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• Immutability of big objects

  - by Malax

  Hi StackOverflow! I have some big (more than 3 fields) Objects which can and should be immutable. Every time I run into that case i tend to create constructor abominations with long parameter lists. It doesn't feel right, is hard to use and readability suffers. It is even worse if the fields are some sort of collection type like lists. A simple addSibling(S s) would ease the object creation so much but renders the object mutable. What do you guys use in such cases? I'm on Scala and Java, but i think the problem is language agnostic as long as the language is object oriented. Solutions I can think of: "Constructor abominations with long parameter lists" The Builder Pattern Thanks for your input!

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• How to keep historic details of modification in a database (Audit trail)?

  - by mada

  I'm a J2EE developer & we are using hibernate mapping with a PostgreSQL database. We have to keep track of any changes occurs in the database, in others words all previous & current values of any field should be saved. Each field can be any type (bytea, int, char...) With a simple table it is easy but we a graph of objects things are more difficult. So we have, speaking in a UML point of view, a graph of objects to store in the database with every changes & the user. Any idea or pattern how to do that?

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• what happens to running/blocked runnables when executorservice is shutdown()

  - by prmatta

  I posted a question about a thread pattern today, and almost everyone suggested that I look into the ExecutorService. While I was looking into the ExecutorService, I think I am missing something. What happens if the service has a running or blocked threads, and someone calls ExecutorService.shutdown(). What happens to threads that are running or blocked? Does the ExecutorService wait for those threads to complete before it terminates? The reason I ask this is because a long time ago when I used to dabble in Java, they deprecated Thread.stop(), and I remember the right way of stopping a thread was to use sempahores and extend Thread when necessary: public void run () { while (!this.exit) { try { block(); //do something } catch (InterruptedException ie) { } } } public void stop () { this.exit = true; if (this.thread != null) { this.thread.interrupt(); this.thread = null; } } How does ExecutorService handle running threads?

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• Why state cannot be part of Presenter in MVP?

  - by rFactor

  I read http://www.codeproject.com/KB/architecture/MVC_MVP_MVVM_design.aspx and it said: As powerful as they are, both MVC and MVP have their problems. One of them is persistence of the View’s state. For instance, if the Model, being a domain object, does not know anything about the UI, and the View does not implement any business logic, then where would we store the state of the View’s elements such as selected items? Fowler comes up with a solution in the form of a Presentation Model pattern. I wonder why Presenter can't hold View state? It already holds all View logic. As far as I understand, in MVC and MVP the state is kept in View. In PM and MVVM the state is kept in the Presentation Model. Why can't Presenter follow PM in this particular case and contain the state of the view? Here is another article which says Presenter does not hold View state, instead the view does: http://www.codeproject.com/KB/aspnet/ArchitectureComparison.aspx

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• How to disable UI control based on domain object's state?

  - by Subb

  Here's my problem. I have a somewhat complex domain object, which, depending on its state, responds to certain actions. I think the state pattern is pretty much the solution for that. However, I need to display which actions are possible at any moment in the UI. Ex: The domain object is an audio player. Some songs can't be skipped (like ads), so I need to disable the "next" and "previous" buttons in the GUI so the user have some kind of feedback of which action he can execute. I've looked at Swing's Action class (note: this is not a Java project), but I think I would need to keep every Actions in my domain object class (audio player), so it can enable or disable them depending on its own state (thus, affecting the UI). Is it the way to do it?

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• OOP App Architecture: Which layer does a lazy loader sit in?

  - by JW

  I am planning the implemention an Inheritance Mapper pattern for an application component http://martinfowler.com/eaaCatalog/inheritanceMappers.html One feature it needs to have is for a domain object to reference a large list of aggreageted items (10,000 other domain objects) So I need some kind of lazy loading collection to be passed out of the aggregate root domain object to other domain objects. To keep my (php) model scripts organised i am storing them in two folders: MyComponent\ controllers\ models\ domain\ <- domain objects, DDD repository, DDD factory daccess\ <- PoEAA data mappers, SQL queries etc views\ But now I am racking my brains wondering where my lazy loading collection sits. Any suggestions / justifications for putting it in one place over another another? DDD = Domain Driven Design Patterns, Eric Evans - book PoEAA = Patterns of Application Architecture Patterns, Martin Fowler - book

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• How to use a 3rd party control inside the viewmodel?

