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  • Passing data between objects in Chain of Responsibility pattern

    - by AbrahamJP
    While implementing the Chain of Responsibility pattern, i came across a dilemma om how to pass data between objects in the chain. The datatypes passed between object in the chain can differ for each object. As a temporary fix I had created a Static class containing a stack where each object in the chain can push the results to the stack while the next object in the chain could pop the results from the stack. Here is a sample code on what I had implemented. public interface IHandler { void Process(); } public static class StackManager { public static Stack DataStack = new Stack(); } //This class doesn't require any input to operate public class OpsA : IHandler { public IHandler Successor {get; set; } public void Process() { //Do some processing, store the result into Stack var ProcessedData = DoSomeOperation(); StackManager.DataStack.Push(ProcessedData); if(Successor != null) Successor(); } } //This class require input data to operate upon public class OpsB : IHandler { public IHandler Successor {get; set; } public void Process() { //Retrieve the results from the previous Operation var InputData = StackManager.DataStack.Pop(); //Do some processing, store the result into Stack var NewProcessedData = DoMoreProcessing(InputData); StackManager.DataStack.Push(NewProcessedData); if(Successor != null) Successor(); } } public class ChainOfResponsibilityPattern { public void Process() { IHandler ProcessA = new OpsA(); IHandler ProcessB = new OpsB(); ProcessA.Successor = ProcessB; ProcessA.Process(); } } Please help me to find a better approach to pass data between handlers objects in the chain.

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  • Sorting out POCO, Repository Pattern, Unit of Work, and ORM

    - by CoffeeAddict
    I'm reading a crapload on all these subjects: POCO Repository Pattern Unit of work Using an ORM mapper ok I see the basic definitions of each in books, etc. but I can't visualize this all together. Meaning an example structure (DL, BL, PL). So what, you have your DL objects that contain your CRUD methods, then your BL objects which are "mapped" using an ORM back to your DL objects? What about DTOs...they're your DL objects right? I'm confused. Can anyone really explain all this together or send me example code? I'm just trying to put this together. I am determining whether to go LINQ to SQL or EF 4 (not sure about NHibrernate yet). Just not getting the concepts as in physical layers and code layers here and what each type of object contains (just properties for DTOs, and CRUDs for your core DL classes that match the table fields???). I just need some guidance here. I'm reading Fowler's books and starting to read Evans but just not all there yet.

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  • Including partial views when applying the Mode-View-ViewModel design pattern

    - by Filip Ekberg
    Consider that I have an application that just handles Messages and Users I want my Window to have a common Menu and an area where the current View is displayed. I can only work with either Messages or Users so I cannot work simultaniously with both Views. Therefore I have the following Controls MessageView.xaml UserView.xaml Just to make it a bit easier, both the Message Model and the User Model looks like this: Name Description Now, I have the following three ViewModels: MainWindowViewModel UsersViewModel MessagesViewModel The UsersViewModel and the MessagesViewModel both just fetch an ObserverableCollection<T> of its regarding Model which is bound in the corresponding View like this: <DataGrid ItemSource="{Binding ModelCollection}" /> The MainWindowViewModel hooks up two different Commands that have implemented ICommand that looks something like the following: public class ShowMessagesCommand : ICommand { private ViewModelBase ViewModel { get; set; } public ShowMessagesCommand (ViewModelBase viewModel) { ViewModel = viewModel; } public void Execute(object parameter) { var viewModel = new ProductsViewModel(); ViewModel.PartialViewModel = new MessageView { DataContext = viewModel }; } public bool CanExecute(object parameter) { return true; } public event EventHandler CanExecuteChanged; } And there is another one a like it that will show Users. Now this introduced ViewModelBase which only holds the following: public UIElement PartialViewModel { get { return (UIElement)GetValue(PartialViewModelProperty); } set { SetValue(PartialViewModelProperty, value); } } public static readonly DependencyProperty PartialViewModelProperty = DependencyProperty.Register("PartialViewModel", typeof(UIElement), typeof(ViewModelBase), new UIPropertyMetadata(null)); This dependency property is used in the MainWindow.xaml to display the User Control dynamicly like this: <UserControl Content="{Binding PartialViewModel}" /> There are also two buttons on this Window that fires the Commands: ShowMessagesCommand ShowUsersCommand And when these are fired, the UserControl changes because PartialViewModel is a dependency property. I want to know if this is bad practice? Should I not inject the User Control like this? Is there another "better" alternative that corresponds better with the design pattern? Or is this a nice way of including partial views?

