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• When designing an event, is it a good idea to prevent listeners from being added twice?

  - by Matt

  I am creating an event-based API where a user can subscribe to an event by adding listener objects (as is common in Java or C#). When the event is raised, all subscribed listeners are invoked with the event information. I initially decided to prevent adding an event listener more than once. If a listener is added that already exists in the listener collection, it is not added again. However, after thinking about it some more, it doesn't seem that most event-based structures actually prevent this. Was my initial instinct wrong? I'm not sure which way to go here. I guess I thought that preventing addition of an existing listener would help to avoid a common programming error. Then again, it could also hide a bug that would lead to code being run multiple times when it shouldn't.

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• Can jQuery perform a compound select against the top level only?

  - by harpo

  Basically, is there a way to write a.children('.outer').children('.inner') without the intermediate selector? I can't write $('.outer > .inner', a) because I don't want to do full-depth search against a — I know that the .outer elements are immediate children of a. It's partly a matter of "elegance", but partly because I'm trying to avoid "throwaway" element sets. Yes, jQuery may in effect do the same thing, but it has a better chance of optimizing (at least in theory), when it knows the full query's intent.

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• Return from parent sub in Perl

  - by JS Bangs

  I want to write a subroutine which causes the caller to return under certain conditions. This is meant to be used as a shortcut for validating input to a function. What I have so far is: sub needs($$) { my ($condition, $message) = @_; if (not $condition) { print "$message\n"; # would like to return from the *parent* here } return $condition; } sub run_find { my $arg = shift @_; needs $arg, "arg required" or return; needs exists $lang{$arg}, "No such language: $arg" or return; # etc. } The advantage of returning from the caller in needs would then be to avoid having to write the repetitive or return inside run_find and similar functions.

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• Selecting one object from a one-to-many relationship in Hibernate

  - by Nick Thomson

  I have two tables: Job job_id, <other data> Job_Link job_link_id, job_id, start_timestamp, end_timestamp, <other data> There may be multiple records in Job_Link specifying the same job_id with the start_timestamp and end_timestamps to indicate when those records are considered "current", it is guaranteed that start_timestamp and end_timestamp will not overlap. We have entities for both the Job and Job_Link tables and defining a one-to-many relationship to load all the job_links wouldn't be a problem. However we'd like to avoid that and have a single job_link item in the Job entity that will contain only the "current" Job_Link object. Is there any way to achive that?

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• Is it possible to use RedirectToAction() inside a custom AuthorizeAttribute class?

  - by Lance McNearney

  Using ASP.Net MVC 2, is there any way to use the RedirectToAction() method of the Controller class inside a class that is based on the AuthorizeAttribute class? public class CustomAttribute : AuthorizeAttribute { protected override bool AuthorizeCore(HttpContextBase context) { // Custom authentication goes here return false; } public override void OnAuthorization(AuthorizationContext context) { base.OnAuthorization(context); // This would be my ideal result context.Result = RedirectToAction("Action", "Controller"); } } I'm looking for a way to re-direct the user to a specific controller / action when they fail the authentication instead of returning them to the login page. Is it possible to have the re-direct URL generated for that controller / action and then use RedirectResult()? I'm trying to avoid the temptation to just hard-code the URL.

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• How to automatically check out a database file in a source controlled web application ?

  - by TheRHCP

  Hello, I am working on an ASP.NET web application, we are a small team (4 students) and we do not have access to a dedicated server to host the database instance. So for this web application we decided just to put the database file in the App_Data folder. The problem is that our project is source controled on TFS, so every time you open the solution and try to launch the web application, we get an expcetion saying that database is read-only. That is logical because the databse file is not automatically checked-out. Is there a workaround to avoid a manual check-out of the database file everytime we open the solution ? Thanks.

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• Jquery function calls more than one time.

  - by Harie

  I am having an aspx page in which I am calling a user control. The user control I am using a pop up to display it when a user clicks a asp:linkbutton. In that user control I am having a textbox and I am calling a Jquery Blur to do some validation. While doing so the function is calling [blur] is calling twice. I just called an alert() with the textbox value.So I can see the alert is coming twice .What I need to do to avoid the second time. I need to do it only whenever the user going out of the textbox and that also one time. $('#<%=txtCategory.ClientID %>').blur(function() { alert($(this).val()); }); This is called twice.Thanks for ur response.

