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• Web-Frameworks for Education Management Systems?

  - by Indebi

  So, I'm working on an idea and I'll go into a brief overview of that but my question is, What are some good web frameworks for this situation? I have some experience in the following languages: C# Python I have considerably more experience in C# than Python, however I am expecting to learn new things. My idea is this, a completely web-based community-oriented Education Management System that focuses on making students and teachers day-to-day lives easier. For students it will provide a centralized place for them to do homework, study for tests, and reinforce concepts learned previously in class. For teachers it will give them a centralized place to handle assignments, attendance, homework, tests, and all other major parts of classroom management. All of that, but in a community-oriented fashion. Everything a teacher does is shared and open to constructive criticism, allowing other teachers to use their assignments/tests and for students or other teachers to comment, rate and criticize their assignments. This encourages an environment of openness that will allow teacher's to focus on teaching and student's to focus on learning. And that community wouldn't be limited to one school or school-district, this system would be completely school-independent. Please note that I have no problem with hearing constructive criticism on this idea, however I would prefer if this post was more focused on my question. I have somewhat explored about the following options: Django ASP.NET Ruby on Rails Silverlight (1) I have Django installed and I played with it for a little bit, I really like how easy setting up databases are and how it handles the database completely for you. I don't really know how to use it very well and I don't quite understand the Model-View-Controller paradigm(?) for it yet but I haven't thought about it much. I also like the fact that it uses Python. (2) I don't really like Visual Studio for developing in ASP.NET, I hate the way the web-designer works and it just feels clunky and old. I like the server-side development part though. I don't like how expensive ASP.NET and overall Visual Studio is, even if I do get it for free for now using DreamSpark (3) I haven't been able to explore much with this, I could not get Rails (or maybe Ruby) properly installed. I first installed it within RadRails and that didn't work so I uninstalled RadRails and then installed the latest version of Ruby off the official Windows Installer and then installed Ruby on Rails through gem and even after all that it still didn't work, so I installed Netbeans and attempted to use it there but it still did not work (4) I like Silverlight in some extents, I've played with this one the most, it's very similar to WPF (which I've used the most) in a lot of ways but I don't like how database connectivity works, at least in comparison to Django. I also dislike how expensive everything with Microsoft is, even if I get it for free for now with DreamSpark. I would like to hear some suggestions from experienced web-developers as to what I should use and why, or at least what some good options are for my scenario Your help would be very appreciated

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• About fork system call and global variables

  - by lurks

  I have this program in C++ that forks two new processes: #include <pthread.h> #include <iostream> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> #include <cstdlib> using namespace std; int shared; void func(){ extern int shared; for (int i=0; i<10;i++) shared++; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } int main(){ extern int shared; pid_t p1,p2; int status; shared=0; if ((p1=fork())==0) {func();exit(0);}; if ((p2=fork())==0) {func();exit(0);}; for(int i=0;i<10;i++) shared++; waitpid(p1,&status,0); waitpid(p2,&status,0);; cout<<"shared variable is: "<<shared<<endl; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } The two forked processes make an increment on the shared variables and the parent process does the same. As the variable belongs to the data segment of each process, the final value is 10 because the increment is independent. However, the memory address of the shared variables is the same, you can try compiling and watching the output of the program. How can that be explained ? I cannot understand that, I thought I knew how the fork() works, but this seems very odd.. I need an explanation on why the address is the same, although they are separate variables.

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• How to communicate between Client and Server in a Client-Server Application?

  - by Sanoj

  I would like to implement an Client-Server Application, where the business-logic, security validations and a database are at the server and the user interface are at the client. I would like to implement clients in different languages i.e. one in WPF/.NET, one Swing/Java , one in Android/Java and maybe one HTML/JavaScript client. The server will be on Internet, so I would like to be able to have encrypted communication. The client will send some lists of items to be added to the database, or update items, and do some transactions. The server will check if the items are already updated by another client, or update the item, add new items or delete items. How do I solve the communication between clients and the server in such a system? I have been thinking about: http/https webserver, and sending messages in JSON or XML and use Web Sockets for bi-directional communication. Use http in a RESTful way, except when WebSockets are needed. But I guess there are better solutions for native desktop applications than http? CORBA - I have just heard about it, and it's old and complex. Not much talk about it these days. XMPP/Jabber - I have just heard about it and I don't know if it fits me at all. EJabberd seams to be a popular implementation. AMQP - I have just heard about it and I don't know if it fits me at all. RabbitMQ seams to be a popular implementation. Windows Communication Foundation, Java RMI, Java Message Service - but are they language independent? I guess some of these alternatives are on different levels, maybe I can have i.e xmpp or amqp in web sockets over https? What technologys are used for this problem in companies today? and what is recommended to use? I have no experience of them other than webservers and http. Please give me some guidance in this jungle. What are the pros and cons of these technologies in my situation?

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• Silverlight? WPF? or Windows Form?

  - by Amit

  After Silverlight 4.0 has been released with new WPF, I am kind of confused with these technologies: Silverlight? WPF? Windows Form? The main motive that we want to achieve for BIG business project is following: Performance Security And platform independent** If I consider all above three points then only Silverlight is the option as I don’t want people buying emulator on MacOS for WPF or Windows Form. Now how good the Silverlight is for Business applications, I was completely against when Silverlight 2.0 was in the market but now it is Silverlight 4.0 and they have provided many new features (but still basics) that is required in any challenging business applications. Comparing Silverlight and WPF -* Silverlight and WPF are very new technology and if I'd to compare from these two then I'd prefer WPF because it can be considered stable and mature. But it is not same as Windows Form. -* If I go with Silverlight then I am sure about keep updating to the latest version of Silverlight. I remembered when we were developing software for version 2.0 then we'd to create our own framework with dynamic loading DLL, and then Navigation concept. But everything was got changed once Silverlight 3.0 came. I don't want this to be happening with this new product. -* If we go with WPF then we don't get the platform independence. Now, why not we just focus on making WPF and then move to Silverlght. As someone (Tim?) from Microsoft has said that the idea is to make Silverlight as close as WPF. But if that is the case then why XAML structure is different; I will not be convinced with by saying that .Net framework for SL is too small.. well the difference is coming from the namespace ? I was searching on this subject and found "Microsoft WPF-Silverlight Comparison Whitepaper v1.1.pdf". This guide is very good that gives you ins-outs about how can we build common apps that runs on both. But again, it is comparing Silverlight 2 and not 4. I am sure many architect/ developers/ project managers must be facing similar kind of questions in their premises and wants to initiate this discussion, if it has not been :). We've still got 2 weeks to make this decision, so I'm expecting everyone to participate, gurus?

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• What is the best practice for adding persistence to an MVC model?

  - by etheros

  I'm in the process of implementing an ultra-light MVC framework in PHP. It seems to be a common opinion that the loading of data from a database, file etc. should be independent of the Model, and I agree. What I'm unsure of is the best way to link this "data layer" into MVC. Datastore interacts with Model //controller public function update() { $model = $this->loadModel('foo'); $data = $this->loadDataStore('foo', $model); $data->loadBar(9); //loads data and populates Model $model->setBar('bar'); $data->save(); //reads data from Model and saves } Controller mediates between Model and Datastore Seems a bit verbose and requires the model to know that a datastore exists. //controller public function update() { $model = $this->loadModel('foo'); $data = $this->loadDataStore('foo'); $model->setDataStore($data); $model->getDataStore->loadBar(9); //loads data and populates Model $model->setBar('bar'); $model->getDataStore->save(); //reads data from Model and saves } Datastore extends Model What happens if we want to save a Model extending a database datastore to a flatfile datastore? //controller public function update() { $model = $this->loadHybrid('foo'); //get_class == Datastore_Database $model->loadBar(9); //loads data and populates $model->setBar('bar'); $model->save(); //saves } Model extends datastore This allows for Model portability, but it seems wrong to extend like this. Further, the datastore cannot make use of any of the Model's methods. //controller extends model public function update() { $model = $this->loadHybrid('foo'); //get_class == Model $model->loadBar(9); //loads data and populates $model->setBar('bar'); $model->save(); //saves } EDIT: Model communicates with DAO //model public function __construct($dao) { $this->dao = $dao; } //model public function setBar($bar) { //a bunch of business logic goes here $this->dao->setBar($bar); } //controller public function update() { $model = $this->loadModel('foo'); $model->setBar('baz'); $model->save(); } Any input on the "best" option - or alternative - is most appreciated.

