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• Mixing table per subclass and per hierarchy in hibernate

  - by Xelluloid

  In my database there are two three tables. The first one, table ABSTRACT, holds three columns id, type, someText This table contains all abstract information for the abstract class abstract. Now the two tables CONCRETEONE and CONCRETETWO contain all information for the concrete classes concreteOne and concreteTwo. Now I know I could use the table per subclass strategy from hibernate to create a mapping with inheritance. But as I have a column that marks the type of the concrete implementation could it be possible to create some mixed behaviour like a table per subclass strategy with an discriminator?

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• Does std::multiset guarntee insertion order?

  - by Naveen

  I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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• Are any of these quad-tree libraries any good?

  - by Noctis Skytower

  It appears that a certain project of mine will require the use of quad-trees, something that I have never worked with before. From what I have read they should allow substantial performance enhancements than a brute-force attempt at the problem would yield. Are any of these python modules any good? Quadtree 0.1.2 <= No: unable to execute in Python 3.1 QuadTree <= Yes: simple while working with rectangles quadtree.py <= No: no support for needed operations EDIT: Does anyone know of a better implementation that the one presented on the pygame wiki article?

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• Events raised by BackgroundWorker not executed on expected thread

  - by Topdown

  A winforms dialog is using BackgroundWorker to perform some asynchronous operations with significant success. On occasion, the async process being run by the background worker will need to raise events to the winforms app for user response (a message that asks the user if they wish to cancel), the response of which captured in an CancelEventArgs type of the event. Being an implementation of threading, I would have expected the RaiseEvent of the worker to fire, and then the worker would continue, hence requiring me to pause the worker until the response is received. Instead however, the worker is held to wait for the code executed by the raise event to complete. It seems like method I am calling via the event call is actually on the worker thread used by the background worker, and I am surprised, since I expected to see it on the Main Thread which is where the mainform is running. Also surprisingly, there are no cross thread exceptions thrown. Can somebody please explain why this is not as I expect?

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• Does "Value Restriction" mean that there is no higher order functional programming?

  - by Sadache

  Does "Value Restriction" mean that there is no higher order functional programming? I have a problem that each time I try to do a bit of HOP I get caught by a VR error. Example: let simple (s:string)= fun rq->1 let oops= simple "" type 'a SimpleType= F of (int ->'a-> 'a) let get a = F(fun req -> id) let oops2= get "" and I would like to know whether it is a problem of a prticular implementation of VR or it is a general problem that has no solution in a mutable type-infered language that doesn't include mutation in the type system.

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• How to instantly termainate an un-supervised script on demand?

  - by errr

  I have a GUI which resembles an interpreter. It allows the user to write a script in Jython (implementation of Python in Java) and run it whenever he wants. Apart from that, I also wish to allow the user to instantly terminate the run whenever he wants. Thing is, I don't really know how to do it. The script is being run on a different Thread, but I don't know of any secure way to stop/interrupt/terminate a thread in the middle of its run, let alone not knowing what is being run by the thread/script (it could be a simple task or maybe some sort of a heavy SQL query against a DB, and a DB is something which requires careful resource handling). How can I instantly terminate such run on demand?

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• Use delegate for Projection in Linq to SQL

  - by Redeemed1

  I have code something like this in an IRepository implementation in Linq to Sql: var newlist = from h in list where h.StringProp1 == "1" select new MyBusinessBO{ firstProp = h.StringProp1, secondProp = h.StringProp2 }; The projection into MyBusinessBO is not difificult but when the Business Object has many properties the projection code becomes very lengthy. Also, as the projection can occur in several places in the Repository we break the DRY principle. Is there any way to abstract out the projection or replace it with a delegate? I.e. replace the code firstProp = h.StringProp1, secondProp = h.StringProp2 with something reusable?

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• Google's OpenID identifier is different depending on the "consumer" domain name. How to avoid potent

  - by JohnnyO

  I'm currently testing an OpenID implementation, and I'm noticing that Google sends a different identifier for different consuming host name / domain name, even for the same user. For example, Google sends a different identifier when the requesting site is localhost, compared to the identifier they send when the requesting site is 127.0.0.1 for the same user. Note: I haven't actually tested this using public domain names, but I can't see why the behavior would be any different. My concern with Google's behavior is that if we ever choose to change our website domain name in the future, then users will no longer be able to log in to the website using Google's OpenId as the identity provider. This seems to be a big problem. Am I missing something, or are all OpenID consuming sites faced with this potential problem? I've also tested this with MyOpenId, but the identifier that MyOpenId creates is fixed, so this wouldn't be a problem with them. Thanks.