  - by Sander

  I have a 3rd party control which among other things performs loading of some data. I want my viewmodel to keep track of this load operation and adjust its own state accordingly. If it were up to me, I'd do the data loading far away from the view, but it is not. So, I seem to be in the situation where my viewmodel depends on my view. How do I best handle this? I feel rather dirty making the view publish events to the viewmodel but I don't see any other reasonable way to get this info into the viewmodel. A similar situation might crop up with standard controls, too - imagine if your viewmodel depends on the events coming from a MediaElement - how do you properly model this? Do you put the MediaElement into the viewmodel? That doesn't sound right. If publishing the events to the viewmodel is indeed the most reasonable way, is there some common pattern used for this? How do you do it?

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• Configuration and Model-View

  - by HH

  I am using the Model-View pattern on a small application I'm writing. Here's the scenario: The model maintains a list of directories from where it can extract the data that it needs. The View has a Configuration or a Setting dialog where the user can modify this list of directories (the dialog has a JList displaying the list in addition to add and remove buttons). I need some advice from the community: The View needs to communicate these changes to the model. I thought first of adding to the model these methods: addDirectory() and removeDirectory(). But I am trying to limit the number of methods (or channels) that the View can use to communicate with and manipulate the model. Is there any good practice for this? Thank you.

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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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• Are today's young programmers getting wrapped around the axle with patterns and practices?

  - by Robert Harvey

  Recently I have noticed a number of questions on SO that look something like this: I am writing a small program to keep a list of the songs that I keep on my ipod. I'm thinking about writing it as a 3-tier MVC Ruby on Rails web application with TDD, DDD and IOC, using a factory pattern to create the classes and a singleton to store my application settings. Do you think I'm taking the right approach? Do you think that we're handing novice programmers a very sharp knife and telling them, "Don't cut yourself with this"? NOTE: Despite the humorous tone, this is a serious (and programming-related) question.

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• Unit Testing User Interface. What is an effective way ?

  - by pierocampanelli

  I have an accounting & payroll client/server application where there are several input form with complex data validation rules. I am finding an effective way to perform unit testing of user interface. For complex validation rules I mean: "Disable button X if I Insert a value in textfield Y" "Enable a combobox if I insert a value in a textfield" ...... ...... Most promising pattern i have found is suggested by M. Fowler (http://martinfowler.com/eaaDev/ModelViewPresenter.html). Have you any experience about Unit Testing of User Interface? As technology stack I am using: .NET 3.5 & Windows Forms Widget Library.

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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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• How big teams work with database

  - by Michael Riva

  Lets say I have a team, 20 developers. And we are making a project on .net. In team every one can easy create their tables according to their modules working on it. And we think to use an ORM, can you tell me how can and which ORM tools for good to working with team. Is there any proven way? I m asking becouse I never work with a team, so I dont know the best practices. So you guys what kind of pattern you use?. I realy wonder. The team members can write their unit tests and supply necessary design patterns. What kind of approach I need to create to manage team? What kind of ORM tools that we have to use?

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• How to solve the "Growing If Statement" problem?

  - by Achilles

  I've been doing some reading about design patterns and wanted some perspective. Consider the following: Dim objGruntWorker as IGruntWorker if SomeCriteria then objGruntWorker = new GoFor() else if SomeOtherCriteria then objGruntWorker = new Newb() else if SomeCriteriaAndTheKitchenSink then objGruntWorker = new CubeRat() end if objGruntWorker.GetBreakfast() system.threading.thread.sleep(GetMilliSecondsFromHours(4)) objGruntWorker.GetLunch() The above code grows each time a new Criteria arises. I've seen code like this all over the place and in ignorance wrote some of it myself. How should this be solved? Does this kind of anti-pattern have a more "formal" name? Thanks for your help!

