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• Glassfish 3: How do I get and use a developers build so I can navigate a stack trace including Glas

  - by Thorbjørn Ravn Andersen

  I am migrating a JSF 1.1 application to JEE 6 Web profile, and doing it in steps. I am in the process of moving from JSP with JSF 1.1 to Facelets under JSF 1.2 using the jsf-facelets.jar for JSF 1.2, and received an "interesting" stack trace when trying to lookup a key in a Map using a "{Bean.foo.map.key}" where the stacktrace complained about "key" not being a valid integer. (After code introspection I am workarounding it using a number as the key). That bug is not what this question is about. In such a situation it is essential to be able to navigate the source of every line in the stack trace. In Eclipse I normally attach a source jar to every jar on the build path, but in this particular case the Glassfish server adapter creates a library automatically containing the jars. Also there is to my knowledge no debug build of Glassfish where sources are included in the bundle. Glassfish is a non-trivial Maven project, and a bit picky too. I am not very familiar with maven, but have managed to checkout the code from Subversion and build it for the 3.0 tag according to http://wiki.glassfish.java.net/Wiki.jsp?page=V3FullBuildInstructions#section-V3FullBuildInstructions-CheckoutTheWorkspace - it appears to be the code corresponding to the official released 3.0 version. After finishing the "mvn -U install" part, I have then tried to create Eclipse projects by first using "mvn -DdownloadSources=true eclipse:eclipse" and then import them in Eclipse JEE 3.5.2 and specifying the M2_REPO variable but many of the projects still have compilation errors, and I cannot locate any instructions from Oracle about how to do this. I'd appreciate some help in just getting a functional IDE workspace reflecting the 3.0 version of Glassfish. I have Eclipse 3.5.2, Netbeans 6.8 and 6.9 beta, and IntelliJ IDEA 9, and Linux/Windows/OS X do do it on.

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• How can I abstract out the core functionality of several Rails applications?

  - by hornairs

  I'd like to develop a number of non-trivial Rails applications which all implement a core set of functionality but each have certain particular customizations, extensions, and aesthetic differences. How can I pull the core functionality (models, controllers, helpers, support classes, tests) common to all these systems out in such a way that updating the core will benefit every application based upon it? I've seen Rails Engines but they seem to be too detached, almost too abstracted to be built upon. I can seem them being useful for adding one component to an existing app, for example bolting on a blog engine to your existing e-commerce site. Since engines seem to be mostly self contained, it seems difficult and inconvenient to override their functionality and views while keeping DRY. I've also considered abstracting the code into a gem, but this seems a little odd. Do I make the gem depend on the Rails gems, and the define models & controllers inside it, and then subclass them in my various applications? Or do I define many modules inside the gem that I include in the different spots inside my various applications? How do I test the gem and then test the set of customizations and overridden functionality on top of it? I'm also concerned with how I'll develop the gem and the Rails apps in tandem, can I vendor a git repository of the gem into the app and push from that so I don't have to build a new gem every iteration? Also, are there private gem hosts/can I set my own gem source up? Also, any general suggestions for this kind of undertaking? Abstraction paradigms to adhere to? Required reading? Comments from the wise who have done this before? Thanks!

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• Simple matrix example using C++ template class

  - by skyeagle

  I am trying to write a trivial Matrix class, using C++ templates in an attempt to brush up my C++, and also to explain something to a fellow coder. This is what I have som far: template class<T> class Matrix { public: Matrix(const unsigned int rows, const unsigned int cols); Matrix(const Matrix& m); Matrix& operator=(const Matrix& m); ~Matrix(); unsigned int getNumRows() const; unsigned int getNumCols() const; template <class T> T getCellValue(unsigned int row, unsigned col) const; template <class T> void setCellValue(unsigned int row, unsigned col, T value) const; private: // Note: intentionally NOT using smart pointers here ... T * m_values; }; template<class T> inline T Matrix::getCellValue(unsigned int row, unsigned col) const { } template<class T> inline void Matrix::setCellValue(unsigned int row, unsigned col, T value) { } I'm stuck on the ctor, since I need to allocate a new[] T, it seems like it needs to be a template method - however, I'm not sure I have come accross a templated ctor before. How can I implemnt the ctor?

