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• Data access strategy for a site like SO - sorted SQL queries and simultaneous updates that affect th

  - by Kaleb Brasee

  I'm working on a Grails web app that would be similar in access patterns to StackOverflow or MyLifeIsAverage - users can vote on entries, and their votes are used to sort a list of entries based on the number of votes. Votes can be placed while the sorted select queries are being performed. Since the selects would lock a large portion of the table, it seems that normal transaction locking would cause updates to take forever (given enough traffic). Has anyone worked on an app with a data access pattern such as this, and if so, did you find a way to allow these updates and selects to happen more or less concurrently? Does anyone know how sites like SO approach this? My thought was to make the sorted selects dirty reads, since it is acceptable if they're not completely up to date all of the time. This is my only idea for possibly improving performance of these selects and updates, but I thought someone might know a better way.

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• Efficient persistent storage for simple id to table of values map for java

  - by wds

  I need to store some data that follows the simple pattern of mapping an "id" to a full table (with multiple rows) of several columns (i.e. some integer values [u, v, w]). The size of one of these tables would be a couple of KB. Basically what I need is to store a persistent cache of some intermediary results. This could quite easily be implemented as simple sql, but there's a couple of problems, namely I need to compress the size of this structure on disk as much as possible. (because of amount of values I'm storing) Also, it's not transactional, I just need to write once and simply read the contents of the entire table, so a relational DB isn't actually a very good fit. I was wondering if anyone had any good suggestions? For some reason I can't seem to come up with something decent atm. Especially something with an API in java would be nice.

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• Using NSThread to solve waiting for image from URL on the iPhone

  - by james.ingham

  So I have the following code in a method which I want to set a UIImageView image to that of one from an online source: [NSThread detachNewThreadSelector:@selector(loadImage) toTarget:self withObject:nil]; Then in the method called by the thread I have this: - (void) loadImage { NSURL *url = [NSURL URLWithString:logoPath]; // logoPath is an NSString with path details NSData *data = [NSData dataWithContentsOfURL:url]; logoImage.image = [UIImage imageWithData:data]; } This works great however I get many warnings within the Debugger Console along the lines of: 2010-05-10 14:30:14.052 ProjectTitle[2930:633f] * _NSAutoreleaseNoPool(): Object 0x169d30 of class NSHTTPURLResponse autoreleased with no pool in place - just leaking This occurs many times each time I call the new thread and then eventually, under no pattern, after calling a few of these threads I get the classic 'EXC_BAD_ACCESS' run-time error. I understand that this is happening because I'm not retaining the object but how can I solve this with the code in 'loadImage' shown above? Thanks

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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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• how to open many files simultaneously for reading in c

  - by monkeyking

  I'm trying to port some of my c++ code into c. I have the following construct class reader{ private: FILE *fp; alot_of_data data;//updated by read_until() method public: reader(const char*filename) read_until(some conditional dependent on the contents of the file, and the arg supplied) } Im then instantiating hundreds of these object and iterate over them using several 'read_until()' for each file until allfiles is at eof. I'm failing to see any clever way to do this in c, the only solution I can come up with is making an array of FILE pointers, and do the same with all the private member data from my class. But this seems very messy, can I implement the functionality of my class as a function pointer, or anything better, I think I'm missing a fundamental design pattern? The files are way to big to have all in memory, so reading everything from every file is not feasible Thanks

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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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• Is it possible to listen to relational database update?

  - by Morgan Cheng

  Is it possible to listen to relation database update? For example, my web app want to send data update to client through Comet technology. I can have the program to poll the database periodically, but that would not be performant and scalable. If app can hood to a "event handler" of database, then app can get notification every time given database table data is updated. This sounds more promising, but I didn't find any concrete example for it. This is listener pattern. Does common relational database support such feature?

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• Do I still have to implement a singleton class by hand in .net, even when using .Net4.0?