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• Java interface and abstract class issue

  - by George2

  Hello everyone, I am reading the book -- Hadoop: The Definitive Guide, http://www.amazon.com/Hadoop-Definitive-Guide-Tom-White/dp/0596521979/ref=sr_1_1?ie=UTF8&s=books&qid=1273932107&sr=8-1 In chapter 2 (Page 25), it is mentioned "The new API favors abstract class over interfaces, since these are easier to evolve. For example, you can add a method (with a default implementation) to an abstract class without breaking old implementations of the class". What does it mean (especially what means "breaking old implementations of the class")? Appreciate if anyone could show me a sample why from this perspective abstract class is better than interface? thanks in advance, George

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• Cepstral Analysis for pitch detection

  - by Ohmu

  Hi! I'm looking to extract pitches from a sound signal. Someone on IRC just explain to me how taking a double FFT achieves this. Specifically: take FFT take log of square of absolute value (can be done with lookup table) take another FFT take absolute value I am attempting this using vDSP I can't understand how I didn't come across this technique earlier. I did a lot of hunting and asking questions; several weeks worth. More to the point, I can't understand why I didn't think of it. I am attempting to achieve this with vDSP library. it looks as though it has functions to handle all of these tasks. However, I'm wondering about the accuracy of the final result. I have previously used a technique which scours the frequency bins of a single FFT for local maxima. when it encounters one, it uses a cunning technique (the change in phase since the last FFT) to more accurately place the actual peak within the bin. I am worried that this precision will be lost with this technique I'm presenting here. I guess the technique could be used after the second FFT to get the fundamental accurately. But it kind of looks like the information is lost in step 2. as this is a potentially tricky process, could someone with some experience just look over what I'm doing and check it for sanity? also, I've heard there is an alternative technique involving fitting a quadratic over neighbouring bins. Is this of comparable accuracy? if so, I would favour it, as it doesn't involve remembering bin phases. so questions: does this approach makes sense? Can it be improved? I'm a bit worried about And the log square component; there seems to be a vDSP function to do exactly that: vDSP_vdbcon however, there is no indication it precalculates a log-table -- I assume it doesn't, as the FFT function requires an explicit pre-calculation function to be called and passed into it. and this function doesn't. Is there some danger of harmonics being picked up? is there any cunning way of making vDSP pull out the maxima, biggest first? Can anyone point me towards some research or literature on this technique? the main question: is it accurate enough? Can the accuracy be improved? I have just been told by an expert that the accuracy IS INDEED not sufficient. Is this the end of the line? Pi PS I get SO annoyed (npi) when I want to create tags, but cannot. :| I have suggested to the maintainers that SO keep track of attempted tags, but I'm sure I was ignored. we need tags for vDSP, accelerate framework, cepstral analysis

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• Java generics: Illegal forward reference

  - by Arian

  Given a generic interface interface Foo<A, B> { } I want to write an implementation that requires A to be a subclass of B. So I want to do class Bar<A, B super A> implements Foo<A, B> { } // --> Syntax error or class Bar<A extends B, B> implements Foo<A, B> { } // --> illegal forward reference But the only solution that seems to work is this: class Bar<B, A extends B> implements Foo<A, B> { } which is kind of ugly, because it reverses the order of the generic parameters. Are there any solutions or workarounds to this problem?

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• Using read() directly into a C++ std:vector

  - by Joe

  I'm wrapping up user space linux socket functionality in some C++ for an embedded system (yes, this is probably reinventing the wheel again). I want to offer a read and write implementation using a vector. Doing the write is pretty easy, I can just pass &myvec[0] and avoid unnecessary copying. I'd like to do the same and read directly into a vector, rather than reading into a char buffer then copying all that into a newly created vector. Now, I know how much data I want to read, and I can allocate appropriately (vec.reserve). I can also read into &myvec[0], though this is probably a VERY BAD IDEA. Obviously doing this doesn't allow myvec.size to return anything sensible. Is there any way of doing this that 1) Doesn't completely feel yucky from a safety/C++ perspective and 2) Doesn't involve two copies of the data block - once from kernel to user space and once from a C char * style buffer into a C++ vector. Any thoughts collective?

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• EXC_BAD_ACCESS when trying to release an ABRecordRef

  - by synic

  I've got the following class that is a wrapper around an ABPerson (ABRecordRef): @interface Recipient : NSObject { ABRecordRef person; } - (id)initWithPerson:(ABRecordRef)person; @end @implementation - (id)initWithPerson:(ABRecordRef)_person { if(self = [super init]) person = CFRetain(_person); return self; } - (void)dealloc { if(person) CFRelease(person); [super dealloc]; } @end I've left some of the methods out, but they aren't relevant to this question. Everything works fine, except I get an EXC_BAD_ACCESS on the if(person) CFRelease(person); line. Why does this happen? I'm not calling CFRelease or CFRetain at all anywhere else in my app.