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• When is Googling it wrong?

  - by Drahcir

  I've been going through Stack Overflow for quite a bit now and noticed certain people (usually experienced programmers) frown upon Googling (researching) certain problems. Since I myself tend to use Google quite a bit to solve certain programming related issues I found certain comments rather demoralising. Now some of you may have come here trigger happy to delete this post but I needed some clarification. I usually Google things that usually syntax related that I would have never figured out on my own. For example I once wondered how to access the properties of a class that I didn't have a direct relationship to. So after a bit of research I discovered reflection and got what I wanted. Now in another scenario is learning a new language, in my case Silverlight were it differs in certain aspects of .NET compared to say ASP.NET. A few weeks ago I had no idea how to load another Silverlight page (usercontrol) and had to Google my way to the solution which I found wasn't as simple as I had imagined. In scenario three is were I myself frown up, that is just stealing a huge chunk of code to avoid doing the work yourself, for example paging a HTML table using JavaScript, where one just copies and pastes the JavasSript code without as much as trying to understand how it works. I do admit I have done this once or twice before for trivial tasks that had very little time limit and weren't all that important but most of the time still have to throw away what I found because it took too much time to adapt it and get what I wanted out of it. In the last scenario, I sometimes have a piece of code that I would be really unhappy about, as in I find it sloppy or too overcomplicated and try to look on the Internet to see other ways to tackle the same problem, let's say filtering through a table. With the knowledge I acquire I learned new coding practices that help me work more efficiently like "Do not repeat yourself" and such. Now in your opinion when do you find it wrong to use Google (or any other researching tool) to find a solution to your problem?

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• AWK: compare apache dates without using regular expression

  - by smallmeans

  I'm writing a loganalysis application and wanted to grab apache log records between two certain dates. Assume that a date is formated as such: 22/Dec/2009:00:19 (day/month/year:hour:minute) Currently, I'm using a regular expression to replace the month name with its numeric value, remove the separators, so the above date is converted to: 221220090019 making a date comparison trivial.. but.. Running a regex on each record for large files, say, one containing a quarter million records, is extremely costly.. is there any other method not involving regex substitution? Thanks in advance Edit: here's the function doing the convertion/comparison function dateInRange(t, from, to) { sub(/[[]/, "", t); split(t, a, "[/:]"); match("JanFebMarAprMayJunJulAugSepOctNovDec", a[2]); a[2] = sprintf("%02d", (RSTART + 2) / 3); s = a[3] a[2] a[1] a[4] a[5]; return s >= from && s <= to; } "from" and "to" are the intervals in the aforementioned format, and "t" is the raw apache log date/time field (e.g [22/Dec/2009:00:19:36)

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• Apache mod_rewrite - forward domain root to subdirectory

  - by DuFace

  I have what I originally assumed to be a simple problem. I am using shared hosting for my website (so I don't have access to the Apache configuration) and have only been given a single folder to store all my content in. This is all well and good but it means that all my subdomains must have their virtual document root's inside public_html, meaning they effectively become a folder on my main domain. What I'd like to do is organise my public_html something like this: public_html/ www/ index.php ... sub1/ index.php ... some_library/ ... This way, all my web content is still in public_html but only a small fraction of it will be served to the client. I can easily achieve this for all the subdomains, but it's the primary domain that I'm having issues with. I created a .htaccess file in public_html with the following: Options +SymLinksIfOwnerMatch # I'm not allowed to use FollowSymLinks RewriteEngine on RewriteBase / RewriteCond %{REQUEST_URI} !^/www [NC] RewriteRule ^(.*)$ /www/$1 [L] This works fairly well, but for some strange reason www.example.com/stuff is translated into a request for www.example.com/www/stuff and hence a 404 error is given. It was my understanding that unless an 'R' flag was specified, mod_rewrite was purely internal so I can't understand why the request is generated as that implies (to me at least) redirection. I assumed this would be a trivial problem to solve as all I actually want to do is forward all requests for the root of www.example.com to a subdirectory, but I've spent hours searching for answers and none are quite correct. I find it difficult to believe I'm the only person to have this issue. I apologise if this question has been answered on here before, I did search and trawl but couldn't find an appropriate answer. Please could someone shed some light on this?

