time which class(es) would be responsible for generating the invoice item for the service and for each vehicle? This should calculate the duration cost knowing that the duration could be invoiced partially so the like is as follows: not yet invoiced stay days * stay price per day. At this moment I have InvoiceItemsGenerator do everything but I am aware that there is a better design.

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• A better alternative to incompatible implementations for the same interface?

  - by glenatron

  I am working on a piece of code which performs a set task in several parallel environments where the behaviour of the different components in the task are similar but quite different. This means that my implementations are quite different but they are all based on the relationships between the same interfaces, something like this: IDataReader -> ContinuousDataReader -> ChunkedDataReader IDataProcessor -> ContinuousDataProcessor -> ChunkedDataProcessor IDataWriter -> ContinuousDataWriter -> ChunkedDataWriter So that in either environment we have an IDataReader, IDataProcessor and IDataWriter and then we can use Dependency Injection to ensure that we have the correct one of each for the current environment, so if we are working with data in chunks we use the ChunkedDataReader, ChunkedDataProcessor and ChunkedDataWriter and if we have continuous data we have the continuous versions. However the behaviour of these classes is quite different internally and one could certainly not go from a ContinuousDataReader to the ChunkedDataReader even though they are both IDataProcessors. This feels to me as though it is incorrect ( possibly an LSP violation? ) and certainly not a theoretically correct way of working. It is almost as though the "real" interface here is the combination of all three classes. Unfortunately in the project I am working on with the deadlines we are working to, we're pretty much stuck with this design, but if we had a little more elbow room, what would be a better design approach in this kind of scenario?

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• Use decorator and factory together to extend objects?

  - by TheClue

  I'm new to OOP and design pattern. I've a simple app that handles the generation of Tables, Columns (that belong to Table), Rows (that belong to Column) and Values (that belong to Rows). Each of these object can have a collection of Property, which is in turn defined as an enum. They are all interfaces: I used factories to get concrete instances of these products, depending on circumnstances. Now I'm facing the problem of extending these classes. Let's say I need another product called "SpecialTable" which in turn has some special properties or new methods like 'getSomethingSpecial' or an extended set of Property. The only way is to extend/specialize all my elements (ie. build a SpecialTableFactory, a SpecialTable interface and a SpecialTableImpl concrete)? What to do if, let's say, I plan to use standard methods like addRow(Column column, String name) that doesn't need to be specialized? I don't like the idea to inherit factories and interfaces, but since SpecialTable has more methods than Table i guess it cannot share the same factory. Am I wrong? Another question: if I need to define product properties at run time (a Table that is upgraded to SpecialTable at runtime), i guess i should use a decorator. Is it possible (and how) to combine both factory and decorator design? Is it better to use a State or Strategy pattern, instead?

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• Run the system configuration once the system has been installed

  - by dierre

  Hi guys, the problem is the following. I have an old computer that mounts a SATA Dvd Burner. The old MoBo (an AsRock P4VT8+) is not able to recognize the freaking burner when booting. So I had to convert my IDE HD to USB HD and mount it on my laptop and install Ubuntu from there. The problem now is that I'm obviously getting kernel panic every now and then so I was wondering if it is possibile to rerun only the system and the hardware configuration.

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• Ubuntu 14.04: After login, top- and sidepanel don't load and system settings don't open

  - by Löwe Simon

  I have Ubuntu 14.04 on a Medion Erazer with the Nvidia GTX570M card. At first, while I had not installed the last nvidia driver, each time I would try to suspend my pc it would freeze frame on the login. Once I managed to install the nvidia drivers, everything seemed to work up until I noticed that suddenly the system settings would not open anymore. I then rebooted my pc, but when I logged in I just end up with my cursor but no top panel or side pannel. Thankfully, I had installed the gnome desktops which works, except for the fact the system settings do not open also in the gnome desktop. I have tried following: Problems after upgrading to 14.04 (only background and pointer after login) except for reinstalling nvidia, since then I would be back at square one with suspend not working. When I try to launch system settings through the terminal, I get: simon@simon-X681X:~$ unity-control-center libGL error: No matching fbConfigs or visuals found libGL error: failed to load driver: swrast (unity-control-center:2806): Gdk-ERROR **: The program 'unity-control-center' received an X Window System error. This probably reflects a bug in the program. The error was 'BadLength (poly request too large or internal Xlib length erro'. (Details: serial 229 error_code 16 request_code 155 (GLX) minor_code 1) (Note to programmers: normally, X errors are reported asynchronously; that is, you will receive the error a while after causing it. To debug your program, run it with the GDK_SYNCHRONIZE environment variable to change this behavior. You can then get a meaningful backtrace from your debugger if you break on the gdk_x_error() function.) Trace/breakpoint trap (core dumped) I know the 2 problems seem unrelated, but since they occured together, I am wondering if that is really the case. Your help is much appreciated, Simon