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• Response.Redirect exception

  - by Tedd Hansen

  Executing the line: Response.Redirect("Whateva.aspx", true); Results in: A first chance exception of type 'System.Threading.ThreadAbortException' occurred in mscorlib.dll An exception of type 'System.Threading.ThreadAbortException' occurred in mscorlib.dll but was not handled in user code The exception is because of the "true" part, telling it to end the current request immediately. Is this how it should be? If we consider: Exceptions are generally considered heavy, and many times the reason for ending the request early is to avoid processing the rest of the page. Exceptions show up in performance monitoring, so monitoring the solution will show a false number of exceptions. Is there an alternative way to achieve the same?

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• What is the accepted way to replace java.util.Date(year,month,day)

  - by dagw

  I'm trying to do something really simple, but starting to realize that dates in Java are a bit of minefield. All I want is to get passed groups of three ints ( a year, a month and a date) create some Date objects, do some simple test on them (along the lines of as date A before date B and after January 1 1990), convert them to java.sql.Date objects and pass them off to the database via JDBC. All very simple and works fine using the java.util.Date(int year,int month,int day) constructor. Of course that constructor is depreciated, and I'd like to avoid using depreciated calls in new code I'm writing. However all the other options to solve this simple problem seem stupidly complicated. Is there really no simple way to do what I want without using depreciated constructors? I know the standard answer to all Java date related questions is "use joda time", but I really don't want to start pulling in third party libraries for such a seemingly trivial problem.

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• "Automatic" class proxy in C++

  - by PierreBdR

  I need to allow the user to change members of two data structures of the same type at the same time. For example: struct Foo { int a, b; } Foo a1 = {1,2}, a2 = {3,4}; dual(a1,a2)->a = 5; // Now a1 = {5,2} and a2 = {5,2} I have a class that works and that change first a1 and then copy a1 into a2. This is fine as long as: the class copied is small the user doesn't mind about everything being copied, not only the part modified. Is there a way to obtain this behavior: dual(a1,a2)->a = 5; // Now a1 = {5,2} and a2 = {5,4} I am opened to alternative syntax, but they should stay simple, and I would like to avoid things like: set_members(a1, a2, &Foo::a, 5); members(a1, a2, &Foo::a) = 5; or anything involving specifying explictely &Foo::

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• ASP.NET GridView - how to enable validation declaratively

  - by Joe

  It it possible to enable validation in an ASP.NET GridView purely declaratively? What I've tried: A GridView bound to an ObjectDataSource with SelectMethod and UpdateMethod defined The GridView contains some ReadOnly BoundField columns and a TemplateField whose EditTemplate contains a TextBox and a RegularExpressionValidator that only allows numeric input in the TextBox. The GridView also contains a CommandField with ShowEditButton=true and CausesValidation=true. If I click on Edit, enter an invalid value, then click on Save, there is a PostBack, and an exception is thrown in the server (Input string was not in a correct format). I can of course avoid this by adding validation code to the RowUpdating event handler on the server (see below), but is there any declarative way to force the validation to be done without adding this code? protected void MyGridView_RowUpdating(object sender, GridViewUpdateEventArgs e) { Page.Validate("MyValidationGroup"); if (!Page.IsValid) { e.Cancel = true; } }

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• Help Fix a bug - Unexpected T_STRING

  - by thecoshman

  So I have just rebuilt my server, just on local network. Stick my site back on it, try to run the code, and I get a anice T_STRING error. This is all very strange, as I have not changed the code :S <?php $window_ID = -1; if(isset($_POST["window_ID"]) AND $_POST["window_ID"] != null){ $window_ID = trim($_POST["window_ID"]); } ?> This is the start of the file, apter this rather loverly snipit of PHP the rest is just XMl, yet on line 6 appertnlty there is an unexpected T_STRING, which is strange considering all that is on that line is the ?>, then the XML starts up... Any one got any ideas what has gone wrong here? Any chance it ould be magic quotes? I had turned it of before, but I want to now update my code to check for the magic quotes and avoid its stupid actions.

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• How do I change the class of an object to a subclass of its current class in C++?

  - by Jared P

  I have an array of pointers to a base class, so that I can make those pointers point to (different) subclasses of the base class, but still interact with them. (really only a couple of methods which I made virtual and overloaded) I'm wondering if I can avoid using the pointers, and instead just make an array of the base class, but have some way to set the class to the subclass of my choosing. I know there must be something there specifying the class, as it needs to use that to look up the function pointer for virtual methods. By the way, the subclasses all have the same ivars and layout. Note: the design is actually based on using a template argument instead of a variable, due to performance increases, so really the abstract base class is just the interface for the subclasses, which are all the same except for their compiled code. Thanks

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• Jquery Accordion and multiple slideshows

  - by Dipesh Parmar

  I've been using a lot of slideshows recently on my sites and one thing thats puzzled me is using more than one slideshow per page. I'm currently working on my own site, experimenting with Jquery Accordion. I've managed to adopt a very simple javascript slideshow, see below: http://dvpwebdesign.com/test/accordion/blank.html However i'm unable to either incorporate or use a different multiple slideshow plugin. I dont need slideshow navigation, so the The Cycle plugin works really well and i know you can use multiple slideshows. But if i either use Cycle alongside the current javascript slideshow, or only use the Cycle slideshow to avoid any possible conflict, the Accordion menu stops working. I just cant see what i am doing wrong, can anyone help?