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• Very simple python functions takes spends long time in function and not subfunctions

  - by John Salvatier

  I have spent many hours trying to figure what is going on here. The function 'grad_logp' in the code below is called many times in my program, and cProfile and runsnakerun the visualize the results reveals that the function grad_logp spends about .00004s 'locally' every call not in any functions it calls and the function 'n' spends about .00006s locally every call. Together these two times make up about 30% of program time that I care about. It doesn't seem like this is function overhead as other python functions spend far less time 'locally' and merging 'grad_logp' and 'n' does not make my program faster, but the operations that these two functions do seem rather trivial. Does anyone have any suggestions on what might be happening? Have I done something obviously inefficient? Am I misunderstanding how cProfile works? def grad_logp(self, variable, calculation_set ): p = params(self.p,self.parents) return self.n(variable, self.p) def n (self, variable, p ): gradient = self.gg(variable, p) return np.reshape(gradient, np.shape(variable.value)) def gg(self, variable, p): if variable is self: gradient = self._grad_logps['x']( x = self.value, **p) else: gradient = __builtin__.sum([self._pgradient(variable, parameter, value, p) for parameter, value in self.parents.iteritems()]) return gradient

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• Ensuring quality of your software and code

  - by Filip Ekberg

  When I usually write code I follow some guidelines to ensure that my code has a certain standard and I as any other developer try to ensure that my code and software is of quality. Try to focus on the programming and not the understanding of the domain or any other pre-programming steps. These are the following steps I live by: Writing unit tests Make it fail ( no code ) Make it Work ( working code ) Analysing abstraction Extracting methods Exteract interfaces Refactoring In addition to the above which is a part of refactoring, I also try to refactor the code with good tools such as ReSharper, CodeRush or others. The question; What is the next step? Commenting the code is trivial and shouldn't even have to be mentioned, but updated comments and xml-comments where it's needed / everywhere is something that I try to have. But all the above helps he ensure that other developers might understand my code, that the code has some sort of quality and follows naming standards. It does however not ensure any product quality. I am looking for tools for post-development quality ensurance, such as profilers and how one would use these tools to increase product quality.

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• Saving a single entity instead of the entire context - revisited

  - by nite

  I’m looking for a way to have fine grained control over what is saved using Entity Framework, rather than the whole ObjectContext.SaveChanges(). My scenario is pretty straight forward, and I’m quite amazed not catered for in EF – pretty basic in NHibernate and all other data access paradigms I’ve seen. I’m generating a bunch of data (in a WPF UI) and allowing the user to fine tune what is proposed and choose what is actually committed to the database. For the proposed entities I’m: getting a bunch of reference entities (eg languages) via my objectcontext, creating the proposed entities and assigning these reference entities to them (as navigation properties), so by virtue of their relationship to the reference entities they’re implicitly added to the objectconext Trying to create & save individual entites based on the proposed entities. I figure this should be really simple & trivial but everything I’ve tried I’ve hit a brick wall, either I set up another objectcontext & add just the entity I need (it then tries to add the whole graph and fails as it’s on another objectcontext). I’ve tried MergeOptions = NoTracking on my reference entities to try to get the Attach/AddObject not to navigate through these to create a graph, no avail. I've removed the navigation properties from the reference entities. I've tried AcceptAllChanges, that works but pretty useless in practice as I do still want to track & save other entities. In a simple test, I can create 2 of my proposed entities, AddObject the one I want to save and then Detach the one I dont then call SaveChanges, this works but again not great in practice. Following are a few links to some of the nifty ideas which in the end don’t help in the end but illustrate the complexity of EF for something so simple. I’m really looking for a SaveSingle/SaveAtomic method, and think it’s a pretty reasonable & basic ask for any DAL, letalone a cutting edge ORM. http://stackoverflow.com/questions/1301460/saving-a-single-entity-instead-of-the-entire-context www.codeproject.com/KB/architecture/attachobjectgraph.aspx?fid=1534536&df=90&mpp=25&noise=3&sort=Position&view=Quick&select=3071122&fr=1 bernhardelbl.spaces.live.com/blog/cns!DB54AE2C5D84DB78!238.entry

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• As an Agile Java developer, what should I be looking for when hiring a C++ developer?

