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• How to make notification to group users with read/unread flag?

  - by user2335065

  I am making a notification system so that when users in a group perform an action, it will notify all the other users in the group. I want the notification to be marked "read" or "unread" for each user of the group. With that, I can easily retreive any unread notification for a user and display it. I am think about creating a notification table that have the following fields. +----------------------+ | notification | +----------------------+ | id | | userid | | content | | status (read/unread) | | time | +----------------------+ My question is: Whether it is the correct way of making the system? As it means that when there is 1,000 users in a group, then I have to insert 1,000 rows to the table. If not, what is the better way of doing this? If it is the way to do this, how can I write the php/mysql codes to do the looping of inserting the rows? Thanks!

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• Process a batch of items, return an object to report on status

  - by Naeem Sarfraz

  I'm looking for a pattern (or good practice) for the following scenario: My function List<BatchItemResponse> Process(List<BatchItem> Data) {..} will process a list of data, and return info on where each item in the batch could be processed. struct BatchItemResponse { int BatchItemID; bool Processed; string Description; } Any thoughts? Is what I've proposed as good as it gets?

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• Lazy loading? Better avoiding it?

  - by Charlie Pigarelli

  I just read about this design pattern: Lazy Load. And, since in the application i'm working on i have all the classes in one folder, i was wondering if this pattern could just make me avoiding the include() function for every class. I mean: It's nice to know that if i forgot to include a class, PHP, before falling into an error, trough an __autoload() function try to get it. But is it fine enough to just don't care about including classes and let PHP do it by your own every time? Or we should write __autoload() just in case it is needed?

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• .Net - Whats the difference between a Session Facade and Business Delegate?

  - by KP65

  What I understand so far: Business Delegate - In the presentation tier, as an ASP component, provides an interface for ASP views to access business components without exposing their API, therefore reducing coupling between the two. Session Facade - In the business tier, as a com+ component, encapsulates business objects, provides a course grain interface for views to access business components. Reduces coupling, hides complex business component interaction from views. So what is the actual difference? They seem pretty similar to me..

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• DI with disposable objects

  - by sunnychaganty

  Suppose my repository class looks like this: class myRepository : IDisposable{ private DataContext _context; public myRepository(DataContext context){ _context = context; } public void Dispose(){ // to do: implement dispose of DataContext } } now, I am using Unity to control the lifetime of my repository & the data context & configured the lifetimes as: DataContext - singleton myRepository - create a new instance each time Does this mean that I should not be implementing the IDisposable on the repository to clean up the DataContext? Any guidance on such items?

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• Why use hashing to create pathnames for large collections of files?

  - by Stephen

  Hi, I noticed a number of cases where an application or database stored collections of files/blobs using a has to determine the path and filename. I believe the intended outcome is a situation where the path never gets too deep, or the folders ever get too full - too many files (or folders) in a folder making for slower access. EDIT: Examples are often Digital libraries or repositories, though the simplest example I can think of (that can be installed in about 30s) is the Zotero document/citation database. Why do this? EDIT: thanks Mat for the answer - does this technique of using a hash to create a file path have a name? Is it a pattern? I'd like to read more, but have failed to find anything in the ACM Digital Library

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• Re-factoring from Active Record to Data Mapper

  - by Owen

  have you re-factored from an Active Record to a Data Mapper pattern? what conditions prompted the switch? i'm primarily interested in web based applications, but would like to know the challenges that accompany such a move in any environment.

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• Converting ASP.NET MVC to n-Tiered Architecture

  - by Jeff

  I just built an application using ASP.NET MVC. The programmers at my company want to build all future modules using n-Tiered (Presentation Layer, Business Logic Layer, Data Access Layer) architecture. I am not the programmer and need to know why this makes sense? Do I have to completely rewrite the entire code or can it be converted? We are building an HRIS system with Business Intelligence. Somebody please explain why or why not this approach does or does not make sense.

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• In M-V-VM where does my code go?