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  • What design pattern to use for one big method calling many private methods

    - by Jeune
    I have a class that has a big method that calls on a lot of private methods. I think I want to extract those private methods into their own classes for one because they contain business logic and I think they should be public so they can be unit tested. Here's a sample of the code: public void handleRow(Object arg0) { if (continueRunning){ hashData=(HashMap<String, Object>)arg0; Long stdReportId = null; Date effDate=null; if (stdReportIds!=null){ stdReportId = stdReportIds[index]; } if (effDates!=null){ effDate = effDates[index]; } initAndPutPriceBrackets(hashData, stdReportId, effDate); putBrand(hashData,stdReportId,formHandlerFor==0?true:useLiveForFirst); putMultiLangDescriptions(hashData,stdReportId); index++; if (stdReportIds!=null && stdReportIds[0].equals(stdReportIds[1])){ continueRunning=false; } if (formHandlerFor==REPORTS){ putBeginDate(hashData,effDate,custId); } //handle logic that is related to pricemaps. lstOfData.add(hashData); } } What design pattern should I apply to this problem?

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  • is this a design pattern?

    - by Michel
    Hi all, i have to build some financial data report, and for making the calculation, there are a lot of 'if then' situations: if it's a large client, subtract 10%, if it's postal code equals '10101', add 10%, if the day is on a saturday, make a difficult calculation etc. so i once read about this kind of example, and what they did was (hope i remember well) create a class with some base info and make it possible to add all kinds of calculationobjects to it. So to put what i remembered in pseudo code Basecalc bc = new baseCalc(); //put the info in the bc so other objects can do their if bc.Add(new Largecustomercalc()); bc.Add(new PostalcodeCalc()); bc.add(new WeekdayCalc()); the the bc would run the Calc() methods of all of the added Calc objects. As i type this i think all the Calc objects must be able to see the Basecalc properties to correctly perform their calculation logic. So all the if's are in the different Calc objects and not ALL in the Basecalc. does this make sense? I was wondering if this is some kind of design pattern?

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  • Pattern for version-specific implementations of a Java class

    - by Mike Monkiewicz
    So here's my conundrum. I am programming a tool that needs to work on old versions of our application. I have the code to the application, but can not alter any of the classes. To pull information out of our database, I have a DTO of sorts that is populated by Hibernate. It consumes a data object for version 1.0 of our app, cleverly named DataObject. Below is the DTO class. public class MyDTO { private MyWrapperClass wrapper; public MyDTO(DataObject data) { wrapper = new MyWrapperClass(data); } } The DTO is instantiated through a Hibernate query as follows: select new com.foo.bar.MyDTO(t1.data) from mytable t1 Now, a little logic is needed on top of the data object, so I made a wrapper class for it. Note the DTO stores an instance of the wrapper class, not the original data object. public class MyWrapperClass { private DataObject data; public MyWrapperClass(DataObject data) { this.data = data; } public String doSomethingImportant() { ... version-specific logic ... } } This works well until I need to work on version 2.0 of our application. Now DataObject in the two versions are very similar, but not the same. This resulted in different sub classes of MyWrapperClass, which implement their own version-specific doSomethingImportant(). Still doing okay. But how does myDTO instantiate the appropriate version-specific MyWrapperClass? Hibernate is in turn instantiating MyDTO, so it's not like I can @Autowire a dependency in Spring. I would love to reuse MyDTO (and my dozens of other DTOs) for both versions of the tool, without having to duplicate the class. Don't repeat yourself, and all that. I'm sure there's a very simple pattern I'm missing that would help this. Any suggestions?

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  • Need advice on C++ coding pattern

    - by Kotti
    Hi! I have a working prototype of a game engine and right now I'm doing some refactoring. What I'm asking for is your opinion on usage of the following C++ coding patterns. I have implemented some trivial algorithms for collision detection and they are implemented the following way: Not shown here - class constructor is made private and using algorithms looks like Algorithm::HandleInnerCollision(...) struct Algorithm { // Private routines static bool is_inside(Point& p, Object& object) { // (...) } public: /** * Handle collision where the moving object should be always * located inside the static object * * @param MovingObject & mobject * @param const StaticObject & sobject * @return void * @see */ static void HandleInnerCollision(MovingObject& mobject, const StaticObject& sobject) { // (...) } So, my question is - somebody advised me to do it "the C++" way - so that all functions are wrapped in a namespace, but not in a class. Is there some good way to preserve privating if I will wrap them into a namespace as adviced? What I want to have is a simple interface and ability to call functions as Algorithm::HandleInnerCollision(...) while not polluting the namespace with other functions such as is_inside(...) Of, if you can advise any alternative design pattern for such kind of logics, I would really appreciate that...

