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• Sort and limit queryset by comment count and date using queryset.extra() (django)

  - by thornomad

  I am trying to sort/narrow a queryset of objects based on the number of comments each object has as well as by the timeframe during which the comments were posted. Am using a queryset.extra() method (using django_comments which utilizes generic foreign keys). I got the idea for using queryset.extra() (and the code) from here. This is a follow-up question to my initial question yesterday (which shows I am making some progress). Current Code: What I have so far works in that it will sort by the number of comments; however, I want to extend the functionality and also be able to pass a time frame argument (eg, 7 days) and return an ordered list of the most commented posts in that time frame. Here is what my view looks like with the basic functionality in tact: import datetime from django.contrib.comments.models import Comment from django.contrib.contenttypes.models import ContentType from django.db.models import Count, Sum from django.views.generic.list_detail import object_list def custom_object_list(request, queryset, *args, **kwargs): '''Extending the list_detail.object_list to allow some sorting. Example: http://example.com/video?sort_by=comments&days=7 Would get a list of the videos sorted by most comments in the last seven days. ''' try: # this is where I started working on the date business ... days = int(request.GET.get('days', None)) period = datetime.datetime.utcnow() - datetime.timedelta(days=int(days)) except (ValueError, TypeError): days = None period = None sort_by = request.GET.get('sort_by', None) ctype = ContentType.objects.get_for_model(queryset.model) if sort_by == 'comments': queryset = queryset.extra(select={ 'count' : """ SELECT COUNT(*) AS comment_count FROM django_comments WHERE content_type_id=%s AND object_pk=%s.%s """ % ( ctype.pk, queryset.model._meta.db_table, queryset.model._meta.pk.name ), }, order_by=['-count']).order_by('-count', '-created') return object_list(request, queryset, *args, **kwargs) What I've Tried: I am not well versed in SQL but I did try just to add another WHERE criteria by hand to see if I could make some progress: SELECT COUNT(*) AS comment_count FROM django_comments WHERE content_type_id=%s AND object_pk=%s.%s AND submit_date='2010-05-01 12:00:00' But that didn't do anything except mess around with my sort order. Any ideas on how I can add this extra layer of functionality? Thanks for any help or insight.

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• Generics vs inheritance (whenh no collection classes are involved)

  - by Ram

  This is an extension of this questionand probably might even be a duplicate of some other question(If so, please forgive me). I see from MSDN that generics are usually used with collections The most common use for generic classes is with collections like linked lists, hash tables, stacks, queues, trees and so on where operations such as adding and removing items from the collection are performed in much the same way regardless of the type of data being stored. The examples I have seen also validate the above statement. Can someone give a valid use of generics in a real-life scenario which does not involve any collections ? Pedantically, I was thinking about making an example which does not involve collections public class Animal<T> { public void Speak() { Console.WriteLine("I am an Animal and my type is " + typeof(T).ToString()); } public void Eat() { //Eat food } } public class Dog { public void WhoAmI() { Console.WriteLine(this.GetType().ToString()); } } and "An Animal of type Dog" will be Animal<Dog> magic = new Animal<Dog>(); It is entirely possible to have Dog getting inherited from Animal (Assuming a non-generic version of Animal)Dog:Animal Therefore Dog is an Animal Another example I was thinking was a BankAccount. It can be BankAccount<Checking>,BankAccount<Savings>. This can very well be Checking:BankAccount and Savings:BankAccount. Are there any best practices to determine if we should go with generics or with inheritance ?

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• Design Pattern for error handling in ASP.NET 3.5 site

  - by Kevin

  I am relatively new to ASP.NET programming, and web programming in general. We have a site we recently ported from .NET 1.1 to 3.5. Currently we have two methods of error handling: either catching the error during data load on a page and displaying the formatted error in a label on the page, or redirecting to a generic error page. Both of these are somewhat annoying, as right now I'm trying to redesign how our errors are displayed. We are soon moving to Master pages, and I'm wondering if there is a way to "build in" an error handling control. What I mean by this is using a ASP.NET user control I've designed that simply gets passed the error string returned from the server. If an error occurs, the page would not display the content, and instead display the error control. This provides us with the ability to retain the current banner/navigation during an error (which we don't get with the generic error page), as well as keeping me from having to add the control to every aspx page we have (which I have to do with using the label-per-page system). Does something like this make sense? Ultimately I just want to have the error control added to a single page, and all other pages have access to it directly. Is this something Master pages help with? Thanks!

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• Did the Unity Team fix that "generics handling" bug back in 2008?

