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  • What elegant method callback design should be used ?

    - by ereOn
    Hi, I'm surprised this question wasn't asked before on SO (well, at least I couldn't find it). Have you ever designed a method-callback pattern (something like a "pointer" to a class method) in C++ and, if so, how did you do it ? I know a method is just a regular function with some hidden this parameter to serve as a context and I have a pretty simple design in mind. However, since things are often more complex than they seem to, I wonder how our C++ gurus would implement this, preferably in an elegant and standard way. All suggestions are welcome !

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  • Question about a possible design pattern...

    - by Aftershock
    I have such a design in my mind.... My aim is to reuse the program with some features included and without some features. What is it called in the literature? class feature1 { void feature1function1(); void feature1function2(); } class feature2 { void feature2function1(); void feature2function2(); } class program: feature1, feature2 { void function1() { feature2function1(); } void function2() { feature1function1(); feature2function1(); } void execute() { function1(); function2(); } }

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  • Design patter for extending Android's activities?

    - by Carl
    While programming on Android, I end up writing a parent activity which is extended by several others. A bit like ListActivity. My parent activity extends Activity. if I intend to use a Map or a List, I can't use my parent activity as superclass - the child activity can only extend one activity obviously. As such I end up writing my parent activities with the same logic for Activity, ListActivity, MapActivity and so forth. What am I looking for is some sort of trait functionality/design pattern which would help in this case. Any suggestions?

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  • commad design pattern usage

    - by sagie
    Hi. I've read 3 descriptions of the command design pattern: wikipedia, dofactory and source making. In all of them, the UML shows a relation between the client to the receiver & the concrete command, but no relation to the invoker. But in all 3 examples the client is the one that initiates the invoker and call its Execute method. I think that should be a relation to the invoker as well. Am I missing somthing in here? Maybe even a basic UML knowladge?

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  • which design choose? - pros and cons

    - by Guarava Makanili
    Which of these 3 approches would choose and why? // This is the one I would choose class Car { } class FeeCalculator { public double calculateFee(Car car) { return 0; } } // in that case the problem might be when we use ORM framework and we try to invoke save with parameter Car class Car { private FeeCalculator calculator; public double calculateFee() { return calculator.calculateFee(this); } } class FeeCalculator { public double calculateFee(Car car) { return 0; } } // in that case the problem mentioned above is solved, but I don't like this design class Car { public double calculateFee(FeeCalculator calculator) { return calculator.calculateFee(this); } } class FeeCalculator { public double calculateFee(Car car) { return 0; } }

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  • How to design model for multi-tiered data?

    - by Chris
    Say I have three types of object: Area, Subarea and Topic. I want to be able to display an Area, which is just a list of Subareas and the Topics contained in those Subareas. I never want to be able to display Subareas separately - they're just for breaking up the Topics. Topics can, however, appear in multiple Areas (but probably under the same Subarea). How would I design a model for this? I could use ForeignKey from Topic to Subarea and from Subarea to Area, but it seems unnecessarily complex given that I never want to interact with subareas themselves. Also, none of these objects are ever altered or added to by the user. They're just for me to represent information. Maybe there is a better way to represent it all?

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  • Design pattern for data entry forms with LINQ2SQL

    - by petebob796
    I am about to start a new winforms data entry application, it already has the database designed which I am comfortable with. I was going to use LINQ2SQL to access the tables to keep things type safe but am now wondering about design patterns, something I am just getting into. Since LINQ is giving me objects to use should I still create classes in between to hold the validation code and helper methods or should these just go in with the UI? It just seems I will end up with classes sat in between with little code which will cause the UI classes to have code just getting and setting values in the intermediate class and returning from validation to flag errors... Any good reading on this? Should I consider the entity framework (or similar) instead?

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  • Comparing Design Patterns

    - by Lijo
    Hi, I am learning design patterns using C#. One of the challenges that I am facing is that they look similar. Could you please help me to distinguish them – basically when to use them? - Why not the other? Bridge and Strategy State and Strategy Façade and Strategy Composite and Strategy I understand that there are lots of resources available in the web. However they does not treat this special question. [Note: I am looking for implementation examples and rationale behind the selection; not mere explanations] It would be great if you are taking examples from any of the following 1) E-Commerce 2) Payroll system 3) Banking 4) Retailing Thanks for your understanding.. Thanks Lijo

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  • Class design question (Disposable and singleton behavior)

    - by user137348
    The Repository class has singleton behavior and the _db implements the disposable pattern. As excepted the _db object gets disposed after the first call and because of the singleton behavior any other call of _db will crash. [ServiceBehavior(InstanceContextMode=InstanceContextMode.Single)] public class Repository : IRepository { private readonly DataBase _db; public Repository(DataBase db) { _db = db; } public int GetCount() { using(_db) { return _db.Menus.Count(); } } public Item GetItem(int id) { using(_db) { return _db.Menus.FirstOrDefault(x=>x.Id == id); } } } My question is, is there any way to design this class to work properly without removing the singleton behavior? The Repositoryclass will be serving big amount of requests.

