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• Producer/consumer in Grails?

  - by Mulone

  Hi all, I'm trying to implement a Consumer/Producer app in Grails, after several unsuccessful attempts at implementing concurrent threads. Basically I want to store all the events coming from a clients (through separate AJAX calls) in a single queue and then process such a queue in a linear way as soon as new events are added. This looks like a Producer/Consumer problem: http://en.wikipedia.org/wiki/Producer-consumer_problem How can I implement this in Grails (maybe with a timer or even better by generating an event 'process queue')? Basically I'd like to a have a singleton service waiting for new events in the queue and processing them linearly (even if the queue is loaded by several concurrent processes). Any hints? Cheers!

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• Unit of Work Pattern in .Net

  - by Jazza

  Does anyone have any concrete examples of a simple Unit of Work pattern in C# or Visual Basic that would handle the following scenario? I'm writing a WinForms application in which a customer can have multiple addresses associated with it. The user can add, edit and delete addresses belonging to the customer before the customer is saved back to the database. Therefore, at the time of saving, all the original addresses need to be deleted from the database and the new addresses added in a single transaction.

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• Multi-tenant Access Control: Repository or Service layer?

  - by FreshCode

  In a multi-tenant ASP.NET MVC application based on Rob Conery's MVC Storefront, should I be filtering the tenant's data in the repository or the service layer? 1. Filter tenant's data in the repository: public interface IJobRepository { IQueryable<Job> GetJobs(short tenantId); } 2. Let the service filter the repository data by tenant: public interface IJobService { IList<Job> GetJobs(short tenantId); } My gut-feeling says to do it in the service layer (option 2), but it could be argued that each tenant should in essence have their own "virtual repository," (option 1) where this responsibility lies with the repository. Which is the most elegant approach: option 1, option 2 or is there a better way? Update: I tried the proposed idea of filtering at the repository, but the problem is that my application provides the tenant context (via sub-domain) and only interacts with the service layer. Passing the context all the way to the repository layer is a mission. So instead I have opted to filter my data at the service layer. I feel that the repository should represent all data physically available in the repository with appropriate filters for retrieving tenant-specific data, to be used by the service layer. Final Update: I ended up abandoning this approach due to the unnecessary complexities. See my answer below.

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• How to avoid game rendering component circular references?

  - by CodexArcanum

  I'm working on a simple game design, and I wanted to break up my game objects into more reusable components. But I'm getting stuck on how exactly to implement the design I have in mind. Here's an example: I have a Logger object, whose job is simply to store a list of messages and render them to screen. You know, logging. Originally the Logger just held the list, and the game loop rendered it's contents. Then I moved the rendering logic into the Logger.Draw() method, and now I want to move it further into a LoggerRenderer object. In effect, I want to have the game loop call RenderAll, which will then call Logger.Render, which will in turn call the LoggerRenderer.Render and finally output the text. So the Logger needs to contain a Renderer object, but the Renderer needs access to the Logger's state (the message queue) in order to render. How do I resolve that? Should I be passing in the message queue and other state information explicitly to the Render method? Or should the game loop be calling the Renderer directly and it links back to the logger, but the RenderAll method never actually sees the logger object itself? This feels kind of like Command pattern, but I'm botching it up terribly.

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• ViewModel updates after Model server roundtrip

  - by Pavel Savara

  I have stateless services and anemic domain objects on server side. Model between server and client is POCO DTO. The client should become MVVM. The model could be graph of about 100 instances of 20 different classes. The client editor contains diverse tab-pages all of them live-connected to model/viewmodel. My problem is how to propagate changes after server round-trip nice way. It's quite easy to propagate changes from ViewModel to DTO. For way back it would be possible to throw away old DTO and replace it whole with new one, but it will cause lot of redrawing for lists/DataTemplates. I could gather the server side changes and transmit them to client side. But the names of fields changed would be domain/DTO specific, not ViewModel specific. And the mapping seems nontrivial to me. If I should do it imperative way after round-trip, it would break SOC/modularity of viewModels. I'm thinking about some kind of mapping rule engine, something like automappper or emit mapper. But it solves just very plain use-cases. I don't see how it would map/propagate/convert adding items to list or removal. How to identify instances in collections so it could merge values to existing instances. As well it should propagate validation/error info. Maybe I should implement INotifyPropertyChanged on DTO and try to replay server side events on it ? And then bind ViewModel to it ? Would binding solve the problems with collection merges nice way ? Is EventAgregator from PRISM useful for that ? Is there any event record-replay component ? Is there better client side pattern for architecture with server side logic ?