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• Embedding mercurial revision information in Visual Studio c# projects automatically

  - by Mark Booth

  Original Problem In building our projects, I want the mercurial id of each repository to be embedded within the product(s) of that repository (the library, application or test application). I find it makes it so much easier to debug an application ebing run by custiomers 8 timezones away if you know precisely what went into building the particular version of the application they are using. As such, every project (application or library) in our systems implement a way of getting at the associated revision information. I also find it very useful to be able to see if an application has been compiled with clean (un-modified) changesets from the repository. 'Hg id' usefully appends a + to the changeset id when there are uncommitted changes in a repository, so this allows is to easily see if people are running a clean or a modified version of the code. My current solution is detailed below, and fulfills the basic requirements, but there are a number of problems with it. Current Solution At the moment, to each and every Visual Studio solution, I add the following "Pre-build event command line" commands: cd $(ProjectDir) HgID I also add an HgID.bat file to the Project directory: @echo off type HgId.pre > HgId.cs For /F "delims=" %%a in ('hg id') Do <nul >>HgID.cs set /p = @"%%a" echo ; >> HgId.cs echo } >> HgId.cs echo } >> HgId.cs along with an HgId.pre file, which is defined as: namespace My.Namespace { /// <summary> Auto generated Mercurial ID class. </summary> internal class HgID { /// <summary> Mercurial version ID [+ is modified] [Named branch]</summary> public const string Version = When I build my application, the pre-build event is triggered on all libraries, creating a new HgId.cs file (which is not kept under revision control) and causing the library to be re-compiled with with the new 'hg id' string in 'Version'. Problems with the current solution The main problem is that since the HgId.cs is re-created at each pre-build, every time we need to compile anything, all projects in the current solution are re-compiled. Since we want to be able to easily debug into our libraries, we usually keep many libraries referenced in our main application solution. This can result in build times which are significantly longer than I would like. Ideally I would like the libraries to compile only if the contents of the HgId.cs file has actually changed, as opposed to having been re-created with exactly the same contents. The second problem with this method is it's dependence on specific behaviour of the windows shell. I've already had to modify the batch file several times, since the original worked under XP but not Vista, the next version worked under Vista but not XP and finally I managed to make it work with both. Whether it will work with Windows 7 however is anyones guess and as time goes on, I see it more likely that contractors will expect to be able to build our apps on their Windows 7 boxen. Finally, I have an aesthetic problem with this solution, batch files and bodged together template files feel like the wrong way to do this. My actual questions How would you solve/how are you solving the problem I'm trying to solve? What better options are out there than what I'm currently doing? Rejected Solutions to these problems Before I implemented the current solution, I looked at Mercurials Keyword extension, since it seemed like the obvious solution. However the more I looked at it and read peoples opinions, the more that I came to the conclusion that it wasn't the right thing to do. I also remember the problems that keyword substitution has caused me in projects at previous companies (just the thought of ever having to use Source Safe again fills me with a feeling of dread *8'). Also, I don't particularly want to have to enable Mercurial extensions to get the build to complete. I want the solution to be self contained, so that it isn't easy for the application to be accidentally compiled without the embedded version information just because an extension isn't enabled or the right helper software hasn't been installed. I also thought of writing this in a better scripting language, one where I would only write HgId.cs file if the content had actually changed, but all of the options I could think of would require my co-workers, contractors and possibly customers to have to install software they might not otherwise want (for example cygwin). Any other options people can think of would be appreciated. Update Partial solution Having played around with it for a while, I've managed to get the HgId.bat file to only overwrite the HgId.cs file if it changes: @echo off type HgId.pre > HgId.cst For /F "delims=" %%a in ('hg id') Do <nul >>HgId.cst set /p = @"%%a" echo ; >> HgId.cst echo } >> HgId.cst echo } >> HgId.cst fc HgId.cs HgId.cst >NUL if %errorlevel%==0 goto :ok copy HgId.cst HgId.cs :ok del HgId.cst Problems with this solution Even though HgId.cs is no longer being re-created every time, Visual Studio still insists on compiling everything every time. I've tried looking for solutions and tried checking "Only build startup projects and dependencies on Run" in Tools|Options|Projects and Solutions|Build and Run but it makes no difference. The second problem also remains, and now I have no way to test if it will work with Vista, since that contractor is no longer with us. If anyone can test this batch file on a Windows 7 and/or Vista box, I would appreciate hearing how it went. Finally, my aesthetic problem with this solution, is even strnger than it was before, since the batch file is more complex and this there is now more to go wrong. If you can think of any better solution, I would love to hear about them.

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• Runge-Kutta Method with adaptive step

  - by infoholic_anonymous

  I am implementing Runge-Kutta method with adaptive step in matlab. I get different results as compared to matlab's own ode45 and my own implementation of Runge-Kutta method with fixed step. What am I doing wrong in my code? Is it possible? function [ result ] = rk4_modh( f, int, init, h, h_min ) % % f - function handle % int - interval - pair (x_min, x_max) % init - initial conditions - pair (y1(0),y2(0)) % h_min - lower limit for h (step length) % h - initial step length % x - independent variable ( for example time ) % y - dependent variable - vertical vector - in our case ( y1, y2 ) function [ k1, k2, k3, k4, ka, y ] = iteration( f, h, x, y ) % core functionality performed within loop k1 = h * f(x,y); k2 = h * f(x+h/2, y+k1/2); k3 = h * f(x+h/2, y+k2/2); k4 = h * f(x+h, y+k3); ka = (k1 + 2*k2 + 2*k3 + k4)/6; y = y + ka; end % constants % relative error eW = 1e-10; % absolute error eB = 1e-10; s = 0.9; b = 5; % initialization i = 1; x = int(1); y = init; while true hy = y; hx = x; %algorithm [ k1, k2, k3, k4, ka, y ] = iteration( f, h, x, y ); % error estimation for j=1:2 [ hk1, hk2, hk3, hk4, hka, hy ] = iteration( f, h/2, hx, hy ); hx = hx + h/2; end err(:,i) = abs(hy - y); % step adjustment e = abs( hy ) * eW + eB; a = min( e ./ err(:,i) )^(0.2); mul = a * s; if mul >= 1 % step length admitted keepH(i) = h; k(:,:,i) = [ k1, k2, k3, k4, ka ]; previous(i,:) = [ x+h, y' ]; %' i = i + 1; if floor( x + h + eB ) == int(2) break; else h = min( [mul*h, b*h, int(2)-x] ); x = x + keepH(i-1); end else % step length requires further adjustments h = mul * h; if ( h < h_min ) error('Computation with given precision impossible'); end end end result = struct( 'val', previous, 'k', k, 'err', err, 'h', keepH ); end The function in question is: function [ res ] = fun( x, y ) % res(1) = y(2) + y(1) * ( 0.9 - y(1)^2 - y(2)^2 ); res(2) = -y(1) + y(2) * ( 0.9 - y(1)^2 - y(2)^2 ); res = res'; %' end The call is: res = rk4( @fun, [0,20], [0.001; 0.001], 0.008 ); The resulting plot for x1 : The result of ode45( @fun, [0, 20], [0.001, 0.001] ) is:

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• Recommendations for a C++ polymorphic, seekable, binary I/O interface