  - by agoudzwaard

  I come from an effective team of Agile Java developers. We've had a lot of success in hiring more people like ourselves - people passionate about technology with experience primarily in the Agile Java/J2EE space. We're looking to hire our first C++ developer to serve as an on-shore resource for maintaining and adding to the C++ portion of our code base. Up until now the entirety of our C++ development has been done out of an off-shore location. We consider our interview process to be fairly thorough: A phone screen centered on Object-Oriented Programming and Java A non-trivial at-home code project using Java An in-person interview covering technical and behavioral competency We look for a demonstration of Agile best practices (expressive code, test-driven development, continuous integration) throughout the entire process, however there is a common conception that Agility is primarily practiced by Java developers. If we retrofit our interview process for C++, should we still expect Agile qualities when interviewing for a C++ role? I'm asking on behalf of a team that has worked with Java too long to know what a good C++ developer looks like. Specifically we're looking to answer the following questions: Can we expect a demonstrated understanding of OO design and Separation of Concerns? In the code project we want the candidate to write unit tests. Would a good C++ developer be surprised by this expectation? Are there any "extra" competencies we can look for? For example with Java developers we always look for a familiarity with Dependency Injection.

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• Indirect property notification

  - by Carlo

  Hello, this question might look a little trivial, but it might not be. I'm just wondering which of the following two cases is better for indirect property notification, or perhaps there is an even better way. The scenario: I have two properties, the first one is an object called HoldingObject, the second one is a boolean called IsHoldingObject, which is false if HoldingObject == null, otherwise it's true. I'm just wondering what is the best notification mechanism for IsHoldingObject: Case (A) - Notify IsHoldingObject changed from the HoldingObject proeperty: public class NotifyingClass1 : INotifyPropertyChanged { private object _holdingObject; public object HoldingObject { get { return _holdingObject; } set { if (_holdingObject != value) { _holdingObject = value; NotifyPropertyChanged("HoldingObject"); // Notify from the property that is being checked NotifyPropertyChanged("IsHoldingObject"); } } } public bool IsHoldingObject { get { return this.HoldingObject == null; } } #region INotifyPropertyChanged Members public event PropertyChangedEventHandler PropertyChanged; private void NotifyPropertyChanged(string propertyName) { if (this.PropertyChanged != null) this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } #endregion } Case (B) - Notify IsHoldingObject changed from the IsHoldingObject directly, by setting it to false or true from HoldingObject property: public class NotifyingClass2 : INotifyPropertyChanged { private object _holdingObject; public object HoldingObject { get { return _holdingObject; } set { if (_holdingObject != value) { _holdingObject = value; NotifyPropertyChanged("HoldingObject"); // 1) Set the property here this.IsHoldingObject = _holdingObject != null; } } } private bool _isHoldingObject; public bool IsHoldingObject { get { return _isHoldingObject; } set { if (_isHoldingObject != value) { _isHoldingObject = value; // 2) Notify directly from the property NotifyPropertyChanged("IsHoldingObject"); } } } #region INotifyPropertyChanged Members public event PropertyChangedEventHandler PropertyChanged; private void NotifyPropertyChanged(string propertyName) { if (this.PropertyChanged != null) this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } #endregion } I personally lean to the first one because it requires less code, but I'm not sure how recommendable it is to do that. Let me know if there is another (better) way. Thanks!