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• Invoicing vs Quoting

  - by FreshCode

  If invoices can be voided, should they be used as quotations? I have an Invoices tables that is created from inventory associated with a Job. I could have a Quotes table as a halfway-house between inventory and invoices, but it feels like I would have duplicate data structures and logic just to handle an "Is this a quote?" bit. From a business perspective, quotes are different from invoices: a quote is sent prior to an undertaking and an invoice is sent once it is complete and payment is due, but how to represent this in my repository and model. What is an elegant way to store and manage quotes & invoices in a database?

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• How to control respond_to based on variable in Rails controller?

  - by smotchkkiss

  The dilemma I'm using a before_filter in my controller that restricts access to admins. However, I want to allow access public access to some methods based on request format. See the index method to understand what I'm talking about. items_controller.rb class ItemsController < ApplicationController before_filter :superuser_required layout 'superuser' def index @items = Item.all respond_to do |format| format.html format.js # I want public to have access to this end end def show @item = Item.find(params[:id]) respond_to do |format| format.html end end def new @item = Item.new respond_to do |format| format.html end end # remaining controller methods # ... def superuser_required redirect_to login_path unless current_user.superuser? end end

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• How to connect remote EJB module from application client

  - by Zeck

  Hi guys, I have a EJB module in remote Glassfish server and application client in my computer. I want to connect from the application client to the remote EJB. Here is the my EJB interface: @Remote public interface BookEJBRemote { public String getTitle(); } Here is the my ejb: @Stateless public class BookEJB implements BookEJBRemote { @Override public String getTitle() { return "Twenty Thousand Leagues Under the Sea"; } } I have several questions : Can I use Dependency Injection in the remote application client to connect to the ejb? If so what can i do to achieve this. Do i need to configure in the sun-ejb-jar.xml and sun-application-client.xml? In other words, if i use DI like @EJB MyEJBRemote ejb; How application client container know what ejb to be injected? Where should i specify the information? How can i run the application client? I tried to run package-appclient in the glassfish server to get appclient.jar and copy it to my computer. Then i type appclient.jar -client myAppClient.jar . It didn't work. How do i point the target server? if i cannot use DI in the client then i guess i have to use JNDI lookup. Do i need to configure jndi name in sun-ejb-jar.xml or in the sun-application-client.xml? No matter how i try i never manage to run application client ? Can you guys put some working example? And thank you for every advises and examples?

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• Mimic remote API or extend existing django model

  - by drozzy

  I am in a process of designing a client for a REST-ful web-service. What is the best way to go about representing the remote resource locally in my django application? For example if the API exposes resources such as: List of Cars Car Detail Car Search Dealership summary So far I have thought of two different approaches to take: Try to wrangle the django's models.Model to mimic the native feel of it. So I could try to get some class called Car to have methods like Car.objects.all() and such. This kind of breaks down on Car Search resources. Implement a Data Access Layer class, with custom methods like: Car.get_all() Car.get(id) CarSearch.search("blah") So I will be creating some custom looking classes. Has anyone encoutered a similar problem? Perhaps working with some external API's (i.e. twitter?) Any advice is welcome. PS: Please let me know if some part of question is confusing, as I had trouble putting it in precise terms.

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• Can you find a pattern to sync files knowing only dates and filenames?