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  • Generic Database table design

    - by Gazeth
    Just trying to figure out the best way to design my table for the following scenario: I have several areas in my system (documents, projects, groups and clients) and each of these can have comments logged against them. My question is should I have one table like this: CommentID DocumentID ProjectID GroupID ClientID etc Where only one of the ids will have data and the rest will be NULL or should I have a seperate CommentType table and have my comments table like this: CommentID CommentTypeID ResourceID (this being the id of the project/doc/client) etc My thoughts are that option 2 would be more efficient from an indexing point of view?

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  • related categories - database design

    - by mike
    Hello! I'm looking for a little database design advice... I have a spreadsheet with a few columns in it. Column 1 being a list of categories and the rest being related categories(to the category in column 1). I'm trying to figure out what the best way to setup the tables would be... My thought so far is to have a table that just lists the categories then have a table with 2 columns that holds the id of the category and the id of a related category.... Would this be the best way to do this? Any better ideas?

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  • C++ Singleton design pattern

    - by Artem Barger
    Recently I've bumped into a realization/implementation of the Singleton design pattern for C++. It has looked like this (I have adopted it from the real life example): // a lot of methods are omitted here class Singleton { public: static Singleton* getInstance( ); ~Singleton( ); private: Singleton( ); static Singleton* instance; }; From this declaration I can deduce that the instance field is initiated on the heap. That means there is a memory allocation. What is completely unclear for me is when exactly the memory is going to be deallocated? Or is there a bug and memory leak? It seems like there is a problem in the implementation. My main question is, how do I implement it in the right way?

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  • Customers and suppliers database design issue

    - by hectorsq
    I am developing a web application in which I will have customers and suppliers. Initially I thought on using a Customers table and a Suppliers table. Then when I was thinking on bank transactions, I noticed that each transaction needs to refer to a customer or a supplier, so I thought on using a single table named Business in which I will save both customers and suppliers. If I use Customers and Suppliers tables when I want to list the bank transactions I will have to search in both tables to get the company name. If I use a Businesses table I will have to use a business type column, and have the union of possible fields for all businesses types. Any suggestions on the design?

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  • Does the following indicate a bad design?

    - by Mewzer
    Hello, I was wondering whether you think the following code usually indicates a bad design ... class X { public: ... private: Y y; }; Class Y { public: Y( X& value ){ x = value; }; private: X& x; } (i.e. there is some sort of cyclic dependency between the classes X and Y).

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  • MVC Architecture

    Model-View-Controller (MVC) is an architectural design pattern first written about and implemented by  in 1978. Trygve developed this pattern during the year he spent working with Xerox PARC on a small talk application. According to Trygve, “The essential purpose of MVC is to bridge the gap between the human user's mental model and the digital model that exists in the computer. The ideal MVC solution supports the user illusion of seeing and manipulating the domain information directly. The structure is useful if the user needs to see the same model element simultaneously in different contexts and/or from different viewpoints.”  Trygve Reenskaug on MVC The MVC pattern is composed of 3 core components. Model View Controller The Model component referenced in the MVC pattern pertains to the encapsulation of core application data and functionality. The primary goal of the model is to maintain its independence from the View and Controller components which together form the user interface of the application. The View component retrieves data from the Model and displays it to the user. The View component represents the output of the application to the user. Traditionally the View has read-only access to the Model component because it should not change the Model’s data. The Controller component receives and translates input to requests on the Model or View components. The Controller is responsible for requesting methods on the model that can change the state of the model. The primary benefit to using MVC as an architectural pattern in a project compared to other patterns is flexibility. The flexibility of MVC is due to the distinct separation of concerns it establishes with three distinct components.  Because of the distinct separation between the components interaction is limited through the use of interfaces instead of classes. This allows each of the components to be hot swappable when the needs of the application change or needs of availability change. MVC can easily be applied to C# and the .Net Framework. In fact, Microsoft created a MVC project template that will allow new project of this type to be created with the standard MVC structure in place before any coding begins. The project also creates folders for the three key components along with default Model, View and Controller classed added to the project. Personally I think that MVC is a great pattern in regards to dealing with web applications because they could be viewed from a myriad of devices. Examples of devices include: standard web browsers, text only web browsers, mobile phones, smart phones, IPads, IPhones just to get started. Due to the potentially increasing accessibility needs and the ability for components to be hot swappable is a perfect fit because the core functionality of the application can be retained and the View component can be altered based on the client’s environment and the View component could be swapped out based on the calling device so that the display is targeted to that specific device.