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  • Which design pattern fits - strategy makes sense ?

    - by user554833
    --Bump *One desperate try to get someone's attention I have a simple database table that stores list of users who have subscribed to folders either by email OR to show up on the site (only on the web UI). In the storage table this is controlled by a number(1 - show on site 2- by email). When I am showing in UI I need to show a checkbox next to each of folders for which the user has subscribed (both email & on site). There is a separate table which stores a set of default subscriptions which would apply to each user if user has not expressed his subscription. This is basically a folder ID and a virtual group name. But, Email subscriptions do not count for applying these default groups. So if no "on site" subscription apply default group. Thats the rule. How about a strategy pattern here (Pseudo code) Interface ISubscription public ArrayList GetSubscriptionData(Pass query object) Public class SubscriptionWithDefaultGroup Implement ArrayList GetSubscriptionData(Pass query object) Public class SubscriptionWithoutDefaultGroup Implement ArrayList GetSubscriptionData(Pass query object) Public class SubscriptionOnlyDefaultGroup Implement ArrayList GetSubscriptionData(Pass query object) does this even make sense? I would be more than glad for receive any criticism / help / notes. I am learning. Cheers

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  • A self-creator: What pattern is this? php

    - by user151841
    I have several classes that are basically interfaces to database rows. Since the class assumes that a row already exists ( __construct expects a field value ), there is a public static function that allows creation of the row and returns an instance of the class. Here's a pseudo-code example : class fruit { public $id; public function __construct( $id ) { $this->id = $id; $sql = "SELECT * FROM Fruits WHERE id = $id"; ... $this->arrFieldValues[$field] = $row[$value]; } public function __get( $var ) { return $this->arrFieldValues[$var]; } public function __set( $var, $val ) { $sql = "UPDATE fruits SET $var = $val WHERE id = $this->id"; } public static function create( $id ) { $sql = "INSERT INTO Fruits ( fruit_name ) VALUE ( '$fruit' )"; $id = mysql_insert_id(); $fruit = & new fruit($id); return $fruit; } } $obj1 = fruit::create( "apple" ); $obj2 = & new fruit( 12 ); What is this pattern called? Edit: I changed the example to one that has more database-interface functionality. For most of the time, this kind of class would be instantiated normally, through __construct(). But sometimes when you need to create a new row first, you would call create().

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  • How should I design my database API commands? [closed]

    - by WebDev
    I am developing a database API for a project, with commands for getting data from the database. For example, I have one gib table, so the command for that is: getgib name alias limit fields If the user pass their name: getgib rahul Then it will return all gib data whose name is like rahul. If an alias is given then it will return all the gib owned by the user whose alias (userid) was given. I want to design the commands: limit: to limit the record in query, fields: extra fields I want to add in the select query. So now the commands are set, but: I want the gibs by the gibid, so how to make this or any suggestion to improve my command is welcome. If the user doesn't want to specify the name, and he wants only the gibs by providing alias, then what separator should I use instead of name?

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  • How do game programmers design their classes to reuse in AI, network and play and pass mode?

    - by Amogh Talpallikar
    For a two player game where, your opponent could be on the network, CPU itself or near you where you would play turn by turn on the same machine. How do people design classes for re-use ? I am in a similar situation and have no experience in making such complex games. But here is what I have thought, If I am a player object , I should only be interacting with the GameManager or GameEngine Singleton , from which I will get various notifications about the game status. I dont care where and who my opponent is, this GameManager depending upon the game mode, will interact with gameNetworkManager , or AI tell me what the opponent played. I am not sure about the scenario where we play and pass [turn by turn on same machine]. Hoping for a brief but clear explanation or at least a link to a similar resource.:)

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  • How to Design a Relational Database; PASS Precon Swag and it’s “Symbolism”

    - by drsql
    Update! 10 more books added to the cadre from my friends at Red-Gate. With less than a week to go, I am starting to pack up for Charlotte and PASS 2013. I love that it is in Charlotte this year so I can drive and bring along some goodies to give away. Books and toys mostly, a variety of which were chosen rather specifically for some manner of symbolism with a tie in to database design for the most part. (Okay, symbolism is perhaps a bit of a stretch, but I have tied everything, even the goofy stuff,...(read more)

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  • Name of web design technique with vertically contiguous but separate screen-sized blocks?

