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  • Learning libraries without books or tutorials

    - by Kawili-wili
    While many ask questions about where to find good books or tutorials, I'd like to take the opposite tack. I consider myself to be an entry-level programmer ready to move up to mid-level. I have written code in c, c++, c#, perl, python, clojure, vb, and java, so I'm not completely clueless. Where I see a problem in moving to the next level is learning to make better use of the literally hundreds upon hundreds of libraries available out there. I seem paralyzed unless there is a specific example in a book or tutorial to hand-hold me, yet I often read in various forums where another programmer attempts to assist with a question. He/she will look through the docs or scan the available classes/methods in their favorite IDE and seem to grok what's going on in a relatively short period of time, even if they had no previous experience with that specific library or function. I yearn to break the umbilical chord of constantly spending hour upon hour searching and reading, searching and reading, searching and reading. Many times there is no book or tutorial, or if there is, the discussion glosses over my specific needs or the examples shown are too far off the path for the usage I had in mind or the information is outdated and makes use of deprecated components or the library itself has fallen out of mainstream, yet is still perfectly usable (but no docs, books, or tutorials to hand-hold). My question is: In the absence of books or tutorials, what is the best way to grok new or unfamiliar libraries? I yearn to slicken the grok path so I can get down to the business of doing what I love most -- coding.

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  • Schema for element with Attributes and Child nodes

    - by Matthew
    I am trying to write xsd type schema for an element that has a custom type to include addition attributes to extend a base type. I am running into trouble getting the syntax right. <xs:element name="graphs"> <xs:complexType> <xs:sequence> <xs:element name="graph" minOccurs="1" maxOccurs="unbounded" type="graphType"> <!-- child elements --> </xs:element> </xs:sequence> </xs:complexType> </xs:element> <xs:complexType name="graphType"> <xs:simpleContent> <xs:extension base="xs:string"> <xs:attribute name="title" type="xs:string"/> <xs:attribute name="type" type="xs:string"/> </xs:extension> </xs:simpleContent> </xs:complexType> I thought this would be something very common, but having read many tuts and forums, I cant seem to find an answer that works for me.

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  • Pro ASP.Net MVC 3 Entity Framework Sports Store tutorial

    - by gary7
    Following the tutorial in the book "Pro ASP.Net MVC 3 Entity Framework" in Chapter 9 - Image Uploads section; asks that the Product class be updated with two new columns - public byte ImageData, and public string ImageType. It also directs that the database be updated with these two columns via the server explorer. After these updates, the discussion directs that the Entity Framework Conceptual Model be updated via the SportsStore.EDMX file. This file does not exist in the source code for the project, and was not used in the project to begin with. Obvious errata for the book. Adding the ADO.NET Entity Data Model to the Project then overrides the EFProduct reposistory (conceptual model used throughout the project) which inherits from the interface IProductsRepository; and results in errors within the mapping. If the project is debugged after the columns are added, an error is thrown related to the new added columns. Has anyone resolved this issue in the project? I haven't found any solutions so far. Thanks!

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  • Element Content Versus Attribute for Simple XML Value

    - by MB
    I know the elements versus attributes debate has come up many times here and elsewhere (e.g. here, here, here, here, and here) but I haven't seen much discussion of elements versus attributes for simple property values. So which of the following approaches do you think is better for storing a simple value? A: Value in Element Content: <TotalCount>553</TotalCount> <CelsiusTemperature>23.5</CelsiusTemperature> <SingleDayPeriod>2010-05-29</SingleDayPeriod> <ZipCodeLocation>12203</ZipCodeLocation> or B: Value in Attribute: <TotalCount value="553"/> <CelsiusTemperature value="23.5"/> <SingleDayPeriod day="2010-05-29"/> <ZipCodeLocation code="12203"/> I suspect that putting the value in the element content (A) might look a little more familiar to most folks (though I'm not sure about that). Putting the value in an attribute (B) might use less characters, but that depends on the length of the element and attribute names. Putting the value in an attribute (B) might be more extensible, because you could potentially include all sorts of extra information as nested elements. Whereas, by putting the value inside the element content (A), you're restricting extensibility to adding more attributes. But then extensibility often isn't a concern for really simple properties - sometimes you know that you'll never need to add additional data. Bottom line might be that it simply doesn't matter, but it would still be great to hear some thoughts and see some votes for the two options.