  - by Trevor Robinson

  I've been using std::istream and ostream as a polymorphic interface for random-access binary I/O in C++, but it seems suboptimal in numerous ways: 64-bit seeks are non-portable and error-prone due to streampos/streamoff limitations; currently using boost/iostreams/positioning.hpp as a workaround, but it requires vigilance Missing operations such as truncating or extending a file (ala POSIX ftruncate) Inconsistency between concrete implementations; e.g. stringstream has independent get/put positions whereas filestream does not Inconsistency between platform implementations; e.g. behavior of seeking pass the end of a file or usage of failbit/badbit on errors Don't need all the formatting facilities of stream or possibly even the buffering of streambuf streambuf error reporting (i.e. exceptions vs. returning an error indicator) is supposedly implementation-dependent in practice I like the simplified interface provided by the Boost.Iostreams Device concept, but it's provided as function templates rather than a polymorphic class. (There is a device class, but it's not polymorphic and is just an implementation helper class not necessarily used by the supplied device implementations.) I'm primarily using large disk files, but I really want polymorphism so I can easily substitute alternate implementations (e.g. use stringstream instead of fstream for unit tests) without all the complexity and compile-time coupling of deep template instantiation. Does anyone have any recommendations of a standard approach to this? It seems like a common situation, so I don't want to invent my own interfaces unnecessarily. As an example, something like java.nio.FileChannel seems ideal. My best solution so far is to put a thin polymorphic layer on top of Boost.Iostreams devices. For example: class my_istream { public: virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) = 0; virtual std::streamsize read(char* s, std::streamsize n) = 0; virtual void close() = 0; }; template <class T> class boost_istream : public my_istream { public: boost_istream(const T& device) : m_device(device) { } virtual std::streampos seek(stream_offset off, std::ios_base::seekdir way) { return boost::iostreams::seek(m_device, off, way); } virtual std::streamsize read(char* s, std::streamsize n) { return boost::iostreams::read(m_device, s, n); } virtual void close() { boost::iostreams::close(m_device); } private: T m_device; };

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• How to obtain a pointer out of a C++ vtable?

  - by Josh Haberman

  Say you have a C++ class like: class Foo { public: virtual ~Foo() {} virtual DoSomething() = 0; }; The C++ compiler translates a call into a vtable lookup: Foo* foo; // Translated by C++ to: // foo->vtable->DoSomething(foo); foo->DoSomething(); Suppose I was writing a JIT compiler and I wanted to obtain the address of the DoSomething() function for a particular instance of class Foo, so I can generate code that jumps to it directly instead of doing a table lookup and an indirect branch. My questions are: Is there any standard C++ way to do this (I'm almost sure the answer is no, but wanted to ask for the sake of completeness). Is there any remotely compiler-independent way of doing this, like a library someone has implemented that provides an API for accessing a vtable? I'm open to completely hacks, if they will work. For example, if I created my own derived class and could determine the address of its DoSomething method, I could assume that the vtable is the first (hidden) member of Foo and search through its vtable until I find my pointer value. However, I don't know a way of getting this address: if I write &DerivedFoo::DoSomething I get a pointer-to-member, which is something totally different. Maybe I could turn the pointer-to-member into the vtable offset. When I compile the following: class Foo { public: virtual ~Foo() {} virtual void DoSomething() = 0; }; void foo(Foo *f, void (Foo::*member)()) { (f->*member)(); } On GCC/x86-64, I get this assembly output: Disassembly of section .text: 0000000000000000 <_Z3fooP3FooMS_FvvE>: 0: 40 f6 c6 01 test sil,0x1 4: 48 89 74 24 e8 mov QWORD PTR [rsp-0x18],rsi 9: 48 89 54 24 f0 mov QWORD PTR [rsp-0x10],rdx e: 74 10 je 20 <_Z3fooP3FooMS_FvvE+0x20> 10: 48 01 d7 add rdi,rdx 13: 48 8b 07 mov rax,QWORD PTR [rdi] 16: 48 8b 74 30 ff mov rsi,QWORD PTR [rax+rsi*1-0x1] 1b: ff e6 jmp rsi 1d: 0f 1f 00 nop DWORD PTR [rax] 20: 48 01 d7 add rdi,rdx 23: ff e6 jmp rsi I don't fully understand what's going on here, but if I could reverse-engineer this or use an ABI spec I could generate a fragment like the above for each separate platform, as a way of obtaining a pointer out of a vtable.

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• Implementing coroutines in Java

  - by JUST MY correct OPINION

  This question is related to my question on existing coroutine implementations in Java. If, as I suspect, it turns out that there is no full implementation of coroutines currently available in Java, what would be required to implement them? As I said in that question, I know about the following: You can implement "coroutines" as threads/thread pools behind the scenes. You can do tricksy things with JVM bytecode behind the scenes to make coroutines possible. The so-called "Da Vinci Machine" JVM implementation has primitives that make coroutines doable without bytecode manipulation. There are various JNI-based approaches to coroutines also possible. I'll address each one's deficiencies in turn. Thread-based coroutines This "solution" is pathological. The whole point of coroutines is to avoid the overhead of threading, locking, kernel scheduling, etc. Coroutines are supposed to be light and fast and to execute only in user space. Implementing them in terms of full-tilt threads with tight restrictions gets rid of all the advantages. JVM bytecode manipulation This solution is more practical, albeit a bit difficult to pull off. This is roughly the same as jumping down into assembly language for coroutine libraries in C (which is how many of them work) with the advantage that you have only one architecture to worry about and get right. It also ties you down to only running your code on fully-compliant JVM stacks (which means, for example, no Android) unless you can find a way to do the same thing on the non-compliant stack. If you do find a way to do this, however, you have now doubled your system complexity and testing needs. The Da Vinci Machine The Da Vinci Machine is cool for experimentation, but since it is not a standard JVM its features aren't going to be available everywhere. Indeed I suspect most production environments would specifically forbid the use of the Da Vinci Machine. Thus I could use this to make cool experiments but not for any code I expect to release to the real world. This also has the added problem similar to the JVM bytecode manipulation solution above: won't work on alternative stacks (like Android's). JNI implementation This solution renders the point of doing this in Java at all moot. Each combination of CPU and operating system requires independent testing and each is a point of potentially frustrating subtle failure. Alternatively, of course, I could tie myself down to one platform entirely but this, too, makes the point of doing things in Java entirely moot. So... Is there any way to implement coroutines in Java without using one of these four techniques? Or will I be forced to use the one of those four that smells the least (JVM manipulation) instead?

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• Throwing cats out of windows

  - by AndrewF

  Imagine you're in a tall building with a cat. The cat can survive a fall out of a low story window, but will die if thrown from a high floor. How can you figure out the longest drop that the cat can survive, using the least number of attempts? Obviously, if you only have one cat, then you can only search linearly. First throw the cat from the first floor. If it survives, throw it from the second. Eventually, after being thrown from floor f, the cat will die. You then know that floor f-1 was the maximal safe floor. But what if you have more than one cat? You can now try some sort of logarithmic search. Let's say that the build has 100 floors and you have two identical cats. If you throw the first cat out of the 50th floor and it dies, then you only have to search 50 floors linearly. You can do even better if you choose a lower floor for your first attempt. Let's say that you choose to tackle the problem 20 floors at a time and that the first fatal floor is #50. In that case, your first cat will survive flights from floors 20 and 40 before dying from floor 60. You just have to check floors 41 through 49 individually. That's a total of 12 attempts, which is much better than the 50 you would need had you attempted to use binary elimination. In general, what's the best strategy and it's worst-case complexity for an n-storied building with 2 cats? What about for n floors and m cats? Assume that all cats are equivalent: they will all survive or die from a fall from a given window. Also, every attempt is independent: if a cat survives a fall, it is completely unharmed. This isn't homework, although I may have solved it for school assignment once. It's just a whimsical problem that popped into my head today and I don't remember the solution. Bonus points if anyone knows the name of this problem or of the solution algorithm.

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• Creating multiple heads in remote repository

  - by Jab

  We are looking to move our team (~10 developers) from SVN to mercurial. We are trying to figure out how to manage our workflow. In particular, we are trying to see if creating remote heads is the right solution. We currently have a very large repository with multiple, related projects. They share a lot of code, but pieces of the project are deployed by different teams (3 teams) independent of other portions of the code-base. So each team is working on concurrent large features. The way we currently handles this in SVN are branches. Team1 has a branch for Feature1, same deal for the other teams. When Team1 finishes their change, it gets merged into the trunk and deployed out. The other teams follow suite when their project is complete, merging of course. So my initial thought are using Named Branches for these situations. Team1 makes a Feature1 branch off of the default branch in Hg. Now, here is the question. Should the team PUSH that branch, in it's current/half-state to the repository. This will create a second head in the core repo. My initial reaction was "NO!" as it seems like a bad idea. Handling multiple heads on our repository just sounds awful, but there are some advantages... First, the teams want to setup Continuous Integration to build this branch during their development cycle(months long). This will only work if the CI can pull this branch from the repo. This is something we do now with SVN, copy a CI build and change the branch. Easy. Second, it makes it easier for any team member to jump onto the branch and start working. Without pushing to the core repo, they would have to receive a push from a developer on that team with the changeset information. It is also possible to lose local commits to hardware failure. The chances increase a lot if it's a branch by a single developer who has followed the "don't push until finished" approach. And lastly is just for ease of use. The developers can easily just commit and push on their branch at any time without consequence(as they do today, in their SVN branches). Is there a better way to handle this scenario that I may be missing? I just want a veteran's opinion before moving forward with the strategy. For bug fixes we like the general workflow of mecurial, anonymous branches that only consist of 1-2 commits. The simplicity is great for those cases. By the way, I've read this , great article which seems to favor Named branches.