    - by Chad Schultz
    I don't know the proper name for this, which makes it hard to Google it or describe this. On a site like http://p2theme.com/ as you scroll down you see that content is arranged into screen-sized chunks, each with its own chunk of content, each with a different background color, making them visually distinctive. I've seen this used more and more frequently on websites, but don't know what it's called. People have tried telling me "responsive design" or "flat UI" or "infinite scroll" or "parallax" -- but those are completely different things. What do you call this technique?

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  • Design for future changes or solve the problem at hand.

    - by Naveen
    While writing the code or during design do you try to generalize the problem at the first instance itself or try to solve that very specific problem. I am asking this because, trying to generalize the problem tends to complicate the things (which may not be necessary) and on the otherhand it will be very difficult to extend the specific solution if there is a change in the requirement. I guess the solution is to find the middle path which is easier said than done. How do you tackle this type of problem ? If you start generalizing it at what point of time you know that this much of generalization is sufficient ?

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  • How to decide whether to implement an operation as Entity operation vs Service operation in Domain Driven Design?

    - by Louis Rhys
    I am reading Evans's Domain Driven Design. The book says that there are entity and there are services. If I were to implement an operation, how to decide whether I should add it as a method on an entity or do it in a service class? e.g. myEntity.DoStuff() or myService.DoStuffOn(myEntity)? Does it depend on whether other entities are involved? If it involves other entities, implement as service operation? But entities can have associations and can traverse it from there too right? Does it depend on stateless or not? But service can also access entities' variable, right? Like in do stuff myService.DoStuffOn, it can have code like if(myEntity.IsX) doSomething(); Which means that it will depend on the state? Or does it depend on complexity? How do you define complex operations?

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  • Is it possible to design a multiplayer game which can be played from different devices?

    - by user9820
    I want to design a online multiplayer game for all gaming devices e.g. Desktop PC, internet browser, android phones, android tablets, iphone, ipad, XBOX 360 etc. Now my main requirement is that, I want all devices can be used to play the game in multiplayer mode toghether i.e. One player can be connected using PC another using android phone and other may be with iphone or ipad. My doubts are - How to make all devices to connect to common game server? What will be the logic for graphics and texture because all devices screen will be of different aspect ratio?

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  • How would you design an application with many target platforms and devices?

    - by Pierre 303
    I'm in a very beginning of the design phase of an application that will have to run in the following platforms/devices: Desktop: Windows, Linux & Mac Mobile: Android, iPhone/iPad & Windows Phone 7 Web: Silverlight I will use C# on Mono and I want to maximize code re-usability. Except for the desktop (I'll use WinForms/GTK#), my concern is related to many different GUI that I will face. What would be your approach? Obviously, the views will be different, but what about the controllers, data access, utility classes, etc. Is it really acceptable to share everything but the views?

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  • Are the technologies used in an application part of the architecture, or do they represent implementation/detailed design details?

    - by m3th0dman
    When designing and writing documentation for a project an architecture needs to be clearly defined: what are the high-level modules of the system, what are their responsibilities, how do they communicate with each other, what protocols are used etc. But in this list, should the concrete technologies be specified or this is actually an implementation detail and need to be specified at a lower level? For example, consider a distributed application that has two modules which communicate asynchronously via AMQP protocol, mediated by a message broker. The fact that these modules use the Spring AMQP library for sending and receiving messages is a fact that needs to be specified in the architecture or is a lower-level detailed design/implementation detail?

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  • Is Domain Driven Design useful / productive for not so complex domains?

    - by Elijah
    When assessing a potential project at work, I suggested that it might be advantageous to use a domain driven design approach to its object model. The project does not have an excessively complex domain, so my coworker threw this at me: It has been said, that DDD is favorable in instances where there is a complex domain model (“...It applies whenever we are operating in a complex, intricate domain” Eric Evans). What I'm lost on is - how you define the complexity of a domain? Can it be defined by the number of aggregate roots in the domain model? Is the complexity of a domain in the interaction of objects? The domain that we are assessing is related online publishing and content management.