  - by rasx

  At my level of experience with Unity it might be faster to ask whether the "generics handling" bug acknowledged by ctavares back in 2008 was fixed in a public release. Here was the problem (which might be my problem today): Hi, I get an exception when using .... container.RegisterType(typeof(IDictionary<,), typeof(Dictionary<,)); The exception is... "Resolution of the dependency failed, type = \"IDictionary2\", name = \"\". Exception message is: The current build operation (build key Build Key[System.Collections.Generic.Dictionary2[System.String,System.String], null]) failed: The current build operation (build key Build Key[System.Collections.Generic.Dictionary2[System.String,System.String], null]) failed: The type Dictionary2 has multiple constructors of length 2. Unable to disambiguate. When I attempt... IDictionary myExampleDictionary = container.Resolve(); Here was the moderated response: There are no books that'll help, Unity is a little too new for publishers to have caught up yet. Unfortunately, you've run into a bug in our generics handling. This is currently fixed in our internal version, but it'll be a little while before we can get the bits out. In the meantime, as a workaround you could do something like this instead: public class WorkaroundDictionary : Dictionary { public WorkaroundDictionary() { } } container.RegisterType(typeof(IDictionary<,),typeof(WorkaroundDictionary<,)); The WorkaroundDictionary only has the default constructor so it'll inject no problem. Since the rest of your app is written in terms of IDictionary, when we get the fixed version done you can just replace the registration with the real Dictionary class, throw out the workaround, and everything will still just work. Sorry about the bug, it'll be fixed soon!

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• Thread-local storage segfaults on NetBSD only?

  - by bortzmeyer

  Trying to run a C++ program, I get segmentation faults which appear to be specific to NetBSD. Bert Hubert wrote the simple test program (at the end of this message) and, indeed, it crashes only on NetBSD. % uname -a NetBSD golgoth 5.0.1 NetBSD 5.0.1 (GENERIC) #0: Thu Oct 1 15:46:16 CEST 2009 +stephane@golgoth:/usr/obj/sys/arch/i386/compile/GENERIC i386 % g++ --version g++ (GCC) 4.1.3 20080704 prerelease (NetBSD nb2 20081120) Copyright (C) 2006 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. % gdb thread-local-storage-powerdns GNU gdb 6.5 Copyright (C) 2006 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386--netbsdelf"... (gdb) run Starting program: /home/stephane/Programmation/C++/essais/thread-local-storage-powerdns Program received signal SIGSEGV, Segmentation fault. 0x0804881b in main () at thread-local-storage-powerdns.cc:20 20 t_a = new Bogo('a'); (gdb) On other Unix, it works fine. Is there a known issue in NetBSD with C++ thread-local storage? #include <stdio.h> class Bogo { public: explicit Bogo(char a) { d_a = a; } char d_a; }; __thread Bogo* t_a; int main() { t_a = new Bogo('a'); Bogo* b = t_a; printf("%c\n", b->d_a); }

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• Set Property Value on Master Page from Content Page

  - by Merk

  Hello, I tried following the advice posted here: http://stackoverflow.com/questions/1071920/set-property-value-on-master-page-from-content-page. Specifically the last post about creating a class. However, visual studio keeps giving me an error on my default.aspx.cs page when i try to set the value: using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; public partial class _Default : BasePage { protected override int NavHighlight { get { return new{0} ; } } protected void Page_Load(object sender, EventArgs e) { } } It throws an error on new, the error being: cannot inplicity convert anonymoustype#1 to int Can someone tell me what i might have done wrong here? Here's what my class looks like: using System; using System.Collections.Generic; using System.Linq; using System.Web; /// <summary> /// Summary description for BasePage /// </summary> public abstract class BasePage : System.Web.UI.Page { protected abstract int NavHighlight { get; } protected override void OnLoad(EventArgs e) { base.OnLoad(e); if (this.Master != null) { //value assignment } } public BasePage() { // // TODO: Add constructor logic here // } } Thanks.