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  • Ruby: how does constant-lookup work in instance_eval/class_eval?

    - by Alan O'Donnell
    I'm working my way through Pickaxe 1.9, and I'm a bit confused by constant-lookup in instance/class_eval blocks. I'm using 1.9.2. It seems that Ruby handles constant-lookup in *_eval blocks the same way it does method-lookup: look for a definition in receiver.singleton_class (plus mixins); then in receiver.singleton_class.superclass (plus mixins); then continue up the eigenchain until you get to #<Class:BasicObject>; whose superclass is Class; and then up the rest of the ancestor chain (including Object, which stores all the constants you define at the top-level), checking for mixins along the way Is this correct? The Pickaxe discussion is a bit terse. Some examples: class Foo CONST = 'Foo::CONST' class << self CONST = 'EigenFoo::CONST' end end Foo.instance_eval { CONST } # => 'EigenFoo::CONST' Foo.class_eval { CONST } # => 'EigenFoo::CONST', not 'Foo::CONST'! Foo.new.instance_eval { CONST } # => 'Foo::CONST' In the class_eval example, Foo-the-class isn't a stop along Foo-the-object's ancestor chain! And an example with mixins: module M CONST = "M::CONST" end module N CONST = "N::CONST" end class A include M extend N end A.instance_eval { CONST } # => "N::CONST", because N is mixed into A's eigenclass A.class_eval { CONST } # => "N::CONST", ditto A.new.instance_eval { CONST } # => "M::CONST", because A.new.class, A, mixes in M

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  • Why is BorderLayout calling setSize() and setBounds()?

    - by ags
    I'm trying to get my head around proper use of the different LayoutManagers to make my GUI design skills more efficient and effective. For me, that usually requires a detailed understanding of what is going on under the hood. I've found some good discussion of the interaction and consequences of a Container using BorderLayout containing a Container using FlowLayout. I understand it for the most part, but wanted to confirm my mental model and to do so I am looking at the code for BorderLayout. In the code snippet below taken from BorderLayout.layoutContainer(), note the calls to the child Component's setSize() method followed by setBounds(). Looking at the source for these methods of Component, setSize() actually calls setBounds() with the current values for Component.x and Component.y. Why is this done (and not entirely redudant?) Doesn't the setBounds() call completely overwrite the results of the setSize() call? if ((c=getChild(NORTH,ltr)) != null) { c.setSize(right - left, c.height); Dimension d = c.getPreferredSize(); c.setBounds(left, top, right - left, d.height); top += d.height + vgap; } I'm also tring to understand where/when the child Component's size is initially set (before the LayoutManager.layoutContainer() method is called). Finally, this post itself raises a "meta-question": in a situation like this, where the source is available elsewhere, is the accepteed protocol to include the entire method? Or some other way to make it easier for folks to participate in the thread? Thanks.

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  • Why doesn't java.lang.Number implement Comparable?

    - by Julien Chastang
    Does anyone know why java.lang.Number does not implement Comparable? This means that you cannot sort Numbers with Collections.sort which seems to me a little strange. Post discussion update: Thanks for all the helpful responses. I ended up doing some more research about this topic. The simplest explanation for why java.lang.Number does not implement Comparable is rooted in mutability concerns. For a bit of review, java.lang.Number is the abstract super-type of AtomicInteger, AtomicLong, BigDecimal, BigInteger, Byte, Double, Float, Integer, Long and Short. On that list, AtomicInteger and AtomicLong to do not implement Comparable. Digging around, I discovered that it is not a good practice to implement Comparable on mutable types because the objects can change during or after comparison rendering the result of the comparison useless. Both AtomicLong and AtomicInteger are mutable. The API designers had the forethought to not have Number implement Comparable because it would have constrained implementation of future subtypes. Indeed, AtomicLong and AtomicInteger were added in Java 1.5 long after java.lang.Number was initially implemented. Apart from mutability, there are probably other considerations here too. A compareTo implementation in Number would have to promote all numeric values to BigDecimal because it is capable of accommodating all the Number sub-types. The implication of that promotion in terms of mathematics and performance is a bit unclear to me, but my intuition finds that solution kludgy.

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  • Adobe Air update error "file version doesn't match" but it's the same!...