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• Is a many-to-many relationship with extra fields the right tool for my job?

  - by whichhand

  Previously had a go at asking a more specific version of this question, but had trouble articulating what my question was. On reflection that made me doubt if my chosen solution was correct for the problem, so this time I will explain the problem and ask if a) I am on the right track and b) if there is a way around my current brick wall. I am currently building a web interface to enable an existing database to be interrogated by (a small number of) users. Sticking with the analogy from the docs, I have models that look something like this: class Musician(models.Model): first_name = models.CharField(max_length=50) last_name = models.CharField(max_length=50) dob = models.DateField() class Album(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) class Instrument(models.Model): artist = models.ForeignKey(Musician) name = models.CharField(max_length=100) Where I have one central table (Musician) and several tables of associated data that are related by either ForeignKey or OneToOneFields. Users interact with the database by creating filtering criteria to select a subset of Musicians based on data the data on the main or related tables. Likewise, the users can then select what piece of data is used to rank results that are presented to them. The results are then viewed initially as a 2 dimensional table with a single row per Musician with selected data fields (or aggregates) in each column. To give you some idea of scale, the database has ~5,000 Musicians with around 20 fields of related data. Up to here is fine and I have a working implementation. However, it is important that I have the ability for a given user to upload there own annotation data sets (more than one) and then filter and order on these in the same way they can with the existing data. The way I had tried to do this was to add the models: class UserDataSets(models.Model): user = models.ForeignKey(User) name = models.CharField(max_length=100) description = models.CharField(max_length=64) results = models.ManyToManyField(Musician, through='UserData') class UserData(models.Model): artist = models.ForeignKey(Musician) dataset = models.ForeignKey(UserDataSets) score = models.IntegerField() class Meta: unique_together = (("artist", "dataset"),) I have a simple upload mechanism enabling users to upload a data set file that consists of 1 to 1 relationship between a Musician and their "score". Within a given user dataset each artist will be unique, but different datasets are independent from each other and will often contain entries for the same musician. This worked fine for displaying the data, starting from a given artist I can do something like this: artist = Musician.objects.get(pk=1) dataset = UserDataSets.objects.get(pk=5) print artist.userdata_set.get(dataset=dataset.pk) However, this approach fell over when I came to implement the filtering and ordering of query set of musicians based on the data contained in a single user data set. For example, I could easily order the query set based on all of the data in the UserData table like this: artists = Musician.objects.all().order_by(userdata__score) But that does not help me order by the results of a given single user dataset. Likewise I need to be able to filter the query set based on the "scores" from different user data sets (eg find all musicians with a score 5 in dataset1 and < 2 in dataset2). Is there a way of doing this, or am I going about the whole thing wrong?

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• ZF Autoloader to load ancestor and requested class

  - by Pekka

  I am integrating Zend Framework into an existing application. I want to switch the application over to Zend's autoloading mechanism to replace dozens of include() statements. I have a specific requirement for the autoloading mechanism, though. Allow me to elaborate. The existing application uses a core library (independent from ZF), for example: /Core/Library/authentication.php /Core/Library/translation.php /Core/Library/messages.php this core library is to remain untouched at all times and serves a number of applications. The library contains classes like class ancestor_authentication { ... } class ancestor_translation { ... } class ancestor_messages { ... } in the application, there is also a Library directory: /App/Library/authentication.php /App/Library/translation.php /App/Library/messages.php these includes extend the ancestor classes and are the ones that actually get instantiated in the application. class authentication extends ancestor_authentication { } class translation extends ancestor_translation { } class messages extends ancestor_messages { } usually, these class definitions are empty. They simply extend their ancestors and provide the class name to instantiate. $authentication = new authentication(); The purpose of this solution is to be able to easily customize aspects of the application without having to patch the core libraries. Now, the autoloader I need would have to be aware of this structure. When an object of the class authentication is requested, the autoloader would have to: 1. load /Core/Library/authentication.php 2. load /App/Library/authentication.php My current approach would be creating a custom function, and binding that to Zend_Loader_Autoloader for a specific namespace prefix. Is there already a way to do this in Zend that I am overlooking? The accepted answer in this question kind of implies there is, but that may be just a bad choice of wording. Are there extensions to the Zend Autoloader that do this? Can you - I am new to ZF - think of an elegant way, conforming with the spirit of the framework, of extending the Autoloader with this functionality? I'm not necessary looking for a ready-made implementation, some pointers (This should be an extension to the xyz method that you would call like this...) would already be enough.

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• ANSI C as core of a C# project? Is this possible?

  - by Nektarios

  I'm writing a NON-GUI app which I want to be cross platform between OS X and Windows. I'm looking at the following architecture, but I don't know if it will work on the windows side: (Platform specific entry point) - ANSI C main loop = ANSI C model code doing data processing / logic = (Platform specific helpers) So the core stuff I'm planning to write in regular ANSI C, because A) it should be platform independent, B) I'm extremely comfortable with C, C) It can do the job and do it well (Platform specific entry point) can be written in whatever necessary to get the job done, this is a small amount of code, doesn't matter to me. (Platform specific helpers) is the sticky thing. This is stuff like parsing XML, accessing databases, graphics toolkit stuff, whatever. Things that aren't easy in C. Things that modern languages/frameworks will give for free. On OS X this code will be written in Objective-C interfacing with Cocoa. On Windows I'm thinking my best bet is to use C# So on Windows my architecture (simplified) looks like (C# or C?) - ANSI C - C# Is this possible? Some thoughts/suggestions so far.. 1) Compile my C core as a .dll -- this is fine, but seems there's no way to call my C# helpers unless I can somehow get function pointers and pass them to my core, but that seems unlikely 2) Compile a C .exe and a C# .exe and have them talk via shared memory or some kind of IPC. I'm not entirely opposed to this but it obviously introduces a lot of complexity so it doesn't seem ideal 3) Instead of C# use C++, it gets me some nice data management stuff and nice helper code. And I can mix it pretty easily. And the work I do could probably easily port to Linux. But I really don't like C++, and I don't want this to turn in to a 3rd-party-library-fest. Not that it's a huge deal, but it's 2010.. anything for basic data management should be built in. And targetting Linux is really not a priority. Note that no "total" alternatives are OK as suggested in other similar questions on SO I've seen; java, RealBasic, mono.. this is an extremely performance intensive application doing soft realtime for game/simulation purposes, I need C & friends here to do it right (maybe you don't, but I do)

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• Web Services, Memory Leaks and CRM

  - by Neil

  Hi, I have a website that allows users to upload a csv file. This calls a service that reads the information from the csv, puts it into DynamicEntity objects and calls the CRM service to Create/Update entities in CRM. When this service creates/updates an entity this kicks off other plugins to apply certain business rules. These rules can also Create or Update entites in CRM. The issue here is that the handle count of the w3wp.exe process that the website is calling increases every time the an entity is created or updated and it never comes back down. I tried putting Garbage Collection code in the business rules and this reduces the handle count of the CRM w3wp process (run by the Network Service), but not the other w3wp process. Should I have Dispose methods on the Web Service that calls the CRM service? I hope that makes sense. I'm not overly familiar with memory management issues so any help is appreciated. Can anybody give me some tips on how to stop this from occurring? Thanks, Neil -- EDIT Okay well the handle count goes up when I call the Service.Create(DynamicEntity) method. I don't think placing any code here would be beneficial. When I exit the method/class/service that contains this call the handle count stays as it is. What I need to know is whether this is something I should be managing or is it something CRM takes care of (or doesn't take care of but I can't do anything about it) -- Another Edit Right this is how it works. 1) We have CRM and its related services 2) We have another service independent of CRM that uses the CRM services (number 1 above) to create entities based on csv info passed into it 3) We have a website that allows a user to upload a csv, and calls service no 2 above to Create/Update entities in CRM 4) We have plugins fired by CRM which use Service 1 above to create/update entities So the user uploads a csv to the website (3), this fires a service(2). When service 2 creates an entity using service 1, Service 4 fires. Service 4 calls also uses service 1 to Create entities, and when these services are called (using the Service.Create() method) the handle count of the process increases. When the method/class/services finish the handle count remains the same, and so when the whole process occurs again the handle count will increased again.

