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  • Java - Is this a bad design pattern?

    - by Walter White
    Hi all, In our application, I have seen code written like this: User.java (User entity) public class User { protected String firstName; protected String lastName; ... getters/setters (regular POJO) } UserSearchCommand { protected List<User> users; protected int currentPage; protected int sortColumnIndex; protected SortOder sortOrder; // the current user we're editing, if at all protected User user; public String getFirstName() {return(user.getFirstName());} public String getLastName() {return(user.getLastName());} } Now, from my experience, this pattern or anti-pattern looks bad to me. For one, we're mixing several concerns together. While they're all user-related, it deviates from typical POJO design. If we're going to go this route, then shouldn't we do this instead? UserSearchCommand { protected List<User> users; protected int currentPage; protected int sortColumnIndex; protected SortOder sortOrder; // the current user we're editing, if at all protected User user; public User getUser() {return(user);} } Simply return the user object, and then we can call whatever methods on it as we wish? Since this is quite different from typical bean development, JSR 303, bean validation doesn't work for this model and we have to write validators for every bean. Does anyone else see anything wrong with this design pattern or am I just being picky as a developer? Walter

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  • What makes MVVM uniquely suited to WPF?

    - by Reed Copsey
    The Model-View-ViewModel is very popular with WPF and Silverlight. I've been using this for my most recent projects, and am a very large fan. I understand that it's a refinement of MVP. However, I am wondering exactly what unique characteristics of WPF (and Silverlight) allow MVVM to work, and prevent (or at least make difficult) this pattern from working using other frameworks or technologies. I know MVVM has a strong dependency on the powerful data binding technology within WPF. This is the one feature which many articles and blogs seem to mention as being the key to WPF providing the means of the strong separation of View from ViewModel. However, data binding exists in many forms in other UI frameworks. There are even projects like Truss that provide WPF-style databinding to POCO in .NET. What features, other than data binding, make WPF and Silverlight uniquely suited to Model-View-ViewModel?

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  • How would you organize a large complex web application (see basic example)?

    - by Anurag
    How do you usually organize complex web applications that are extremely rich on the client side. I have created a contrived example to indicate the kind of mess it's easy to get into if things are not managed well for big apps. Feel free to modify/extend this example as you wish - http://jsfiddle.net/NHyLC/1/ The example basically mirrors part of the comment posting on SO, and follows the following rules: Must have 15 characters minimum, after multiple spaces are trimmed out to one. If Add Comment is clicked, but the size is less than 15 after removing multiple spaces, then show a popup with the error. Indicate amount of characters remaining and summarize with color coding. Gray indicates a small comment, brown indicates a medium comment, orange a large comment, and red a comment overflow. One comment can only be submitted every 15 seconds. If comment is submitted too soon, show a popup with appropriate error message. A couple of issues I noticed with this example. This should ideally be a widget or some sort of packaged functionality. Things like a comment per 15 seconds, and minimum 15 character comment belong to some application wide policies rather than being embedded inside each widget. Too many hard-coded values. No code organization. Model, Views, Controllers are all bundled together. Not that MVC is the only approach for organizing rich client side web applications, but there is none in this example. How would you go about cleaning this up? Applying a little MVC/MVP along the way? Here's some of the relevant functions, but it will make more sense if you saw the entire code on jsfiddle: /** * Handle comment change. * Update character count. * Indicate progress */ function handleCommentUpdate(comment) { var status = $('.comment-status'); status.text(getStatusText(comment)); status.removeClass('mild spicy hot sizzling'); status.addClass(getStatusClass(comment)); } /** * Is the comment valid for submission */ function commentSubmittable(comment) { var notTooSoon = !isTooSoon(); var notEmpty = !isEmpty(comment); var hasEnoughCharacters = !isTooShort(comment); return notTooSoon && notEmpty && hasEnoughCharacters; } // submit comment $('.add-comment').click(function() { var comment = $('.comment-box').val(); // submit comment, fake ajax call if(commentSubmittable(comment)) { .. } // show a popup if comment is mostly spaces if(isTooShort(comment)) { if(comment.length < 15) { // blink status message } else { popup("Comment must be at least 15 characters in length."); } } // show a popup is comment submitted too soon else if(isTooSoon()) { popup("Only 1 comment allowed per 15 seconds."); } });

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  • MVC: Model View Controller -- does the View call the Model?

