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• Annoying Captcha >> How to programm a form that can SMELL difference between human and robot?

  - by Sam

  Hi folks. On the comment of my old form needing a CAPTHA, I felt I share my problem, perhaps you recognize it and find its time we had better solutions: FACTUAL PROBLEM I know most of my clients (typical age= 40~60) hate CAPTCHA things. Now, I myself always feel like a robot, when I have to sueeze my eyes and fill in the strange letters from the Capcha... Sometimes I fail! Go back etc. Turnoff. I mean comon its 2011, shouldnt the forms have better A.I. by now? MY NEW IDEA (please dont laugh) Ive thought about it and this is my idea's to tell difference between human and robot: My idea is to give credibility points. 100 points = human 0% = robot. require real human mouse movements require mousemovements that dont follow any mathematical pattern require non-instantaneous reading delays, between load and first input in form when typing in form, delays are measured between letters and words approve as human when typical human behaviour measured (deleting, rephrasing etc) dont allow instant pasting or all fields give points for real keyboard pressures retract points for credibility when hyperlinks in form Test wether fake email field (invisible by human) is populated (suggested by Tomalak) when more than 75% human cretibility, allow to be sent without captcha when less than 25% human crecibility, force captcha puzzle to be sure Could we write a A.I. PHP that replaces the human-annoying capthas, meanwhile stopping most spamservers filing in the data? Not only for the fun of it, but also actually to provide a 99% better alternative than CAPTHCA's. Imagine the userfriendlyness of your forms! Your site distinguishing itself from others, showing your audience your sites KNOWS the difference between a robot and a human. Imagine the advangage. I am trying to capture the essense of that distinguishing edge. PROGRAMMING QUESTION: 1) Are such things possible to programm? 2) If so how would you start such programm? 3) Are there already very good working solutions available elsewhere? 4) If it isn't so hard, your are welcome to share your answer/solutions below. 5) upon completion of hints and new ideas, could this page be the start of a new AI captcha, OR should I forget about it and just go with the flow, forget about the whole AI dream, and use captcha like everyone else.

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• Vim + OmniCppComplete: Completing on Class Members which are STL containers

  - by Robert S. Barnes

  Completion on class members which are STL containers is failing. Completion on local objects which are STL containers works fine. For example, given the following files: // foo.h #include <string> class foo { public: void set_str(const std::string &); std::string get_str_reverse( void ); private: std::string str; }; // foo.cpp #include "foo.h" using std::string; string foo::get_str_reverse ( void ) { string temp; temp.assign(str); reverse(temp.begin(), temp.end()); return temp; } /* ----- end of method foo::get_str ----- */ void foo::set_str ( const string &s ) { str.assign(s); } /* ----- end of method foo::set_str ----- */ I've generated the tags for these two files using: ctags -R --c++-kinds=+pl --fields=+iaS --extra=+q . When I type temp. in the cpp I get a list of string member functions as expected. But if I type str. omnicppcomplete spits out "Pattern Not Found". I've noticed that the temp. completion only works if I have the using std::string; declaration. How do I get completion to work on my class members which are STL containers? Edit I found that completion on members which are STL containers works if I make the follow modifications to the header: // foo.h #include <string> using std::string; class foo { public: void set_str(const string &); string get_str_reverse( void ); private: string str; }; Basically, if I add using std::string; and then remove the std:: name space qualifier from the string str; member and regenerate the tags file then OmniCppComplete is able to do completion on str.. It doesn't seem to matter whether or not I have let OmniCpp_DefaultNamespaces = ["std", "_GLIBCXX_STD"] set in the .vimrc. The problem is that putting using declarations in header files seems like a big no-no, so I'm back to square one.

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• Can a conforming C implementation #define NULL to be something wacky

  - by janks

  I'm asking because of the discussion that's been provoked in this thread: http://stackoverflow.com/questions/2597142/when-was-the-null-macro-not-0/2597232 Trying to have a serious back-and-forth discussion using comments under other people's replies is not easy or fun. So I'd like to hear what our C experts think without being restricted to 500 characters at a time. The C standard has precious few words to say about NULL and null pointer constants. There's only two relevant sections that I can find. First: 3.2.2.3 Pointers An integral constant expression with the value 0, or such an expression cast to type void * , is called a null pointer constant. If a null pointer constant is assigned to or compared for equality to a pointer, the constant is converted to a pointer of that type. Such a pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function. and second: 4.1.5 Common definitions <stddef.h> The macros are NULL which expands to an implementation-defined null pointer constant; The question is, can NULL expand to an implementation-defined null pointer constant that is different from the ones enumerated in 3.2.2.3? In particular, could it be defined as: #define NULL __builtin_magic_null_pointer Or even: #define NULL ((void*)-1) My reading of 3.2.2.3 is that it specifies that an integral constant expression of 0, and an integral constant expression of 0 cast to type void* must be among the forms of null pointer constant that the implementation recognizes, but that it isn't meant to be an exhaustive list. I believe that the implementation is free to recognize other source constructs as null pointer constants, so long as no other rules are broken. So for example, it is provable that #define NULL (-1) is not a legal definition, because in if (NULL) do_stuff(); do_stuff() must not be called, whereas with if (-1) do_stuff(); do_stuff() must be called; since they are equivalent, this cannot be a legal definition of NULL. But the standard says that integer-to-pointer conversions (and vice-versa) are implementation-defined, therefore it could define the conversion of -1 to a pointer as a conversion that produces a null pointer. In which case if ((void*)-1) would evaluate to false, and all would be well. So what do other people think? I'd ask for everybody to especially keep in mind the "as-if" rule described in 2.1.2.3 Program execution. It's huge and somewhat roundabout, so I won't paste it here, but it essentially says that an implementation merely has to produce the same observable side-effects as are required of the abstract machine described by the standard. It says that any optimizations, transformations, or whatever else the compiler wants to do to your program are perfectly legal so long as the observable side-effects of the program aren't changed by them. So if you are looking to prove that a particular definition of NULL cannot be legal, you'll need to come up with a program that can prove it. Either one like mine that blatantly breaks other clauses in the standard, or one that can legally detect whatever magic the compiler has to do to make the strange NULL definition work. Steve Jessop found an example of way for a program to detect that NULL isn't defined to be one of the two forms of null pointer constants in 3.2.2.3, which is to stringize the constant: #define stringize_helper(x) #x #define stringize(x) stringize_helper(x) Using this macro, one could puts(stringize(NULL)); and "detect" that NULL does not expand to one of the forms in 3.2.2.3. Is that enough to render other definitions illegal? I just don't know. Thanks!