  - by Robert MacLean

  Imagine if you will a operating system that had the following methods for files Create File: Creates (writes) a new file to disk. Calling this if a file exists causes a fault. Update File: Updates an existing file. Call this if a file doesn't exist causes a fault. Read File: Reads data from a file. Enumerate files: Gets all files in a folder. Files themselves in this operating system only have the following meta data: Created Time: The original date and time the file was created, by the Create File method. Modified Time: The date and time the file was last modified by the Update File method. If the file has never been modified, this will equal the Create Time. You have been given the task of writing an application which will sync the files between two directories (lets call them bill and ted) on a machine. However it is not that simple, the client has required that The application never faults (see methods above). That while the application is running the users can add and update files and those will be sync'd next time the application runs. Files can be added to either the ted or bill directories. File names cannot be altered. The application will perform one sync per time it is run. The application must be almost entirely in memory, in other words you cannot create a log of filenames and write that to disk and then check that the next time. The exception to point 6 is that you can store date and times between runs. Each date/time is associated with a key labeled A through J (so you have 10 to use) so you can compare keys between runs. There is no way to catch exceptions in the application. Answer will be accepted based on the following conditions: First answer to meet all requirements will be accepted. If there is no way to meet all requirements, the answer which ensures the smallest amount of missed changes per sync will be accepted. A bounty will be created (100 points) as soon as possible for the prize. The winner will be selected one day before the bounty ends. Please ask questions in the comments and I will gladly update and refine the question on those.

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• Does overloading Grails static 'mapping' property to bolt on database objects violate DRY?

  - by mikesalera

  Does Grails static 'mapping' property in Domain classes violate DRY? Let's take a look at the canonical domain class: class Book {      Long id      String title      String isbn      Date published      Author author      static mapping = {             id generator:'hilo', params:[table:'hi_value',column:'next_value',max_lo:100]      } } or: class Book { ...         static mapping = {             id( generator:'sequence', params:[sequence_name: "book_seq"] )     } } And let us say, continuing this thought, that I have my Grails application working with HSQLDB or MySQL, but the IT department says I must use a commercial software package (written by a large corp in Redwood Shores, Calif.). Does this change make my web application nobbled in development and test environments? MySQL supports autoincrement on a primary key column but does support sequence objects, for example. Is there a cleaner way to implement this sort of 'only when in production mode' without loading up the domain class?

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• Best way to handle multiple getView calls from inside an Adapter

  - by Samuh

  I have a ListView with custom ArrayAdapter. Each of the row in this ListView has an icon and some text. These icons are downloaded in background,cached and then using a callback, substituted in their respective ImageViews. The logic to get a thumbnail from cache or download is triggered every time getView() runs. Now, according to Romain Guy: "there is absolutely no guarantee on the order in which getView() will be called nor how many times." I have seen this happen, for a row of size two getView() was being called six times! How do I change my code to avoid duplicate thumbnail-fetch-requests and also handle view recycling? Thanks.

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• Flexible design - customizable entity model, UI and workflow

  - by Ngm

  Hi All, I want to achieve the following aspects in the software I am building: 1. Customizable entity model 2. Customizable UI 3. Customizable workflow I have thought about an approach to achieve this, I want you to review this and make suggestions: Entity objects should be plain objects and will hold just data Separate Entity model and DB Schema by using an framework (like NHibernate?). This will allow easy modification of entity objects. Business logic to fetch/modify entities has to be granular enough so that they can be invoked as part of the workflow. Business objects should not hold any state, and hence will contain only static methods The workflow will decide depending upon the "state" of an entity/entities which methods on business object/objects to invoke. The workflow should obtain the results of the processing and then pass on the business objects to the appropriate UI screen. The UI screen has to contain instructions about how to display a given entity/entites. Possibly the UI has to be generated dynamically based on a set of UI instructions. (like XUL) What do you think about this approach? Suggest which existing frameworks (like NHiberante, Window Workflow) fit into this model, so that I will not spend time on coding these frameworks Also suggest is there any asp.net framework that can generate dynamic asp.net ajax pages based on a set of UI instructions (like Mozilla XUL)? I have recently been exploring Apache Ofbiz and was impressed by its ability to customize most areas of the application: UI, workflow, entities. Is there any similar (not necessarily an ERP system) application developed in C#/.Net which offers a similar level of customization? I am looking for examples of applications developed in C# that are highly customizable in terms of UI, Workflow and Entity Model

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• Performance Related features for migration from .net 2003 Framework 1.1 to .net 2008 framework 3.5?