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• Reusability, testability, code complexity reduction and showing-off-ability programming importance

  - by Andrew Florko

  There are lots of programming and architecture patterns. Patterns allow to make code cleaner, reusable, more testable & at last (but not at least) to feel the follower a real cool developer. How do you rank these considerations for you? What does affect you most when you decide to apply pattern? I wonder how many times code reusability (especially for MVP, MVC patterns) was important? For example DAL library often shared between projects (it's reusable) but how often controllers/views (abstracted via interfaces) are reused?

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• Using Remote Web Server to Initialize iPhone App

  - by Chris_K

  My iPhone app relies on a vendor's XML feed to provide data. But that feed is not locked down. The vendor could change the format of the XML at any time, although so far they've promised not to. Since I might want to tell my app to use a different URL for its data source, I'd like to set up a single "Command Central" Web page, on my own server, to direct the app to the correct data source. In other words, each time my app starts, in the background and unseen by the user, it would visit "http://www.myserver.com/iphoneapp_data_sources.xml" to retrieve the URL for retrieving data from my vendor. That way, if my vendor suddenly changes the exact URL or the XML feed that the app needs, I can update that Web page and ensure that all installations of the app are using the correct XML feed. Does anyone have any advice or examples showing this kind of approach? It seems as if this must be a common problem, but so far I haven't found a well-established design pattern that fits it.

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• ASP.NET MVC Filters: How to set Viewdata for Dropdown based on action paramter

  - by CRice

  Hi, Im loading an entity 'Member' from its id in route data. [ListItemsForMembershipType(true)] public ActionResult Edit(Member someMember) {...} The attribute on the action loads the membership type list items for a dropdown box and sticks it in viewdata. This is fine for add forms, and search forms (it gets all active items) but I need the attribute to execute BASED ON THE VALUE someMember.MembershipTypeId, because its current value must always be present when loading the item (i.e. all active items, plus the one from the loaded record). So the question is, what is the standard pattern for this? How can my attribute accept the value or should I be loading the viewdata for the drop down in a controller supertype or during model binding or something else? It is in an attribute now because the code to set the viewdata would otherwise be duplicated in each usage in each action.

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• What are the common patterns in web programming?

  - by lankerisms

  I have been trying to write my first big web app (more than one cgi file) and as I kept moving forward with the rough prototype, paralelly trying to predict more tasks, this is the todo that got accumulated (In no particular order). * Validations and input sanitizations * Object versioning (to avoid edit conflicts. I dont want hard locks) * Exception handling * memcache * xss and injection protections * javascript * html * ACLs * phonetics in search, match and find duplicates (for form validation) * Ajaxify!!! (I have snipped off the project specific items.) I know that each todo will be quite tied up to its project and technologies used. What I am wondering though, is if there is a pattern in your todo items as well as the sequence in which you experienced guys have come across them.

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• Stuck with the math in a Flash project, would parsing engine help?

  - by VideoDnd

  I've been stuck with the math in a Flash project? It's a loose design pattern my director formulated. My goal is to keep the project object oriented, and get 'non Flash obstacles' off my plate. Do you recommend using parsing engines for processing math? XML values going to AS3, updating a changing acceleration formula. I don't hate math, but it just doesn't seem OOP or good project planning to have the math stuck in Flash. Your comments are welcome.

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• Buffering db inserts in multithreaded program

  - by Winter

  I have a system which breaks a large taks into small tasks using about 30 threads as a time. As each individual thread finishes it persists its calculated results to the database. What I want to achieve is to have each thread pass its results to a new persisance class that will perform a type of double buffering and data persistance while running in its own thread. For example, after 100 threads have moved their data to the buffer the persistance class then the persistance class swaps the buffers and persists all 100 entries to the database. This would allow utilization of prepared statements and thus cut way down on the I/O between the program and the database. Is there a pattern or good example of this type of multithreading double buffering?