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• Entity system and rendering types

  - by Papi75

  I would like to implement entity system in my game and I've got some question about entity system and rendering. Currently, my renderer got two types of elements: Current design Mesh : A default renderable with a Material, a Geometry and a Transformable Sprite : A type of mesh with some methods like "flip" and "setRect" methods and a rect member (With an imposed geometry, a quad) This objects inherit from "Spacial" class. Questions: How can I handle this two types in an entity system? I'm thinking about using "MeshComponent" and "SpriteComponent", but if I do that, an entity could have a Mesh and a Sprite at the same type, it's look stupid, right? I thought the idea to have a parent "rendering" component : "RenderableComponent" for "MeshComponent" and "SpriteComponent" but it will be difficult to handle "cast" in the game (ex: did I need to ask entity-getComponent or SpineComponent, …) Thanks a lot for reading me! My entity system work like that: --------------------------------------------------------------------------- Entity* entity = world->createEntity(); MeshComponent* mesh = entity->addComponent<MeshComponent>(material); mesh->loadFromFile("monkey.obj"); PhysicComponent* physic = entity->addComponent<PhysicComponent>(); physic->setMass(5.4f); physic->setVelocity( 0.5f, 2.f ); --------------------------------------------------------------------------- class RenderingSystem { private: Scene scene; public: void onEntityAdded( Entity* entity ) { scene.addMesh( entity->getComponent<MeshComponent>() ); } } class PhysicSystem { private: World world; public: void onEntityAdded( Entity* entity ) { world.addBody( entity->getComponent<PhysicComponent>()->getBody() ); } void process( Entity* entity ) { PhysicComponent* physic = entity->getComponent<PhysicComponent>(); } } ---------------------------------------------------------------------------

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• Executing Components in an Entity Component System

  - by John

  Ok so I am just starting to grasp the whole ECS paradigm right now and I need clarification on a few things. For the record, I am trying to develop a game using C++ and OpenGL and I'm relatively new to game programming. First of all, lets say I have an Entity class which may have several components such as a MeshRenderer,Collider etc. From what I have read, I understand that each "system" carries out a specific task such as calculating physics and rendering and may use more that one component if needed. So for example, I would have a MeshRendererSystem act on all entities with a MeshRenderer component. Looking at Unity, I see that each Gameobject has, by default, got components such as a renderer, camera, collider and rigidbody etc. From what I understand, an entity should start out as an empty "container" and should be filled with components to create a certain type of game object. So what I dont understand is how the "system" works in an entity component system. http://docs.unity3d.com/ScriptReference/GameObject.html So I have a GameObject(The Entity) class like class GameObject { public: GameObject(std::string objectName); ~GameObject(void); Component AddComponent(std::string name); Component AddComponent(Component componentType); }; So if I had a GameObject to model a warship and I wanted to add a MeshRenderer component, I would do the following: warship->AddComponent(new MeshRenderer()); In the MeshRenderers constructor, should I call on the MeshRendererSystem and "subscribe" the warship object to this system? In that case, the MeshRendererSystem should probably be a Singleton("shudder"). From looking at unity's GameObject, if each object potentially has a renderer or any of the components in the default GameObject class, then Unity would iterate over all objects available. To me, this seems kind of unnecessary since some objects might not need to be rendered for example. How, in practice, should these systems be implemented?

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• USE case to Class Diagram - How do I?

  - by 01010011

  Hi, I would like your guidance on how to create classes and their relationships (generalization, association, aggregation and composition) accurately from my USE case diagram (please see below). I am trying to create this class diagram so I can use it to create a simple online PHP application that allows the user to register an account, login and logout, and store, search and retrieve data from a MySQL database. Are my classes correct? Or should I create more classes? And if so, what classes are missing? What relationships should I use when connecting the register, login, logout, search_database and add_to_database to the users? I'm new to design patterns and UML class diagrams but from my understanding, the association relationship relates one object with another object; the aggregation relationship is a special kind of association that allows "a part" to belong to more than one "whole" (e.g. a credit card and its PIN - the PIN class can also be used in a debit card class); and a composition relationship is a special form of aggregation that allows each part to belong to only one whole at a time. I feel like I have left out some classes or something because I just can't seem to find the relationships from my understanding of relationships. Any assistance will be really appreciated. Thanks in advance. USE CASE DIAGRAM CLASS DIAGRAM

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