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• C# reflection instantiation

  - by NickLarsen

  I am currently trying to create a generic instance factory for which takes an interface as the generic parameter (enforced in the constructor) and then lets you get instantiated objects which implement that interface from all types in all loaded assemblies. The current implementation is as follows:     public class InstantiationFactory     {         protected Type Type { get; set; }         public InstantiationFactory()         {             this.Type = typeof(T);             if (!this.Type.IsInterface)             {                 // is there a more descriptive exception to throw?                 throw new ArgumentException(/* Crafty message */);             }         }         public IEnumerable GetLoadedTypes()         {             // this line of code found in other stack overflow questions             var types = AppDomain.CurrentDomain.GetAssemblies()                 .SelectMany(a = a.GetTypes())                 .Where(/* lambda to identify instantiable types which implement this interface */);             return types;         }         public IEnumerable GetImplementations(IEnumerable types)         {             var implementations = types.Where(/* lambda to identify instantiable types which implement this interface */                 .Select(x = CreateInstance(x));             return implementations;         }         public IEnumerable GetLoadedImplementations()         {             var loadedTypes = GetLoadedTypes();             var implementations = GetImplementations(loadedTypes);             return implementations;         }         private T CreateInstance(Type type)         {             T instance = default(T);             var constructor = type.GetConstructor(Type.EmptyTypes);             if (/* valid to instantiate test */)             {                 object constructed = constructor.Invoke(null);                 instance = (T)constructed;             }             return instance;         }     } It seems useful to me to have my CreateInstance(Type) function implemented as an extension method so I can reuse it later and simplify the code of my factory, but I can't figure out how to return a strongly typed value from that extension method. I realize I could just return an object:     public static class TypeExtensions     {         public object CreateInstance(this Type type)         {             var constructor = type.GetConstructor(Type.EmptyTypes);             return /* valid to instantiate test */ ? constructor.Invoke(null) : null;         }     } Is it possible to have an extension method create a signature per instance of the type it extends? My perfect code would be this, which avoids having to cast the result of the call to CreateInstance():     Type type = typeof(MyParameterlessConstructorImplementingType);     MyParameterlessConstructorImplementingType usable = type.CreateInstance();

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• List<object>.RemoveAll - How to create an appropriate Predicate

  - by CJM

  This is a bit of noob question - I'm still fairly new to C# and generics and completely new to predicates, delegates and lamda expressions... I have a class 'Enquiries' which contains a generic list of another class called 'Vehicles'. I'm building up the code to add/edit/delete Vehicles from the parent Enquiry. And at the moment, I'm specifically looking at deletions. From what I've read so far, it appears that I can use Vehicles.RemoveAll() to delete an item with a particular VehicleID or all items with a particular EnquiryID. My problem is understanding how to feed .RemoveAll the right predicate - the examples I have seen are too simplistic (or perhaps I am too simplistic given my lack of knowledge of predicates, delegates and lambda expressions). So if I had a List<Of Vehicle> Vehicles where each Vehicle had an EnquiryID, how would I use Vehicles.RemoveAll() to remove all vehicles for a given EnquiryID? I understand there are several approaches to this so I'd be keen to hear the differences between approaches - as much as I need to get something working, this is also a learning exercise. As an supplementary question, is a Generic list the best repository for these objects? My first inclination was towards a Collection, but it appears I am out of date. Certainly Generics seem to be preferred, but I'm curious as to other alternatives. Thanks

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• C++ Returning Multiple Items

  - by Travis Parks

  I am designing a class in C++ that extracts URLs from an HTML page. I am using Boost's Regex library to do the heavy lifting for me. I started designing a class and realized that I didn't want to tie down how the URLs are stored. One option would be to accept a std::vector<Url> by reference and just call push_back on it. I'd like to avoid forcing consumers of my class to use std::vector. So, I created a member template that took a destination iterator. It looks like this: template <typename TForwardIterator, typename TOutputIterator> TOutputIterator UrlExtractor::get_urls( TForwardIterator begin, TForwardIterator end, TOutputIterator dest); I feel like I am overcomplicating things. I like to write fairly generic code in C++, and I struggle to lock down my interfaces. But then I get into these predicaments where I am trying to templatize everything. At this point, someone reading the code doesn't realize that TForwardIterator is iterating over a std::string. In my particular situation, I am wondering if being this generic is a good thing. At what point do you start making code more explicit? Is there a standard approach to getting values out of a function generically?