  - by KuldipMCA

  I am work on VB.net 2003 Framework 1.1 for last 3.5 years in windows Application. We are currently migrating to VB.net 2008 framework 3.5, but i don't know about the features which related to ADO.net and which is important to performance. I know linq to SQL but our architecture is made in .net 2003 so we should follow this. Any features which is very important to enhance the performance?

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• Builder pattern and singletons

  - by Berryl

  Does anyone have any links to some code they like that shows a good example of this in c#? As an example of bad code, here is what a builder I have now looks like. I'm trying to have a way to keep the flexibility of the builder pattern but not rebuild the properties. Cheers, Berryl public abstract class ActivityBuilder { public abstract ActivityBuilder Build(); public bool IsBuilt { get; protected set; } public IEnumerable<Project> Projects { get { if(_projects==null) { Build(); } return _projects; } } protected IEnumerable<Project> _projects; // .. other properties }

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• What is the best way to handle validity dates in applications ?

  - by user214626

  Hello, How do we model these objects ? Scenario 1: Price changes in a time period EffectiveDate ExpiryDate Price 2009-01-01 2009-01-31 800$ 2009-02-01 Null 900$ So, if the price changes to 910$ on 2009-02-15, then the system should automatically update the expiry date on the previous effective price to 2009-02-14, to keep it consistent. Scenario 2: No price specified between 2009-02-01 to 2009-02-28 EffectiveDate ExpiryDate Price 2009-01-01 2009-01-31 800$ 2009-03-01 Null 900$ So, if new price is specified for 2009-02-15 onwards , then the system should automatically set the expiry date on the record to be inserted to 2009-02-28, because already a record effective from 2009-03-01 exists. Please suggest an effective way to handle these scenarios to model my framework, or are there any frameworks around that can do this . Thanks

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• More pythonic way to iterate

  - by fmark

  I am using a module that is part of a commercial software API. The good news is there is a python module - the bad news is that its pretty unpythonic. To iterate over rows, the follwoing syntax is used: cursor = gp.getcursor(table) row = cursor.Next() while row: #do something with row row = cursor.next() What is the most pythonic way to deal with this situation? I have considered creating a first class function/generator and wrapping calls to a for loop in it: def cursor_iterator(cursor): row = cursor.Next() while row: yield row row = cursor.next() [...] cursor = gp.getcursor(table) for row in cursor_iterator(cursor): # do something with row This is an improvement, but feels a little clumsy. Is there a more pythonic approach? Should I create a wrapper class around the table type?

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• Downloading RSS using python

  - by Vojtech R.

  Hi, I have list of 200 rss feeds, which I have to downloading. It's continuous process - I have to download every post, nothing can be missing, but also no duplicates. So best practice should be remember last update of feed and control it for change in x-hour interval? And how to handle if downloader will be restarted? So downloader should remember, what were downloaded and dont download it again... It's somewhere implemented yet? Or any tips for article? Thanks

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• Is jQuery always the answer?

  - by Kibbee

  I've come across a couple questions, such as this one, and I really have to wonder why "Use jQuery" seems to be the answer when somebody asks how to do something in JavaScript. I understand that jQuery can save you a lot of time, and can help you out a lot, especially when you are doing a lot of fancy JavaScript in your site. However, in instances like this, and in many other instances, it seems like it's just jumping around the problem instead of answering the question. I also feel like this builds too much dependency into libraries. I've seen way too many developers that simply rely too much on libraries, and if they encounter a situation where they didn't have the library, they would be completely unable to function. I feel like there are already enough developers who don't know JavaScript, without just telling everybody to not learn JavaScript, and use jQuery. So, just to reiterate the question. Do you think there's too much of a tendency to use jQuery, for small pieces of JavaScript, when most of the functionality of jQuery isn't being used. Should developers be fluent in the use of bare JavaScript so they don't get too dependent on using libraries? [Additional related conversation topic] Does the existence of jQuery give too much slack to web browser developers who write the JavaScript engines? If we just have workarounds to cover all the inconsistencies in JavaScript, what pressure is there on browser makers to ensure that their JavaScript library works as it should. I feel like this extrapolates the same problem discussed in SO Podcast #36 of "be conservative in what you send, liberal in what you accept". By being so liberal with bad JavaScript engines, and using a common library to work around the flaws, we are promoting their use, and extending the problem.