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• Variable mysteriously changing value

  - by Eitan

  I am making a simple tcp/ip chat program for practicing threads and tcp/ip. I was using asynchronous methods but had a problem with concurrency so I went to threads and blocking methods (not asynchronous). I have two private variables defined in the class, not static: string amessage = string.Empty; int MessageLength; and a Thread private Thread BeginRead; Ok so I call a function called Listen ONCE when the client starts: public virtual void Listen(int byteLength) { var state = new StateObject {Buffer = new byte[byteLength]}; BeginRead = new Thread(ReadThread); BeginRead.Start(state); } and finally the function to receive commands and process them, I'm going to shorten it because it is really long: private void ReadThread(object objectState) { var state = (StateObject)objectState; int byteLength = state.Buffer.Length; while (true) { var buffer = new byte[byteLength]; int len = MySocket.Receive(buffer); if (len <= 0) return; string content = Encoding.ASCII.GetString(buffer, 0, len); amessage += cleanMessage.Substring(0, MessageLength); if (OnRead != null) { var e = new CommandEventArgs(amessage); OnRead(this, e); } } } Now, as I understand it only one thread at a time will enter BeginRead, I call Receive, it blocks until I get data, and then I process it. The problem: the variable amessage will change it's value between statements that do not touch or alter the variable at all, for example at the bottom of the function at: if (OnRead != null) "amessage" will be equal to 'asdf' and at if (OnRead != null) "amessage" will be equal to qwert. As I understand it this is indicative of another thread changing the value/running asynchronously. I only spawn one thread to do the receiving and the Receive function is blocking, how could there be two threads in this function and if there is only one thread how does amessage's value change between statements that don't affect it's value. As a side note sorry for spamming the site with these questions but I'm just getting a hang of this threading story and it's making me want to sip cyanide. Thanks in advance. EDIT: Here is my code that calls the Listen Method in the client: public void ConnectClient(string ip,int port) { client.Connect(ip,port); client.Listen(5); } and in the server: private void Accept(IAsyncResult result) { var client = new AbstractClient(MySocket.EndAccept(result)); var e = new CommandEventArgs(client, null); Clients.Add(client); client.Listen(5); if (OnClientAdded != null) { var target = (Control) OnClientAdded.Target; if (target != null && target.InvokeRequired) target.Invoke(OnClientAdded, this, e); else OnClientAdded(this, e); } client.OnRead += OnRead; MySocket.BeginAccept(new AsyncCallback(Accept), null); } All this code is in a class called AbstractClient. The client inherits the Abstract client and when the server accepts a socket it create's it's own local AbstractClient, in this case both modules access the functions above however they are different instances and I couldn't imagine threads from different instances combining especially as no variable is static.

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• How to deploy a visual studio custom tool?

  - by Aen Sidhe

  Hello. I have a my own custom tool for Visual Studio 2008 SP1. It consists of 5 assemblies: 3 assemblies with code that used heavily in my other projects, 1 assembly-wrapper above VS2008 SDK and assembly with the tool. If I'd debug my tool from visual studio, using "Run external program" option with command line "C:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\IDE\devenv.exe" and arguments "/ranu /rootsuffix Exp" all work perfectly. After that I trying to deploy it to my working VS copy, not to experimental hive doing: gacutil /i Asm1.dll for all my assemblies and doing RegAsm Asm1.dll only for assembly with custom tool. Neither of utils prints any error, all work as planned, even registry keys appeared. But my tool don't work even after PC restart. What did I do wrong? Wrapper looks like that: [ComVisible(true)] public abstract class CustomToolBase : IVsSingleFileGenerator, IObjectWithSite { #region IVsSingleFileGenerator Members int IVsSingleFileGenerator.DefaultExtension(out string pbstrDefaultExtension) { pbstrDefaultExtension = ".cs"; return 0; } int IVsSingleFileGenerator.Generate(string wszInputFilePath, string bstrInputFileContents, string wszDefaultNamespace, IntPtr[] rgbOutputFileContents, out uint pcbOutput, IVsGeneratorProgress pGenerateProgress) { GenerationEventArgs gea = new GenerationEventArgs( bstrInputFileContents, wszInputFilePath, wszDefaultNamespace, new ServiceProvider(Site as Microsoft.VisualStudio.OLE.Interop.IServiceProvider) .GetService(typeof(ProjectItem)) as ProjectItem, new GenerationProgressFacade(pGenerateProgress) ); if (OnGenerateCode != null) { OnGenerateCode(this, gea); } byte[] bytes = gea.GetOutputCodeBytes(); int outputLength = bytes.Length; rgbOutputFileContents[0] = Marshal.AllocCoTaskMem(outputLength); Marshal.Copy(bytes, 0, rgbOutputFileContents[0], outputLength); pcbOutput = (uint)outputLength; return VSConstants.S_OK; } #endregion #region IObjectWithSite Members void IObjectWithSite.GetSite(ref Guid riid, out IntPtr ppvSite) { IntPtr pUnk = Marshal.GetIUnknownForObject(Site); IntPtr intPointer = IntPtr.Zero; Marshal.QueryInterface(pUnk, ref riid, out intPointer); ppvSite = intPointer; } void IObjectWithSite.SetSite(object pUnkSite) { Site = pUnkSite; } #endregion #region Public Members public object Site { get; private set; } public event EventHandler<GenerationEventArgs> OnGenerateCode; [ComRegisterFunction] public static void Register(Type type) { using (var parent = Registry.LocalMachine.OpenSubKey(@"Software\Microsoft\VisualStudio\9.0", true)) foreach (CustomToolRegistrationAttribute ourData in type.GetCustomAttributes(typeof(CustomToolRegistrationAttribute), false)) ourData.Register(x => parent.CreateSubKey(x), (x, name, value) => x.SetValue(name, value)); } [ComUnregisterFunction] public static void Unregister(Type type) { using (var parent = Registry.LocalMachine.OpenSubKey(@"Software\Microsoft\VisualStudio\9.0", true)) foreach (CustomToolRegistrationAttribute ourData in type.GetCustomAttributes(typeof(CustomToolRegistrationAttribute), false)) ourData.Unregister(x => parent.DeleteSubKey(x, false)); } #endregion } My tool code: [ComVisible(true)] [Guid("55A6C192-D29F-4e22-84DA-DBAF314ED5C3")] [CustomToolRegistration(ToolName, typeof(TransportGeneratorTool))] [ProvideObject(typeof(TransportGeneratorTool))] public class TransportGeneratorTool : CustomToolBase { private const string ToolName = "TransportGeneratorTool"; public TransportGeneratorTool() { OnGenerateCode += GenerateCode; } private static void GenerateCode(object s, GenerationEventArgs e) { try { var serializer = new XmlSerializer(typeof (Parser.System)); using (var reader = new StringReader(e.InputText)) using (var writer = new StringWriter(e.OutputCode)) { Generator.System = (Parser.System) serializer.Deserialize(reader); Generator.System.Namespace = e.Namespace; Generator.GenerateSource(writer); } } catch (Exception ex) { e.Progress.GenerateError(ex.ToString()); } } } Resulting registry keys: Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\9.0\Generators] [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\9.0\Generators\{FAE04EC1-301F-11D3-BF4B-00C04F79EFBC}] [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\9.0\Generators\{FAE04EC1-301F-11D3-BF4B-00C04F79EFBC}\TransportGeneratorTool] @="TransportGeneratorTool" "CLSID"="{55a6c192-d29f-4e22-84da-dbaf314ed5c3}" "GeneratesDesignTimeSource"=dword:00000001 "GeneratesSharedDesignTimeSource"=dword:00000001

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• Design Question - how do you break the dependency between classes using an interface?