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• Inner join and outer join options in Entity Framework 4.0

  - by bigb

  I am using EF 4.0 and I need to implement query with one inner join and with N outer joins I started to implement this using different approaches but get into trouble at some point. Here is two examples how I started of doing this using ObjectQuery<'T' and Linq to Entity 1)Using ObjectQuery<'T' I implement flexible outer join but I don't know how to perform inner join with entity Rules in that case (by default Include("Rules") doing outer join, but i need to inner join by Id). public static IEnumerable<Race> GetRace(List<string> includes, DateTime date) { IRepository repository = new Repository(new BEntities()); ObjectQuery<Race> result = (ObjectQuery<Race>)repository.AsQueryable<Race>(); //perform outer joins with related entities if (includes != null) foreach (string include in includes) result = result.Include(include); //here i need inner join insteard of default outer join result = result.Include("Rules"); return result.ToList(); } 2)Using Linq To Entity I need to have kind of outer join(somethin like in GetRace()) where i may pass a List with entities to include) and also i need to perform correct inner join with entity Rules public static IEnumerable<Race> GetRace2(List<string> includes, DateTime date) { IRepository repository = new Repository(new BEntities()); IEnumerable<Race> result = from o in repository.AsQueryable<Race>() from b in o.RaceBetRules select new { o }); //I need here: // 1. to perform the same way inner joins with related entities like with ObjectQuery above //here i getting List<AnonymousType> which i cant cast to //IEnumerable<Race> when i did try to cast like //(IEnumerable<Race>)result.ToList(); i did get error: //Unable to cast object of type //'System.Collections.Generic.List`1[<>f__AnonymousType0`1[BetsTipster.Entity.Tip.Types.Race]]' //to type //'System.Collections.Generic.IEnumerable`1[BetsTipster.Entity.Tip.Types.Race]'. return result.ToList(); } May be someone have some ideas about that.

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• Create a strongly typed view which inherites a class which is concrete

  - by Ashwani K

  Hello All: I am having one class called BaseClass which contains some logic applicable to whole web site. In order to create a strongly typed view we need to inherit the page from System.Web.Mvc.ViewPage generic class. But In our case I have to Inherit the BaseClass from System.Web.Mvc.ViewPage to apply some common settings, but the BaseClass should be inherited from System.Web.Mvc.ViewPage< generic version. But I cannot inherit the BaseClass from System.Web.Mvc.ViewPage< as it will change other class also. So I created one more class of type BaseClass< inheriting it from System.Web.Mvc.ViewPage< and copied the whole code of BaseClass in BaseClass<. But the code in BaseClass is controlled by other team so it will be changed frequently so my BaseClass< should be in sync with BaseClass. Please help me in eliminating the code duplication or any other approach to make strongly typed View. Thanks Ashwani

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• Android getting XML values

  - by Nils

  Hello, I have the following XML code, which I got by a UPnP device and like to get the res value - the RTSP URL. In this case rtsp://10.42.0.103:554/live.sdp How can I do this? I heard that Android has some built-in support for reading XML. Is that true? <DIDL-Lite xmlns="urn:schemas-upnp-org:metadata-1-0/DIDL-Lite/" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:upnp="urn:schemas-upnp-org:metadata-1-0/upnp/"> <item id="11" parentID="1" restricted="1"> <dc:title>Network Camera Stream 1</dc:title> <upnp:class>object.item.videoItem</upnp:class> <res protocolInfo="rtsp-rtp-udp:*:video/mpeg4-generic:*" resolution="640x480">rtsp://10.42.0.103:554/live.sdp</res> </item> <item id="12" parentID="1" restricted="1"> <dc:title>Network Camera Stream 2</dc:title> <upnp:class>object.item.videoItem</upnp:class> <res protocolInfo="rtsp-rtp-udp:*:video/mpeg4-generic:*" resolution="176x144">rtsp://10.42.0.103:554/live2.sdp</res> </item> </DIDL-Lite>

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• Why does operator<< not work with something returned by operator-?

  - by Felix

  Here's a small test program I wrote: #include <iostream> using namespace std; class A { public: int val; A(int _val=0):val(_val) { } A operator+(A &a) { return A(val + a.val); } A operator-(A &a) { return A(val - a.val); } friend ostream& operator<<(ostream &, A &); }; ostream& operator<<(ostream &out, A &a) { out<<a.val; return out; } int main() { A a(3), b(4), c = b - a; cout<<c<<endl; // this works cout<<(b-a)<<endl; // this doesn't return 0; } I can't seem to get why the line marked "this works" works and the one marked "this doesn't" doesn't. When I try to compile the program with the cout<<(b-a); line, here's what I get: [felix@the-machine C]$ g++ test.cpp test.cpp: In function ‘int main()’: test.cpp:26:13: error: no match for ‘operator<<’ in ‘std::cout << b.A::operator-(((A&)(& a)))’ /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:108:7: note: candidates are: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type& (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:117:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type& (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>, std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:127:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:165:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:169:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:173:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/bits/ostream.tcc:91:5: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:180:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/bits/ostream.tcc:105:5: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:191:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:200:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:204:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:209:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:213:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:221:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/ostream:225:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>] /usr/lib/gcc/i686-pc-linux-gnu/4.5.0/../../../../include/c++/4.5.0/bits/ostream.tcc:119:5: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>] test.cpp:18:11: note: std::ostream& operator<<(std::ostream&, A&) [felix@the-machine C]$ Quite nasty.