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  • Which are the best tools for Graphic Designing?

    - by Jen
    Hello, I want to take up Graphic Designing as my profession. I would be designing Logos, Icons, Stationery, Brochures, Handouts, Book Covers, etc. But I am thoroughly confused as to which tools are the best and which books/resources will help me learn these tools and graphic designing like a professional. I am ready to shell out money to purchase the resources. Please help me out! Thanks, Jen

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  • SSIS 2005 Error while using script component Designer: "Cannot fetch a row from OLE DB provider "BUL

    - by user150541
    I am trying to debug a dts package in SSIS. I have a script component designer where I pass in the input variables to increment a counter. When I try to msgbox the counter value, I get the following error. Error: 0xC0202009 at STAGING1 to STAGING2, STAGING2 Destination [1056]: An OLE DB error has occurred. Error code: 0x80040E14. An OLE DB record is available. Source: "Microsoft SQL Native Client" Hresult: 0x80040E14 Description: "Cannot fetch a row from OLE DB provider "BULK" for linked server "(null)".". An OLE DB record is available. Source: "Microsoft SQL Native Client" Hresult: 0x80040E14 Description: "The OLE DB provider "BULK" for linked server "(null)" reported an error. The provider did not give any information about the error.". An OLE DB record is available. Source: "Microsoft SQL Native Client" Hresult: 0x80040E14 Description: "Reading from DTS buffer timed out.". Below is the part of the code within the script component designer : Imports System Imports System.Data Imports System.Math Imports Microsoft.SqlServer.Dts.Pipeline.Wrapper Imports Microsoft.SqlServer.Dts.Runtime.Wrapper Public Class ScriptMain Inherits UserComponent Dim iCounter As Integer Dim iCurrentVal As Integer Dim sCurrentOracleSeq As String Dim sSeqName As String Dim sSeqAltProcName As String Public Overrides Sub Input0_ProcessInputRow(ByVal Row As Input0Buffer) ' ' Add your code here ' Row.SEQIDNCASE = iCounter + iCurrentVal iCounter += 1 MsgBox(iCounter + iCurrentVal, MsgBoxStyle.Information, "Input0") End Sub Public Overrides Sub PreExecute() sCurrentOracleSeq = Me.Variables.VSEQIDCurVal iCurrentVal = CInt(sCurrentOracleSeq) MsgBox(iCurrentVal, MsgBoxStyle.Information, "No Title") iCounter = 0 sSeqName = Me.Variables.VSEQIDName sSeqAltProcName = Me.Variables.VSEQIDAlterProc End Sub Public Overrides Sub PostExecute() Me.Variables.VSEQIDUpdateSQL = "Begin " & sSeqAltProcName & "('" & sSeqName & "'," & (iCounter + iCurrentVal) & "); End;" End Sub End Class Note that the above part of code works perfectly fine if I comment out the lines that has Msgbox.

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  • How should I prepare the design of a web page for a web developer?

    - by jackal
    What techniques, software or practices do you use to prepare a description of a web page for further development? I am doing some research (with little luck) in how to create description for web developers - what should be included on the web page (inputs widths, font sizes, images placement, etc). Right now I use a combination of Excel and Word documents. In complex cases this is inefficient. Any other suggestions?

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  • Is there a clean separation of my layers with this attempt at Domain Driven Design in XAML and C#