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• Repeat Customers Each Year (Retention)

  - by spazzie

  I've been working on this and I don't think I'm doing it right. |D Our database doesn't keep track of how many customers we retain so we looked for an alternate method. It's outlined in this article. It suggests you have this table to fill in: Year Number of Customers Number of customers Retained in 2009 Percent (%) Retained in 2009 Number of customers Retained in 2010 Percent (%) Retained in 2010 .... 2008 2009 2010 2011 2012 Total The table would go out to 2012 in the headers. I'm just saving space. It tells you to find the total number of customers you had in your starting year. To do this, I used this query since our starting year is 2008: select YEAR(OrderDate) as 'Year', COUNT(distinct(billemail)) as Customers from dbo.tblOrder where OrderDate >= '2008-01-01' and OrderDate <= '2008-12-31' group by YEAR(OrderDate) At the moment we just differentiate our customers by email address. Then you have to search for the same names of customers who purchased again in later years (ours are 2009, 10, 11, and 12). I came up with this. It should find people who purchased in both 2008 and 2009. SELECT YEAR(OrderDate) as 'Year',COUNT(distinct(billemail)) as Customers FROM dbo.tblOrder o with (nolock) WHERE o.BillEmail IN (SELECT DISTINCT o1.BillEmail FROM dbo.tblOrder o1 with (nolock) WHERE o1.OrderDate BETWEEN '2008-1-1' AND '2009-1-1') AND o.BillEmail IN (SELECT DISTINCT o2.BillEmail FROM dbo.tblOrder o2 with (nolock) WHERE o2.OrderDate BETWEEN '2009-1-1' AND '2010-1-1') --AND o.OrderDate BETWEEN '2008-1-1' AND '2013-1-1' AND o.BillEmail NOT LIKE '%@halloweencostumes.com' AND o.BillEmail NOT LIKE '' GROUP BY YEAR(OrderDate) So I'm just finding the customers who purchased in both those years. And then I'm doing an independent query to find those who purchased in 2008 and 2010, then 08 and 11, and then 08 and 12. This one finds 2008 and 2010 purchasers: SELECT YEAR(OrderDate) as 'Year',COUNT(distinct(billemail)) as Customers FROM dbo.tblOrder o with (nolock) WHERE o.BillEmail IN (SELECT DISTINCT o1.BillEmail FROM dbo.tblOrder o1 with (nolock) WHERE o1.OrderDate BETWEEN '2008-1-1' AND '2009-1-1') AND o.BillEmail IN (SELECT DISTINCT o2.BillEmail FROM dbo.tblOrder o2 with (nolock) WHERE o2.OrderDate BETWEEN '2010-1-1' AND '2011-1-1') --AND o.OrderDate BETWEEN '2008-1-1' AND '2013-1-1' AND o.BillEmail NOT LIKE '%@halloweencostumes.com' AND o.BillEmail NOT LIKE '' GROUP BY YEAR(OrderDate) So you see I have a different query for each year comparison. They're all unrelated. So in the end I'm just finding people who bought in 2008 and 2009, and then a potentially different group that bought in 2008 and 2010, and so on. For this to be accurate, do I have to use the same grouping of 2008 buyers each time? So they bought in 2009 and 2010 and 2011, and 2012? This is where I'm worried and not sure how to proceed or even find such data. Any advice would be appreciated! Thanks!

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• How can I improve my select query for storing large versioned data sets?

  - by Jason Francis

  At work, we build large multi-page web applications, consisting mostly of radio and check boxes. The primary purpose of each application is to gather data, but as users return to a page they have previously visited, we report back to them their previous responses. Worst-case scenario, we might have up to 900 distinct variables and around 1.5 million users. For several reasons, it makes sense to use an insert-only approach to storing the data (as opposed to update-in-place) so that we can capture historical data about repeated interactions with variables. The net result is that we might have several responses per user per variable. Our table to collect the responses looks something like this: CREATE TABLE [dbo].[results]( [id] [bigint] IDENTITY(1,1) NOT NULL, [userid] [int] NULL, [variable] [varchar](8) NULL, [value] [tinyint] NULL, [submitted] [smalldatetime] NULL) Where id serves as the primary key. Virtually every request results in a series of insert statements (one per variable submitted), and then we run a select to produce previous responses for the next page (something like this): SELECT t.id, t.variable, t.value FROM results t WITH (NOLOCK) WHERE t.userid = '2111846' AND (t.variable='internat' OR t.variable='veteran' OR t.variable='athlete') AND t.id IN (SELECT MAX(id) AS id FROM results WITH (NOLOCK) WHERE userid = '2111846' AND (t.variable='internat' OR t.variable='veteran' OR t.variable='athlete') GROUP BY variable) Which, in this case, would return the most recent responses for the variables "internat", "veteran", and "athlete" for user 2111846. We have followed the advice of the database tuning tools in indexing the tables, and against our data, this is the best-performing version of the select query that we have been able to come up with. Even so, there seems to be significant performance degradation as the table approaches 1 million records (and we might have about 150x that). We have a fairly-elegant solution in place for sharding the data across multiple tables which has been working quite well, but I am open for any advice about how I might construct a better version of the select query. We use this structure frequently for storing lots of independent data points, and we like the benefits it provides. So the question is, how can I improve the performance of the select query? I assume the nested select statement is a bad idea, but I have yet to find an alternative that performs as well. Thanks in advance. NB: Since we emphasize creating over reading in this case, and since we never update in place, there doesn't seem to be any penalty (and some advantage) for using the NOLOCK directive in this case.

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• Binding on a port with netpipes/netcat

  - by mindas

  I am trying to write a simple bash script that is listening on a port and responding with a trivial HTTP response. My specific issue is that I am not sure if the port is available and in case of bind failure I fall back to next port until bind succeeds. So far to me the easiest way to achieve this was something like: for (( i=$PORT_BASE; i < $(($PORT_BASE+$PORT_RANGE)); i++ )) do if [ $DEBUG -eq 1 ] ; then echo trying to bind on $i fi /usr/bin/faucet $i --out --daemon echo test 2>/dev/null if [ $? -eq 0 ] ; then #success? port=$i if [ $DEBUG -eq 1 ] ; then echo "bound on port $port" fi break fi done Here I am using faucet from netpipes Ubuntu package. The problem with this is that if I simply print "test" to the output, curl complains about non-standard HTTP response (error code 18). That's fair enough as I don't print HTTP-compatible response. If I replace echo test with echo -ne "HTTP/1.0 200 OK\r\n\r\ntest", curl still complains: user@server:$ faucet 10020 --out --daemon echo -ne "HTTP/1.0 200 OK\r\n\r\ntest" ... user@client:$ curl ip.of.the.server:10020 curl: (56) Failure when receiving data from the peer I think the problem lies in how faucet is printing the response and handling the connection. For example if I do the server side in netcat, curl works fine: user@server:$ echo -ne "HTTP/1.0 200 OK\r\n\r\ntest\r\n" | nc -l 10020 ... user@client:$ curl ip.of.the.server:10020 test user@client:$ I would be more than happy to replace faucet with netcat in my main script, but the problem is that I want to spawn independent server process to be able to run client from the same base shell. faucet has a very handy --daemon parameter as it forks to background and I can use $? (exit status code) to check if bind succeeded. If I was to use netcat for a similar purpose, I would have to fork it using & and $? would not work. Does anybody know why faucet isn't responding correctly in this particular case and/or can suggest a solution to this problem. I am not married neither to faucet nor netcat but would like the solution to be implemented using bash or it's utilities (as opposed to write something in yet another scripting language, such as Perl or Python).