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  • If all variables are a subset of the superkey, is the database design 5NF? [migrated]

    - by Lukazoid
    I have a table called LogMessages, which has the following columns: Level A numeric value which represents Trace, Debug, Info, Warning, Error or Fatal Time A UTC time Message Foreign key to a Messages table Source Foreign key to a Sources table User Foreign key to a Users table From what I can see, all of these columns are a part of the super key; if any single value differs to an existing row, a new row can be created. My question is, does this design comply to fifth normal form? I am unsure as some groups of data will be repeating, however I don't believe this violates 5NF? (correct me if I'm wrong)

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  • How are design-by-contract and property-based testing (QuickCheck) related?

    - by Todd Owen
    Is their only similarity the fact that they are not xUnit (or more precisely, not based on enumerating specific test cases), or is it deeper than that? Property-based testing (using QuickCheck, ScalaCheck, etc) seem well-suited to a functional programming style where side-effects are avoided. On the other hand, Design by Contract (as implemented in Eiffel) is more suited to OOP languages: you can express post-conditions about the effects of methods, not just their return values. But both of them involve testing assertions that are true in general (rather than assertions that should be true for a specific test case). And both can be tested using randomly generated inputs (with QuickCheck this is the only way, whereas with Eiffel I believe it is an optional feature of the AutoTest tool). Is there an umbrella term to encompass both approaches? Or am I imagining a relationship that doesn't really exist.

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  • How far can you get in iOS without learning PhotoShop or another graphic design program? [on hold]

    - by Aerovistae
    I'm in the process of learning iOS, and I'm coming from a web dev background where CSS controls 70-90% of the UI, and Python/C++ desktop dev where there are highly customizable UI toolkits for most things. I'm trying to figure out how people make good-looking apps without graphic design skills. You always hear about some 8 year old or 14 year old who made a successful app. So I assume that even if the required code was relatively basic, the app must have looked good if it was a success. But I find it really unlikely that these kids have advanced PhotoShop skills as well as having learned iOS programming at such a young age. Frankly, the same goes for most independent app developers....as they say, unicorns don't exist. So what's the deal? Can you make a good-looking, market quality app without those skills? What are the limitations?

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  • Are there any resources for motion-planning puzzle design?

    - by Salano Software
    Some background: I'm poking at a set of puzzles along the lines of Rush Hour/Sokoban/etc; for want of a better description, call them 'motion planning' puzzles - the player has to figure out the correct sequence of moves to achieve a particular configuration. (It's the sort of puzzle that's generically PSPACE-complete if that actually helps anyone's mental image). While I have a few straightforward 'building blocks' that I can use for puzzle crafting and I have a few basic examples put together, I'm trying to figure out how to avoid too much sameness over a large swath of these kinds of puzzles, and I'm also trying to figure out how to make puzzles that have more of a feel of logical solution than trial-and-error. Does anyone know of good resources out there for designing instances of this sort of puzzle once the core puzzle rules are in place? Most of what I've found on puzzle design only covers creating the puzzle rules, not building interesting puzzles out of a set of rules.

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  • Design application to send messages by marking circle on the map where you want to send message

    - by jhamb
    This is question asked to me by an interviewer, in which a map of world is given, and for those country you want to send message, just marked circle on that area, and just send to all the people comes in that area. Question visual link is : Design this application The approach that I told him: Firstly build whole person's data (contacts , place information and all) Then where you mark on the map, just build a cluster of that country using Hadoop and fire the message to all the person's contact comes in that cluster. So help me for better understandings of this problem, and if have another good approach (all back-end ad front-end) , then please tell me or discuss here with me. Thanks in advance.

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  • "Never do in code what you can get the SQL server to do well for you" - Is this a recipe for a bad design?

    - by PhonicUK
    It's an idea I've heard repeated in a handful of places. Some more or less acknowledging that once trying to solve a problem purely in SQL exceeds a certain level of complexity you should indeed be handling it in code. The logic behind the idea is that for the large majority of cases, the database engine will do a better job at finding the most efficient way of completing your task than you could in code. Especially when it comes to things like making the results conditional on operations performed on the data. Arguably with modern engines effectively JIT'ing + caching the compiled version of your query it'd make sense on the surface. The question is whether or not leveraging your database engine in this way is inherently bad design practice (and why). The lines become blurred further when all the logic exists inside the database and you're just hitting it via an ORM.

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