  - by Seth Spearman

  Hello, I apologize in advance but this will be a long question. I'm stuck. I am trying to learn unit testing, C#, and design patterns - all at once. (Maybe that's my problem.) As such I am reading the Art of Unit Testing (Osherove), and Clean Code (Martin), and Head First Design Patterns (O'Reilly). I am just now beginning to understand delegates and events (which you would see if you were to troll my SO questions of recent). I still don't quite get lambdas. To contextualize all of this I have given myself a learning project I am calling goAlarms. I have an Alarm class with members you'd expect (NextAlarmTime, Name, AlarmGroup, Event Trigger etc.) I wanted the "Timer" of the alarm to be extensible so I created an IAlarmScheduler interface as follows... public interface AlarmScheduler { Dictionary<string,Alarm> AlarmList { get; } void Startup(); void Shutdown(); void AddTrigger(string triggerName, string groupName, Alarm alarm); void RemoveTrigger(string triggerName); void PauseTrigger(string triggerName); void ResumeTrigger(string triggerName); void PauseTriggerGroup(string groupName); void ResumeTriggerGroup(string groupName); void SetSnoozeTrigger(string triggerName, int duration); void SetNextOccurrence (string triggerName, DateTime nextOccurrence); } This IAlarmScheduler interface define a component that will RAISE an alarm (Trigger) which will bubble up to my Alarm class and raise the Trigger Event of the alarm itself. It is essentially the "Timer" component. I have found that the Quartz.net component is perfectly suited for this so I have created a QuartzAlarmScheduler class which implements IAlarmScheduler. All that is fine. My problem is that the Alarm class is abstract and I want to create a lot of different KINDS of alarm. For example, I already have a Heartbeat alarm (triggered every (int) interval of minutes), AppointmentAlarm (triggered on set date and time), Daily Alarm (triggered every day at X) and perhaps others. And Quartz.NET is perfectly suited to handle this. My problem is a design problem. I want to be able to instantiate an alarm of any kind without my Alarm class (or any derived classes) knowing anything about Quartz. The problem is that Quartz has awesome factories that return just the right setup for the Triggers that will be needed by my Alarm classes. So, for example, I can get a Quartz trigger by using TriggerUtils.MakeMinutelyTrigger to create a trigger for the heartbeat alarm described above. Or TriggerUtils.MakeDailyTrigger for the daily alarm. I guess I could sum it up this way. Indirectly or directly I want my alarm classes to be able to consume the TriggerUtils.Make* classes without knowing anything about them. I know that is a contradiction, but that is why I am asking the question. I thought about putting a delegate field into the alarm which would be assigned one of these Make method but by doing that I am creating a hard dependency between alarm and Quartz which I want to avoid for both unit testing purposes and design purposes. I thought of using a switch for the type in QuartzAlarmScheduler per here but I know it is bad design and I am trying to learn good design. If I may editorialize a bit. I've decided that coding (predefined) classes is easy. Design is HARD...in fact, really hard and I am really fighting feeling stupid right now. I guess I want to know if you really smart people took a while to really understand and master this stuff or should I feel stupid (as I do) because I haven't grasped it better in the couple of weeks/months I have been studying. You guys are awesome and thanks in advance for your answers. Seth

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• [C#] Not enough memory or not enough handles?

  - by Nayan

  I am working on a large scale project where a custom (pretty good and robust) framework has been provided and we have to use that for showing up forms and views. There is abstract class StrategyEditor (derived from some class in framework) which is instantiated whenever a new StrategyForm is opened. StrategyForm (a customized window frame) contains StrategyEditor. StrategyEditor contains StrategyTab. StrategyTab contains StrategyCanvas. This is a small portion of the big classes to clarify that there are many objects that will be created if one StrategyForm object is allocated in memory at run-time. My component owns all these classes mentioned above except StrategyForm whose code is not in my control. Now, at run-time, user opens up many strategy objects (which trigger creation of new StrategyForm object.) After creating approx. 44 strategy objects, we see that the USER OBJECT HANDLES (I'll use UOH from here onwards) created by the application reaches to about 20k+, while in registry the default amount for handles is 10k. Read more about User Objects here. Testing on different machines made it clear that the number of strategy objects opened is different for message to pop-up - on one m/c if it is 44, then it can be 40 on another. When we see the message pop-up, it means that the application is going to respond slowly. It gets worse with few more objects and then creation of window frames and subsequent objects fail. We first thought that it was not-enough-memory issue. But then reading more about new in C# helped in understanding that an exception would be thrown if app ran out of memory. This is not a memory issue then, I feel (task manager also showed 1.5GB+ available memory.) M/C specs Core 2 Duo 2GHz+ 4GB RAM 80GB+ free disk space for page file Virtual Memory set: 4000 - 6000 My questions Q1. Does this look like a memory issue and I am wrong that it is not? Q2. Does this point to exhaustion of free UOHs (as I'm thinking) and which is resulting in failure of creation of window handles? Q3. How can we avoid loading up of an StrategyEditor object (beyond a threshold, keeping an eye on the current usage of UOHs)? (we already know how to fetch number of UOHs in use, so don't go there.) Keep in mind that the call to new StrategyForm() is outside the control of my component. Q4. I am bit confused - what are Handles to user objects exactly? Is MSDN talking about any object that we create or only some specific objects like window handles, cursor handles, icon handles? Q5. What exactly cause to use up a UOH? (almost same as Q4) I would be really thankful to anyone who can give me some knowledgeable answers. Thanks much! :)

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• C# Asynchronous Network IO and OutOfMemoryException

  - by The.Anti.9

  I'm working on a client/server application in C#, and I need to get Asynchronous sockets working so I can handle multiple connections at once. Technically it works the way it is now, but I get an OutOfMemoryException after about 3 minutes of running. MSDN says to use a WaitHandler to do WaitOne() after the socket.BeginAccept(), but it doesn't actually let me do that. When I try to do that in the code it says WaitHandler is an abstract class or interface, and I can't instantiate it. I thought maybe Id try a static reference, but it doesnt have teh WaitOne() method, just WaitAll() and WaitAny(). The main problem is that in the docs it doesn't give a full code snippet, so you can't actually see what their "wait handler" is coming from. its just a variable called allDone, which also has a Reset() method in the snippet, which a waithandler doesn't have. After digging around in their docs, I found some related thing about an AutoResetEvent in the Threading namespace. It has a WaitOne() and a Reset() method. So I tried that around the while(true) { ... socket.BeginAccept( ... ); ... }. Unfortunately this makes it only take one connection at a time. So I'm not really sure where to go. Here's my code: class ServerRunner { private Byte[] data = new Byte[2048]; private int size = 2048; private Socket server; static AutoResetEvent allDone = new AutoResetEvent(false); public ServerRunner() { server = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); IPEndPoint iep = new IPEndPoint(IPAddress.Any, 33333); server.Bind(iep); Console.WriteLine("Server initialized.."); } public void Run() { server.Listen(100); Console.WriteLine("Listening..."); while (true) { //allDone.Reset(); server.BeginAccept(new AsyncCallback(AcceptCon), server); //allDone.WaitOne(); } } void AcceptCon(IAsyncResult iar) { Socket oldserver = (Socket)iar.AsyncState; Socket client = oldserver.EndAccept(iar); Console.WriteLine(client.RemoteEndPoint.ToString() + " connected"); byte[] message = Encoding.ASCII.GetBytes("Welcome"); client.BeginSend(message, 0, message.Length, SocketFlags.None, new AsyncCallback(SendData), client); } void SendData(IAsyncResult iar) { Socket client = (Socket)iar.AsyncState; int sent = client.EndSend(iar); client.BeginReceive(data, 0, size, SocketFlags.None, new AsyncCallback(ReceiveData), client); } void ReceiveData(IAsyncResult iar) { Socket client = (Socket)iar.AsyncState; int recv = client.EndReceive(iar); if (recv == 0) { client.Close(); server.BeginAccept(new AsyncCallback(AcceptCon), server); return; } string receivedData = Encoding.ASCII.GetString(data, 0, recv); //process received data here byte[] message2 = Encoding.ASCII.GetBytes("reply"); client.BeginSend(message2, 0, message2.Length, SocketFlags.None, new AsyncCallback(SendData), client); } }

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• Matlab wont extract first row & column because of matrix dimensions !