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• Segmentation fault on returning from main (very short and simple code, no arrays or pointers)

  - by Gábor Kovács

  I've been wondering why the following trivial code produces a segmentation fault when returning from main(): //Produces "Error while dumping state (probably corrupted stack); Segmentation fault" #include <iostream> #include <fstream> #include <vector> using namespace std; class Test { vector<int> numbers; }; int main() { Test a; ifstream infile; cout << "Last statement..." << endl; // this gets executed return 0; } Interestingly, 1) if only one of the two variables is declared, I don't get the error, 2) if I declare a vector variable instead of an object with a vector member, everything's fine, 3) if I declare an ofstream instead of an ifstream, again, everything works fine. Something appears to be wrong with this specific combination... Could this be a compiler bug? I use gcc version 3.4.4 with cygwin. Thanks for the tips in advance. Gábor

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• Python file iterator over a binary file with newer idiom.

  - by drewk

  In Python, for a binary file, I can write this: buf_size=1024*64 # this is an important size... with open(file, "rb") as f: while True: data=f.read(buf_size) if not data: break # deal with the data.... With a text file that I want to read line-by-line, I can write this: with open(file, "r") as file: for line in file: # deal with each line.... Which is shorthand for: with open(file, "r") as file: for line in iter(file.readline, ""): # deal with each line.... This idiom is documented in PEP 234 but I have failed to locate a similar idiom for binary files. I have tried this: >>> with open('dups.txt','rb') as f: ... for chunk in iter(f.read,''): ... i+=1 >>> i 1 # 30 MB file, i==1 means read in one go... I tried putting iter(f.read(buf_size),'') but that is a syntax error because of the parens after the callable in iter(). I know I could write a function, but is there way with the default idiom of for chunk in file: where I can use a buffer size versus a line oriented? Thanks for putting up with the Python newbie trying to write his first non-trivial and idiomatic Python script.

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• Turning a series of raw images into movie frames in Android

  - by Nicholas Killewald

  I've got an Android project I'm working on that, ultimately, will require me to create a movie file out of a series of still images taken with a phone's camera. That is to say, I want to be able to take raw image frames and string them together, one by one, into a movie. Audio is not a concern at this stage. Looking over the Android API, it looks like there are calls in it to create movie files, but it seems those are entirely geared around making a live recording from the camera on an immediate basis. While nice, I can't use that for my purposes, as I need to put annotations and other post-production things on the images as they come in before they get fed into a movie (plus, the images come way too slowly to do a live recording). Worse, looking over the Android source, it looks like a non-trivial task to rewire that to do what I want it to do (at least without touching the NDK). Is there any way I can use the API to do something like this? Or alternatively, what would be the best way to go about this, if it's even feasible on cell phone hardware (which seems to keep getting more and more powerful, strangely...)?

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• Can the Visual Studio (2010) Command Window handle "external tools" with project/solution relative p

  - by ee

  I have been playing with the Command Window in Visual Studio (View-Other Windows-Command Window). It is great for several mouse-free scenarios. (The autocompleting file "Open" command rocks in a non-trivial solution.) That success got me thinking and experimenting: Possibility 1.1: You can use the Alias commands to create custom commands Possibility 1.2: You can use the Shell command to run arbitrary executables and specify parameters (and pipe the result to the output or command windows) Possibility 2: A previously setup external tool definition (with project-relative path variables) could be run from the command window What I am stuck on is: There doesn't appear to be a way to send parameters to an aliased command (and thus the underlying Shell call) There doesn't appear to be a way to use project/solution relative paths ($SolutionDir/$ProjectDir) on a Shell call Using absolute paths in Shell works, but is fragile and high-maintenance (one alias for each needed use case). Typically you want the command to run against a file relative to your project/solution. It seems you can't run the traditional external tools (Tools-External Tools...) in the command window Ultimately I want the external tool functionality in the command window in some way. Can anyone see a way to do this? Or am I barking up the wrong tree? So my questions: Can an "external tool" of some sort (using relative project/solution path parameters) be used in the Command Window? If yes, How? If no, what might be a suitable alternative?