    - by Gary Green
    I've been reading about MVC design for a while now and it seems officially the View calls objects and methods in the Model, builds and outputs a view. I think this is mainly wrong. The Controller should act and retrieve/update objects inside the Model, select an appropriate View and pass the information to it so it may display. Only crude and rudiementary PHP variables/simple if statements should appear inside the View. If the View gets the information it needs to display from the Model, surely there will be a lot of PHP inside the View -- completely violating the point of seperating presentation logic.

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  • MVC - Calling Controller Methods

    - by JT703
    Hello, My application is following the MVC design pattern. The problem I keep running into is needing to call methods inside a Controller class from outside that Controller class (ex. A View class wants to call a Controller method, or a Manager class wants to call a Controller method). Is calling Controller methods in this way allowed in MVC? If it's allowed, what's the proper way to do it? According to the version of MVC that I am following (there seems to be so many different versions out there), the View knows of the Model, and the Controller knows of the View. Doing it this way, I can't access the controller. Here's the best site I've found and the one describing the version of MVC I'm following: http://leepoint.net/notes-java/GUI/structure/40mvc.html. The Main Program code block really shows how this works. Thanks for any answers.

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  • ASIHTTPRequest code design

    - by nico
    I'm using ASIHTTPRequest to communicate with the server asynchronously. It works great, but I'm doing requests in different controllers and now duplicated methods are in all those controllers. What is the best way to abstract that code (requests) in a single class, so I can easily re-use the code, so I can keep the controllers more simple. I can put it in a singleton (or in the app delegate), but I don't think that's a good approach. Or maybe make my own protocol for it with delegate callback. Any advice on a good design approach would be helpful. Thanks.

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  • Advantages of Thread pooling in embedded systems

    - by Microkernel
    I am looking at the advantages of threadpooling design pattern in Embedded systems. I have listed few advantages, please go through them, comment and please suggest any other possible advantages that I am missing. Scalability in systems like ucos-2 where there is limit on number of threads. Increasing capability of any task when necessary like Garbage collection (say in normal systems if garbage collection is running under one task, its not possible to speed it up, but in threadpooling we can easily speed it up). Can set limit on the max system load. Please suggest if I am missing anything.

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  • Advice on displaying and allowing editing of data using ASP.NET MVC?

    - by Remnant
    I am embarking upon my first ASP.NET MVC project and I would like to get some input on possible ways to display database data and general best practice. In short, the body of my webpage will show data from my database in a table like format, with each table row showing similar data. For example: Name Age Position Date Joined Jon Smith 23 Striker 18th Mar 2005 John Doe 38 Defender 3rd Jan 1988 In terms of functionality, primarily I’d like to give the user the ability to edit the data and, after the edit, commit the edit to the database and refresh the view.The reason I want to refresh the view is because the data is date ordered and I will need to re-sort if the user edits a date field. My main question is what architecture / tools would be best suited to this fulfil my requirements at a high level? From the research I have done so far my initial conclusions were: ADO.NET for data retrieval. This is something I have used before and feel comfortable with. I like the look of LINQ to SQL but don’t want to make the learning curve any steeper for my first outing into MVC land just yet. Partial Views to create a template and then iterate through a datatable that I have pulled back from my database model. jQuery to allow the user to edit data in the table, error check edited data entries etc. Also, my intial view was that caching the data would not be a key requirement here. The only field a user will be able to update is the field and, if they do, I will need to commit that data to the database immediately and then refresh the view (as the data is date sorted). Any thoughts on this? Alternatively, I have seen some jQuery plug-ins that emulate a datagrid and provide associated functionality. My first thoughts are that I do not need all the functionality that comes with these plug-ins (e.g. zebra striping, ability to sort by column using sort glyph in column headers etc .) and I don’t really see any benefit to this over and above the solution I have outlined above. Again, is there reason to reconsider this view? Finally, when a user edits a date , I will need to refresh the view. In order to do this I had been reading about Html.RenderAction and this seemed like it may be a better option than using Partial Views as I can incorporate application logic into the action method. Am I right to consider Html.RenderAction or have I misunderstood its usage? Hope this post is clear and not too long. I did consider separate posts for each topic (e.g. Partial View vs. Html.RenderAction, when to use jQury datagrid plug-in) but it feels like these issues are so intertwined that they need to be dealt with in contect of each other. Thanks

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  • Are SOLID principles really solid?