  - by ZaZu

  Hey guys, I am tracking an object that is thrown in air, and this object governs a parabolic pattern. Im tracking the object through a series of 30 images. I managed to exclude all the background and keep the object apparent, then used its centroid to get its coordinates and plot them. Now im supposed to predict where the object is going to fall, so I used polyfit & polyval .. the problem is, matlab says ??? Index exceeds matrix dimensions. Now the centroid creates its own structure with a row and 2 columns. Everytime the object moves in the loop, it updates the first row only .. Here is part of the code : For N=1:30 . . . x=centroid(1,1); % extract first row and column for x y=centroid(1,2); % extract secnd row and column for x plot_xy=plot(x,y) set(plot_xy,'XData',x(1:N),'YData',y(1:N)); fitting=polyfit(x(1:N),y(1:N),2); parabola=plot(x,nan(23,1)); evaluate=polyval(fitting,x); set(parabola,'YData',evaluate) . . end The error message I get is ??? Index exceeds matrix dimensions. It seems that (1:N) is causing the problems .. I honestly do not know why .. But when I remove N, the object is plotted along with its points, but polyfitting wont work, it gives me an error saying : Warning: Polynomial is not unique; degree >= number of data points. > In polyfit at 72 If I made it (1:N-1) or something, it plots more points before it starts giving me the same error (not unique ...) . Any ideas why ?? Thanks alot !!

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• has_one and has_many associations: which side of the association is saved first

  - by SeeBees

  I have three simplified models: class Team < ActiveRecord::Base has_many :players has_one :coach end class Player < ActiveRecord::Base belongs_to :team validates_presence_of :team_id end class Coach < ActiveRecord::Base belongs_to :team validates_presence_of :team_id end I use the following code to test these models: t = Team.new team.coach = Coach.new team.save! team.save! returns true. But in another test: t = Team.new team.players << Player.new team.save! team.save! gives the following error: > ActiveRecord::RecordInvalid: > Validation failed: Players is invalid > from > /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/validations.rb:1090:in > `save_without_dirty!' from > /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/dirty.rb:87:in `save_without_transactions!' from > /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/transactions.rb:200:in > `save!' from > /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/connection_adapters/abstract/database_statements.rb:136:in > `transaction' from > /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/transactions.rb:182:in > `transaction' from > /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/transactions.rb:200:in > `save!' from > /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/transactions.rb:208:in > `rollback_active_record_state!' from > /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.4/lib/active_record/transactions.rb:200:in > `save!' from (irb):14 I figured out when team.save! is called, it first calls player.save!. player needs to validate the presence of the id of the associated team. But at the time player.save! is called, team hasn't been saved yet, and therefore, team_id doesn't yet exist for player. This fails the player's validation, so the error occurs. But on the other hand, team is saved before coach.save!, otherwise the first example will get the same error as the second. So I've concluded that when a has_many bs, a.save! will save bs prior to a. When a has_one b, a.save! will save a prior to b. If I am right, why is this the case? It doesn't seem logical to me. Why has_one and has_many association have different order in saving? Any ideas? Thanks.

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• Is it a oop good design ?

  - by remi bourgarel

  Hi all, I'd like to know what you think about this part of our program is realized : We have in our database a list of campsite. Partners call us to get all the campsites near a GPS location or all the campsites which provide a bar (we call it a service). So how I realized it ? Here is our database : Campsite - ID - NAME - GPS_latitude - GPS_longitude CampsiteServices -Campsite_ID -Services_ID So my code (c# but it's not relevant, let say it's an OO language) looks like this public class SqlCodeCampsiteFilter{ public string SqlCode; public Dictionary<string, object> Parameters; } interface ISQLCampsiteFilter{ SqlCodeEngineCore CreateSQLCode(); } public class GpsLocationFilter : ISQLCampsiteFilter{ public float? GpsLatitude; public float? GpsLongitude; public SqlCodeEngineCore CreateSQLCode() { --return an sql code to filter on the gps location like dbo.getDistance(@gpsLat,@gpsLong,campsite.GPS_latitude,campsite.GPS_longitude) with the parameters } } public class ServiceFilter : : ISQLCampsiteFilter{ public int[] RequiredServicesID; public SqlCodeEngineCore CreateSQLCode() { --return an sql code to filter on the services "where ID IN (select CampsiteServices.Service_ID FROm CampsiteServices WHERE Service_ID in ...) } } So in my webservice code : List<ISQLFilterEngineCore> filters = new List<ISQLFilterEngineCore>(); if(gps_latitude.hasvalue && gps_longitude.hasvalue){ filters.Add (new GpsLocationFilter (gps_latitude.value,gps_longitude.value)); } if(required_services_id != null){ filters.Add (new ServiceFilter (required_services_id )); } string sql = "SELECT ID,NAME FROM campsite where 1=1" foreach(ISQLFilterEngineCore aFilter in filters){ SqlCodeCampsiteFilter code = aFilter.CreateSQLCode(); sql += code.SqlCode; mySqlCommand.AddParameters(code.Parameters);//add all the parameters to the sql command } return mySqlCommand.GetResults(); 1/ I don't use ORM for the simple reason that the system exists since 10 years and the only dev who is here since the beginning is starting to learn about difference between public and private. 2/ I don't like SP because : we can do override, and t-sql is not so funny to use :) So what do you think ? Is it clear ? Do you have any pattern that I should have a look to ? If something is not clear please ask

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• Unintentional concatenation in Bison/Yacc grammar.

  - by troutwine

  I am experimenting with lex and yacc and have run into a strange issue, but I think it would be best to show you my code before detailing the issue. This is my lexer: %{ #include <stdlib.h> #include <string.h> #include "y.tab.h" void yyerror(char *); %} %% [a-zA-Z]+ { yylval.strV = yytext; return ID; } [0-9]+ { yylval.intV = atoi(yytext); return INTEGER; } [\n] { return *yytext; } [ \t] ; . yyerror("invalid character"); %% int yywrap(void) { return 1; } This is my parser: %{ #include <stdio.h> int yydebug=1; void prompt(); void yyerror(char *); int yylex(void); %} %union { int intV; char *strV; } %token INTEGER ID %% program: program statement EOF { prompt(); } | program EOF { prompt(); } | { prompt(); } ; args: /* empty */ | args ID { printf(":%s ", $<strV>2); } ; statement: ID args { printf("%s", $<strV>1); } | INTEGER { printf("%d", $<intV>1); } ; EOF: '\n' %% void yyerror(char *s) { fprintf(stderr, "%s\n", s); } void prompt() { printf("> "); } int main(void) { yyparse(); return 0; } A very simple language, consisting of no more than strings and integer and a basic REPL. Now, you'll note in the parser that args are output with a leading colon, the intention being that, when combined with the first pattern of the rule of the statement the interaction with the REPL would look something like this: > aaa aa a :aa :a aaa> However, the interaction is this: > aaa aa a :aa :a aaa aa aa > Why does the token ID in the following rule statement: ID args { printf("%s", $<strV>1); } | INTEGER { printf("%d", $<intV>1); } ; have the semantic value of the total input string, newline included? How can my grammar be reworked so that the interaction I intended?