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• Need advice on C++ coding pattern

  - by Kotti

  Hi! I have a working prototype of a game engine and right now I'm doing some refactoring. What I'm asking for is your opinion on usage of the following C++ coding patterns. I have implemented some trivial algorithms for collision detection and they are implemented the following way: Not shown here - class constructor is made private and using algorithms looks like Algorithm::HandleInnerCollision(...) struct Algorithm { // Private routines static bool is_inside(Point& p, Object& object) { // (...) } public: /** * Handle collision where the moving object should be always * located inside the static object * * @param MovingObject & mobject * @param const StaticObject & sobject * @return void * @see */ static void HandleInnerCollision(MovingObject& mobject, const StaticObject& sobject) { // (...) } So, my question is - somebody advised me to do it "the C++" way - so that all functions are wrapped in a namespace, but not in a class. Is there some good way to preserve privating if I will wrap them into a namespace as adviced? What I want to have is a simple interface and ability to call functions as Algorithm::HandleInnerCollision(...) while not polluting the namespace with other functions such as is_inside(...) Of, if you can advise any alternative design pattern for such kind of logics, I would really appreciate that...

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• Building a survey to put in a WordPress website using Python/Django

  - by chiurox

  So I've been given a task to build a survey to get data regarding time slot preferences of prospective students for a particular course. I know there are really quick solutions to this like Google Forms, SurveyMonkey, but since it's not unusually hard, I want to implement the survey myself in a totally new language as an opportunity to get started with it and also be able to customize and provide dynamic info to the users who are voting. Although I have done some stuff in PHP, C++, javascript, etc, I'm pretty new to Python+Django framework but it's something I've been meaning to get into since a long time ago. Initially, what I want is to make a grid with the days of the week as columns and time-durations as rows. In each cell I want to provide users a way to choose how strong (high/medium/low) their preference for this particular day+time is. I also want to show how many "votes" have already been cast for this particular preference because this will influence a lot in their decisions and as a result make this process easier when we are going to define the classes. I'll probably store the data in MySQL. Could anyone point me to some really good Python+Django tutorials for my particular purpose? Does anyone think I'm wasting my time with this trivial task by choosing new tools and that I should just use something I already know (like PHP) or a free service or plugin for Wordpress? Thanks!

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• When is it safe to use a broken hash function?

  - by The Rook

  It is trivial to use a secure hash function like SHA256 and continuing to use md5 is reckless behavior. However, there are some complexities to hash function vulnerabilities that I would like to better understand. Collisions have been generated for md4 and md5. According to NIST md5() is not a secure hash function. It only takes 2^39th operations to generate a collision and should never be used for passwords. However SHA1 is vulnerable to a similar collision attack in which a collision can be found in 2^69 operations, where as brute force is 2^80th. No one has generated a sha1 collision and NIST still lists sha1 as a secure message digest function. So when is it safe to use a broken hash function? Even though a function is broken it can still be "big enough". According to Schneier a hash function vulnerable to a collsion attack can still be used as an HMAC. I believe this is because the security of an HMAC is Dependant on its secret key and a collision cannot be found until this key is obtained. Once you have the key used in a HMAC its already broken, so its a moot point. What hash function vulnerabilities would undermine the security of an HMAC? Lets take this property a bit further. Does it then become safe to use a very weak message digest like md4 for passwords if a salt is perpended to the password? Keep in mind the md4 and md5 attacks are prefixing attacks, and if a salt is perpended then an attacker cannot control the prefix of the message. If the salt is truly a secret, and isn't known to the attacker, then does it matter if its a appended to the end of the password? Is it safe to assume that an attacker cannot generate a collision until the entire message has been obtained? Do you know of other cases where a broken hash function can be used in a security context without introducing a vulnerability? (Please post supporting evidence because it is awesome!)