  - by Hamish Grubijan

  Once the singleton pattern is understood, writing subsequent singleton classes in C# is a brainless exercise. I would hope that the framework would help you by providing an interface or a base class to do that. Here is how I envision it: public sealed class Schablone : ISingleton<Schablone> { // Stuff forced by the interface goes here // Extra logic goes here } Does what I am looking for exist? Is there some syntactic sugar for constructing a singleton class - whether with an interface, a class attribute, etc.? Can one write a useful and bullet-proof ISingleton themselves? Care to try? Thanks!

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• Is it a bad idea to use the new Dynamic Keyword as a replacement switch statement?

  - by WeNeedAnswers

  I like the new Dynamic keyword and read that it can be used as a replacement visitor pattern. It makes the code more declarative which I prefer. Is it a good idea though to replace all instances of switch on 'Type' with a class that implements dynamic dispatch. class VistorTest { public string DynamicVisit(object obj) { return Visit((dynamic)obj); } private string Visit(string str) { return "a string was called with value " + str; } private string Visit(int value) { return "an int was called with value " + value; } }

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• URL rewrite module for IIS7

  - by Learner

  I am trying to test if the redirect that I wrote works or not. If I do IISReset the redirect does not work. But if I recycle the app then this works. Is this how it works? <rule name="RedirectToanothercity" patternSyntax="ECMAScript" stopProcessing="true"> <match url="^home/cities.aspx?$" /> <conditions> <add input="{QUERY_STRING}" pattern="city=jerseycity" /> </conditions> <action type="Redirect" url="jerseycity" appendQueryString="false" />

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• JSF tags not being rendered as HTML

  - by Toto

  I'm following the Java EE firstcup tutorial using Netbeans and Glassfish. When I execute the JSF web tier I've been instructed to code, the browser gets the same JSF markup coded in the .xhtml file, and the tags are not rendered as HTML tags. I know this by using the view source code in my browser. For example, for this code: <html xmlns="http://www.w3.org/1999/xhtml" xmlns:f="http://java.sun.com/jsf/core" xmlns:h="http://java.sun.com/jsf/html"> <h:head> <title>Page title here</title> </h:head> <h:body> <h2> <h:outputText value="#{bundle.WelcomeMessage}" /> </h2> </h:body> </html> The browser should get something like: <html ...> <head> <title>Page title here</title> </head> <body> <h2> the welcome message goes here </h2> </body> </html> Right? Well, my browser is getting jsf code (the first piece of code above) and not the html code (the second piece of code above). It seems to be a configuration problem in netbeans or glassfish but don't know what. Any ideas? This is my web.xml file: <?xml version="1.0" encoding="UTF-8"?> <web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"> <context-param> <param-name>javax.faces.PROJECT_STAGE</param-name> <param-value>Development</param-value> </context-param> <servlet> <servlet-name>Faces Servlet</servlet-name> <servlet-class>javax.faces.webapp.FacesServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>Faces Servlet</servlet-name> <url-pattern>/firstcup/*</url-pattern> </servlet-mapping> <session-config> <session-timeout> 30 </session-timeout> </session-config> <welcome-file-list> <welcome-file>greetings.xhtml</welcome-file> </welcome-file-list> </web-app> This is my faces-config.xml file: <?xml version='1.0' encoding='UTF-8'?> <!-- =========== FULL CONFIGURATION FILE ================================== --> <faces-config version="2.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facesconfig_2_0.xsd"> <application> <resource-bundle> <base-name>firstcup.web.WebMessages</base-name> <var>bundle</var> </resource-bundle> <locale-config> <default-locale>en</default-locale> <supported-locale>es</supported-locale> </locale-config> </application> <navigation-rule> <from-view-id>/greetings.xhtml</from-view-id> <navigation-case> <from-outcome>success</from-outcome> <to-view-id>/response.xhtml</to-view-id> </navigation-case> </navigation-rule> </faces-config> Moreover: The url I'm entering in the browser is http://localhost:8081/firstcup/ but I've also tried: http://localhost:8081/firstcup/greetings.xhtml I've checked Glassfish logs and there's no information about not being able to load FacesServlet

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• VS 2010 Entity Repository Error Class member EntityBase.id is unmapped.