  - by Nate Bross

  So, this is a pretty basic question I hope. I have a web service that I've added through Add Service Reference. It has some methods to get list and get detail of a perticular table in my database. What I'm trying to do is setup a UI as follows: App Load Load service proxy Call the GetList(); method display the results in a ListBox control User Double Clicks item in ListBox, display a modal dialog with a "detail" view I'm extremely new to using MVVM, so any help would be greatly appreciated. Additional information: // Service Interface (simplification): interface IService { IEnumerable<MyObject> GetList(); MyObject GetDetail(int id); } // Data object (simplification) class MyObject { public int ID { get; set; } public string Name { get; set; } } I'm thinking I should have something like this: MainWindow MyObjectViewUserControl Displays list Opens modal window on double click Specific Questions: What would my ViewModel class look like? Where does the code to handle the double click go? Inside the UserControl? Sorry for the long details, but I'm very new to the whole thing and I'm not educated enough to ask the right questions. I checked out the MVVM Sample from wpf.codeplex.com and something isn't quite clicking for me yet, because it seems very confusing.

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• Observer pattern and violation of Single Responsibility Principle

  - by Devil Jin

  I have an applet which repaints itself once the text has changed Design 1: //MyApplet.java public class MyApplet extends Applet implements Listener{ private DynamicText text = null; public void init(){ text = new DynamicText("Welcome"); } public void paint(Graphics g){ g.drawString(text.getText(), 50, 30); } //implement Listener update() method public void update(){ repaint(); } } //DynamicText.java public class DynamicText implements Publisher{ // implements Publisher interface methods //notify listeners whenever text changes } Isn't this a violation of Single Responsibility Principle where my Applet not only acts as Applet but also has to do Listener job. Same way DynamicText class not only generates the dynamic text but updates the registered listeners. Design 2: //MyApplet.java public class MyApplet extends Applet{ private AppletListener appLstnr = null; public void init(){ appLstnr = new AppletListener(this); // applet stuff } } // AppletListener.java public class AppletListener implements Listener{ private Applet applet = null; public AppletListener(Applet applet){ this.applet = applet; } public void update(){ this.applet.repaint(); } } // DynamicText public class DynamicText{ private TextPublisher textPblshr = null; public DynamicText(TextPublisher txtPblshr){ this.textPblshr = txtPblshr; } // call textPblshr.notifyListeners whenever text changes } public class TextPublisher implments Publisher{ // implements publisher interface methods } Q1. Is design 1 a SPR violation? Q2. Is composition a better choice here to remove SPR violation as in design 2.

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• .net design pattern question

  - by user359562

  Hi. I am trying to understand design pattern problems. I am trying to modify the code like this in winforms and trying to see if any design pattern suits my requirement. Please suggest which is the best design pattern in this scenario. This is very basic code containing 2 tab pages which might have different controls can be added dynamically and read out different files on click of particular tab. To elaborate more... I have written this code to learn and understand design pattern. This is just a scenario where user click on a particular tab which will show dynamic controls generated. public partial class Form1 : Form { public Form1() { InitializeComponent(); } private void tabControl1_SelectedIndexChanged(object sender, EventArgs e) { if (tabControl1.SelectedTab.Name.Equals("tabPage1")) { GeneratedynamicControlsForTab1(); } else if (tabControl1.SelectedTab.Name.Equals("tabPage2")) { GeneratedynamicControlsForTab2(); } } private void GeneratedynamicControlsForTab1() { Label label1 = new Label(); label1.Text = "Label1"; tabPage1.Controls.Add(label1); ReadCSVFile(); } private void GeneratedynamicControlsForTab2() { tabPage1.Controls.Clear(); Label label2 = new Label(); label2.Text = "Label2"; tabPage2.Controls.Add(label2); ReadTextFile(); } private void ReadCSVFile() { } private void ReadTextFile() { } }

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• Architecture of a single-page JavaScript web application?

  - by fig-gnuton

  How should a complex single-page JS web application be structured on the client-side? Specifically I'm curious about how to cleanly structure the application in terms of its model objects, UI components, any controllers, and objects handling server persistence. MVC seemed like a fit at first. But with UI components nested at various depths (each with their own way of acting on/reacting to model data, and each generating events which they themselves may or may not handle directly), it doesn't seem like MVC can be cleanly applied. (But please correct me if that's not the case.) -- (This question resulted in two suggestions of using ajax, which is obviously needed for anything other than the most trivial one-page app.)

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• Explain "Leader/Follower" Pattern

  - by Alex B

  I can't seem to find a good explanation of "Leader/Follower" pattern. All explanations either simply refer to it in the context of some problem, or are completely meaningless. Can anyone explain to the the mechanics of how this pattern works, and why and how it improves performance over more traditional asynchronous IO models? Examples and links to diagrams are appreciated too.