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• How to pass a Lambda Expression as method parameter with EF

  - by Registered User

  How do I pass an EF expression as a method argument? To illustrate my question I have created a pseudo code example: The first example is my method today. The example utilizes EF and a Fancy Retry Logic. What I need to do is to encapsulate the Fancy Retry Logic so that it becomes more generic and does not duplicate. In the second example is how I want it to be, with a helper method that accepts the EF expression as an argument. This would be a trivial thing to do with SQL, but I want to do it with EF so that I can benefit from the strongly typed objects. First Example: public static User GetUser(String userEmail) { using (MyEntities dataModel = new MyEntities ()) { var query = FancyRetryLogic(() => { (dataModel.Users.FirstOrDefault<User>(x => x.UserEmail == userEmail))); }); return query; } } Second Example: T RetryHelper<T>(Expression<Func<T, TValue>> expression) { using (MyEntities dataModel = new (MyEntities ()) { var query = FancyRetryLogic(() => { return dataModel.expression }); } } public User GetUser(String userEmail) { return RetryHelper<User>(<User>.FirstOrDefault<User>(x => x.UserEmail == userEmail)) }

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• Sphinx - delimiters

  - by yoda

  Hi, I would like to know if the Sphinx engine works with any delimiters (like commas and periods in normal MySQL). My question comes from the urge, not to use them at all, but to escape them or at least thay they don't enter in conflict when performing MATCH operations with FULLTEXT searches, since I have problems dealing with them in MySQL by default and I would prefer not to be forced to replace those delimiters by any other characters to provide a good set of results. Sorry if I'm saying something stupid, but I don't have experience with Sphinx or other complementary (?) search engines. To give you an example, if I perform a search with "Passat 2.0 TDI" MySQL by default would identify the period in this case as a delimiter and since the "2" and "0" are too short to be considered words by default, the results would be a bit messed up. Is it easy to handle with Sphinx (or other search engine)? I'm open to suggestions. This is for a large project, with probably more than 500.000 possible records (not trivial at all). Cheers!

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• Data structure to build and lookup set of integer ranges

  - by actual

  I have a set of uint32 integers, there may be millions of items in the set. 50-70% of them are consecutive, but in input stream they appear in unpredictable order. I need to: Compress this set into ranges to achieve space efficient representation. Already implemented this using trivial algorithm, since ranges computed only once speed is not important here. After this transformation number of resulting ranges is typically within 5 000-10 000, many of them are single-item, of course. Test membership of some integer, information about specific range in the set is not required. This one must be very fast -- O(1). Was thinking about minimal perfect hash functions, but they do not play well with ranges. Bitsets are very space inefficient. Other structures, like binary trees, has complexity of O(log n), worst thing with them that implementation make many conditional jumps and processor can not predict them well giving poor performance. Is there any data structure or algorithm specialized in integer ranges to solve this task?

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• Extracting DCT coefficients from encoded images and video

  - by misha

  Is there a way to easily extract the DCT coefficients (and quantization parameters) from encoded images and video? Any decoder software must be using them to decode block-DCT encoded images and video. So I'm pretty sure the decoder knows what they are. Is there a way to expose them to whomever is using the decoder? I'm implementing some video quality assessment algorithms that work directly in the DCT domain. Currently, the majority of my code uses OpenCV, so it would be great if anyone knows of a solution using that framework. I don't mind using other libraries (perhaps libjpeg, but that seems to be for still images only), but my primary concern is to do as little format-specific work as possible (I don't want to reinvent the wheel and write my own decoders). I want to be able to open any video/image (H.264, MPEG, JPEG, etc) that OpenCV can open, and if it's block DCT-encoded, to get the DCT coefficients. In the worst case, I know that I can write up my own block DCT code, run the decompressed frames/images through it and then I'd be back in the DCT domain. That's hardly an elegant solution, and I hope I can do better. Presently, I use the fairly common OpenCV boilerplate to open images: IplImage *image = cvLoadImage(filename); // Run quality assessment metric The code I'm using for video is equally trivial: CvCapture *capture = cvCaptureFromAVI(filename); while (cvGrabFrame(capture)) { IplImage *frame = cvRetrieveFrame(capture); // Run quality assessment metric on frame } cvReleaseCapture(&capture); In both cases, I get a 3-channel IplImage in BGR format. Is there any way I can get the DCT coefficients as well?