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• Messing with the stack in assembly and c++

  - by user246100

  I want to do the following: I have a function that is not mine (it really doesn't matter here but just to say that I don't have control over it) and that I want to patch so that it calls a function of mine, preserving the arguments list (jumping is not an option). What I'm trying to do is, to put the stack pointer as it was before that function is called and then call mine (like going back and do again the same thing but with a different function). This doesn't work straight because the stack becomes messed up. I believe that when I do the call it replaces the return address. So, I did a step to preserve the return address saving it in a globally variable and it works but this is not ok because I want it to resist to recursitivy and you know what I mean. Anyway, i'm a newbie in assembly so that's why I'm here. Please, don't tell me about already made software to do this because I want to make things my way. Of course, this code has to be compiler and optimization independent. My code (If it is bigger than what is acceptable please tell me how to post it): // A function that is not mine but to which I have access and want to patch so that it calls a function of mine with its original arguments void real(int a,int b,int c,int d) { } // A function that I want to be called, receiving the original arguments void receiver(int a,int b,int c,int d) { printf("Arguments %d %d %d %d\n",a,b,c,d); } long helper; // A patch to apply in the "real" function and on which I will call "receiver" with the same arguments that "real" received. __declspec( naked ) void patch() { _asm { // This first two instructions save the return address in a global variable // If I don't save and restore, the program won't work correctly. // I want to do this without having to use a global variable mov eax, [ebp+4] mov helper,eax push ebp mov ebp, esp // Make that the stack becomes as it were before the real function was called add esp, 8 // Calls our receiver call receiver mov esp, ebp pop ebp // Restores the return address previously saved mov eax, helper mov [ebp+4],eax ret } } int _tmain(int argc, _TCHAR* argv[]) { FlushInstructionCache(GetCurrentProcess(),&real,5); DWORD oldProtection; VirtualProtect(&real,5,PAGE_EXECUTE_READWRITE,&oldProtection); // Patching the real function to go to my patch ((unsigned char*)real)[0] = 0xE9; *((long*)((long)(real) + sizeof(unsigned char))) = (char*)patch - (char*)real - 5; // calling real function (I'm just calling it with inline assembly because otherwise it seems to works as if it were un patched // that is strange but irrelevant for this _asm { push 666 push 1337 push 69 push 100 call real add esp, 16 } return 0; }

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• How can I represent a line of music notes in a way that allows fast insertion at any index?

  - by chairbender

  For "fun", and to learn functional programming, I'm developing a program in Clojure that does algorithmic composition using ideas from this theory of music called "Westergaardian Theory". It generates lines of music (where a line is just a single staff consisting of a sequence of notes, each with pitches and durations). It basically works like this: Start with a line consisting of three notes (the specifics of how these are chosen are not important). Randomly perform one of several "operations" on this line. The operation picks randomly from all pairs of adjacent notes that meet a certain criteria (for each pair, the criteria only depends on the pair and is independent of the other notes in the line). It inserts 1 or several notes (depending on the operation) between the chosen pair. Each operation has its own unique criteria. Continue randomly performing these operations on the line until the line is the desired length. The issue I've run into is that my implementation of this is quite slow, and I suspect it could be made faster. I'm new to Clojure and functional programming in general (though I'm experienced with OO), so I'm hoping someone with more experience can point out if I'm not thinking in a functional paradigm or missing out on some FP technique. My current implementation is that each line is a vector containing maps. Each map has a :note and a :dur. :note's value is a keyword representing a musical note like :A4 or :C#3. :dur's value is a fraction, representing the duration of the note (1 is a whole note, 1/4 is a quarter note, etc...). So, for example, a line representing the C major scale starting on C3 would look like this: [ {:note :C3 :dur 1} {:note :D3 :dur 1} {:note :E3 :dur 1} {:note :F3 :dur 1} {:note :G3 :dur 1} {:note :A4 :dur 1} {:note :B4 :dur 1} ] This is a problematic representation because there's not really a quick way to insert into an arbitrary index of a vector. But insertion is the most frequently performed operation on these lines. My current terrible function for inserting notes into a line basically splits the vector using subvec at the point of insertion, uses conj to join the first part + notes + last part, then uses flatten and vec to make them all be in a one-dimensional vector. For example if I want to insert C3 and D3 into the the C major scale at index 3 (where the F3 is), it would do this (I'll use the note name in place of the :note and :dur maps): (conj [C3 D3 E3] [C3 D3] [F3 G3 A4 B4]), which creates [C3 D3 E3 [C3 D3] [F3 G3 A4 B4]] (vec (flatten previous-vector)) which gives [C3 D3 E3 C3 D3 F3 G3 A4 B4] The run time of that is O(n), AFAIK. I'm looking for a way to make this insertion faster. I've searched for information on Clojure data structures that have fast insertion but haven't found anything that would work. I found "finger trees" but they only allow fast insertion at the start or end of the list. Edit: I split this into two questions. The other part is here.

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• progress at work

  - by noopize

  I work in a small department in a very large company. Our department operates largely as a independent unit within the company. Each member of the team has a different role. My role within the team is a operations/admin and no one knew of my skills in programing as I never said anything before about it. I just did my work and in the free time read up on things for my own development Our developer who used to look after our websites has left a few months ago. Now when we require edits to our websites even basic HTML changes we outsource the work. We are getting shafted big time. I could of so said something sooner to highlight my skills in this area but I guess I was just happy to do my own development projects. And one reason was they are using asp.net and I have mainly done things in php. I only hinted before that I have done things but I did not want to reveal them before I had completed anything. I was working on something for myself that the company was also trying to implement something similar(e commerce site). I used open source and they decided to go for a propriety solution. Now I have finished my project and showed it to my boss, their project is still not completed and is quite expensive. He was impressed with what I showed him and suggested I should go for courses to learn asp.net. that I may be able to do the development work for them and there are some big upcoming projects in the future. He said this would be a benefit for me that I should look to be doing a better then role then admin. My employer does have a policy if relevent to the role they may support the costs of courses. Now how do I play this what should I say to my boss. I want to get advise on which MS certified courses would be good for asp.net and how to best approach my boss to see if they will pay all the amount for the course. And how much different will asp.net be from php.

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• ASP.NET MVC 3 Hosting :: New Features in ASP.NET MVC 3

