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• Cancelling Two Way Data Binding In Silverlight

  - by DaveB

  I have an ObervableCollection of data items. This collection is bound to a ListBox. When the user selects a item from the listbox and clicks the Edit button a UserControl with the details of that item is displayed with the various properties bound to text boxes. Each binding mode is set for TwoWay. On this details UserControl, I would like to implement 2 buttons, OK and Cancel. This would be consistent with UIs in Windows. This application is using the Model-View_ViewModel pattern. Here is my question: 1) How can I implement the Cancel button when all the changes have already been committed?

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• Asynchrous calls cause StaleObjectStateException

  - by Mulone

  Hi all, I'm struggling with a Grails service. The service gets AJAX calls from the clients and behaves like a simple local cache for remote objects: void **someCallFromClient**() { // extract params def results = remoteService.queryService(params) results.each{ // try to fetch result object from local DB def obj = SomeClass.findBySomeField(result.someField) if (!obj){ obj = new Result(params) obj.save() } // do stuff on obj } } The service works fine when only one client is connected, but as soon as 2 or more clients start bombing the server with requests, I start getting: 2010-05-24 13:09:49,764 [30893094@qtp-26315919-2] ERROR errors.GrailsExceptionResolver - Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [ some object #892901] org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [ some object #892901] // very long stactrace It probably happens when 2 calls are trying to create the same object concurrently. I suppose this is a rather typical situation to end up in. Could you recommend any pattern/good practice to fix this issue? For example, is there a way to say to one of the service instances to hang on and wait for the other to finish its stuff and try again? Cheers!

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• Avoiding configSections in .NET app.config files

  - by Chris Clark

  I'm looking for a way to avoid declaring my configuration section in the configSections inside the App.config file. Basically, I want to specify my configuration information just like I do for built-in .NET systems. For instance, when configuring WCF, I just put stuff in the <system.serviceModel>, I don't have to declare a section in the configSections up top. The same thing applies for <system.diagnostics> and many other namespaces. I know I could just load it up as an XML file and parse through it, but I'd prefer to stick with the pattern if possible. Moreover, looking at the WCF configuration with Reflector, I notice that it uses the same configuration subsystem (defined in System.Configuration). If you're wondering why this is important, it's because it's confusing our IT people. If it were self contained in one place, it would be much easier on them. I also realize I'll lose the ability to have multiple of the same section type, but that's not important in our case.

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• Behavior with primitive data types' value out of range & C99's PRI* macros

  - by Yktula

  Say we have an 8-bit unsigned integer n (UINT8_MAX=255); what is the behavior of the compiler for n=256? Where can I find a table of default behavior when the value of a data type is out of range for different data types? Is there a pattern to how they behave when set out of range? #include <stdio.h> #include <inttypes.h> uint8_t n = UINT8_MAX; int main() { printf("%hhu ",n++); printf("%hhu",n); return 0; } Compiling with gcc -std=c99 -Wall *.c, this prints: 255 0 Also, is it acceptable to use C99's PRI* macros? How are they named?

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• Setting up Matcher for String phrase match in file

  - by randomCoder

  Having trouble figuring out how to match a phrase string to a phrase in file stream. The file I'm dealing with contains random words such as: 3 little pigs built houses and 1 little pig went to the market etc. for many lines Using "little pig" as my pattern and matcher.find() I can locate 2 matches: "little pig" and "little pigs". However, I only want it to match "little pig". What can I do? I thought about using matcher.lookingAt() but I wouldn't know how to set a proper region when I can't rely on the file string phrases I'm matching being on separate lines.

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• Django - Static content display based on URL

  - by Steven Potter

  I'm working on a Django site with a basic three column design. Left column navigation, center column content and right column URL specific content blocks. My question is about the best method of controlling the URL specific content blocks in the right column. I am thinking of something along the lines of the Flatpages app that will make the content available to the template context if the URL matches a pre-determined pattern (perhaps regex?). Does anyone know if such an app already exists? If not, I am looking for some advice about the best way to implement it. Particularly in relation to the matching of patterns to the current URL. Is there any good way to re-use parts of the Django URL dispatcher for this use?