    - by baroquedub
    I'm using Claus Wahlers' AIR Remote Updater class (codeazur.com.br/lab/airremoteupdater/). All works fine and an update is triggered if the remote version is newer. The newer file is downloaded and the update starts. However I then get "an error has occured" message: "This application cannot be installed because this installer has been mis-configured" (The same file will update without errors when run manually "Would you like to replace the currently installed version?" Choosing 'replace' works fine) I have enabled Air Application Installer logging and I can see that both the app id and the pub id match - this seems to be a common reason for this problem (forums.adobe.com/thread/243421?tstart=60) The error given in the log file is as follows: AIR file version doesn't match Requested version: ; AIR file version: 1.0.2 But if I unzip the new app file and look at META-INF\AIR\application.xml the version designator shows <version>1.0.2</version> As requested! The log file is also showing me where the newer file is being downloaded and unpacked. If I look at the application.xml file in that directory: Unpackaging to C:\Documents and Settings\myusername\Local Settings\Temp\fla893D.tmp the version designator also shows <version>1.0.2</version> I don't get it?! The log tells me that the requested file version doesn't match but it's exactly the same as what's shown in the version designator of the downloaded update package... This is driving me crazy. Can anyone help?

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  • How To Deal With Exceptions In Large Code Bases

    - by peter
    Hi All, I have a large C# code base. It seems quite buggy at times, and I was wondering if there is a quick way to improve finding and diagnosing issues that are occuring on client PCs. The most pressing issue is that exceptions occur in the software, are caught, and even reported through to me. The problem is that by the time they are caught the original cause of the exception is lost. I.e. If an exception was caught in a specific method, but that method calls 20 other methods, and those methods each call 20 other methods. You get the picture, a null reference exception is impossible to figure out, especially if it occured on a client machine. I have currently found some places where I think errors are more likely to occur and wrapped these directly in their own try catch blocks. Is that the only solution? I could be here a long time. I don't care that the exception will bring down the current process (it is just a thread anyway - not the main application), but I care that the exceptions come back and don't help with troubleshooting. Any ideas? I am well aware that I am probably asking a question which sounds silly, and may not have a straightforward answer. All the same some discussion would be good.

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  • PayPal sandbox anomalies

    - by Christian
    When testing some donations on my local machine, I set various key=value pairs to do various things (return to specific thank you page, get POST data from PayPal and not GET data and others) I also built my code around the response from the PayPal sandbox. BUT, when my code goes to the production server and we switch on live payments and test with real accounts and money, a few strange things happen; We get a GET response from PayPal - the URL is filled with crap. We get no transaction details. This is the biggie, no name, no txn_id, no dates, nothing. We get a handful of keys etc, its not totally empty and the payment has gone through, but nowhere near the verbosity of the sandbox. Curious about why this might be? It doesn't really make sense to have a sandbox (or dev environment) that is substantially different from the production environment. Or, am I missing something? EDIT: Still no response to my question in the PayPal Developer Forums. I don't even get a donation amount back from PayPal. Is this a setting maybe? EDIT #2: Two of you have suggested to check PDT and Auto-Return. The data analytics guy for the project only 2 hrs ago suggested the same. I have asked the client to confirm this. I can't see a setting for it in the Sandbox so can assume that it is enabled by default?

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  • ps: Clean way to only get parent processes?

    - by shkschneider
    I use ps ef and ps rf a lot. Here is a sample output for ps rf: PID TTY STAT TIME COMMAND 3476 pts/0 S 0:00 su ... 3477 pts/0 S 0:02 \_ bash 8062 pts/0 T 1:16 \_ emacs -nw ... 15733 pts/0 R+ 0:00 \_ ps xf 15237 ? S 0:00 uwsgi ... 15293 ? S 0:00 \_ uwsgi ... 15294 ? S 0:00 \_ uwsgi ... And today I needed to retrieve only the master process of uwsgi in a script (so I want only 15237 but not 15293 nor 15294). As of today, I tried some ps rf | grep -v ' \\_ '... but I would like a cleaner way. I also came accross another solution from unix.com's forums: ps xf | sed '1d' | while read pid tty stat time command ; do [ -n "$(echo $command | egrep '^uwsgi')" ] && echo $pid ; done But still a lot of pipes and ugly tricks. Is there really no ps option or cleaner tricks (maybe using awk) to accomplish that?