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• How do I determine the cause of Qt's "*** is not a valid Qt plugin" error?

  - by chadjoan

  When I print the value of errorString from my QPluginLoader object, I get this: The file 'C:/pyprojects/test/qsqlpsqld4.dll' is not a valid Qt plugin. I would like to avoid some days worth of doing the time consuming "guess-and-check" methodology that my current internet searches reveal (so far none of them seem relevant anyways). Is there a way for me to get the Qt library itself to tell me why it is refusing to load this plugin? I don't want to guess; I want to know. Context: I am on Windows 7 running Qt 4.8.5 (32-bit, MinGW) and the qsqlpsqld4.dll file is also 32-bit and compiled with MinGW. I am using PySide to interact with Qt.

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• Can using non primitive Integer/ Long datatypes too frequently in the application, hurt the performance??

  - by Marcos

  I am using Long/Integer data types very frequently in my application, to build Generic datatypes. I fear that using these wrapper objects instead of primitive data types may be harmful for performance since each time it needs to create objects which is an expensive operation. but also it seems that I have no other choice(when I have to use primtives with generics) rather than just using them. However, still it would be great if you can suggest if there is anything I could do to make it better. or any way if I could just avoid it ?? Also What may be the downsides of this ? Suggestions welcomed!

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• Post-back + Page Refresh. Post/Redirect/Get pattern alternatives?

  - by Andrew Florko

  When user posts back a web form and then tries to refresh the page - dialog "would you like to resend information" pops up (Opera works silently though). To avoid this we can redirect browser to the page we'd like to show after postback. Now, when user refreshes the page, he duplicates get-request and no pop-ups. Everything is ok but post/redirect/get approach requires additional roundtrip. Is there better alternatives. Send form data with ajax aynchronously, for example? Thank you in advance!

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• Set Hibernate session's flush mode in Spring

  - by glaz666

  I am writing integration tests and in one test method I'd like to write some data to DB and then read it. @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(locations = {"classpath:applicationContext.xml"}) @TransactionConfiguration() @Transactional public class SimpleIntegrationTest { @Resource private DummyDAO dummyDAO; /** * Tries to store {@link com.example.server.entity.DummyEntity}. */ @Test public void testPersistTestEntity() { int countBefore = dummyDAO.findAll().size(); DummyEntity dummyEntity = new DummyEntity(); dummyDAO.makePersistent(dummyEntity); //HERE SHOULD COME SESSION.FLUSH() int countAfter = dummyDAO.findAll().size(); assertEquals(countBefore + 1, countAfter); } } As you can see between storing and reading data, the session should be flushed because the default FushMode is AUTO thus no data can be actually stored in DB. Question: Can I some how set FlushMode to ALWAYS in session factory or somewhere else to avoid repeating session.flush() call? All DB calls in DAO goes with HibernateTemplate instance. Thanks in advance.

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• Are AJAX calls to a sub-domain considered Cross Site Scripting?

  - by AaronPresley

  I have Server A (www.example.com) sending information to Server B. I can only have HTML / JS on Server A (and have to do the "crunching" on Server B) so I'm trying to send form data via AJAX (trying to avoid a form post to Server B - don't ask). Obviously doing an AJAX call cross-domain is considered XSS and a big no-no, but if I were to put Server B in a subdomain (sub.example.com), would that be considered okay? How are cross-domain errors detected? Does the browser look up DNS records? IP address? Thanks in advance for you help.

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• How can I load an MP3 or similar music file for display and anaysis in wxWdigets?

  - by Jon Cage

  I'm developing a GUI in wxPython which allows a user to generate sequences of colours for some toys I'm building. Part of the program needs to load an MP3 (and potentially other formats further down the line) and display it to the user. That shuold be sufficient to get started but later I'd like to add features like identifying beats and some crude frequency analysis. Is there any simple way of loading / understanding an MP3's contents to display a plot of it's amplitudes to the screen using wxWidgets? I later intend to port to C++/wxWidgets for speed and to avoid having to distribute wxPython.