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• What's a good unit test framework for Common Lisp projects?

  - by Lorenzo V.

  I need to write a unit test suite for a project I am developing in my spare time. Being a CL newbie I was overwhelmed by the amount of choices for a CL implementation, I spent quite some time to choose one. Now I am facing exactly the same thing with unit test frameworks. A quick glance at http://www.cliki.net/test%20framework shows 20 unit test frameworks! Choice is good but for a novice like me this can be a bit confusing and given the number of frameworks it would be painful to try them all. I would like to use a framework which: Is reasonably well maintained Easy to use but with some degree of flexibility Offers some sort of integration with Emacs (or it is possible to easily integrate it with Emacs) Integration with git post-commit hooks Integration with a continous integration system (such as buildbot) What are your experiences in this field?

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• Preferred Method Of Application Purchase

  - by Chuck

  This is more of a "programmers" question, but felt that it was technical enough to belong on Stack Overflow instead. I'm launching an application soon that will follow the shareware model of purchase. I've thought about implementing this in a few ways: Limited access to the application until they purchase Full access to the application but expires after 30 day, requiring them to purchase to retain utility. Full access to the application indefinitely, but with a 10-15 second pop-up box on start-up asking them to register -- like mIRC does (or used to do). The method of authentication will be web-based. I'll provide them with an authentication key and they'll put it in the application. Whenever the application boots up, it'll check my web service and determine whether the application is genuine or not. This isn't my question. My question is: Is there a preferred method of implementation? I'd like to piss off the users as little as possible, but I'd also like to get paid for my work.

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• Java's ThreadPoolExecutor equivalent for C#?

  - by chillitom

  Hi Guys, I used to make good use of Java's ThreadPoolExecutor class and have yet to find a good equivalent in C#. I know of ThreadPool.QueueUserWorkItem which is useful in many cases but no good if you want to control the number of threads assigned to a task or have multiple individual queues for different task types. For example I liked to use a ThreadPoolExecutor with a single thread to guarantee sequential execution of asynchronous calls.. Is there an easy way to do this in C#? Is there a non-static thread pool implementation? Thanks, T.

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• E4X in ActionScript

  - by Brian Genisio

  Hey all, Looking at the E4X implementation in ActionScript, it occurs to me that they had to figure out how to do three things that I am not sure can be done within ActionScript regularly: Properties/Getters prefixed with @: var myAttribute = xmlPerson.@name; Nameless functions for filtering: xmlData.person.(/* predicate */) lambda syntax for predicates: xmlData.person.(@name == "Brian") So here is my question: Are these just one-off capabilities (much like Vector.<>) they put in just for E4X, therefore keeping out of reach for us? Or do we, as ActionScript developers, have access to these features? More specifically, I'd love to get access to the expression tree of that lambda predicate for my own code (not tied to the XML classes in any way). I figured out that this is called the "filter operator"... but I am not sure how to harness it. Not sure I can... since ActionScript does not allow for operator overloading :(

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• Help Me Understand C++ Header files and Classes

  - by JamesW

  OK, So I am trying to transition from intermediate Delphi to C++ Object Oriented programing. I have read Ivar Horton's book on visual C++ 2010. I can pull off the simple console applications no problem. I get the language itself (kinda). Where I am struggling is with headers and classes. I also understand what header files and classes do in general. What I am not getting is the implementation when do I use a header or a class? Do I need to create classes for everything I do? Do my actual work functions need to be in header files or in CPP files? I'm lost on the proper uses of these and could use some real world guidance from more experienced programmers. I am trying to transition to windows applications using the MFC if that is helpful.

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• Working with OAuth on Google with Python

  - by Dan Loewenherz

  I'm having a very frustrating time creating a valid signature for Google's OAuth implementation. I have narrowed it all down to the fact that my signature-generation code has an error of some sort; what it is I have no idea. This is the signature base string in its entirety: GET&https%3A%2F%2Fwww.google.com%2Faccounts%2FOAuthGetAccessToken&oauth_consumer_key%3Ddlosplayground.appspot.com%26oauth_nonce%3D72815d55697cb24301fab03e1f7f1d66%26oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D1274327867%26oauth_token%3D4%252FX2cZ54JuseQbgRwzTBzZ7lqIwqof%26oauth_verifier%3Dihf0F2Fx%252FpnCmwbVQnk2xMre%26oauth_version%3D1.0 The OAuth Playground returns an oauth_signature of gF8qAfWjpdKjKb4KR%2FvA2Gy0vhU%3D. My code gives me ikMpIKJQJ58jseg%2BKPBTecjmYPE%3D, so obviously I'm doing something wrong. Here's my signature generation code (equivalent to that of the standard oauth.py library): binascii.b2a_base64(hmac.new(CONSUMER_SECRET, BASE_STRING, hashlib.sha1).digest())[:-1] Any thoughts?