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• Dependency Injection & Singleton Design pattern

  - by SysAdmin

  How do we identify when to use dependency injection or singleton pattern. I have read in lot of websites where they say "Use Dependency injection over singleton pattern". But I am not sure if I totally agree with them. For my small or medium scale projects I definitely see the use of singleton pattern straightforward. For example Logger. I could use Logger.GetInstance().Log(...) But, instead of this, why do I need to inject every class I create, with the logger's instance?.

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• Improving MVP in Scala

  - by Alexey Romanov

  The classical strongly typed MVP pattern looks like this in Scala: trait IView { } trait Presenter[View <: IView] { // or have it as an abstract type member val view : View } case class View1(...) extends IView { ... } case object Presenter1 extends Presenter[View1] { val view = View1(...) } Now, I wonder if there is any nice way to improve on it which I am missing...

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• 'is instanceof' Interface bad design

  - by peterRit

  Say I have a class A class A { Z source; } Now, the context tells me that 'Z' can be an instance of different classes (say, B and C) which doesn't share any common class in their inheritance tree. I guess the naive approach is to make 'Z' an Interface class, and make classes B and C implement it. But something still doesn't convince me because every time an instance of class A is used, I need to know the type of 'source'. So all finishes in multiple 'ifs' making 'is instanceof' which doesn't sound quite nice. Maybe in the future some other class implements Z, and having hardcoded 'ifs' of this type definitely could break something. The escence of the problem is that I cannot resolve the issue by adding functions to Z, because the work done in each instance type of Z is different. I hope someone can give me and advice, maybe about some useful design pattern. Thanks

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• Searching for the right pattern to handle login data

  - by stevebot

  Hi all, I'm working on a controller that handles logins for a Web app. These logins will come from multiple clients but will all contain the same data. However, depending on the client, this data will be interpreted into common entities for our webapp differently. For instance, we have a user code that gets sent in, and in one case we may use the first four digits of the code, and in another case 12 digits of the code to map to a field on a User entity. Instead of handling this all in the controller and having big nasty if blocks of logic, I would like to use a pattern to handle how this information gets ingested into our application. What are your opinions?

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• DDD: Enum like entities

  - by Chris

  Hi all, I have the following DB model: **Person table** ID | Name | StateId ------------------------------ 1 Joe 1 2 Peter 1 3 John 2 **State table** ID | Desc ------------------------------ 1 Working 2 Vacation and domain model would be (simplified): public class Person { public int Id { get; } public string Name { get; set; } public State State { get; set; } } public class State { private int id; public string Name { get; set; } } The state might be used in the domain logic e.g.: if(person.State == State.Working) // some logic So from my understanding, the State acts like a value object which is used for domain logic checks. But it also needs to be present in the DB model to represent a clean ERM. So state might be extended to: public class State { private int id; public string Name { get; set; } public static State New {get {return new State([hardCodedIdHere?], [hardCodeNameHere?]);}} } But using this approach the name of the state would be hardcoded into the domain. Do you know what I mean? Is there a standard approach for such a thing? From my point of view what I am trying to do is using an object (which is persisted from the ERM design perspective) as a sort of value object within my domain. What do you think? Question update: Probably my question wasn't clear enough. What I need to know is, how I would use an entity (like the State example) that is stored in a database within my domain logic. To avoid things like: if(person.State.Id == State.Working.Id) // some logic or if(person.State.Id == WORKING_ID) // some logic

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• Design pattern to integrate Rails with a Comet server

  - by empire29

  I have a Ruby on Rails (2.3.5) application and an APE (Ajax Push Engine) server. When records are created within the Rails application, i need to push the new record out on applicable channels to the APE server. Records can be created in the rails app by the traditional path through the controller's create action, or it can be created by several event machines that are constantly monitoring various inputstream and creating records when they see data that meets a certain criteria. It seems to me that the best/right place to put the code that pushes the data out to the APE server (which in turn pushes it out to the clients) is in the Model's after_create hook (since not all record creations will flow through the controller's create action). The final caveat is I want to push a piece of formatted HTML out to the APE server (rather than a JSON representation of the data). The reason I want to do this is 1) I already have logic to produce the desired layout in existing partials 2) I don't want to create a javascript implementation of the partials (javascript that takes a JSON object and creates all the HTML around it for presentation). This would quickly become a maintenance nightmare. The problem with this is it would require "rendering" partials from within the Model (which im having trouble doing anyhow because they don't seem to have access to Helpers when they're rendered in this manner). Anyhow - Just wondering what the right way to go about organizing all of this is. Thanks

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• When NOT to use MVVM?