  - by Steve

  In my project I have it set up so that all the tables in the DB has the property "id" and then I have the entity objects inherit from the EntityBase class using a repository pattern. I then set the inheritance modifier for "id" property in the dbml file o/r designer to "overrides" Public MustInherit Class EntityBase MustOverride Property id() As Integer End Class Public MustInherit Class RepositoryBase(Of T As EntityBase) Protected _Db As New DataClasses1DataContext Public Function GetById(ByVal Id As Integer) As T Return (From a In _Db.GetTable(Of T)() Where a.id = Id).SingleOrDefault End Function End Class Partial Public Class Entity1 Inherits EntityBase End Class Public Class TestRepository Inherits RepositoryBase(Of Entity1) End Class the line Return (From a In _Db.GetTable(Of T)() Where a.id = Id).SingleOrDefault however produces the error "Class member EntityBase.id is unmapped" when i use VS 2010 using the 4.0 framework but I never received that error with the old one. Any help would be greatly appreciated. Thanks in advance.

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• Singelton on iPhone Simulator vs Singelton on real Device

  - by Helge Becker

  I am using a Singelton for some shared stuff. In the simulator, the app crashes ocasionally. Tracking the crash down shows that the the properties of my Singelton became dealocated. Those crashes never happend on a real device. Does the iPHone simulator handle memory managemend different? GC maybe? Changed the singelton to match this pattern. The iPhone Simulator dont crash now, but I am not sure about the memory handling on the real device. I assume that this solution will cause problems. What do you think?

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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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• Architecting a generic search result web control

  - by Bartek Tatkowski

  In a project I'm currently working for we've stumbled upon the need for several kinds of search results presentation controls. The search result are similar, but not identical. For example, in the "office search" result we might want to present the office name and location, while in the "document search" could contain document name, author and publishing date. These fields should be sortable. My current strategy is to employ the Factory pattern and do something like this: ISearchResult officeResults = SearchResultFactory.CreateOfficeSearchResults(data); ISearchResult documentResults = SearchResultFactory.CreateDocumentSearchResults(data); The problem is: I don't know how to implement the markup code. Should I just do Controls.Add(officeResults); in the containing page? Or is there some ASPX trickery to create generic web controls? Or maybe I'm overthinking this and just should create five classes? ;)

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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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• regular expression and escaping

  - by pstanton

  Sorry if this has been asked, my search brought up many off topic posts. I'm trying to convert wildcards from a user defined search string (wildcard is "*") to postgresql like wildcard "%". I'd like to handle escaping so that "%" => "\%" and "\*" => "*" I know i could replace \* with something else prior to replacing * and then swap it back, but i'd prefer not to and instead only convert * using a pattern that selects it when not proceeded by \. String convertWildcard(String like) { like = like.replaceAll("%", "\\%"); like = like.replaceAll("\\*", "%"); return like; } Assert.assertEquals("%", convertWildcard("*")); Assert.assertEquals("\%", convertWildcard("%")); Assert.assertEquals("*", convertWildcard("\*")); // FAIL Assert.assertEquals("a%b", convertWildcard("a*b")); Assert.assertEquals("a\%b", convertWildcard("a%b")); Assert.assertEquals("a*b", convertWildcard("a\*b")); // FAIL ideas welcome.

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• preg_replace hell

  - by Jason

  I'm trying to use preg_replace to get some data from a remote page, but I'm having a bit of an issue when it comes to sorting out the pattern. function getData($Url){ $str = file_get_contents($Url); if(strlen($str)>0){ preg_match("/\<span class=\"SectionHeader\"\>title\</span>/<br/>/\<div class=\"header2\"\>(.*)\</div\></span\>/",$str,$title); return $title[1]; } } Here's the HTML as is before I ended up throwing a million slashes at it (looks like I forgot a part or two): <span class="cell CellFullWidth"><span class="SectionHeader">mytitle</span><br/><div class="Center">Event Name</div></span> Where Event Name is the data I want to return in my function. Thanks a lot guys, this is a pain in the ass.