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• New to C# and trying to use a global variable

  - by Andrew G. Johnson

  Is it possible to use global variables in C#? I'm coming from mainly a PHP background so variables are either accessible everywhere or just a global definition away. My main issue is I have a User class that I built myself to wrap around the current users table on my company's database. I am defining it in the MasterPage but can't seem to access it from the actual pages (I don't know if there's a better word to describe them but they are the pages that inherit the styles and format from the MasterPage) Any general tips or implementation practices for me? EDIT: here's some code snippets of what I'm trying to do: Site.master.cs public partial class SiteMaster : System.Web.UI.MasterPage { public User user = new User(); } logout.aspx <%@ Page Title="" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeFile="logout.aspx.cs" Inherits="logout" %> <%@ MasterType virtualPath="~/Site.master"%> logout.aspx.cs public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { User user = Master.user; } }

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• How do I get hyphens in my attribute names in Flex?

  - by John Leonard

  Flex has an issue with hyphens in xml. I need to generate an xml object with hyphens in the attribute for a Google Checkout implementation. I can get away with: var xml:XML = <item-description/>; and var xml:XML = <item-description the-name="foo"/>; but what I need to do is set the value of an attribute like this: var timestamp:String = methodToGetMyTimestampString(); var xml:XML = <item-desc/>; xml@start-date = timestamp; but I can't do that. Since flex doesn't like the hyphens, I don't know how to get or set attributes with hyphens in the name.

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• Is Boost.Tuple compatible with C++0x variadic templates ?

  - by Thomas Petit

  Hi, I was playing around with variadic templates (gcc 4.5) and hit this problem : template <typename... Args> boost::tuple<Args...> my_make_tuple(Args... args) { return boost::tuple<Args...>(args...); } int main (void) { boost::tuple<int, char> t = my_make_tuple(8, 'c'); } GCC error message : sorry, unimplemented: cannot expand 'Arg ...' into a fixed-length argument list In function 'int my_make_tuple(Arg ...)' If I replace every occurrence of boost::tuple by std::tuple, it compiles fine. Is there a problem in boost tuple implementation ? Or is this a gcc bug ? I must stick with Boost.Tuple for now. Do you know any workaround ? Thanks.

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• Loose Coupling of Components

  - by David

  I have created a class library (assembly) that provides messaging, email and sms. This class library defines an interface IMessenger which the classes EmailMessage and SmsMessage both implement. I see this is a general library that would be part of my infrastructure layer and would / can be used across any development. Now, in my application layer I have a class that requires to use a messaging component, I obviously want to use the messaging library that I have created. Additionally, I will be using an IoC container (Spring.net) to allow me to inject my implementation i.e. either email or sms. Therefore, I want to program against an interface in my application layer class, do I then need to reference my message class library from my application layer class? Is this tightly coupling my application layer class to my message class library? Should I be defining the interface - IMessenger in a seperate library? Or should I be doing something else?

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• [Python] How can I speed up unpickling large objects if I have plenty of RAM?

  - by conradlee

  It's taking me up to an hour to read a 1-gigabyte NetworkX graph data structure using cPickle (its 1-GB when stored on disk as a binary pickle file). Note that the file quickly loads into memory. In other words, if I run: import cPickle as pickle f = open("bigNetworkXGraph.pickle","rb") binary_data = f.read() # This part doesn't take long graph = pickle.loads(binary_data) # This takes ages How can I speed this last operation up? Note that I have tried pickling the data both in using both binary protocols (1 and 2), and it doesn't seem to make much difference which protocol I use. Also note that although I am using the "loads" (meaning "load string") function above, it is loading binary data, not ascii-data. I have 128gb of RAM on the system I'm using, so I'm hoping that somebody will tell me how to increase some read buffer buried in the pickle implementation.

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• Why implement DB connection pointer object as a reference counting pointer? (C++)

  - by DVK

  At our company one of the core C++ classes (Database connection pointer) is implemented as a reference counting pointer. To be clear, the objects are NOT DB connections themselves, but pointers to a DB connection object. The library is very old, and nobody who designed is around anymore. So far, nether I, nor any C++ experts in the company that I asked have come up with a good reason for why this particular design was chosen. Any ideas? It is introducing some problems (partially due to awful reference pointer implementation used), and I'm trying to understand if this design actually has some deep underlying reasons? The usage pattern these days seems to be that the DB connection pointer object is returned by a DB connection manager class, and it's somewhat unclear whether DB connection pointers were designed to be able to be used independently of DB connection manager.

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