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• Should I dive into ASP.NET MVC or start with ASP.NET Webforms?

  - by Sahat

  I plan to pick up Silverlight in the future. Possibility of going into Microsoft WPF. Currently learning Objective-C 2.0 w/ Cocoa. I already know Pros and Cons of ASP.NET MVC vs ASP.NET Webforms. What I want to know is what would be more "efficient" for me to learn given the circumstances above? By efficient I mean learning one design pattern once and then re-using it. Objective-C I believe uses MVC approach? What about Silverlight? WPF? So what do you think? Also as a side question is it true that ASP.NET Webforms is often used by freelancers/small companies and ASP.NET MVC in large enterprises?

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• What is a good architecture for a Lift-JPA application?

  - by egervari

  I was wondering what is the best practice for a JPA model in Lift? I noticed that in the jpa demo application, there is just a Model object that is like a super object that does everything. I don't think this can be the most scalable approach, no? Is it is wise to still do the DAO pattern in Lift? For example, there's some code that looks a tad bloated and could be simplified across all model objects: Model.remove(Model.getReference(classOf[Author], someId)) Could be: AuthorDao.remove(someId) I'd appreciate any tips for setting up something that will work with the way Lift wants to work and is also easy to organize and maintain. Preferably from someone who has actually used JPA on a medium to large Lift site rather than just postulating what Spring does (we know how to do that) ;) The first phase of development will be around 30-40 tables, and will eventually get to over 100... we need a scalable, neat approach.

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• ASP.NET MVC Filters: How to set Viewdata for Dropdown based on action parameter

  - by CRice

  Hi, Im loading an entity 'Member' from its id in route data. [ListItemsForMembershipType(true)] public ActionResult Edit(Member someMember) {...} The attribute on the action loads the membership type list items for a dropdown box and sticks it in viewdata. This is fine for add forms, and search forms (it gets all active items) but I need the attribute to execute BASED ON THE VALUE someMember.MembershipTypeId, because its current value must always be present when loading the item (i.e. all active items, plus the one from the loaded record). So the question is, what is the standard pattern for this? How can my attribute accept the value or should I be loading the viewdata for the drop down in a controller supertype or during model binding or something else? It is in an attribute now because the code to set the viewdata would otherwise be duplicated in each usage in each action.

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• Using Remote Web Page to Initialize iPhone App

  - by Chris_K

  My iPhone app relies on a vendor's XML feed to provide data. But that feed is not locked down. The vendor could change the format of the XML at any time, although so far they've promised not to. Since I might want to tell my app to use a different URL for its data source, I'd like to set up a single "Command Central" Web page, on my own server, to direct the app to the correct data source. In other words, each time my app starts, in the background and unseen by the user, it would visit "http://www.myserver.com/iphoneapp_data_sources.xml" to retrieve the URL for retrieving data from my vendor. That way, if my vendor suddenly changes the exact URL or the XML feed that the app needs, I can update that Web page and ensure that all installations of the app are using the correct XML feed. Does anyone have any advice or examples showing this kind of approach? It seems as if this must be a common problem, but so far I haven't found a well-established design pattern that fits it.

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• Javascript object encapsulation that tracks changes

  - by Raynos

  Is it possible to create an object container where changes can be tracked Said object is a complex nested object of data. (compliant with JSON). The wrapper allows you to get the object, and save changes, without specifically stating what the changes are Does there exist a design pattern for this kind of encapsulation Deep cloning is not an option since I'm trying to write a wrapper like this to avoid doing just that. The solution of serialization should only be considered if there are no other solutions. An example of use would be var foo = state.get(); // change state state.update(); // or state.save(); client.tell(state.recentChange()); A jsfiddle snippet might help : http://jsfiddle.net/Raynos/kzKEp/ It seems like implementing an internal hash to keep track of changes is the best option. [Edit] To clarify this is actaully done on node.js on the server. The only thing that changes is that the solution can be specific to the V8 implementation.

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