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• silverlight vs ASP.NET MVC

  - by magellings

  I'm debating whether to use Silverlight 2.0 vs ASP.NET MVC for a web application. The web application will be a subscription free service marketing all age groups. It's important the source is highly testable, but also with the Web 2.0 movement a graphical web application is important as well for competitive reasons. I'm assuming silverlight is better than the ajax helpers/MVC graphically, but foundation-wise testing is better/easier with MVC. Possibly an MVP pattern with Silverlight could increase the testability of the source. Could anyone elaborate on the pros/cons of each technology and recommend one or the other based on the above? (addition 9/22/08) In regards to allowing search engines to index the site, using either technology it will utilize a backend database whereas a lot of the content will be dynamically generated. Based on some of the comments, when we talk of the searchable content would the home page of the application if written in silverlight be searchable? Would I be able to get the site to appear in a google search?

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• How, in general, can web framework support REST style?

  - by juro

  I would like to know, what are the ways a web framework may be suitable for designing a RESTful app, in general. One goal is for example to provide http request routing, so they are automatically sent to appropriate controllers. From architectural point of view, web framework based on MVC pattern are more suitable for REST. What other features of web frameworks are helpful by building apps satisfying the REST constraints? Is there any reason why you consider certain languages(python/java) or web frameworks(django/turbogears/jersey/restlets/...) as the most applicable ones?

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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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• Why is 'using' improving C# performances

  - by Wernight

  It seems that in most cases the C# compiler could call Dispose() automatically. Like most cases of the using pattern look like: public void SomeMethod() { ... using (var foo = new Foo()) { ... } // Foo isn't use after here (obviously). ... } Since foo isn't used (that's a very simple detection) and since its not provided as argument to another method (that's a supposition that applies to many use cases and can be extended), the compiler could automatically call Dispose() without the developper requiring to do it. This means that in most cases the using is pretty useless if the compiler does some smart job. IDisposable seem low level enough to me to be taken in account by a compiler. Now why isn't this done? Wouldn't that improve the performances (if the developpers are... dirty).

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• General approach for posting business logic status messages to UI?

  - by generalt

  Hello all. I have been struggling with this question for awhile now, and I haven't reached a conclusion. I'm not typically a UI programmer, so forgive the noobishness. I'm writing a typical application with a UI layer (WPF) and a business layer. I want to post status messages to the UI from the business layer (perhaps deep within the business layer), but I don't want the business layer to have any knowledge of the UI. Is there a generally accepted pattern for this? I was thinking to have a message queue of some sort to which the business layer posts status messages, and have the view model of the UI subscribe to that queue and intercept messages from the queue and route them to the UI. Is that a good approach? Is there somewhere else I should start? Thank you.

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• Boost singleton and undefined reference

  - by Ockonal

  Hello, I globally use singleton pattern in my project. To make it easier - boost::singleton. Current project uses Ogre3d library for rendering. Here is some class: class GraphicSystem : public singleton<GraphicSystem> { private: Ogre::RenderWindow *mWindow; public: Ogre::RenderWindow *getWindow() const { return mWindow; } }; In GraphicSystem constructor I fill the mWindow value: mWindow = mRoot->createRenderWindow(...); I cheked it, everything makes normally. So, now I have to use handler for the window in input system (to get window handle). Somewhere else in another class: Ogre::RenderWindow *temp = GraphicSystem::get_mutable_instance().getWindow(); GraphicSystem::get_mutable_instance().getWindow()->getCustomAttribute("WINDOW", &mWindowHandle); temp is 0x00, and there is segfault at last line (getting custon attribute). I can't understand, why does singleton returns undefined pointer for the window. All another singleton-based classes work well.

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• Recommendations with hierarchical data on non-relational databases?

  - by Luki

  I'm developing an web application that uses a non-relational database as a backend (django-nonrel + AppEngine). I need to store some hierarchical data (projects/subproject_1/subproject_N/tasks), and I'm wondering which pattern should I use. For now I thought of: Adjacency List (store the item's parent id) Nested sets (store left and right values for the item) In my case, the depth of nesting for a normal user will not exceed 4-5 levels. Also, on the UI, I would like to have a pagination for the items on the first level, to avoid to load too many items at the first page load. From what I understand so far, nested sets are great when the hierarchy is used more for displaying. Adjacency lists are great when editing on the tree is done often. In my case I guess I need the displaying more than the editing (when using nested sets, even if the display would work great, the above pagination could complicate things on editing). Do you have any thoughts and advice, based on your experience with the non-relational databases?

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• ASP.NET 3.5 Stateless Session Managment and connection pooling?