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• ASP.net file operations delay

  - by mtranda

  Ok, so here's the problem: I'm reading the stream from a FileUpload control, reading in chunks of n bytes and writing the array in a loop until I reach the stream's end. Now the reason I do this is because I need to check several things while the upload is still going on (rather than doing a Save(); which does the whole thing in one go). Here's the problem: when doing this from the local machine, I can see the file just fine as it's uploading and its size increases (had to add a Sleep(); clause in the loop to actually get to see the file being written). However, when I upload the file from a remote machine, I don't get to see it until the the file has completed uploading. Also, I've added another call to write the progress to a text file as the progress is going on, and I get the same thing. Local: the file updates as the upload goes on, remote: the token file only appears after the upload's done (which is somewhat useless since I need it while the upload's still happening). Is there some sort of security setting in (or ASP.net) that maybe saves files in a temporary location for remote machines as opposed to the local machine and then moves them to the specified destination? I would liken this with ASP.net displaying error messages when browsing from the local machine (even on the public hostname) as opposed to the generic compilation error page/generic exception page that is shown when browsing from a remote machine (and customErrors are not off) Any clues on this? Thanks in advance.

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• Add additional content to the middle of string from within a method

  - by Sammy T

  I am working with a log file and I have a method which is creating a generic entry in to the log. The generic log entry looks like this: public StringBuilder GetLogMessage(LogEventType logType, object message) { StringBuilder logEntry = new StringBuilder(); logEntry.AppendFormat("DATE={0} ", DateTime.Now.ToString("dd-MMM-yyyy", new CultureInfo(CommonConfig.EnglishCultureCode))); logEntry.AppendFormat("TIME={0} ", DateTime.Now.ToString("HH:mm:ss", new CultureInfo(CommonConfig.EnglishCultureCode))); logEntry.AppendFormat("ERRORNO={0} ", base.RemoteIPAddress.ToString().Replace(".", string.Empty)); logEntry.AppendFormat("IP={0}", base.RemoteIPAddress.ToString()); logEntry.AppendFormat("LANG={0} ", base.Culture.TwoLetterISOLanguageName); logEntry.AppendFormat("PNR={0} ", this.RecordLocator); logEntry.AppendFormat("AGENT={0} ", base.UserAgent); logEntry.AppendFormat("REF={0} ", base.Referrer); logEntry.AppendFormat("SID={0} ", base.CurrentContext.Session.SessionID); logEntry.AppendFormat("LOGTYPE={0} ", logType.ToString() ); logEntry.AppendFormat("MESSAGE={0} ", message); return logEntry; } What would be the best approach for adding additional parameters before "MESSAGE="? For example if I wanted to add "MODULE=" from a derived class when the GetLogMessage is being run. Would a delegate be what I am looking for or marking the method as virtual and overriding it or do I need something entirely different? Any help would be appreciated.

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• Boost lambda: Invoke method on object

  - by ckarras

  I'm looking at boost::lambda as a way to to make a generic algorithm that can work with any "getter" method of any class. The algorithm is used to detect duplicate values of a property, and I would like for it to work for any property of any class. In C#, I would do something like this: class Dummy { public String GetId() ... public String GetName() ... } IEnumerable<String> FindNonUniqueValues<ClassT> (Func<ClassT,String> propertyGetter) { ... } Example use of the method: var duplicateIds = FindNonUniqueValues<Dummy>(d => d.GetId()); var duplicateNames = FindNonUniqueValues<Dummy>(d => d.GetName()); I can get the for "any class" part to work, using either interfaces or template methods, but have not found yet how to make the "for any method" part work. Is there a way to do something similar to the "d = d.GetId()" lambda in C++ (either with or without Boost)? Alternative, more C++ian solutions to make the algorithm generic are welcome too. I'm using C++/CLI with VS2008, so I can't use C++0x lambdas.