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  • How do I handle the messages for a simple web-based live chat, on the server side?

    - by Carson Myers
    I'm building a simple live chat into a web application running on Django, but one thing I'm confused about is how I should store the messages between users. The chat will support multiple users, and a chat "session" is composed of users connected to one user that is the "host." The application is a sort of online document collaboration thing, so user X has a document, and users Y and Z would connect to user X to talk about the document, and that would be one chat session. If user Y disconnected for five minutes, and then signed back in and reconnected to user X, he should not get any of the messages shared between users X and Z while he was away. if users X, Y, and Z can have a chat session about user X's document, then users X and Y can connect to a simultaneous, but separate discussion about user Z's document. How should I handle this? Should I keep each message in the database? Each message would have an owner user and a target user (the host), and a separate table would be used to connect users with messages (which messages are visible to what users). Or should I store each session as an HTML file on the server, which messages get appended to? The problem is, I can't just send messages directly between clients. They have to be sent to the server in a POST request, and then each client has to periodically check for the messages in a GET request. Except I can't just have each message cleared after a client fetches it, because there could be multiple clients. How should I set this up? Any suggestions?

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  • Is there a best practice for concatenating MP3 Files, adjusting sample rates to match, while preserving original files?

    - by Scott
    Hello overflow community! Does anyone know if there is a "best practice" to concatenate mp3 files to create new files, while preserving the original files? I am working on a CentOS Linux machine, in command line. I will eventually call the command line from a PHP script. I have been doing research and I have come up with a process that I think could work. It combines general advice from different forums, blogs, and sources like this one. So here I go: Create a temporary folder Loop through files to create a new, converted copy, of file into a "raw" format (which one, I don't know. I didn't know "raw" files existed before too long ago. I could use some suggestions on this) Store the path to the temporary files, in the temporary folder, and then loop through the files to concatenate them and then put the new merged file the final "processed directory" Delete the contents of the temporary file with the temporary raw files inside. Convert the final file from "raw" to mp3 and enjoy the finished result I'm thinking that this course of action might be best because I can't necessarily control the quality of the original "source" mp3s. The only other option I could think of would be to create a script that would perform a similar process upon files being added to the system leaving only the files with the "proper" format and removing the original "erroneous" file. Hopefully you can see that I have put some thought into this and that I'm trying to leverage the collective knowledge of this community to choose the best direction. Perhaps there is a better path that I could take? By concatenate, I mean to join together in sequence to create a new audio file from the "concatenated files."

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  • Moving Multiple Divs With Same Class Inside Parent

    - by superzilla
    So, My website is hosted on enjin.com and when you give users a tag with an image it appears on the forums under their name, however it's a vertical list with the tag names. I want to organize it so all of the tag images appear on one line and all of the tag names appear on a horizontal list below it. They use div tags somewhat like this <div class="tag"> <div class="tag-image"></div> <!-- If the tag lacks an image this is excluded --> <div class="tag-text">Tag Name</div> <!-- If you want the name to be hidden this is excluded --> </div> They then pretty much repeat this for every tag. Somewhat the same thing is used for forum posts too. So, I want to move all the tag-image divs together on a single line and all of the tag-text divs down and give each it's own line. I only want to move them within their parent element (to avoid images/tags from one forum user from going to another). I know how to append things with jquery and have googled how to move elements around, but I'm afraid that they're all going to end up together under another user's avatar.

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  • Gathering entropy in web apps to create (more) secure random numbers

    - by H M
    after several days of research and discussion i came up with this method to gather entropy from visitors (u can see the history of my research here) when a user visits i run this code: $entropy=sha1(microtime().$pepper.$_SERVER['REMOTE_ADDR'].$_SERVER['REMOTE_PORT']. $_SERVER['HTTP_USER_AGENT'].serialize($_POST).serialize($_GET).serialize($_COOKIE)); note: pepper is a per site/setup random string set by hand. then i execute the following (My)SQL query: $query="update `crypto` set `value`=sha1(concat(`value`, '$entropy')) where name='entropy'"; that means we combine the entropy of the visitor's request with the others' gathered already. that's all. then when we want to generate random numbers we combine the gathered entropy with the output: $query="select `value` from `crypto` where `name`='entropy'"; //... extract(unpack('Nrandom', pack('H*', sha1(mt_rand(0, 0x7FFFFFFF).$entropy.microtime())))); note: the last line is a part of a modified version of the crypt_rand function of the phpseclib. please tell me your opinion about the scheme and other ideas/info regarding entropy gathering/random number generation. ps: i know about randomness sources like /dev/urandom. this system is just an auxiliary system or (when we don't have (access to) these sources) a fallback scheme.