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• Adding NavigationControl to a TabBar Application containing UITableViews

  - by kungfuslippers

  Hi, I'm new to iPhone dev and wanted to get advice on the general design pattern / guide for putting a certain kind of app together. I'm trying to build a TabBar type application. One of the tabs needs to display a TableView and selecting a cell from within the table view will do something else - maybe show another table view or a web page. I need a Navigation Bar to be able to take me back from the table view/web page. The approach I've taken so far is to: Create an app based around UITabBarController as the rootcontroller i.e. @interface MyAppDelegate : NSObject <UIApplicationDelegate> { IBOutlet UIWindow *window; IBOutlet UITabBarController *rootController; } Create a load of UIViewController derived classes and associated NIBs and wire everything up in IB so when I run the app I get the basic tabs working. I then take the UIViewController derived class and modify it to the following: @interface MyViewController : UIViewController<UITableViewDataSource, UITableViewDelegate> { } and I add the delegate methods to the implementation of MyViewController - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { return 2; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; } if (indexPath.row == 0) { cell.textLabel.text = @"Mummy"; } else { cell.textLabel.text = @"Daddy"; } return cell; } Go back to IB , open MyViewController.xib and drop a UITableView onto it. Set the Files Owner to be MyViewController and then set the delegate and datasource of the UITableView to be MyViewController. If I run the app now, I get the table view appearing with mummy and daddy working nicely. So far so good. The question is how do I go about incorporating a Navigation Bar into my current code for when I implement: - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath() { // get row selected NSUInteger row = [indexPath row]; if (row == 0) { // Show another table } else if (row == 1) { // Show a web view } } Do I drop a NavigationBar UI control onto MyControllerView.xib ? Should I create it programmatically? Should I be using a UINavigationController somewhere ? I've tried dropping a NavigationBar onto my MyControllerView.xib in IB but its not shown when I run the app, only the TableView is displayed.

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• XSLT - make xsl:analyze-string return string instead of sequence of strings?

  - by tohuwawohu

  Is it possible to make xsl:analyze-string return one string instead of a sequence of strings? Background: I'd like to use xsl:analyze-string in a xsl:function that should encapsulate the pattern matching. Ideally, the function should return an xs:string to be used as sort criteria in an xsl:sort element. At the moment, i have to apply string-join() on every result of the function call since xsl:analyze-string returns a sequence of strings, and xsl:sort doesn't accept such a sequence as sort criteria. See line 24 of the stylesheet: <?xml version="1.0" encoding="UTF-8"?> <xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:my="www.my-personal-namespa.ce" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xsl:output indent="yes" method="xml" /> <xsl:function name="my:sortierung" > <xsl:param name="inputstring" as="xs:string"/> <xsl:analyze-string select="$inputstring" regex="[0-9]+"> <xsl:matching-substring> <xsl:value-of select="format-number(number(.), '00000')" /> </xsl:matching-substring> <xsl:non-matching-substring> <xsl:value-of select="." /> </xsl:non-matching-substring> </xsl:analyze-string> </xsl:function> <xsl:template match="/input"> <result> <xsl:apply-templates select="value" > <xsl:sort select="string-join((my:sortierung(.)), ' ')" /> </xsl:apply-templates> </result> </xsl:template> <xsl:template match="value"> <xsl:copy-of select="." /> </xsl:template> </xsl:stylesheet> with this input: <?xml version="1.0" encoding="UTF-8"?> <input> <value>A 1 b 120</value> <value>A 1 b 1</value> <value>A 1 b 2</value> <value>A 1 b 1a</value> </input> In my example, is there a way to modify the xsl:function to return a xs:string instead of a sequence?

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• What Amazon S3 .NET Library is most useful and efficient?

  - by Geo

  There are two main open source .net Amazon S3 libraries. Three Sharp LitS3 I am currently using LitS3 in our MVC demo project, but there is some criticism about it. Has anyone here used both libraries so they can give an objective point of view. Below some sample calls using LitS3: On demo controller: private S3Service s3 = new S3Service() { AccessKeyID = "Thekey", SecretAccessKey = "testing" }; public ActionResult Index() { ViewData["Message"] = "Welcome to ASP.NET MVC!"; return View("Index",s3.GetAllBuckets()); } On demo view: <% foreach (var item in Model) { %> <p> <%= Html.Encode(item.Name) %> </p> <% } %> EDIT 1: Since I have to keep moving and there is no clear indication of what library is more effective and kept more up to date, I have implemented a repository pattern with an interface that will allow me to change library if I need to in the future. Below is a section of the S3Repository that I have created and will let me change libraries in case I need to: using LitS3; namespace S3Helper.Models { public class S3Repository : IS3Repository { private S3Service _repository; #region IS3Repository Members public IQueryable<Bucket> FindAllBuckets() { return _repository.GetAllBuckets().AsQueryable(); } public IQueryable<ListEntry> FindAllObjects(string BucketName) { return _repository.ListAllObjects(BucketName).AsQueryable(); } #endregion If you have any information about this question please let me know in a comment, and I will get back and edit the question. EDIT 2: Since this question is not getting attention, I integrated both libraries in my web app to see the differences in design, I know this is probably a waist of time, but I really want a good long run solution. Below you will see two samples of the same action with the two libraries, maybe this will motivate some of you to let me know your thoughts. WITH THREE SHARP LIBRARY: public IQueryable<T> FindAllBuckets<T>() { List<string> list = new List<string>(); using (BucketListRequest request = new BucketListRequest(null)) using (BucketListResponse response = service.BucketList(request)) { XmlDocument bucketXml = response.StreamResponseToXmlDocument(); XmlNodeList buckets = bucketXml.SelectNodes("//*[local-name()='Name']"); foreach (XmlNode bucket in buckets) { list.Add(bucket.InnerXml); } } return list.Cast<T>().AsQueryable(); } WITH LITS3 LIBRARY: public IQueryable<T> FindAllBuckets<T>() { return _repository.GetAllBuckets() .Cast<T>() .AsQueryable(); }

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• LINQ Query Returning Multiple Copies Of First Result

  - by Mike G

  I'm trying to figure out why a simple query in LINQ is returning odd results. I have a view defined in the database. It basically brings together several other tables and does some data munging. It really isn't anything special except for the fact that it deals with a large data set and can be a bit slow. I want to query this view based on a long. Two sample queries below show different queries to this view. var la = Runtime.OmsEntityContext.Positions.Where(p => p.AccountNumber == 12345678).ToList(); var deDa = Runtime.OmsEntityContext.Positions.Where(p => p.AccountNumber == 12345678).Select(p => new { p.AccountNumber, p.SecurityNumber, p.CUSIP }).ToList(); The first one should hand back a List. The second one will be a list of anonymous objects. When I do these queries in entities framework the first one will hand me back a list of results where they're all exactly the same. The second query will hand me back data where the account number is the one that I queried and the other values differ. This seems to do this on a per account number basis, ie if I were to query for one account number or another all the Position objects for one account would have the same value (the first one in the list of Positions for that account) and the second account would have a set of Position objects that all had the same value (again, the first one in it's list of Position objects). I can write SQL that is in effect the same as either of the two EF queries. They both come back with results (say four) that show the correct data, one account number with different securities numbers. Why does this happen??? Is there something that I could be doing wrong so that if I had four results for the first query above that the first record's data also appears in the 2-4th's objects??? I cannot fathom what would/could be causing this. I've searched Google for all kinds of keywords and haven't seen anyone with this issue. We partial class out the Positions class for added functionality (smart object) and some smart properties. There are even some constructors that provide some view model type support. None of this is invoked in the request (I'm 99% sure of this). However, we do this same pattern all over the app. The only thing I can think of is that the mapping in the EDMX is screwy. Is there a way that this would happen if the "primary keys" in the EDMX were not in fact unique given the way the view is constructed? I'm thinking that the dev who imported this model into the EDMX let the designer auto select what would be unique. Any help would give a haggered dev some hope!

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• what's wrong with my producer-consumer queue design?