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• .net runtime type casting when using reflection

  - by Mike

  I have need to cast a generic list of a concrete type to a generic list of an interface that the concrete types implement. This interface list is a property on an object and I am assigning the value using reflection. I only know the value at runtime. Below is a simple code example of what I am trying to accomplish: public void EmployeeTest() { IList<Employee> initialStaff = new List<Employee> { new Employee("John Smith"), new Employee("Jane Doe") }; Company testCompany = new Company("Acme Inc"); //testCompany.Staff = initialStaff; PropertyInfo staffProperty = testCompany.GetType().GetProperty("Staff"); staffProperty.SetValue(testCompany, (staffProperty.PropertyType)initialStaff, null); } Classes are defined like so: public class Company { private string _name; public string Name { get { return _name; } set { _name = value; } } private IList<IEmployee> _staff; public IList<IEmployee> Staff { get { return _staff; } set { _staff = value; } } public Company(string name) { _name = name; } } public class Employee : IEmployee { private string _name; public string Name { get { return _name; } set { _name = value; } } public Employee(string name) { _name = name; } } public interface IEmployee { string Name { get; set; } } Any thoughts? I am using .NET 4.0. Would the new covariant or contravariant features help? Thanks in advance.

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• How can I properly handle 404s in ASP.NET MVC?

  - by Brian

  I am just getting started on ASP.NET MVC so bear with me. I've searched around this site and various others and have seen a few implementations of this. EDIT: I forgot to mention I am using RC2 Using URL Routing: routes.MapRoute( "Error", "{*url}", new { controller = "Errors", action = "NotFound" } //404s ); The above seems to take care of requests like this (assuming default route tables setup by initial MVC project): "/blah/blah/blah/blah" Overriding HandleUnknownAction() in the controller itself: //404s - handle here (bad action requested protected override void HandleUnknownAction(string actionName) { ViewData["actionName"] = actionName; View("NotFound").ExecuteResult(this.ControllerContext); } However the previous strategies do not handle a request to a Bad/Unknown controller. For example, I do not have a "/IDoNotExist", if I request this I get the generic 404 page from the web server and not my 404 if I use routing + override. So finally, my question is: Is there any way to catch this type of request using a route or something else in the MVC framework itself? OR should I just default to using Web.Config customErrors as my 404 handler and forget all this? I assume if I go with customErrors I'll have to store the generic 404 page outside of /Views due to the Web.Config restrictions on direct access. Anyway any best practices or guidance is appreciated.

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• Populating dropdownlist in asp.net mvc doesn't seem to work for me...

  - by Pandiya Chendur

  I use a dropdownlist in one of my create.aspx but it some how doesnt seem to work... public IEnumerable<Materials> FindAllMeasurements() { var mesurements = from mt in db.MeasurementTypes select new Materials() { Id= Convert.ToInt64(mt.Id), Mes_Name= mt.Name }; return mesurements; } and my controller, public ActionResult Create() { var mesurementTypes = consRepository.FindAllMeasurements().AsEnumerable(); ViewData["MeasurementType"] = new SelectList(mesurementTypes, "Id", "Mes_Name"); return View(); } and my create.aspx has this, <p> <label for="MeasurementTypeId">MeasurementType:</label> <%= Html.DropDownList("MeasurementType", ViewData["MeasurementType"])%> <%= Html.ValidationMessage("MeasurementTypeId", "*") %> </p> When i execute this i got these errors, System.Web.Mvc.HtmlHelper<CrMVC.Models.Material>' does not contain a definition for 'DropDownList' and the best extension method overload 'System.Web.Mvc.Html.SelectExtensions.DropDownList(System.Web.Mvc.HtmlHelper, string, System.Collections.Generic.IEnumerable<System.Web.Mvc.SelectListItem>)' has some invalid arguments 2.cannot convert from 'object' to 'System.Collections.Generic.IEnumerable<System.Web.Mvc.SelectListItem>

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• Are there pitfalls to using static class/event as an application message bus

  - by Doug Clutter

  I have a static generic class that helps me move events around with very little overhead: public static class MessageBus<T> where T : EventArgs { public static event EventHandler<T> MessageReceived; public static void SendMessage(object sender, T message) { if (MessageReceived != null) MessageReceived(sender, message); } } To create a system-wide message bus, I simply need to define an EventArgs class to pass around any arbitrary bits of information: class MyEventArgs : EventArgs { public string Message { get; set; } } Anywhere I'm interested in this event, I just wire up a handler: MessageBus<MyEventArgs>.MessageReceived += (s,e) => DoSomething(); Likewise, triggering the event is just as easy: MessageBus<MyEventArgs>.SendMessage(this, new MyEventArgs() {Message="hi mom"}); Using MessageBus and a custom EventArgs class lets me have an application wide message sink for a specific type of message. This comes in handy when you have several forms that, for example, display customer information and maybe a couple forms that update that information. None of the forms know about each other and none of them need to be wired to a static "super class". I have a couple questions: fxCop complains about using static methods with generics, but this is exactly what I'm after here. I want there to be exactly one MessageBus for each type of message handled. Using a static with a generic saves me from writing all the code that would maintain the list of MessageBus objects. Are the listening objects being kept "alive" via the MessageReceived event? For instance, perhaps I have this code in a Form.Load event: MessageBus<CustomerChangedEventArgs>.MessageReceived += (s,e) => DoReload(); When the Form is Closed, is the Form being retained in memory because MessageReceived has a reference to its DoReload method? Should I be removing the reference when the form closes: MessageBus<CustomerChangedEventArgs>.MessageReceived -= (s,e) => DoReload();