    - by Arseny
    The first pattern stands for this acronym is SRP. Here is a quote. the single responsibility principle states that every object should have a single responsibility, and that responsibility should be entirely encapsulated by the class. That's is simple and clear till we start to code ) Suppose we have a class with well defined SRP. To serialize this class instances we need to add special atrributes to that class. So now the class have other responsibility. Dosen't it violate SRP? Let's see other story. Interface implementation. Then we implement an interface we simply add other responsibility say dispose its resorces or compare its instances or whatever. So my question. Is it possible to keep SRP complete? How can we do it?

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  • Create inherited class from base class

    - by Raj
    public class Car { private string make; private string model; public Car(string make, string model) { this.make = make; this.model = model; } public virtual void Display() { Console.WriteLine("Make: {0}", make); Console.WriteLine("Model: {0}", model); } public string Make { get{return make;} set{make = value;} } public string Model { get{return model;} set{model = value;} } } public class SuperCar:Car { private Car car; private int horsePower; public SuperCar(Car car) { this.car = car; } public int HorsePower { get{return horsePower;} set{horsepower = value;} } public override void Display() { base.Display(); Console.WriteLine("I am a super car"); } When I do something like Car myCar = new Car("Porsche", "911"); SuperCar mySupcar = new SuperCar(myCar); mySupcar.Display(); I only get "I am a supercar" but not the properties of my base class. Should I explicitly assign the properties of my base class in the SuperCar constructor? In fact I'm trying Decorator pattern where I want a class to add behaviour to a base class.

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  • Validation without ServiceLocator

    - by Dmitriy Nagirnyak
    Hi, I am getting back again and again to it thinking about the best way to perform validation on POCO objects that need access to some context (ISession in NH, IRepository for example). The only option I still can see is to use S*ervice Locator*, so my validation would look like: public User : ICanValidate { public User() {} // We need this constructor (so no context known) public virtual string Username { get; set; } public IEnumerable<ValidationError> Validate() { if (ServiceLocator.GetService<IUserRepository>().FindUserByUsername(Username) != null) yield return new ValidationError("Username", "User already exists.") } } I already use Inversion Of control and Dependency Injection and really don't like the ServiceLocator due to number of facts: Harder to maintain implicit dependencies. Harder to test the code. Potential threading issues. Explicit dependency only on the ServiceLocator. The code becomes harder to understand. Need to register the ServiceLocator interfaces during the testing. But on the other side, with plain POCO objects, I do not see any other way of performing the validation like above without ServiceLocator and only using IoC/DI. So the question would be: is there any way to use DI/IoC for the situation described above? Thanks, Dmitriy.

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  • How to avoid using this in a contructor

    - by Paralife
    I have this situation: interface MessageListener { void onMessageReceipt(Message message); } class MessageReceiver { MessageListener listener; public MessageReceiver(MessageListener listener, other arguments...) { this.listener = listener; } loop() { Message message = nextMessage(); listener.onMessageReceipt(message); } } and I want to avoid the following pattern: (Using the this in the Client constructor) class Client implements MessageListener { MessageReceiver receiver; MessageSender sender; public Client(...) { receiver = new MessageReceiver(this, other arguments...); sender = new Sender(...); } . . . @Override public void onMessageReceipt(Message message) { if(Message.isGood()) sender.send("Congrtulations"); else sender.send("Boooooooo"); } } The reason why i need the above functionality is because i want to call the sender inside the onMessageReceipt() function, for example to send a reply. But I dont want to pass the sender into a listener, so the only way I can think of is containing the sender in a class that implements the listener, hence the above resulting Client implementation. Is there a way to achive this without the use of 'this' in the constructor? It feels bizare and i dont like it, since i am passing myself to an object(MessageReceiver) before I am fully constructed. On the other hand, the MessageReceiver is not passed from outside, it is constructed inside, but does this 'purifies' the bizarre pattern? I am seeking for an alternative or an assurance of some kind that this is safe, or situations on which it might backfire on me.