  - by toasteroven

  I'm starting with the C# code example here. I'm trying to adapt it for a couple reasons: 1) in my scenario, all tasks will be put in the queue up-front before consumers will start, and 2) I wanted to abstract the worker into a separate class instead of having raw Thread members within the WorkerQueue class. My queue doesn't seem to dispose of itself though, it just hangs, and when I break in Visual Studio it's stuck on the _th.Join() line for WorkerThread #1. Also, is there a better way to organize this? Something about exposing the WaitOne() and Join() methods seems wrong, but I couldn't think of an appropriate way to let the WorkerThread interact with the queue. Also, an aside - if I call q.Start(#) at the top of the using block, only some of the threads every kick in (e.g. threads 1, 2, and 8 process every task). Why is this? Is it a race condition of some sort, or am I doing something wrong? using System; using System.Collections.Generic; using System.Text; using System.Messaging; using System.Threading; using System.Linq; namespace QueueTest { class Program { static void Main(string[] args) { using (WorkQueue q = new WorkQueue()) { q.Finished += new Action(delegate { Console.WriteLine("All jobs finished"); }); Random r = new Random(); foreach (int i in Enumerable.Range(1, 10)) q.Enqueue(r.Next(100, 500)); Console.WriteLine("All jobs queued"); q.Start(8); } } } class WorkQueue : IDisposable { private Queue _jobs = new Queue(); private int _job_count; private EventWaitHandle _wh = new AutoResetEvent(false); private object _lock = new object(); private List _th; public event Action Finished; public WorkQueue() { } public void Start(int num_threads) { _job_count = _jobs.Count; _th = new List(num_threads); foreach (int i in Enumerable.Range(1, num_threads)) { _th.Add(new WorkerThread(i, this)); _th[_th.Count - 1].JobFinished += new Action(WorkQueue_JobFinished); } } void WorkQueue_JobFinished(int obj) { lock (_lock) { _job_count--; if (_job_count == 0 && Finished != null) Finished(); } } public void Enqueue(int job) { lock (_lock) _jobs.Enqueue(job); _wh.Set(); } public void Dispose() { Enqueue(Int32.MinValue); _th.ForEach(th = th.Join()); _wh.Close(); } public int GetNextJob() { lock (_lock) { if (_jobs.Count 0) return _jobs.Dequeue(); else return Int32.MinValue; } } public void WaitOne() { _wh.WaitOne(); } } class WorkerThread { private Thread _th; private WorkQueue _q; private int _i; public event Action JobFinished; public WorkerThread(int i, WorkQueue q) { _i = i; _q = q; _th = new Thread(DoWork); _th.Start(); } public void Join() { _th.Join(); } private void DoWork() { while (true) { int job = _q.GetNextJob(); if (job != Int32.MinValue) { Console.WriteLine("Thread {0} Got job {1}", _i, job); Thread.Sleep(job * 10); // in reality would to actual work here if (JobFinished != null) JobFinished(job); } else { Console.WriteLine("Thread {0} no job available", _i); _q.WaitOne(); } } } } }

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• ASP.NET MVC 2 AJAX dilemma: Lose Models concept or create unmanageable JavaScript

  - by Slightly Frustrated

  Hi, Ok, let's assume we are working with ASP.NET MVC 2 (latest and greatest preview) and we want to create AJAX user interface with jQuery. So what are our real options here? Option 1 - Pass Json from the Controller to the view, and then the view submits Json back to the controller. This means (in the order given): User opens some View (let's say - /Invoices/January) which has to visualize a list of data (e.g. <IEnumerable<X.Y.Z.Models.Invoice>>) Controller retrieves the Model from the repository (assuming we are using repository pattern). Controller creates a new instance of a class which we will serialize to Json. The reasaon we do this, is because the model may not be serializable (circular reference ftl) Controller populates the soon-to-be-serialized class with data Controller serializes the class to Json and passes it the view. User does some change and submits the 'form' The View submits back Json to the controller The Controller now must 'manually' validate the input, because the Json passed does not bind to a Model See, if our View is communicating to the controller via Json, we lose the Model validation, which IMHO is incredible disadvantage. In this case, forget about data annotations and stuff. Option 2 - Ok, the alternative of the first approach is to pass the Models to the Views, which is the default behavior in the template when you start a new project. We pass a strong typed model to the view The view renders the appropriate html and javascript, sticking to the model property names. This is important! The user submits the form. If we stick to the model names, when we .serialize() the form and submit it to the controller it will map to a model. There is no Json mapping. The submitted form directly binds to a strongly typed model, hence, we can use the model validation. E.g. we keep the business logic where it should be. Problem with this approach is, if we refactor some of the Models (change property names, types, etc), the javascript we wrote would become invalid. We will have to manually refactor the scripting and hope we don't miss something. There is no way you can test it either. Ok, the question is - how to write an AJAX front end, which keeps the business logic validation in the model (e.g. controller passes and receives a Model type), but in the same time doesn't screw up the javascript and html when we refactor the model?

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• Peer did not return a certificate

  - by pfista

  I am trying to get two way SSL authentication working between a Python server and an Android client application. I have access to both the server and client, and would like to implement client authentication using my own certificate. So far I have been able to verify the server certificate and connect without client authentication. What sort of certificate does the client need and how do I get it to automatically send it to the server during the handshake process? Here is the client and server side code that I have so far. Is my approach wrong? Server Code while True: # Keep listening for clients c, fromaddr = sock.accept() ssl_sock = ssl.wrap_socket(c, keyfile = "serverPrivateKey.pem", certfile = "servercert.pem", server_side = True, # Require the client to provide a certificate cert_reqs = ssl.CERT_REQUIRED, ssl_version = ssl.PROTOCOL_TLSv1, ca_certs = "clientcert.pem", #TODO must point to a file of CA certificates?? do_handshake_on_connect = True, ciphers="!NULL:!EXPORT:AES256-SHA") print ssl_sock.cipher() thrd = sock_thread(ssl_sock) thrd.daemon = True thrd.start() I suspect I may be using the wrong file for ca_certs...? Client Code private boolean connect() { try { KeyStore keystore = KeyStore.getInstance("BKS"); // Stores the client certificate, to be sent to server KeyStore truststore = KeyStore.getInstance("BKS"); // Stores the server certificate we want to trust // TODO: change hard coded password... THIS IS REAL BAD MKAY truststore.load(mSocketService.getResources().openRawResource(R.raw.truststore), "test".toCharArray()); keystore.load(mSocketService.getResources().openRawResource(R.raw.keystore), "test".toCharArray()); // Use the key manager for client authentication. Keys in the key manager will be sent to the host KeyManagerFactory keyFManager = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm()); keyFManager.init(keystore, "test".toCharArray()); // Use the trust manager to determine if the host I am connecting to is a trusted host TrustManagerFactory trustMFactory = TrustManagerFactory.getInstance(TrustManagerFactory .getDefaultAlgorithm()); trustMFactory.init(truststore); // Create the socket factory and add both the trust manager and key manager SSLCertificateSocketFactory socketFactory = (SSLCertificateSocketFactory) SSLCertificateSocketFactory .getDefault(5000, new SSLSessionCache(mSocketService)); socketFactory.setTrustManagers(trustMFactory.getTrustManagers()); socketFactory.setKeyManagers(keyFManager.getKeyManagers()); // Open SSL socket directly to host, host name verification is NOT performed here due to // SSLCertificateFactory implementation mSSLSocket = (SSLSocket) socketFactory.createSocket(mHostname, mPort); mSSLSocket.setSoTimeout(TIMEOUT); // Most SSLSocketFactory implementations do not verify the server's identity, allowing man-in-the-middle // attacks. This implementation (SSLCertificateSocketFactory) does check the server's certificate hostname, // but only for createSocket variants that specify a hostname. When using methods that use InetAddress or // which return an unconnected socket, you MUST verify the server's identity yourself to ensure a secure // connection. verifyHostname(); // Safe to proceed with socket now ... I have generated a client private key, a client certificate, a server private key, and a server certificate using openssl. I then added the client certificate to keystore.bks (which I store in /res/raw/keystore.bks) I then added the server certificate to the truststore.bks So now when the client tries to connect I am getting this error server side: ssl.SSLError: [Errno 1] _ssl.c:504: error:140890C7:SSL routines:SSL3_GET_CLIENT_CERTIFICATE:peer did not return a certificate And when I try to do this in the android client SSLSession s = mSSLSocket.getSession(); s.getPeerCertificates(); I get this error: javax.net.ssl.SSLPeerUnverifiedException: No peer certificate So obviously the keystore I am using doesn't appear to have a correct peer certificate in it and thus isn't sending one to the server. What should I put in the keystore to prevent this exception? Furthermore, is this method of two way SSL authentication safe and effective?