  - by mbridge

  Razor View Engine The Razor view engine is a new view engine option for ASP.NET MVC that supports the Razor templating syntax. The Razor syntax is a streamlined approach to HTML templating designed with the goal of being a code driven minimalist templating approach that builds on existing C#, VB.NET and HTML knowledge. The result of this approach is that Razor views are very lean and do not contain unnecessary constructs that get in the way of you and your code. ASP.NET MVC 3 Preview 1 only supports C# Razor views which use the .cshtml file extension. VB.NET support will be enabled in later releases of ASP.NET MVC 3. For more information and examples, see Introducing “Razor” – a new view engine for ASP.NET on Scott Guthrie’s blog. Dynamic View and ViewModel Properties A new dynamic View property is available in views, which provides access to the ViewData object using a simpler syntax. For example, imagine two items are added to the ViewData dictionary in the Index controller action using code like the following: public ActionResult Index() {          ViewData["Title"] = "The Title";          ViewData["Message"] = "Hello World!"; } Those properties can be accessed in the Index view using code like this: <h2>View.Title</h2> <p>View.Message</p> There is also a new dynamic ViewModel property in the Controller class that lets you add items to the ViewData dictionary using a simpler syntax. Using the previous controller example, the two values added to the ViewData dictionary can be rewritten using the following code: public ActionResult Index() {     ViewModel.Title = "The Title";     ViewModel.Message = "Hello World!"; } “Add View” Dialog Box Supports Multiple View Engines The Add View dialog box in Visual Studio includes extensibility hooks that allow it to support multiple view engines, as shown in the following figure: Service Location and Dependency Injection Support ASP.NET MVC 3 introduces improved support for applying Dependency Injection (DI) via Inversion of Control (IoC) containers. ASP.NET MVC 3 Preview 1 provides the following hooks for locating services and injecting dependencies: - Creating controller factories. - Creating controllers and setting dependencies. - Setting dependencies on view pages for both the Web Form view engine and the Razor view engine (for types that derive from ViewPage, ViewUserControl, ViewMasterPage, WebViewPage). - Setting dependencies on action filters. Using a Dependency Injection container is not required in order for ASP.NET MVC 3 to function properly. Global Filters ASP.NET MVC 3 allows you to register filters that apply globally to all controller action methods. Adding a filter to the global filters collection ensures that the filter runs for all controller requests. To register an action filter globally, you can make the following call in the Application_Start method in the Global.asax file: GlobalFilters.Filters.Add(new MyActionFilter()); The source of global action filters is abstracted by the new IFilterProvider interface, which can be registered manually or by using Dependency Injection. This allows you to provide your own source of action filters and choose at run time whether to apply a filter to an action in a particular request. New JsonValueProviderFactory Class The new JsonValueProviderFactory class allows action methods to receive JSON-encoded data and model-bind it to an action-method parameter. This is useful in scenarios such as client templating. Client templates enable you to format and display a single data item or set of data items by using a fragment of HTML. ASP.NET MVC 3 lets you connect client templates easily with an action method that both returns and receives JSON data. Support for .NET Framework 4 Validation Attributes and IvalidatableObject The ValidationAttribute class was improved in the .NET Framework 4 to enable richer support for validation. When you write a custom validation attribute, you can use a new IsValid overload that provides a ValidationContext instance. This instance provides information about the current validation context, such as what object is being validated. This change enables scenarios such as validating the current value based on another property of the model. The following example shows a sample custom attribute that ensures that the value of PropertyOne is always larger than the value of PropertyTwo: public class CompareValidationAttribute : ValidationAttribute {     protected override ValidationResult IsValid(object value,              ValidationContext validationContext) {         var model = validationContext.ObjectInstance as SomeModel;         if (model.PropertyOne > model.PropertyTwo) {            return ValidationResult.Success;         }         return new ValidationResult("PropertyOne must be larger than PropertyTwo");     } } Validation in ASP.NET MVC also supports the .NET Framework 4 IValidatableObject interface. This interface allows your model to perform model-level validation, as in the following example: public class SomeModel : IValidatableObject {     public int PropertyOne { get; set; }     public int PropertyTwo { get; set; }     public IEnumerable<ValidationResult> Validate(ValidationContext validationContext) {         if (PropertyOne <= PropertyTwo) {            yield return new ValidationResult(                "PropertyOne must be larger than PropertyTwo");         }     } } New IClientValidatable Interface The new IClientValidatable interface allows the validation framework to discover at run time whether a validator has support for client validation. This interface is designed to be independent of the underlying implementation; therefore, where you implement the interface depends on the validation framework in use. For example, for the default data annotations-based validator, the interface would be applied on the validation attribute. Support for .NET Framework 4 Metadata Attributes ASP.NET MVC 3 now supports .NET Framework 4 metadata attributes such as DisplayAttribute. New IMetadataAware Interface The new IMetadataAware interface allows you to write attributes that simplify how you can contribute to the ModelMetadata creation process. Before this interface was available, you needed to write a custom metadata provider in order to have an attribute provide extra metadata. This interface is consumed by the AssociatedMetadataProvider class, so support for the IMetadataAware interface is automatically inherited by all classes that derive from that class (notably, the DataAnnotationsModelMetadataProvider class). New Action Result Types In ASP.NET MVC 3, the Controller class includes two new action result types and corresponding helper methods. HttpNotFoundResult Action The new HttpNotFoundResult action result is used to indicate that a resource requested by the current URL was not found. The status code is 404. This class derives from HttpStatusCodeResult. The Controller class includes an HttpNotFound method that returns an instance of this action result type, as shown in the following example: public ActionResult List(int id) {     if (id < 0) {                 return HttpNotFound();     }     return View(); } HttpStatusCodeResult Action The new HttpStatusCodeResult action result is used to set the response status code and description. Permanent Redirect The HttpRedirectResult class has a new Boolean Permanent property that is used to indicate whether a permanent redirect should occur. A permanent redirect uses the HTTP 301 status code. Corresponding to this change, the Controller class now has several methods for performing permanent redirects: - RedirectPermanent - RedirectToRoutePermanent - RedirectToActionPermanent These methods return an instance of HttpRedirectResult with the Permanent property set to true. Breaking Changes The order of execution for exception filters has changed for exception filters that have the same Order value. In ASP.NET MVC 2 and earlier, exception filters on the controller with the same Order as those on an action method were executed before the exception filters on the action method. This would typically be the case when exception filters were applied without a specified order Order value. In MVC 3, this order has been reversed in order to allow the most specific exception handler to execute first. As in earlier versions, if the Order property is explicitly specified, the filters are run in the specified order. Known Issues When you are editing a Razor view (CSHTML file), the Go To Controller menu item in Visual Studio will not be available, and there are no code snippets.

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• Week in Geek: New Security Flaw Confirmed for Internet Explorer Edition

  - by Asian Angel

  This week we learned how to use a PC to stay entertained while traveling for the holidays, create quality photo prints with free software, share links between any browser and any smartphone, create perfect Christmas photos using How-To Geek’s 10 best how-to photo guides, and had fun decorating Firefox with a collection of Holiday 2010 Personas themes. Photo by Repoort. Random Geek Links Photo by Asian Angel. Critical 0-Day Flaw Affects All Internet Explorer Versions, Microsoft Warns Microsoft has confirmed a zero-day vulnerability affecting all supported versions of Internet Explorer, including IE8, IE7 and IE6. Note: Article contains link to Microsoft Security Advisory detailing two work-arounds until a security update is released. Hackers targeting human rights, indie media groups Hackers are increasingly hitting the Web sites of human rights and independent media groups in an attempt to silence them, says a new study released this week by Harvard University’s Berkman Center for Internet & Society. OpenBSD: audits give no indication of back doors So far, the analyses of OpenBSD’s crypto and IPSec code have not provided any indication that the system contains back doors for listening to encrypted VPN connections. But the developers have already found two bugs during their current audits. Sophos: Beware Facebook’s new facial-recognition feature Facebook’s new facial recognition software might result in undesirable photos of users being circulated online, warned a security expert, who urged users to keep abreast with the social network’s privacy settings to prevent the abovementioned scenario from becoming a reality. Microsoft withdraws flawed Outlook update Microsoft has withdrawn update KB2412171 for Outlook 2007, released last Patch Tuesday, after a number of user complaints. Skype: Millions still without service Skype was still working to right itself going into the holiday weekend from a major outage that began this past Wednesday. Mozilla improves sync setup and WebGL in Firefox 4 beta 8 Firefox 4.0 beta 8 brings better support for WebGL and introduces an improved setup process for Firefox Sync that simplifies the steps for configuring the synchronization service across multiple devices. Chrome OS the litmus test for cloud The success or failure of Google’s browser-oriented Chrome OS will be the litmus test to decide if the cloud is capable of addressing user needs for content and services, according to a new Ovum report released Monday. FCC Net neutrality rules reach mobile apps The Federal Communications Commission (FCC) finally released its long-expected regulations on Thursday and the related explanations total a whopping 194 pages. One new item that was not previously disclosed: mobile wireless providers can’t block “applications that compete with the provider’s” own voice or video telephony services. KDE and the Document Foundation join Open Invention Network The KDE e.V. and the Document Foundation (TDF) have both joined the Open Invention Network (OIN) as licensees, expanding the organization’s roster of supporters. Report: SEC looks into Hurd’s ousting from HP The scandal surrounding Mark Hurd’s departure from the world’s largest technology company in August has officially drawn attention from the U.S. Securities and Exchange Commission. Report: Google requests delay of new Google TVs Google TV is apparently encountering a bit of static that has resulted in a programming change. Geek Video of the Week This week we have a double dose of geeky video goodness for you with the original Mac vs PC video and the trailer for the sequel. Photo courtesy of Peacer. Mac vs PC Photo courtesy of Peacer. Mac vs PC 2 Trailer Random TinyHacker Links Awesome Tools To Extract Audio From Video Here’s a list of really useful, and free tools to rip audio from videos. Getting Your iPhone Out of Recovery Mode Is your iPhone stuck in recovery mode? This tutorial will help you get it out of that state. Google Shared Spaces Quickly create a shared space and collaborate with friends online. McAfee Internet Security 2011 – Upgrade not worthy of a version change McAfee has released their 2011 version of security products. And as this review details, the upgrades are minimal when compared to their 2010 products. For more information, check out the review. 200 Countries Plotted Hans Rosling’s famous lectures combine enormous quantities of public data with a sport’s commentator’s style to reveal the story of the world’s past, present and future development. Now he explores stats in a way he has never done before – using augmented reality animation. Super User Questions Enjoy looking through this week’s batch of popular questions and answers from Super User. How to restore windows 7 to a known working state every time it boots? Is there an easy way to mass-transfer all files between two computers? Coffee spilled inside computer, damaged hard drive Computer does not boot after ram upgrade Keyboard not detected when trying to install Ubuntu 10.10 How-To Geek Weekly Article Recap Have you had a super busy week while preparing for the holiday weekend? Then here is your chance to get caught up on your reading with our five hottest articles for the week. Ask How-To Geek: Rescuing an Infected PC, Installing Bloat-free iTunes, and Taming a Crazy Trackpad How to Use the Avira Rescue CD to Clean Your Infected PC Eight Geektacular Christmas Projects for Your Day Off VirtualBox 4.0 Rocks Extensions and a Simplified GUI Ask the Readers: How Many Monitors Do You Use with Your Computer? One Year Ago on How-To Geek Here are more great articles from one year ago for you to read and enjoy during the holiday break. Enjoy Distraction-Free Writing with WriteMonkey Shutter is a State of Art Screenshot Tool for Ubuntu Get Hex & RGB Color Codes the Easy Way Find User Scripts for Your Favorite Websites the Easy Way Access Your Unsorted Bookmarks the Easy Way (Firefox) The Geek Note That “wraps” things up for this week and we hope that everyone enjoys the rest of their holiday break! Found a great tip during the break? Then be sure to send it in to us at [email protected]. Photo by ArSiSa7. Latest Features How-To Geek ETC How to Use the Avira Rescue CD to Clean Your Infected PC The Complete List of iPad Tips, Tricks, and Tutorials Is Your Desktop Printer More Expensive Than Printing Services? 20 OS X Keyboard Shortcuts You Might Not Know HTG Explains: Which Linux File System Should You Choose? HTG Explains: Why Does Photo Paper Improve Print Quality? Simon’s Cat Explores the Christmas Tree! [Video] The Outdoor Lights Scene from National Lampoon’s Christmas Vacation [Video] The Famous Home Alone Pizza Delivery Scene [Classic Video] Chronicles of Narnia: The Voyage of the Dawn Treader Theme for Windows 7 Cardinal and Rabbit Sharing a Tree on a Cold Winter Morning Wallpaper An Alternate Star Wars Christmas Special [Video]