  - by Norm

  I am designing an ASP.NET (3.5) web application that connects to a Rocket Software UniVerse database. I am in the planning stages right now and need some help in being pointed in the right direction. I am brand new to ASP and C#. I am shooting for a RESTful design and a MVC pattern. Rocket provides a .NET library called UniObjects.NET which handles everything for connecting and retrieving information from the database. What would be the best way to in general to log my users into the database, then use that session via connection pooling? I see that in 3.5 there is the ASP.NET Routing Infrastructure and that looks promising am I in the right direction on this? Also does C# support decorators like Python and Java?

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• How can I make CAPTCHA work across multiple pages?

  - by jm04469

  Ever visit a website such as myspace where they leverage CAPTCHA to prevent spam? The typical pattern is to present a challenge to each URL that is opened, yet the challenge doesn't actually belong to the page itself which causes additional bandwidth usage. So, if I open up six pages at the same time and want to present a challenge on each page. I want the challenge to be tied to the page and not to the session. How can I make this work with Spring and/or Struts.

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• How to check for undefined or null variable in javascript

  - by Thomas Wanner

  We are frequently using the following code pattern in our javascript code if(typeof(some_variable) != 'undefined' && some_variable != null) { // do something with some_variable } and I'm wondering whether there is a less verbose way of checking that has the same effect. According to some forums and literature saying simply if(some_variable) { // do something with some_variable } should have the same effect. Unfortunately, Firebug evaluates such a statement as error on runtime when some_variable is undefined, whereas the first one is just fine for him. Is this only an (unwanted) behavior of Firebug or is there really some difference between those two ways ?

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• CommandManager "cannot resolve symbol"

  - by Budda

  After adding "RelayCommand" class (that uses CommandManager class) into my Silverlight App I've got an error: The name 'CommandManager' does not exist in the current context This class is a member of System.Windows.Input namespace that is in PresentationCore.dll assembly. The problem is that I can't add this dll into my app... I am having a strange assumption: this class (CommmandManager) can't be used in the Silverlight. Am I right? How can I implement MVVM-pattern (http://msdn.microsoft.com/en-us/magazine/dd419663.aspx)? Thanks.

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• Removing final bash script argument

  - by ctuffli

  I'm trying to write a script that searches a directory for files and greps for a pattern. Something similar to the below except the find expression is much more complicated (excludes particular directories and files). #!/bin/bash if [ -d "${!#}" ] then path=${!#} else path="." fi find $path -print0 | xargs -0 grep "$@" Obviously, the above doesn't work because "$@" still contains the path. I've tried variants of building up an argument list by iterating over all the arguments to exclude path such as args=${@%$path} find $path -print0 | xargs -0 grep "$path" or whitespace="[[:space:]]" args="" for i in "${@%$path}" do # handle the NULL case if [ ! "$i" ] then continue # quote any arguments containing white-space elif [[ $i =~ $whitespace ]] then args="$args \"$i\"" else args="$args $i" fi done find $path -print0 | xargs -0 grep --color "$args" but these fail with quoted input. For example, # ./find.sh -i "some quoted string" grep: quoted: No such file or directory grep: string: No such file or directory Note that if $@ doesn't contain the path, the first script does do what I want.

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• Model View Presenter plus ASP.NET Web Service; where does the asmx live?

  - by Dirk

  I've been slowly transitioning from a traditional web forms architecture to the MVP pattern (Passive View). So far, it's been fairly easy to implement b/c the views I've dealt with have all employed a classic PostBack model. However, I've come across my first view that will refresh portions of itself via web services. I can't grok where the web service should live (Presenter I think) or how to expose that asmx end point to my View while still maintaining the clean separation of concerns/testability that MVP affords me. I've searched far and wide for some examples on how this might be implemented and have come up with nothing. Please help!

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• Managing Data Prefetching and Dependencies with .NET Typed Datasets

  - by Derek Morrison

  I'm using .NET typed datasets on a project, and I often get into situations where I prefetch data from several tables into a dataset and then pass that dataset to several methods for processing. It seems cleaner to let each method decide exactly which data it needs and then load the data itself. However, several of the methods work with the same data, and I want the performance benefit of loading data in the beginning only once. My problem is that I don't know of a good way or pattern to use for managing dependencies (I want to be sure I load all the data that I'm going to need for each class/method that will use the dataset). Currently, I just end up looking through the code for the various classes that will use the dataset to make sure I'm loading everything appropriately. What are good approaches or patterns to use in this situation? Am I doing something fundamentally wrong? Although I'm using typed datasets, this seems like it would be a common situation where prefetching data is used. Thanks!