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• Javascript Callback when variable is set to X

  - by Erik

  Hey everyone, Have an issue I can't seem to wrap my head around. I'm wanting to write a generic javascript function that will accept a variable and a callback, and continue to execute until that variable is something other than false. For example, the variable SpeedFeed.user.sid is false until something else happens in the code, but I don't want to execute a particular callback until it has been set. The call: SpeedFeed.helper_ready(SpeedFeed.user.sid, function(){ alert(SpeedFeed.user.sid); // Run function that requires sid to be set. }); The function: helper_ready: function(vtrue, callback){ if(vtrue != false){ callback(); } else { setTimeout(function(){ SpeedFeed.helper_ready(vtrue, callback); }, SpeedFeed.apiCheckTime); } } The issue I've narrowed it down to appears to be that because in the setTimeout I call vtrue instead of the actual SpeedFeed.user.sid, it's going to be set to false always. I realize I could write a specific function for each time that just evaluates the SpeedFeed.user.sid, but I'd like to have a generic method that I could use throughout the application. Thanks for any insight :)

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• how to read in a list of custom configuration objects

  - by Johnny

  hi, I want to implement Craig Andera's custom XML configuration handler in a slightly different scenario. What I want to be able to do is to read in a list of arbitrary length of custom objects defined as: public class TextFileInfo { public string Name { get; set; } public string TextFilePath { get; set; } public string XmlFilePath { get; set; } } I managed to replicate Craig's solution for one custom object but what if I want several? Craig's deserialization code is: public class XmlSerializerSectionHandler : IConfigurationSectionHandler { public object Create(object parent, object configContext, XmlNode section) { XPathNavigator nav = section.CreateNavigator(); string typename = (string)nav.Evaluate("string(@type)"); Type t = Type.GetType(typename); XmlSerializer ser = new XmlSerializer(t); return ser.Deserialize(new XmlNodeReader(section)); } } I think I could do this if I could get Type t = Type.GetType("System.Collections.Generic.List<TextFileInfo>") to work but it throws Could not load type 'System.Collections.Generic.List<Test1.TextFileInfo>' from assembly 'Test1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

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• How to update GUI thread/class from worker thread/class?

  - by user315182

  First question here so hello everyone. The requirement I'm working on is a small test application that communicates with an external device over a serial port. The communication can take a long time, and the device can return all sorts of errors. The device is nicely abstracted in its own class that the GUI thread starts to run in its own thread and has the usual open/close/read data/write data basic functions. The GUI is also pretty simple - choose COM port, open, close, show data read or errors from device, allow modification and write back etc. The question is simply how to update the GUI from the device class? There are several distinct types of data the device deals with so I need a relatively generic bridge between the GUI form/thread class and the working device class/thread. In the GUI to device direction everything works fine with [Begin]Invoke calls for open/close/read/write etc. on various GUI generated events. I've read the thread here (How to update GUI from another thread in C#?) where the assumption is made that the GUI and worker thread are in the same class. Google searches throw up how to create a delegate or how to create the classic background worker but that's not at all what I need, although they may be part of the solution. So, is there a simple but generic structure that can be used? My level of C# is moderate and I've been programming all my working life, given a clue I'll figure it out (and post back)... Thanks in advance for any help.