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• Performance tuning of a Hibernate+Spring+MySQL project operation that stores images uploaded by user

  - by Umar

  Hi I am working on a web project that is Spring+Hibernate+MySQL based. I am stuck at a point where I have to store images uploaded by a user into the database. Although I have written some code that works well for now, but I believe that things will mess up when the project would go live. Here's my domain class that carries the image bytes: @Entity public class Picture implements java.io.Serializable{ long id; byte[] data; ... // getters and setters } And here's my controller that saves the file on submit: public class PictureUploadFormController extends AbstractBaseFormController{ ... protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response, Object command, BindException errors) throws Exception{ MutlipartFile file; // getting MultipartFile from the command object ... // beginning hibernate transaction ... Picture p=new Picture(); p.setData(file.getBytes()); pictureDAO.makePersistent(p); // this method simply calls getSession().saveOrUpdate(p) // committing hiernate transaction ... } ... } Obviously a bad piece of code. Is there anyway I could use InputStream or Blob to save the data, instead of first loading all the bytes from the user into the memory and then pushing them into the database? I did some research on hibernate's support for Blob, and found this in Hibernate In Action book: java.sql.Blob and java.sql.Clob are the most efficient way to handle large objects in Java. Unfortunately, an instance of Blob or Clob is only useable until the JDBC transaction completes. So if your persistent class defines a property of java.sql.Clob or java.sql.Blob (not a good idea anyway), you’ll be restricted in how instances of the class may be used. In particular, you won’t be able to use instances of that class as detached objects. Furthermore, many JDBC drivers don’t feature working support for java.sql.Blob and java.sql.Clob. Therefore, it makes more sense to map large objects using the binary or text mapping type, assuming retrieval of the entire large object into memory isn’t a performance killer. Note you can find up-to-date design patterns and tips for large object usage on the Hibernate website, with tricks for particular platforms. Now apparently the Blob cannot be used, as it is not a good idea anyway, what else could be used to improve the performance? I couldn't find any up-to-date design pattern or any useful information on Hibernate website. So any help/recommendations from stackoverflowers will be much appreciated. Thanks

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• What does the `forall` keyword in Haskell/GHC do?

  - by JUST MY correct OPINION

  I've been banging my head on this one for (quite literally) years now. I'm beginning to kinda/sorta understand how the foreach keyword is used in so-called "existential types" like this: data ShowBox = forall s. Show s => SB s (This despite the confusingly-worded explanations of it in the fragments found all around the web.) This is only a subset, however, of how foreach is used and I simply cannot wrap my mind around its use in things like this: runST :: forall a. (forall s. ST s a) -> a Or explaining why these are different: foo :: (forall a. a -> a) -> (Char,Bool) bar :: forall a. ((a -> a) -> (Char, Bool)) Or the whole RankNTypes stuff that breaks my brain when "explained" in a way that makes me want to do that Samuel L. Jackson thing from Pulp Fiction. (Don't follow that link if you're easily offended by strong language.) The problem, really, is that I'm a dullard. I can't fathom the chicken scratchings (some call them "formulae") of the elite mathematicians that created this language seeing as my university years are over two decades behind me and I never actually had to put what I learnt into use in practice. I also tend to prefer clear, jargon-free English rather than the kinds of language which are normal in academic environments. Most of the explanations I attempt to read on this (the ones I can find through search engines) have these problems: They're incomplete. They explain one part of the use of this keyword (like "existential types") which makes me feel happy until I read code that uses it in a completely different way (like runST, foo and bar above). They're densely packed with assumptions that I've read the latest in whatever branch of discrete math, category theory or abstract algebra is popular this week. (If I never read the words "consult the paper whatever for details of implementation" again, it will be too soon.) They're written in ways that frequently turn even simple concepts into tortuously twisted and fractured grammar and semantics. (I suspect that the last two items are the biggest problem. I wouldn't know, though, since I'm too much a dullard to comprehend them.) It's been asked why Haskell never really caught on in industry. I suspect, in my own humble, unintelligent way, that my experience in figuring out one stupid little keyword -- a keyword that is increasingly ubiquitous in the libraries being written these days -- are also part of the answer to that question. It's hard for a language to catch on when even its individual keywords cause years-long quests to comprehend. Years-long quests which end in failure. So... On to the actual question. Can anybody completely explain the foreach keyword in clear, plain English (or, if it exists somewhere, point to such a clear explanation which I've missed) that doesn't assume I'm a mathematician steeped in the jargon?

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• Internal class and access to external members.

  - by Knowing me knowing you

  I always thought that internal class has access to all data in its external class but having code: template<class T> class Vector { template<class T> friend std::ostream& operator<<(std::ostream& out, const Vector<T>& obj); private: T** myData_; std::size_t myIndex_; std::size_t mySize_; public: Vector():myData_(nullptr), myIndex_(0), mySize_(0) { } Vector(const Vector<T>& pattern); void insert(const T&); Vector<T> makeUnion(const Vector<T>&)const; Vector<T> makeIntersection(const Vector<T>&)const; class Iterator : public std::iterator<std::bidirectional_iterator_tag,T> { private: T** itData_; public: Iterator()//<<<<<<<<<<<<<------------COMMENT { /*HERE I'M TRYING TO USE ANY MEMBER FROM Vector<T> AND I'M GETTING ERR SAYING: ILLEGAL CALL OF NON-STATIC MEMBER FUNCTION*/} Iterator(T** ty) { itData_ = ty; } Iterator operator++() { return ++itData_; } T operator*() { return *itData_[0]; } bool operator==(const Iterator& obj) { return *itData_ == *obj.itData_; } bool operator!=(const Iterator& obj) { return *itData_ != *obj.itData_; } bool operator<(const Iterator& obj) { return *itData_ < *obj.itData_; } }; typedef Iterator iterator; iterator begin()const { assert(mySize_ > 0); return myData_; } iterator end()const { return myData_ + myIndex_; } }; See line marked as COMMENT. So can I or I can't use members from external class while in internal class? Don't bother about naming, it's not a Vector it's a Set. Thank you.

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• How do I add a trailing slash for Django MPTT-based categorization app?