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  • HELP ME !! I am Not able to update form data to mysql using php and jquery

    - by Jimson Jose
    i tired and was unable to find the answer i am looking for an answer. my problem is that i am unable to update the values enterd in the form. I have attached all the files i'm using MYSQL database to fetch data. what happens is that i'm able to add and delete records from form using jquery and PHP scripts to MYSQL database, but i am not able to update data which was retrived from database. the file structure is as follows index.php is a file with jquery functions where it displays form for adding new data to MYSQL using save.php file and list of all records are view without refrishing page (calling load-list.php to view all records from index.php works fine, and save.php to save data from form) - Delete is an function called from index.php to delete record from mysql database (function calling delete.php works fine) - Update is an function called from index.php to update data using update-form.php by retriving specific record from mysql tabel, (works fine) Problem lies in updating data from update-form.php to update.php (in which update query is wrriten for mysql) i had tried in many ways at last i had figured out that data is not being transfred from update-form.php to update.php there is a small problem in jquery ajax function where it is not transfering data to update.php page. some thing is missing in calling update.php page it is not entering into that page I am new bee in programming i had collected this script from many forums and made this one.So i was limited in solving this problem i cam to know that this is good platform for me and many where we get a help to create new things.. please guide me with your help to complete my effors !!!!! i will be greatfull to all including ths site which gave me an oppurtunity to present my self..... please find the link below to download all files which is of 35kb (virus free assurance) download mysmallform files in ZIPped format, including mysql query thanks a lot in advance, May GOD bless YOU and THIS SITE

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  • How can I invoke a .Net DLL from a LabView 6.1 VI?

    - by tw1k
    I work in a manufacturing company that uses LabView for testing the devices we make. Most of the test engineers are using 7.1 which can natively reference a .Net assembly. However, there is a group that is stuck on LabView 6.1. I would like for them to be able to use my .Net assembly which is basically a proxy to some web services. I have created a test assembly that is nothing more than Hello World, and I'm trying to consume it in a VI. I made it COM visible, and registered it with regasm.exe and created a type library, which I'm not sure I need. I can see it in Visual Studio in the list of COM objects when I open the Add Reference window, so I know it's registered properly. I'm very unfamiliar with VI's. I'm only looking at it because no one I have spoken to in manufacturing knows anything about invoking a COM object in a VI. I'm basically looking for some names of controls or menu options to get the test engineers pointed in the right direction. I did a bunch of web searching on Google and the NI forums, but didn't find much. Alternatively, would it be easier to write a C or C++ DLL that acts as a proxy to my .Net DLL? Or is there a simple way to invoke a web service from a VI? That might obviate the need for a DLL altogether. I'm currently reading through this document from NI for help, but it obviously knows nothing about .Net and might not be able to help me choose the best path forward.

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  • difference between http.context.user and thread.currentprincipal and when to use them?

    - by yamspog
    I have just recently run into an issue running an asp.net web app under visual studio 2008. I get the error 'type is not resolved for member...customUserPrincipal'. Tracking down various discussion groups it seems that there is an issue with Visual Studio's web server when you assign a custom principal against the Thread.CurrentPrincipal. In my code, I now use... HttpContext.Current.User = myCustomPrincipal //Thread.CurrentPrincipal = myCustomPrincipal I'm glad that I got the error out of the way, but it begs the question "What is the difference between these two methods of setting a principal?". There are other stackoverflow questions related to the differences but they don't get into the details of the two approaches. I did find one tantalizing post that had the following grandiose comment but no explanation to back up his assertions... Use HttpConext.Current.User for all web (ASPX/ASMX) applications. Use Thread.CurrentPrincipal for all other applications like winForms, console and windows service applications. Can any of you security/dot.net gurus shed some light on this subject?

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  • Good Replacement for User Control?