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• ActionScript 3.0: placing code on stage/MC timelines a la AS2 instead of in classes

  - by BoltClock

  I'm aware that ActionScript 3.0 is designed from the ground up to be a largely object-oriented language and using it means less or even no timeline code in Flash documents. I'm quite experienced with OOP and am comfortable writing classes. However, since I mostly use Flash for animations, I hardly ever need to write ActionScript code other than for preloaders, subtitles, quality controls, website links and so on. In fact, I still set my Flash movies to use AS2 to this day because I'm used to gotoAndPlay()/gotoAndStop(), AS2 preloaders, subtitles, quality controls and even getURL(). Of course, I really want to move on now that practically everyone's on Flash Player 9 or 10 and now that I've dabbled with other OO languages like Java, C# and Objective-C too. I'm a complete newcomer to AS3 and am not very learned with AS2 either. Considering my current use of ActionScript, are there any cases where it's still OK to use very simple AS3 code in the timeline instead of moving code to a class, especially since moving to a class might mean unnecessarily increasing the number of LOC from 4 to 40? (Heck, is the latter case ('instead of ...') even a valid concern at all?)

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• Committing when changing source formatting?

  - by chrisgoyal

  Is it accepted practice to commit even when you're just changing things like whitespace, code formatting, etc.?

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• Singleton class design in C#, are these two classes equivalent?

  - by Oskar

  I was reading up on singleton class design in C# on this great resource and decided to go with alternative 4: public sealed class Singleton1 { static readonly Singleton1 _instance = new Singleton1(); static Singleton1() { } Singleton1() { } public static Singleton1 Instance { get { return _instance; } } } Now I wonder if this can be rewritten using auto properties like this? public sealed class Singleton2 { static Singleton2() { Instance = new Singleton2(); } Singleton2() { } public static Singleton2 Instance { get; private set; } } If its only a matter of readability I definitely prefer the second version, but I want to get it right.

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• How to specify lib folder for JARs when using Android-generated ant build file ?

  - by Eno

  Im using an ant build file that has been generated by android. Our Android application requires a JAR file that lives inside the lib folder of our project, so I need to adjust the classpath that ant is using when it builds stuff. When I run: ant -lib lib debug the project builds just fine, but this should really be inside the build file itself. The build file that android generates references the android_rules.xml so a lot of this stuff is automated. I guess my question, what the best practice here when working with the Android build rules ?

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• Is there a way of using one method to handle others to avoid code duplication?

  - by Artur

  I wonder if there is a way of writing a method or a class that would add to any method some code that is shared between many methods. The methods return different things and some of them are just void. Below is a part of the code that is duplicated in the methods. StartTimer(MethodBase.GetCurrentMethod().Name); try { // Actual method body } catch (Exception ex) { bool rethrow = ExceptionPolicy.HandleException(ex, "DALPolicy"); if (rethrow) { throw; } } finally { StopTimer(MethodBase.GetCurrentMethod().Name); } Any help would be greatly appreciated.

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• What is best practice (and implications) for packaging projects into JAR's?

  - by user245510

  What is considered best practice deciding how to define the set of JAR's for a project (for example a Swing GUI)? There are many possible groupings: JAR per layer (presentation, business, data) JAR per (significant?) GUI panel. For significant system, this results in a large number of JAR's, but the JAR's are (should be) more re-usable - fine-grained granularity JAR per "project" (in the sense of an IDE project); "common.jar", "resources.jar", "gui.jar", etc I am an experienced developer; I know the mechanics of creating JAR's, I'm just looking for wisdom on best-practice. Personally, I like the idea of a JAR per component (e.g. a panel), as I am mad-keen on encapsulation, and the holy-grail of re-use accross projects. I am concerned, however, that on a practical, performance level, the JVM would struggle class loading over dozens, maybe hundreds of small JAR's. Each JAR would contain; the GUI panel code, necessary resources (i.e. not centralised) so each panel can stand alone. Does anyone have wisdom to share?

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