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• Store interface in array list java

  - by agazerboy

  Hi all, I am learning java. I am trying to use composite design pattern. I am trying to use following logic. ( Don't laugh I know it is very basic :) ) Item -> interface Folder -> class File -> class In folder class, can I create an arraylist of Item to store files information? ArrayList<Item> info = ArrayList<Item>(); Or should I use Folder Arraylist? ArrayList<Folder> info = ArrayList<Folder>(); I don't know if interface can store real data as there is no variable just function definitions. Thanks for helping a newbie :)

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• Why should I use MVVM when it breaks built in functionality

  - by Jakob

  I'm struggling to grasp why MVVM is really a good pattern to implement in riaserivces, To me there's nothing but trouble to it, it just add's another tier that I have to code. I Get that I could change the UI, but really I don't need to. Instead i won't be able to user out of the box functionality with riaservices, datagrid, dataform all controls require some implementation. Why can't it just be simple? Is there really no way to get MVVM to automatically set "IsBusy" and all the dataform edit functionality. It's like reinventing the wheel to me, and it seems that I'd be able to write code much faster just using riaservices

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• How to deal with the new line character in the Silverlight TextBox

  - by Ian Oakes

  When using a multi-line TextBox (AcceptsReturn="True") in Silverlight, line feeds are recorded as \r rather than \r\n. This is causing problems when the data is persisted and later exported to another format to be read by a Windows application. I was thinking of using a regular expression to replace any single \r characters with a \r\n, but I suck at regex's and couldn't get it to work. Because there may be a mixture of line endings just blindy replacing all \r with \r\n doesn't cut it. So two questions really... If regex is the way to go what's the correct pattern? Is there a way to get Silverlight to respect it's own Environment.NewLine character in TextBox's and have it insert \r\n rather just a single \r?

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• How do I determine inactivity in a MVVM application?

  - by Jordan

  I have an MVVM kiosk application that I need to restart when it has been inactive for a set amount of time. I'm using Prism and Unity to facilitate the MVVM pattern. I've got the restarting down and I even know how to handle the timer. What I want to know is how to know when activity, that is any mouse event, has taken occurred. The only way I know how to do that is by subscribing to the preview mouse events of the main window. That breaks MVVM thought, doesn't it? I've thought about exposing my window as an interface that exposes those events to my application, but that would require that the window implement that interface which also seems to break MVVM.

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• Dependency Injection -Colloquial explanation

  - by nettguy

  Recently I was asked to express the DI in colloquial explanation. I answered : 1) I am going to a hotel.I ordered food.The hotel management asks me to clean the plates and clean the tables.So here i am a client,I am responsible for managing the service (Instantiating,executing,disposing).But DI decouples such tasks so the service consumer no need not worry about controlling the life cycle of the service. 2) He also asked is there any microsoft API follows DI ?.I answered (This was my guess) In WCF you can create a Proxy using ChannelFactory that controls the life time of your factory. for item (1) he said only 10% is correct for item(2) he said that is factory pattern not dependency injection. Actually what went wrong in my explanation (apart from my bad English) ? What is the real answers for those? I am waiting for your valuable suggestions.

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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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• Dynamically loading JavaScript synchronously

  - by spoon16

  I'm using the module pattern, one of the things I want to do is dynamically include an external JavaScript file, execute the file, and then use the functions/variables in the file in the return { } of my module. I can't figure out how to do this easily. Are there any standard ways of performing a pseudo synchronous external script load? function myModule() { var tag = document.createElement("script"); tag.type = "text/javascript"; tag.src = "http://some/script.js"; document.getElementsByTagName('head')[0].appendChild(tag); //something should go here to ensure file is loaded before return is executed return { external: externalVariable } }

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