    - by David Lively
    I found user controls to be incredibly useful when working with ASP.NET webforms. By encapsulating the code required for displaying a control with the markup, creation of reusable components was very straightforward and very, very useful. While MVC provides convenient separation of concerns, this seems to break encapsulation (ie, you can add a control without adding or using its supporting code, leading to runtime errors). Having to modify a controller every time I add a control to a view seems to me to integrate concerns, not separate them. I'd rather break the purist MVC ideology than give up the benefits of reusable, packaged controls. I need to be able to include components similar to webforms user controls throughout a site, but not for the entire site, and not at a level that belongs in a master page. These components should have their own code not just markup (to interact with the business layer), and it would be great if the page controller didn't need to know about the control. Since MVC user controls don't have codebehind, I can't see a good way to do this. I've searched previous SO questions, and have yet to find a good answer. Options so far In an attempt to avoid turning the comments section into a discussion... RenderAction This allows the view to call another controller, which will be responsible for interacting with the BLL and whatever data is necessary to its corresponding view. The calling view needs to be aware of the sub controller. This seems to provide a nice way to encapsulate partial views and controls, without having to modify the calling controller. RenderPartial The calling controller is still responsible for executing whatever code is associated with the partial view, and making sure that the model passed to the partial view contains the data it expects. Effectively, modifying the partial view potentially means modifying the calling controller. Annoying especially if this is used in multiple places. Portable Areas Place each control in its own project/area?

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  • How to implement a single instance app manager in java (CVM PhoneME)?

    - by Marcus
    Hi, I'm working on a application manager for embeded platform based on the CVM PhoneME VM. The VM is started by a C++ app which configures the CVM and then triggers the VM itself. This C++ app is called form the command line passing the main class name and the classpath of a java application. There is a main java app (lets call it Manager) which loads the app using classloaders. I want this manager to be a single instance application so it could track all running apps. In other words: The first time I start an app (app1 for instance), the VM will launch and the Manager will load the app1. In further calls to load other apps (app2, app3 and so on), the same instance of the Manager would load those apps. The manager is working fine, except for the fact that this is not a single instance. Is it possible to do what I want? I found this: http://www.knowledgesutra.com/forums/topic/59760-how-to-implement-single-instance-application-on-java/ This is almost the same I want, except for the app loading part. However, the necessary packages are not available in the CVM implementation. Thanks very much.

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  • Hibernate Envers : How to delete entries from my audit table?

    - by Laurent T
    Hi everyone, I am currently working with Hibernate Envers. My problem is the following : How to delete entries in the audit table related to the entity I want to delete? My entity has no relation with other entities. I figured out that I have to do that in onPostDelete method of my custom listener : import org.hibernate.envers.event.AuditEventListener; import org.hibernate.event.PostCollectionRecreateEvent; import org.hibernate.event.PostDeleteEvent; import org.hibernate.event.PostInsertEvent; import org.hibernate.event.PostUpdateEvent; import org.hibernate.event.PreCollectionRemoveEvent; import org.hibernate.event.PreCollectionUpdateEvent; public class MyListener extends AuditEventListener { ... @Override public void onPostDelete(PostDeleteEvent arg0) { // TODO Auto-generated method stub super.onPostDelete(arg0); } ... } I've read the documentation, forums, many things but I can't figure it out. May be it's not possible, I don't know. Has someone ever done this before? Thank you :)

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  • Appropriate uses of Monad `fail` vs. MonadPlus `mzero`

    - by jberryman
    This is a question that has come up several times for me in the design code, especially libraries. There seems to be some interest in it so I thought it might make a good community wiki. The fail method in Monad is considered by some to be a wart; a somewhat arbitrary addition to the class that does not come from the original category theory. But of course in the current state of things, many Monad types have logical and useful fail instances. The MonadPlus class is a sub-class of Monad that provides an mzero method which logically encapsulates the idea of failure in a monad. So a library designer who wants to write some monadic code that does some sort of failure handling can choose to make his code use the fail method in Monad or restrict his code to the MonadPlus class, just so that he can feel good about using mzero, even though he doesn't care about the monoidal combining mplus operation at all. Some discussions on this subject are in this wiki page about proposals to reform the MonadPlus class. So I guess I have one specific question: What monad instances, if any, have a natural fail method, but cannot be instances of MonadPlus because they have no logical implementation for mplus? But I'm mostly interested in a discussion about this subject. Thanks! EDIT: One final thought occured to me. I recently learned (even though it's right there in the docs for fail) that monadic "do" notation is desugared in such a way that pattern match failures, as in (x:xs) <- return [] call the monad's fail. It seems like the language designers must have been strongly influenced by the prospect of some automatic failure handling built in to haskell's syntax in their inclusion of fail in Monad.