  - by Patrick Beeson

  I'm using Django-MPTT to develop a categorization app for my Django project. But I can't seem to get the regex pattern for adding a trailing slash that doesn't also break on child categories. Here's an example URL: http://mydjangoapp.com/categories/parentcat/childcat/ I'd like to be able to use http://mydjangoapp.com/categories/parentcat and have it redirect to the trailing slash version. The same should apply to http://mydjangoapp.com/categories/parentcat/childcat (it should redirect to http://mydjangoapp.com/categories/parentcat/childcat/). Here's my urls.py: from django.conf.urls.defaults import patterns, include, url from django.views.decorators.cache import cache_page from storefront.categories.models import Category from storefront.categories.views import SimpleCategoryView urlpatterns = patterns('', url(r'^(?P<full_slug>[-\w/]+)', cache_page(SimpleCategoryView.as_view(), 60 * 15), name='category_view'), ) And here is my view: from django.core.exceptions import ImproperlyConfigured from django.core.urlresolvers import reverse from django.views.generic import TemplateView, DetailView from django.views.generic.detail import SingleObjectTemplateResponseMixin, SingleObjectMixin from django.utils.translation import ugettext as _ from django.contrib.syndication.views import Feed from storefront.categories.models import Category class SimpleCategoryView(TemplateView): def get_category(self): return Category.objects.get(full_slug=self.kwargs['full_slug']) def get_context_data(self, **kwargs): context = super(SimpleCategoryView, self).get_context_data(**kwargs) context["category"] = self.get_category() return context def get_template_names(self): if self.get_category().template_name: return [self.get_category().template_name] else: return ['categories/category_detail.html'] And finally, my model: from django.db import models from mptt.models import MPTTModel from mptt.fields import TreeForeignKey class CategoryManager(models.Manager): def get(self, **kwargs): defaults = {} defaults.update(kwargs) if 'full_slug' in defaults: if defaults['full_slug'] and defaults['full_slug'][-1] != "/": defaults['full_slug'] += "/" return super(CategoryManager, self).get(**defaults) class Category(MPTTModel): title = models.CharField(max_length=255) description = models.TextField(blank=True, help_text='Please use <a href="http://daringfireball.net/projects/markdown/syntax">Markdown syntax</a> for all text-formatting and links. No HTML is allowed.') slug = models.SlugField(help_text='Prepopulates from title field.') full_slug = models.CharField(max_length=255, blank=True) template_name = models.CharField(max_length=70, blank=True, help_text="Example: 'categories/category_parent.html'. If this isn't provided, the system will use 'categories/category_detail.html'. Use 'categories/category_parent.html' for all parent categories and 'categories/category_child.html' for all child categories.") parent = TreeForeignKey('self', null=True, blank=True, related_name='children') objects = CategoryManager() class Meta: verbose_name = 'category' verbose_name_plural = 'categories' def save(self, *args, **kwargs): orig_full_slug = self.full_slug if self.parent: self.full_slug = "%s%s/" % (self.parent.full_slug, self.slug) else: self.full_slug = "%s/" % self.slug obj = super(Category, self).save(*args, **kwargs) if orig_full_slug != self.full_slug: for child in self.get_children(): child.save() return obj def available_product_set(self): """ Returns available, prioritized products for a category """ from storefront.apparel.models import Product return self.product_set.filter(is_available=True).order_by('-priority') def __unicode__(self): return "%s (%s)" % (self.title, self.full_slug) def get_absolute_url(self): return '/categories/%s' % (self.full_slug)

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• How to access static members in a Velocity template?

  - by matt b

  I'm not sure if there is a way to do this in Velocity or not: I have a User POJO which a property named Status, which looks like an enum (but it is not, since I am stuck on Java 1.4), the definition looks something like this: public class User { // default status to User private Status status = Status.USER; public void setStatus(Status status) { this.status = status; } public Status getStatus() { return status; } And Status is a static inner class: public static final class Status { private String statusString; private Status(String statusString) { this.statusString = statusString; } public final static Status USER = new Status("user"); public final static Status ADMIN = new Status("admin"); public final static Status STATUS_X = new Status("blah"); //.equals() and .hashCode() implemented as well } With this pattern, a user status can easily be tested in a conditional such as if(User.Status.ADMIN.equals(user.getStatus())) ... ... without having to reference any constants for the status ID, any magic numbers, etc. However, I can't figure out how to test these conditionals in my Velocity template with VTL. I'd like to just print a simple string based upon the user's status, such as: Welcome <b>${user.name}</b>! <br/> <br/> #if($user.status == com.company.blah.User.Status.USER) You are a regular user #elseif($user.status == com.company.blah.User.Status.ADMIN) You are an administrator #etc... #end But this throws an Exception that looks like org.apache.velocity.exception.ParseErrorException: Encountered "User" at webpages/include/dashboard.inc[line 10, column 21] Was expecting one of: "[" ... From the VTL User Guide, there is no mention of accessing a Java class/static member directly in VTL, it appears that the right hand side (RHS) of a conditional can only be a number literal, string literal, property reference, or method reference. So is there any way that I can access static Java properties/references in a Velocity template? I'm aware that as a workaround, I could embed the status ID or some other identifier as a reference in my controller (this is a web MVC application using Velocity as the View technology), but I strongly do not want to embed any magic numbers or constants in the view layer.

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• Var null and not an object when using document.getElementById

  - by Dean

  Hi, I'm doing some work in HTML and JQuery. I have a problem of my textarea and submit button not appearing after the radio button is selected. My HTML looks like this: <html> <head><title>Publications Database | Which spotlight for Publications</title> <script type="text/javascript" src="./jquery.js"></script> <script src="./addSpotlight.js" type="text/javascript" charset="utf-8"></script> </head> <body> <div class="wrapper"> <div class="header"> <div class="headerText">Which spotlight for Publications</div> </div> <div class="mainContent"> <p>Please select the publication that you would like to make the spotlight of this month:</p> <form action="addSpotlight" method="POST" id="form" name="form"> <div class="div29" id="div29"><input type="radio" value="29" name="publicationIDs" >A System For Dynamic Server Allocation in Application Server Clusters, IEEE International Symposium on Parallel and Distributed Processsing with Applications, 2008 </div> <div class="div30" id="div30"><input type="radio" value="30" name="publicationIDs" >Analysing BitTorrent's Seeding Strategies, 7th IEEE/IFIP International Conference on Embedded and Ubiquitous Computing (EUC-09), 2009 </div> <div class="div31" id="div31"><input type="radio" value="31" name="publicationIDs" >The Effect of Server Reallocation Time in Dynamic Resource Allocation, UK Performance Engineering Workshop 2009, 2009 </div> <div class="div32" id="div32"><input type="radio" value="32" name="publicationIDs" >idk, hello, 1992 </div> <div class="div33" id="div33"><input type="radio" value="33" name="publicationIDs" >sad, safg, 1992 </div> <div class="abstractWriteup" id="abstractWriteup"><textarea name="abstract"></textarea> <input type="submit" value="Add Spotlight"></div> </form> </div> </div> </body> </html> My javascript looks like this: $(document).ready( function() { $('.abstractWriteup').hide(); addAbstract(); }); function addAbstract() { var abstractWU = document.getElementById('.abstractWriteup'); $("input[name='publicationIDs']").change(function() { var abstractWU = document.getElementById('.abstractWriteup'); var classNameOfSelected = $("input[name='publicationIDs']").val(); var radioSelected = document.getElementById("div"+classNameOfSelected); var parentDiv = radioSelected.parentNode; parentDiv.insertBefore(radioSelected, abstractWU.nextSibling); $('.abstractWriteup').show(); });}; I have developed this by using Node#insertBefore. When I have had it working it has been rearranging the radio buttons. Thanks in Advance Dean

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