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  • Confused about this factory, as it doesn't look like an Abstract Factory nor Factory Method

    - by Pin
    I'm looking into Guice and I've been reading its documentation recently. Reading the motivation section I don't understand the factories part, why they name it that way. To me that factory is just a wrapper for the implementing class they want it to return after calling getInstance(). public class CreditCardProcessorFactory { private static CreditCardProcessor instance; public static void setInstance(CreditCardProcessor creditCardProcessor) { instance = creditCardProcessor; } public static CreditCardProcessor getInstance() { if (instance == null) { throw new IllegalStateException("CreditCardProcessorFactory not initialized. " + "Did you forget to call CreditCardProcessor.setInstance() ?"); } return instance; } } Why do they call it factory as well if it is neither an abstract factory nor a factory method? Or am I missing something? Thanks.

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  • DRY programming dilemma

    - by fayer
    the situation is like this: im creating a Logger class that can write to a file but the write_to_file() function is in a helper class as a static function. i could call that function but then the Log class would be dependent to the helper class. isn't dependency bad? but if i can let it use a helper function then what is the point of having helper functions? what should one prioritize here: using helper functions and have to include this helper class everywhere (but the other 99 methods wont be useful) or just copy and paste into the Log class (but then if i have done this 100 times and then make a change i have to change in 100 places). share your thoughts and experience!

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  • good way to implement NotSpecification: isSpecialCaseOf?

    - by koen
    I'm implementing the specification pattern. The NotSpecification seems simple at first: NotSpecification.IsSpecialCaseOf(otherSpecification) return !this.specification.isSpecialCaseOf(otherSpecification) But it doesn't work for all Specifications: Not(LesserThan(5)).IsSpecialCaseOf(GreaterThan(4)) This should be true. So far I think that the only way to accomplish the isSpecialCaseOf the NotSpecification is to implement the remainderUnsatisfiedBy (partial subsumption in the paper on the specification pattern). But maybe I am missing something more simple or a logical insight that makes this unnecessary. Question: Is there another way of implementing this by not using remainderUnsatisfiedBy?

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  • Business Layer Pattern on Rails? MVCL

    - by Fabiano PS
    That is a broad question, and I appreciate no short/dumb asnwers like: "Oh that is the model job, this quest is retarded (period)" PROBLEM Where I work at people created a system over 2 years for managing the manufacture process over demand in the most simplified still broad as possible, involving selling, buying, assemble, The system is coded over Ruby On Rails. The result has been changed lots of times and the result is a mess on callbacks (some are called several times), 200+ models, and fat controllers: Total bad. The QUESTION is, if there is a gem, or pattern designed to handle Rails large app logic? The logic whould be able to fully talk to models (whose only concern would be data format handling and validation) What I EXPECT is to reduce complexity from various controllers, and hard to track callbacks into files with the responsibility to handle a business operation logic. In some cases there is the need to wait for a response, in others, only validation of the input is enough and a bg process would take place. ie: -- Sell some products (need to wait the operation to finish) 1. Set a View able to get the products input 2. Controller gets the product list inputed by employee and call the logic Logic::ExecuteWithResponse('sell', 'products', :prods => @product_list_with_qtt, :when => @date, :employee => current_user() ) This Logic would handle buying order, assemble order, machine schedule, warehouse reservation, and others

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  • Sub-Schemas in SQL Server 2005/2008

    - by Maushu
    This is a simple question yet I was unable to find any information at all about this. Is it possible to have sub-schemas in SQL Server 2005/2008? Example: Having a HR (Human Resources) schema with a sub-schema called Training (with tables related to this). It would end up like HR.Training.* where * would be the tables.

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  • Which is the most memory leak safe approach.

    - by MattC
    I have a table of frequently updated information. This is presented using a container div with a div for each row, each row containing 10 divs. I am using setInterval to call a an asmx webservice that returns some json formatted information. On the success callback I call $("#myContainer").empty(); on the container div and recreate the rows and 10 nested divs for each row's columns. This page may be left to run for a whole day, so I am wary of updating the DOM like this as I have noticed that memory does rise for the browser over time (IE8). The other approach I am considering is to add an idea to the row div. When new results process each item of data, look for the corresponding row, if it exists overwrite the data in each div. If it doesn't exist (new data for example), append the row. What approaches have others used for this sort of long lived pseudo realtime information display. TIA

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  • Taking the data mapper approach in Zend Framework