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• Any techniques to interrupt, kill, or otherwise unwind (releasing synchronization locks) a single de

  - by gojomo

  I have a long-running process where, due to a bug, a trivial/expendable thread is deadlocked with a thread which I would like to continue, so that it can perform some final reporting that would be hard to reproduce in another way. Of course, fixing the bug for future runs is the proper ultimate resolution. Of course, any such forced interrupt/kill/stop of any thread is inherently unsafe and likely to cause other unpredictable inconsistencies. (I'm familiar with all the standard warnings and the reasons for them.) But still, since the only alternative is to kill the JVM process and go through a more lengthy procedure which would result in a less-complete final report, messy/deprecated/dangerous/risky/one-time techniques are exactly what I'd like to try. The JVM is Sun's 1.6.0_16 64-bit on Ubuntu, and the expendable thread is waiting-to-lock an object monitor. Can an OS signal directed to an exact thread create an InterruptedException in the expendable thread? Could attaching with gdb, and directly tampering with JVM data or calling JVM procedures allow a forced-release of the object monitor held by the expendable thread? Would a Thread.interrupt() from another thread generate a InterruptedException from the waiting-to-lock frame? (With some effort, I can inject an arbitrary beanshell script into the running system.) Can the deprecated Thread.stop() be sent via JMX or any other remote-injection method? Any ideas appreciated, the more 'dangerous', the better! And, if your suggestion has worked in personal experience in a similar situation, the best!

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• breaking datetime into constituent parts ASP.NET MVC form

  - by nick

  hi guys, i have searched the web relentlessly for this and have not found anything - which is surprising because i would think it is such a common scenario! Basically, on my model i have a DateTime field which i wish the user to populate through a form. I am using the Html helper to render all other parts of the form (along with validation) So this question is in two parts... Html Helper Firstly, is there any way to use the Html helper to split the DateTime field to be rendered as the three constituent parts of a date: day, month, year (since i do not care about the time part). This could be rendered as text boxes, drop down lists or a combination of both. Model Binding And then when the form is posted, what is the best approach for binding back up to the model? I have seen Scott Hanselmann's solution to this, but it seems a little bloated for what i need - i was hoping for a slightly more elegant solution. Is it recommended to extend DefaultModelBinder and set that as default binder (since all dates would be handled in this way) or write a class that implements IModelBionder and set it as the default binder for the DateTime type? Thanks for all the help in advance :-) i'm loving MVC but it's infuriating me that something so trivial is causing so much headaches!

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• Modular Inverse and BigInteger division

  - by dano82

  I've been working on the problem of calculating the modular inverse of an large integer i.e. a^-1 mod n. and have been using BigInteger's built in function modInverse to check my work. I've coded the algorithm as shown in The Handbook of Applied Cryptography by Menezes, et al. Unfortunately for me, I do not get the correct outcome for all integers. My thinking is that the line q = a.divide(b) is my problem as the divide function is not well documented (IMO)(my code suffers similarly). Does BigInteger.divide(val) round or truncate? My assumption is truncation since the docs say that it mimics int's behavior. Any other insights are appreciated. This is the code that I have been working with: private static BigInteger modInverse(BigInteger a, BigInteger b) throws ArithmeticException { //make sure a >= b if (a.compareTo(b) < 0) { BigInteger temp = a; a = b; b = temp; } //trivial case: b = 0 => a^-1 = 1 if (b.equals(BigInteger.ZERO)) { return BigInteger.ONE; } //all other cases BigInteger x2 = BigInteger.ONE; BigInteger x1 = BigInteger.ZERO; BigInteger y2 = BigInteger.ZERO; BigInteger y1 = BigInteger.ONE; BigInteger x, y, q, r; while (b.compareTo(BigInteger.ZERO) == 1) { q = a.divide(b); r = a.subtract(q.multiply(b)); x = x2.subtract(q.multiply(x1)); y = y2.subtract(q.multiply(y1)); a = b; b = r; x2 = x1; x1 = x; y2 = y1; y1 = y; } if (!a.equals(BigInteger.ONE)) throw new ArithmeticException("a and n are not coprime"); return x2; }

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