  - by Vitalij

  I have started using MVVM pattern recently. I have had several projects where I used it and with every new one, I start to see that it will fit great within that new project. And now I start to ask myself are there situation when it's better NOT to use MVVM. Or is it such a nice pattern which you can use anywhere? Could you please describe several scenarios where MVVM wouldn't be the best choice?

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• Is this physical collection class that contains only static methods an Anti-Pattern?

  - by Tj Kellie

  I'm trying to figure out if I should continue on with a current pattern in an application I'm working in, or refactor this into something else. I have a set of collection classes off a generic base of List. These classes have public constructors but contain only static methods that return collections. They look like this: public class UserObjCollection : BaseCollection<UserObj> { public static UserObjCollection GetAllUserObj() { UserObjCollection obj = new UserObjCollection(); obj.MapObjects(new UserObjDataService().GetAllUserObj()); return obj; } } Is this a Pattern or Anti-Pattern and what are the merits of this over a straight factory pattern?

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• How to implement Administrator rights in Java Application?

  - by Yatendra Goel

  I am developing a Data Modeling Software that is implemented in Java. This application converts the textual data (stored in a database) to graphical form so that users can interpret the data in a more efficient form. Now, this application will be accessed by 3 kinds of persons: 1. Managers (who can fill the database with data and they can also view the visual form of the data after entering the data into the database) 2. Viewers (who can only view the visual form of data that has been filled by managers) 3. Administrators (who can create and manage other administrators, managers and viewers) Now, how to implement 3 diff. views of the same application. Note: Managers, Viewers and Administrators can be located in any part of the world and should access the application through internet. One idea that came in my mind is as follows: Step1: Code all the business logic in EJBs so that it can be used in distributed environment (means which can be accessed by several users through internet) Step2: Code 3 Swing GUI Clients: One for administrators, one for managers and one for viewers. These 3 GUI clients can access business logic written in EJBs. Step3: Distribute the clients corresponding to their users. For instance, manager client to managers. =================================QUESTIONS======================================= Q1. Is the above approach is correct? Q2. This is very common functionality that various softwares have. So, Do they implement this kind of functionality through this way or any other way? Q3. If any other approach would be more better, then what is that approach?

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• Is the a pattern for iterating over lists held by a class (dynamicly typed OO languages)

  - by Roman A. Taycher

  If I have a class that holds one or several lists is it better to allow other classes to fetch those lists(with a getter) or to implement a doXList/eachXList type method for that list that take a function and call that function on each element of the list contained by that object. I wrote a program that did a ton of this and I hated passing around all these lists sometimes with method in class a calling method in class B to return lists contained in class C, B contains a C or multiple C's (note question is about dynamically typed OO languages languages like ruby or smalltalk) ex. (that came up in my program) on a Person class containing scheduling preferences and a scheduler class needing to access them.

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• Implementing the procducer-consumer pattern with .NET 4.0

  - by bitbonk

  With alle the new paralell programming features in .NET 4.0, what would be a a simple and fast way to implement the producer-consumer pattern (where at least one thread is producing/enqueuing task items and another thread executes/dequeues these tasks). Can we benfit from all these new APIs? What is your preferred implementation of this pattern?

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• Conceptually, how does replay work in a game?

  - by SnOrfus

  I was kind of curious as to how replay might be implemented in a game. Initially, I thought that there would be just a command list of every player/ai action that was taken in the game, and it then 're-plays' the game and lets the engine render as usual. However, I have looked at replays in FPS/RTS games, and upon careful inspection even things like the particles and graphical/audible glitches are consistent (and those glitches are generally *in*consistent). So How does this happen. In fixed camera angle games I though it might just write every frame of the whole scene to a stream that gets stored and then just replays the stream back, but that doesn't seem like enough for games that allow you to pause and move the camera around. You'd have to store the locations of everything in the scene at all points in time (No?). So for things like particles, that's a lot of data to push which seems like a significant draw on the game's performance whilst playing.

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