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• iOS Downloading Videos and saving in Application Support folder

  - by Satyam svv

  In my application, i've to download videos around 10 to my application and play accordingly. Each video is around 50 MB. I'm using following code and then after downloading the video, i'm saving it to Application support folder to avoid icloud sync. But the problem is that when downloading the videos its crashing. [NSURLConnection sendAsynchronousRequest:req queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *rcvdDat, NSError * err) { . . . } What I'm thinking is that, while downloading the video, it resides in memory and so the total memory occupying by the app is increasing. Finally iOS is making the app to close. I would like to download the video and when ever a stream of data received, write to temp file and when completes move it to application support folder. Can some one help me on how to write it to file and save it at the end? I cannot use 3rd party libraries (unless its small) due to legal issues.

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• NoneType has no attribute Append

  - by Rosarch

  I'm new to Python. I can't understand why a variable is None at a certain point in my code: class UsersInRoom(webapp.RequestHandler): def get(self): room_id = self.request.get("room_id") username = self.request.get("username") UserInRoom_entities = UserInRoom.gql("WHERE room = :1", room_id).get() if UserInRoom_entities: for user_in_room in UserInRoom_entities: if user_in_room.username == username: user_in_room.put() # last_poll auto updates to now whenenever user_in_room is saved else: user_in_room = UserInRoom() user_in_room.username = username user_in_room.put() UserInRoom_entities = [] UserInRoom_entities.append(user_in_room) // error here # name is `user_at_room` intead of `user_in_room` to avoid confusion usernames = [user_at_room.username for user_at_room in UserInRoom_entities] self.response.out.write(json.dumps(usernames)) The error is: Traceback (most recent call last): File "C:\Program Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py", line 507, in __call__ handler.get(*groups) File "path\to\chat.py", line 160, in get AttributeError: 'NoneType' object has no attribute 'append' How is this possible? I'm setting UserInRoom_entities = [] immediately before that call. Or is something else the None in question?

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• Status corresponding to Minimum value

  - by Lijo

  Hi Team, I am using SQL Server 2005. I have a table as given below. There can be multiple cancellations for each FundingID. I want to select the FundingCancellationReason corrersponding to minimum date for each funding. I wrote a query as follows. It is an SQL error 1) Could you please help me to avoid the SQL Error? 2) Is there any better logic to achieve the same? CREATE TABLE #FundingCancellation( [FundingCancellationID] INT IDENTITY(1,1) NOT NULL, [FundingID] INT , FundingCancellationDt SMALLDATETIME , FundingCancellationReason VARCHAR(50) ) SELECT FundingID, MIN(FundingCancellationDt), ( SELECT FundingCancellationReason FROM #FundingCancellation FC2 WHERE FC1.FundingID = FC2.FundingID AND FC2.FundingCancellationDt = MIN(FundingCancellationDt) ) [Reason Corresponding Minimum Date] FROM #FundingCancellation FC1 GROUP BY FundingID -- An aggregate may not appear in the WHERE clause unless it is in a subquery contained in a HAVING clause or a select list, and the column being aggregated is an outer reference. I have seen the similar approach working in a somewhat complex query. So I believe tehre will be a way to correct my query Thanks Lijo

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• How can I add floats together in different orders, and always get the same total?

  - by splicer

  Let's say I have three 32-bit floating point values, a, b, and c, such that (a + b) + c != a + (b + c). Is there summation algorithm, perhaps similar to Kahan summation, that guarantees that these values can be summed in any order and always arrive at the exact same (fairly accurate) total? I'm looking for the general case (i.e. not a solution that only deals with 3 numbers). Is arbitrary precision arithmetic the only way to go? I'm dealing with very large data sets, so I'd like to avoid the overhead of using arbitrary precision arithmetic if possible. Thanks!

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• How to synchronize two (or n) replication processes for MS SQL databases?

  - by Yauheni Sivukha

  There are two master databases and two read-only copies updated by standard transactional replication. It is needed to map some entity from both read-only databases, lets say that A databases contains orders and B databases contains lines. The problem is that replication to one database can lag behind replication of second database, and at the moment of mapping R-databases will have inconsistent data. For example. We stored 2 orders with lines at 19:00 and 19:03. Mapping process started at 19:05, but to the moment of mapping A database replication processed all changes up to 19:03, but B database replication processed only changes up to 19:00. After mapping we will have order entity with order as of 19:03 and lines as of 19:00. The troubles are guaranteed:) In my particular case both databases have temporal model, so it is possible to fetch data for every time slice, but the problem is to identify time of latest replication. Question: How to synchronize replication processes for several databases to avoid situation described above?

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