    - by Buddy James
    I'm working on an application. I'm using a mixture of TDD and DDD. I'm working hard to separate the layers of my application and that is where my question comes in. My solution is laid out as follows Solution MyApp.Domain (WinRT class library) Entity (Folder) Interfaces(Folder) IPost.cs (Interface) BlogPosts.cs(Implementation of IPost) Service (Folder) Interfaces(Folder) IDataService.cs (Interface) BlogDataService.cs (Implementation of IDataService) MyApp.Presentation(Windows 8 XAML + C# application) ViewModels(Folder) BlogViewModel.cs App.xaml MainPage.xaml (Contains a property of BlogViewModel MyApp.Tests (WinRT Unit testing project used for my TDD) So I'm planning to use my ViewModel with the XAML UI I'm writing a test and define my interfaces in my system and I have the following code thus far. [TestMethod] public void Get_Zero_Blog_Posts_From_Presentation_Layer_Returns_Empty_Collection() { IBlogViewModel viewModel = _container.Resolve<IBlogViewModel>(); viewModel.LoadBlogPosts(0); Assert.AreEqual(0, viewModel.BlogPosts.Count, "There should be 0 blog posts."); } viewModel.BlogPosts is an ObservableCollection<IPost> Now.. my first thought is that I'd like the LoadBlogPosts method on the ViewModel to call a static method on the BlogPost entity. My problem is I feel like I need to inject the IDataService into the Entity object so that it promotes loose coupling. Here are the two options that I'm struggling with: Not use a static method and use a member method on the BlogPost entity. Have the BlogPost take an IDataService in the constructor and use dependency injection to resolve the BlogPost instance and the IDataService implementation. Don't use the entity to call the IDataService. Put the IDataService in the constructor of the ViewModel and use my container to resolve the IDataService when the viewmodel is instantiated. So with option one the layers will look like this ViewModel(Presentation layer) - Entity (Domain layer) - IDataService (Service Layer) or ViewModel(Presentation layer) - IDataService (Service Layer)

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  • Design Anti-Patterns - C# - Do you call this a God object?

    - by Reddy S R
    I am writing Portfolio module for my web site and it has 3 components. Gallery Category, Gallery, & Gallery Images. I am doing all the request handling, (creating, reading, updating, other), for the above 3 components in 1 class, Portfolio. DB handling jobs for Portfolio module is done in another file. My question is, even just for request handling purpose, can you do all the operations in 1 class? -Reddy

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  • Where can I ask web design questions of a more amateur nature?

    - by Warren van Rooyen
    I don't want to bother pro web designers with simple questions as I see most of the questions here are quite technical. An example would be, 'I have a template I've downloaded. The folder contains a css folder and PHP files. How would I bring this into Dreamweaver?' It's unfortunately in a space between what I'd be able to find on Google and asking here without feeling like a hinderance for those who don't want to answer such simple questions. Thanks, Warren.

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  • What are the design decisions involved in choosing how to expose a Java web application?

    - by Gary Rowe
    There are many ways to expose a Java web application to the consumer: application container (JBoss etc), servlet container (Tomcat etc), OSGi (Knopflerfish etc), self-executable WAR (Winstone etc) and so on. Are there any clear considerations where one approach should be favoured over another? As an example, could a collection of self-executable WARs running as raw Unix processes outperform the same applications deployed within Tomcat taking into account administration and scalability concerns?

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  • What is the best way to design a table with an arbitrary id?

    - by P.Brian.Mackey
    I have the need to create a table with a unique id as the PK. The ID is a surrogate key. Originally, I had a natural key, but requirement changes have undermined this idea. Then, I considered adding an auto incrementing identity. But, this presents problems. A. I can't specify my own ID. B. The ID's are difficult to reset. Both of these together make it difficult to copy over this table with new data or move the table across domains, e.g. Dev to QA. I need to refer to these ID's from the front end, JavaScript...so they must not change. So, the only way I am aware of to meet all these challenges is to make a GUID ID. This way, I can overwrite the ID's when I need to or I can generate a new one without concern for order (E.G. an int based id would require I know the last inserted ID). Is a GUID the best way to accomplish my goals? Considering that a GUID is a string and joining on a string is an expensive task, is there a better way?

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  • How to Identify Which Hardware Component is Failing in Your Computer