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• WinInet Apps failing when Internet Explorer is set to Offline Mode

  - by Rick Strahl

  Ran into a nasty issue last week when all of a sudden many of my old applications that are using WinInet for HTTP access started failing. Specifically, the WinInet HttpSendRequest() call started failing with an error of 2, which when retrieving the error boils down to: WinInet Error 2: The system cannot find the file specified Now this error can pop up in many legitimate scenarios with WinInet such as when no Internet connection is available or the HTTP configuration (usually configured in Internet Explorer’s options) is misconfigured. The error typically means that the server in question cannot be found or more specifically an Internet connection can’t be established. In this case the problem started suddenly and was causing some of my own applications (old Visual FoxPro apps using my own wwHttp library) and all Adobe Air applications (which apparently uses WinInet for its basic HTTP stack) along with a few more oddball applications to fail instantly when trying to connect via HTTP. Most other applications – all of my installed browsers, email clients, various social network updaters all worked just fine. It seems it was only WinInet apps that were failing. Yet oddly Internet Explorer appeared to be working. So the problem seemed to be isolated to those ‘classic’ applications using WinInet. WinInet’s base configuration uses the Internet Explorer options dialog. To check this out I typically go to the Internet Explorer options and find the Connection tab, and check out the LAN Setup. Make sure there are no rogue proxy settings or configuration scripts that are invalid. Trying with Auto-configuration on and off also can often fix ‘real’ configuration errors. This time however this wasn’t a problem – nothing in the LAN configuration was set (all default). I also played with the Automatic detection of settings which also had no effect. I also tried to use Fiddler to see if that would tell me something. Fiddler has a few additional WinInet configuration options in its configuration. Running Fiddler and hitting an HTTP request using WinInet would never actually hit Fiddler – the failure would occur before WinInet ever fired up the HTTP connection to go through the Fiddler HTTP proxy. And the Culprit is: Internet Explorer’s Work Offline Option The culprit in this situation was Internet Explorer which at some point, unknown to me switched into Offline Mode and was then shut down: When this Offline mode is checked when IE is running *or* if IE gets shut down with this flag set, all applications using WinInet by default assume that it’s running in offline mode. Depending on your caching HTTP headers and whether the page was cached previously you may or may not get a response or an error. For an independent non-browser application this will be highly unpredictable and likely result in failures getting online – especially if the application forces requests to always reload by disabling HTTP caching (as I do on most of my dynamic HTTP clients). What makes this especially tricky is that even when IE is in offline mode in the browser, you can still browse around the Web *if* you have a connection. IE will try to load anything it has cached from the local cache, but as soon as you hit a URL that isn’t cached it will automatically try to access that URL and uncheck the Work Offline option. Conversely if you get knocked off the Internet and browse in IE 9, IE will automatically go into offline mode. I never explicitly set offline mode – it just automatically sets itself on and off depending on the connection. Problem is if you’re not using IE all the time (as I do – rarely and just for testing so usually a few commonly used URLs) and you left it in offline mode when you exit, offline mode stays set which results in the above head scratcher. Ack. This isn’t new behavior in IE 9 BTW – this behavior has always been there, but I think what’s different is that IE now automatically switches between online and offline modes without notifying you at all, so it’s hard to tell when you are offline. Fixing the Issue in your Code If you have an application that is using WinInet, there’s a WinInet option called INTERNET_OPTION_IGNORE_OFFLINE. I just checked this out in my own applications and Internet Explorer 9 and it works, but apparently it’s been broken for some older releases (I can’t confirm how far back though) – lots of posts seem to suggest the flag doesn’t work. However, in IE 9 at least it does seem to work if you call InternetSetOption before you call HttpOpenRequest with the Http Session handle. In FoxPro code I use: DECLARE INTEGER InternetSetOption ;    IN WININET.DLL ;    INTEGER HINTERNET,;    INTEGER dwFlags,;    INTEGER @dwValue,;    INTEGER cbSize lnOptionValue = 1   && BOOL TRUE pass by reference   *** Set needed SSL flags lnResult=InternetSetOption(this.hHttpSession,;    INTERNET_OPTION_IGNORE_OFFLINE ,;  && 77    @lnOptionValue ,4)   DECLARE INTEGER HttpOpenRequest ;    IN WININET.DLL ;    INTEGER hHTTPHandle,;    STRING lpzReqMethod,;    STRING lpzPage,;    STRING lpzVersion,;    STRING lpzReferer,;    STRING lpzAcceptTypes,;    INTEGER dwFlags,;    INTEGER dwContextw     hHTTPResult=HttpOpenRequest(THIS.hHttpsession,;    lcVerb,;    tcPage,;    NULL,NULL,NULL,;    INTERNET_FLAG_RELOAD + ;    IIF(THIS.lsecurelink,INTERNET_FLAG_SECURE,0) + ;    this.nHTTPServiceFlags,0) …  And this fixes the issue at least for IE 9… In my FoxPro wwHttp class I now call this by default to never get bitten by this again… This solves the problem permanently for my HTTP client. I never want to see offline operation in an HTTP client API – it’s just too unpredictable in handling errors and the last thing you want is getting unpredictably stale data. Problem solved but this behavior is – well ugly. But then that’s to be expected from an API that’s based on Internet Explorer, eh?© Rick Strahl, West Wind Technologies, 2005-2011Posted in HTTP  Windows  

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