    - by Seeker
    Let's assume the following tables setup for a Zend Framework app. user (id) groups (id) groups_users (id, user_id, group_id, join_date) I took the Data Mapper approach to models which basically gives me: Model_User, Model_UsersMapper, Model_DbTable_Users Model_Group, Model_GroupsMapper, Model_DbTable_Groups Model_GroupUser, Model_GroupsUsersMapper, Model_DbTable_GroupsUsers (for holding the relationships which can be seen as aentities; notice the "join_date" property) I'm defining the _referenceMap in Model_DbTable_GroupsUsers: protected $_referenceMap = array ( 'User' => array ( 'columns' => array('user_id'), 'refTableClass' => 'Model_DbTable_Users', 'refColumns' => array('id') ), 'App' => array ( 'columns' => array('group_id'), 'refTableClass' => 'Model_DbTable_Groups', 'refColumns' => array('id') ) ); I'm having these design problems in mind: 1) The Model_Group only mirrors the fields in the groups table. How can I return a collection of groups a user is a member of and also the date the user joined that group for every group? If I just added the property to the domain object, then I'd have to let the group mapper know about it, wouldn't I? 2) Let's say I need to fetch the groups a user belongs to. Where should I put this logic? Model_UsersMapper or Model_GroupsUsersMapper? I also want to make use of the referencing map (dependent tables) mechanism and probably use findManyToManyRowset or findDependentRowset, something like: $result = $this->getDbTable()->find($userId); $row = $result->current(); $groups = $row->findManyToManyRowset( 'Model_DbTable_Groups', 'Model_DbTable_GroupsUsers' ); This would produce two queries when I could have just written it in a single query. I will place this in the Model_GroupsUsersMapper class. An enhancement would be to add a getGroups method to the Model_User domain object which lazily loads the groups when needed by calling the appropriate method in the data mapper, which begs for the second question. Should I allow the domain object know about the data mapper?

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  • Examples of IOC/DI over Singleton

    - by Amitd
    Hi, Just started learning/reading about DI and IOC frameworks. Also I read many articles on SO and internet that say that one should prefer DI/IOC over singleton. Can anyone give/link examples of exactly how DI/IOC eliminates/solves the various issues regarding the Singleton pattern? (hopefully code and explanation for better understanding) Also given a system has already implemented Singleton pattern, how to refactor/implement DI/IOC for the same? (any examples for the same?) (Language/Framework no bars..C# would be helpful) Thanks

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  • Example with Visitor Pattern

    - by devoured elysium
    public class Song { public string Genre { get; protected set; } public string Name { get; protected set; } public string Band { get; protected set; } public Song(string name, string band, string genre) { Name = name; Genre = genre; Band = band; } } public interface IMusicVisistor { void Visit(List<Song> items); } public class MusicLibrary { List<Song> _songs = new List<Song> { ...songs ... }; public void Accept(IMusicVisitor visitor) { visitor.Visit(_songs); } } and now here's one Visitor I made: public class RockMusicVisitor : IMusicVisitor { public List<Song> Songs { get; protected set; } public void Visit(List<Song> items) { Songs = items.Where(x => x.Genre == "Rock").ToList(); } } Why is this any better than just putting a public property Songs and then letting any kind of class do with it anything that it wants to? This example comes from this post.

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  • CQRS - The query side

    - by mattcodes
    A lot of the blogsphere articles related to CQRS (command query repsonsibility) seperation seem to imply that all screens/viewmodels are flat. e.g. Name, Age, Location Of Birth etc.. and thus the suggestion that implementation wise we stick them into fast read source etc.. single table per view mySQL etc.. and pull them out with something like primitive SqlDataReader, kick that nasty nhibernate ORM etc.. However, whilst I agree that domain models dont mapped well to most screens, many of the screens that I work with are more dimensional, and Im sure this is pretty common in LOB apps. So my question is how are people handling screen where by for example it displays a summary of customer details and then a list of their orders with a [more detail] link etc.... I thought about keeping with the straight forward SQL query to the Query Database breaking off the outer join so can build a suitable ViewModel to View but it seems like overkill? Alternatively (this is starting to feel yuck) in CustomerSummaryView table have a text/big (whatever the type is in your DB) column called Orders, and the columns for the Order summary screen grid are seperated by , and rows by |. Even with XML datatype it still feeel dirty. Any thoughts on an optimal practice?

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