    - by Chris Hoffman
    Concluding that your computer has a hardware problem is just the first step. If you’re dealing with a hardware issue and not a software issue, the next step is determining what hardware problem you’re actually dealing with. If you purchased a laptop or pre-built desktop PC and it’s still under warranty, you don’t need to care about this. Have the manufacturer fix the PC for you — figuring it out is their problem. If you’ve built your own PC or you want to fix a computer that’s out of warranty, this is something you’ll need to do on your own. Blue Screen 101: Search for the Error Message This may seem like obvious advice, but searching for information about a blue screen’s error message can help immensely. Most blue screens of death you’ll encounter on modern versions of Windows will likely be caused by hardware failures. The blue screen of death often displays information about the driver that crashed or the type of error it encountered. For example, let’s say you encounter a blue screen that identified “NV4_disp.dll” as the driver that caused the blue screen. A quick Google search will reveal that this is the driver for NVIDIA graphics cards, so you now have somewhere to start. It’s possible that your graphics card is failing if you encounter such an error message. Check Hard Drive SMART Status Hard drives have a built in S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology) feature. The idea is that the hard drive monitors itself and will notice if it starts to fail, providing you with some advance notice before the drive fails completely. This isn’t perfect, so your hard drive may fail even if SMART says everything is okay. If you see any sort of “SMART error” message, your hard drive is failing. You can use SMART analysis tools to view the SMART health status information your hard drives are reporting. Test Your RAM RAM failure can result in a variety of problems. If the computer writes data to RAM and the RAM returns different data because it’s malfunctioning, you may see application crashes, blue screens, and file system corruption. To test your memory and see if it’s working properly, use Windows’ built-in Memory Diagnostic tool. The Memory Diagnostic tool will write data to every sector of your RAM and read it back afterwards, ensuring that all your RAM is working properly. Check Heat Levels How hot is is inside your computer? Overheating can rsult in blue screens, crashes, and abrupt shut downs. Your computer may be overheating because you’re in a very hot location, it’s ventilated poorly, a fan has stopped inside your computer, or it’s full of dust. Your computer monitors its own internal temperatures and you can access this information. It’s generally available in your computer’s BIOS, but you can also view it with system information utilities such as SpeedFan or Speccy. Check your computer’s recommended temperature level and ensure it’s within the appropriate range. If your computer is overheating, you may see problems only when you’re doing something demanding, such as playing a game that stresses your CPU and graphics card. Be sure to keep an eye on how hot your computer gets when it performs these demanding tasks, not only when it’s idle. Stress Test Your CPU You can use a utility like Prime95 to stress test your CPU. Such a utility will fore your computer’s CPU to perform calculations without allowing it to rest, working it hard and generating heat. If your CPU is becoming too hot, you’ll start to see errors or system crashes. Overclockers use Prime95 to stress test their overclock settings — if Prime95 experiences errors, they throttle back on their overclocks to ensure the CPU runs cooler and more stable. It’s a good way to check if your CPU is stable under load. Stress Test Your Graphics Card Your graphics card can also be stress tested. For example, if your graphics driver crashes while playing games, the games themselves crash, or you see odd graphical corruption, you can run a graphics benchmark utility like 3DMark. The benchmark will stress your graphics card and, if it’s overheating or failing under load, you’ll see graphical problems, crashes, or blue screens while running the benchmark. If the benchmark seems to work fine but you have issues playing a certain game, it may just be a problem with that game. Swap it Out Not every hardware problem is easy to diagnose. If you have a bad motherboard or power supply, their problems may only manifest through occasional odd issues with other components. It’s hard to tell if these components are causing problems unless you replace them completely. Ultimately, the best way to determine whether a component is faulty is to swap it out. For example, if you think your graphics card may be causing your computer to blue screen, pull the graphics card out of your computer and swap in a new graphics card. If everything is working well, it’s likely that your previous graphics card was bad. This isn’t easy for people who don’t have boxes of components sitting around, but it’s the ideal way to troubleshoot. Troubleshooting is all about trial and error, and swapping components out allows you to pin down which component is actually causing the problem through a process of elimination. This isn’t a complete guide to everything that could likely go wrong and how to identify it — someone could write a full textbook on identifying failing components and still not cover everything. But the tips above should give you some places to start dealing with the more common problems. Image Credit: Justin Marty on Flickr     

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  • How can I refactor client side functionality to create a product line-like generic design?

    - by Nupul
    Assume the following situation similar to that of Stack Overflow: I have a system with a front-end that can perform various manipulations on the data (by sending messages to REST back-end): Posting Editing and deleting Adding labels and tags Now in the first version we created it well modularized but the need as of now for 'evolving' the system similar to Stack Overflow. My question is how best to separate the commonality and how to incorporate the variability with respect to the following: Commonality: The above 'functionalities' and sending/receiving the data from the server Look and feel (also a variability as explained below) HTTP verbs associated with the above actions Variability: The RESTful URLs where the requests are sent The text/style of the UI (the commonality is analogous to Stack Overflow - the functionality of upvotes, posting a question remains the same, but the words, the icons, the look and feel is still different across sites) I think this is entirely a client-side code organization/refactoring issue. I'm heavily using jQuery, javascript and backbone for front-end development. My question is how best should I isolate the same to be able to create multiple such aspects to the tool we are currently working on?

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