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  • Converting image to Black & White image on iPhone SDK issues.

    - by KfirS
    Hello, I've used a familiar code to convert image to Black & White which I've founded on several forums. The code is: CGColorSpaceRef colorSapce = CGColorSpaceCreateDeviceGray(); CGContextRef context = CGBitmapContextCreate(nil, originalImage.size.width, originalImage.size.height, 8, originalImage.size.width, colorSapce, kCGImageAlphaNone); CGContextSetInterpolationQuality(context, kCGInterpolationHigh); CGContextSetShouldAntialias(context, NO); CGContextDrawImage(context, CGRectMake(0, 0, originalImage.size.width, originalImage.size.height), [originalImage CGImage]); CGImageRef bwImage = CGBitmapContextCreateImage(context); CGContextRelease(context); CGColorSpaceRelease(colorSapce); UIImage *resultImage = [UIImage imageWithCGImage:bwImage]; // This is result B/W image. CGImageRelease(bwImage); return resultImage; When I'm using this code with on Horizontal image it's work fine, but when I'm trying a to use this code on Vertical image, the result is disproportionate image and rotate 90 degree left. Can anyone know what could be the problem? Thanks, Kfir.

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  • How to design data storage for partitioned tagging system?

    - by Morgan Cheng
    How to design data storage for huge tagging system (like digg or delicious)? There is already discussion about it, but it is about centralized database. Since the data is supposed to grow, we'll need to partition the data into multiple shards soon or later. So, the question turns to be: How to design data storage for partitioned tagging system? The tagging system basically has 3 tables: Item (item_id, item_content) Tag (tag_id, tag_title) TagMapping(map_id, tag_id, item_id) That works fine for finding all items for given tag and finding all tags for given item, if the table is stored in one database instance. If we need to partition the data into multiple database instances, it is not that easy. For table Item, we can partition its content with its key item_id. For table Tag, we can partition its content with its key tag_id. For example, we want to partition table Tag into K databases. We can simply choose number (tag_id % K) database to store given tag. But, how to partition table TagMapping? The TagMapping table represents the many-to-many relationship. I can only image to have duplication. That is, same content of TagMappping has two copies. One is partitioned with tag_id and the other is partitioned with item_id. In scenario to find tags for given item, we use partition with tag_id. If scenario to find items for given tag, we use partition with item_id. As a result, there is data redundancy. And, the application level should keep the consistency of all tables. It looks hard. Is there any better solution to solve this many-to-many partition problem?

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  • iOS: display modal view over the top of a UIWebView

    - by Sly
    Is it possible to display a modal view over the top of a UIWebView? I have a UIViewController that loads a WebView. I then want to push a Modal View Controller over the top so that a modal view covers up the WebView temporarily... The WebView is working fine; here's how it's loaded in the View Controller: - (void)loadView { // Initialize webview and add as a subview to LandscapeController's view myWebView = [[[UIWebView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]] autorelease]; myWebView.scalesPageToFit = YES; myWebView.autoresizesSubviews = YES; myWebView.autoresizingMask = (UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight); myWebView.delegate = self; self.view = myWebView; } If I attempt to load a Modal View controller from within viewDidLoad, however, no modal view appears: - (void)viewDidLoad { [super viewDidLoad]; // Edit dcftable.html with updated figures NSMutableString *updated_html = [self _updateHTML:@"dcftable"]; // Load altered HTML file as an NSURL request [self.myWebView loadHTMLString:updated_html baseURL:nil]; // If user hasn't paid for dcftable, then invoke the covering modal view if (some_condition) { LandscapeCoverController *landscapeCoverController = [[[LandscapeCoverController alloc] init] autorelease ]; [self presentModalViewController:landscapeCoverController animated:YES]; } } I suspect that there's something that needs to be done with the UIWebView delegate to get it to receive the new modal view...but can't find any discussion or examples of this anywhere...again, the objective is to invoke a modal view that covers over the top of the WebView. Thanks for any thoughts in advance!

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