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• How to properly match the following message id format in a case statement

  - by hsatterwhite

  I'm trying to get this regex pattern working in a case statement to match a particular type of ID, which could be passed to the script. I need to match the exact number of alphanumeric characters with the dashes to differentiate this message id from anything else, which may be passed to this bash script. An example of the message id format: c7c3e910-c9d2-71e1-0999-0aec446b0000 #!/bin/bash until [ -z "$1" ] do case "$1" in "") echo "No value passed" ;; [a-z0-9]\{8\}-[a-z0-9]\{4\}-[a-z0-9]\{4\}-[a-z0-9]\{4\}-[a-z0-9]\{12\}) echo "Found message ID: $1" ;; *) echo "Server $1" ;; esac shift done

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• What are some of the useful concepts to know about when building Silverlight apps?

  - by cody

  The Silverlight(& WPF) space seems to have a whole new nomenclature around it so at times I'm having a hard time figuring our what is important and useful to research a bit more. For example I 'know' about the MVVM pattern but I'm looking for things that are a bit smaller in scope, that is topics, ideas, programming constructs that might be used in implementing MVVM and would need to know before hand. So basically I'm looking for some of the key topics and concepts that people have found useful or are important when creating a Silverlight apps. And maybe why it is useful or important and when\where it might be applied or used. Thanks.

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• Is there a performance gain from defining routes in app.yaml versus one large mapping in a WSGIAppli

  - by jgeewax

  Scenario 1 This involves using one "gateway" route in app.yaml and then choosing the RequestHandler in the WSGIApplication. app.yaml - url: /.* script: main.py main.py from google.appengine.ext import webapp class Page1(webapp.RequestHandler): def get(self): self.response.out.write("Page 1") class Page2(webapp.RequestHandler): def get(self): self.response.out.write("Page 2") application = webapp.WSGIApplication([ ('/page1/', Page1), ('/page2/', Page2), ], debug=True) def main(): wsgiref.handlers.CGIHandler().run(application) if __name__ == '__main__': main() Scenario 2: This involves defining two routes in app.yaml and then two separate scripts for each (page1.py and page2.py). app.yaml - url: /page1/ script: page1.py - url: /page2/ script: page2.py page1.py from google.appengine.ext import webapp class Page1(webapp.RequestHandler): def get(self): self.response.out.write("Page 1") application = webapp.WSGIApplication([ ('/page1/', Page1), ], debug=True) def main(): wsgiref.handlers.CGIHandler().run(application) if __name__ == '__main__': main() page2.py from google.appengine.ext import webapp class Page2(webapp.RequestHandler): def get(self): self.response.out.write("Page 2") application = webapp.WSGIApplication([ ('/page2/', Page2), ], debug=True) def main(): wsgiref.handlers.CGIHandler().run(application) if __name__ == '__main__': main() Question What are the benefits and drawbacks of each pattern? Is one much faster than the other?

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• trying to prune down a list of files

  - by romunov

  I have a list of files and I'm trying to extract all layer1_*.grd files. Is there a way of doing this in one grep expression? lof <- c("layer1_1.grd", "layer1_1.gri", "layer1_2.grd", "layer1_2.gri", "layer1_3.grd", "layer1_3.gri", "layer1_4.grd", "layer1_4.gri", "layer1_5.grd", "layer1_5.gri", "layer2_1.grd", "layer2_1.gri", "layer2_2.grd", "layer2_2.gri", "layer2_3.grd", "layer2_3.gri", "layer2_4.grd", "layer2_4.gri", "layer2_5.grd", "layer2_5.gri", "layer3_1.grd", "layer3_1.gri", "layer3_2.grd", "layer3_2.gri", "layer3_3.grd", "layer3_3.gri", "layer3_4.grd", "layer3_4.gri", "layer3_5.grd", "layer3_5.gri", "layer4_1.grd", "layer4_1.gri", "layer4_2.grd", "layer4_2.gri", "layer4_3.grd", "layer4_3.gri", "layer4_4.grd", "layer4_4.gri", "layer4_5.grd", "layer4_5.gri" I tried doing this in two steps: list.of.files <- list.files(pattern = c("1_")) list.of.files <- list.of.files[grep(".grd", list.of.files)] Can someone enlighten me how to do this with grep in one step? I naively tried passing list() and c() to the grep but, as you can imagine, it doesn't work. list.of.files <- list.files() list.of.files <- list.of.files[grep(list("1_", ".grd"), list.of.files)]

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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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