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• (500) Internal Server Error with C# and Web Dev 2008 Express

  - by user32848

  The code below is generic, found in a variety of places, including a book I have. I have used it as a base for a working program in VS 2005. Now I've resurrected it with my current Visual Web Developer 2008 Express Edition and I seem to have problems connecting it to my default development server (I don't have IIS on my XP). The error is: (500) Internal Server Error. Is this saying what I thought it did (above) or something else, and how do I solve this problem? using System; using System.Collections; using System.Collections.Generic; using System.Configuration; using System.IO; using System.Net; using System.Linq; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; using System.Text.RegularExpressions; public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { string strResult = ""; string url = "http://weather.unisys.com"; WebResponse objResponse; WebRequest objRequest; try { objRequest = System.Net.HttpWebRequest.Create(url); } catch { objRequest = System.Net.HttpWebRequest.Create("http://"+ url); } objResponse = objRequest.GetResponse(); using (StreamReader sr = new StreamReader(objResponse.GetResponseStream())) { strResult = sr.ReadToEnd(); sr.Close(); } } }

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• Null-free "maps": Is a callback solution slower than tryGet()?

  - by David Moles

  In comments to "How to implement List, Set, and Map in null free design?", Steven Sudit and I got into a discussion about using a callback, with handlers for "found" and "not found" situations, vs. a tryGet() method, taking an out parameter and returning a boolean indicating whether the out parameter had been populated. Steven maintained that the callback approach was more complex and almost certain to be slower; I maintained that the complexity was no greater and the performance at worst the same. But code speaks louder than words, so I thought I'd implement both and see what I got. The original question was fairly theoretical with regard to language ("And for argument sake, let's say this language don't even have null") -- I've used Java here because that's what I've got handy. Java doesn't have out parameters, but it doesn't have first-class functions either, so style-wise, it should suck equally for both approaches. (Digression: As far as complexity goes: I like the callback design because it inherently forces the user of the API to handle both cases, whereas the tryGet() design requires callers to perform their own boilerplate conditional check, which they could forget or get wrong. But having now implemented both, I can see why the tryGet() design looks simpler, at least in the short term.) First, the callback example: class CallbackMap<K, V> { private final Map<K, V> backingMap; public CallbackMap(Map<K, V> backingMap) { this.backingMap = backingMap; } void lookup(K key, Callback<K, V> handler) { V val = backingMap.get(key); if (val == null) { handler.handleMissing(key); } else { handler.handleFound(key, val); } } } interface Callback<K, V> { void handleFound(K key, V value); void handleMissing(K key); } class CallbackExample { private final Map<String, String> map; private final List<String> found; private final List<String> missing; private Callback<String, String> handler; public CallbackExample(Map<String, String> map) { this.map = map; found = new ArrayList<String>(map.size()); missing = new ArrayList<String>(map.size()); handler = new Callback<String, String>() { public void handleFound(String key, String value) { found.add(key + ": " + value); } public void handleMissing(String key) { missing.add(key); } }; } void test() { CallbackMap<String, String> cbMap = new CallbackMap<String, String>(map); for (int i = 0, count = map.size(); i < count; i++) { String key = "key" + i; cbMap.lookup(key, handler); } System.out.println(found.size() + " found"); System.out.println(missing.size() + " missing"); } } Now, the tryGet() example -- as best I understand the pattern (and I might well be wrong): class TryGetMap<K, V> { private final Map<K, V> backingMap; public TryGetMap(Map<K, V> backingMap) { this.backingMap = backingMap; } boolean tryGet(K key, OutParameter<V> valueParam) { V val = backingMap.get(key); if (val == null) { return false; } valueParam.value = val; return true; } } class OutParameter<V> { V value; } class TryGetExample { private final Map<String, String> map; private final List<String> found; private final List<String> missing; public TryGetExample(Map<String, String> map) { this.map = map; found = new ArrayList<String>(map.size()); missing = new ArrayList<String>(map.size()); } void test() { TryGetMap<String, String> tgMap = new TryGetMap<String, String>(map); for (int i = 0, count = map.size(); i < count; i++) { String key = "key" + i; OutParameter<String> out = new OutParameter<String>(); if (tgMap.tryGet(key, out)) { found.add(key + ": " + out.value); } else { missing.add(key); } } System.out.println(found.size() + " found"); System.out.println(missing.size() + " missing"); } } And finally, the performance test code: public static void main(String[] args) { int size = 200000; Map<String, String> map = new HashMap<String, String>(); for (int i = 0; i < size; i++) { String val = (i % 5 == 0) ? null : "value" + i; map.put("key" + i, val); } long totalCallback = 0; long totalTryGet = 0; int iterations = 20; for (int i = 0; i < iterations; i++) { { TryGetExample tryGet = new TryGetExample(map); long tryGetStart = System.currentTimeMillis(); tryGet.test(); totalTryGet += (System.currentTimeMillis() - tryGetStart); } System.gc(); { CallbackExample callback = new CallbackExample(map); long callbackStart = System.currentTimeMillis(); callback.test(); totalCallback += (System.currentTimeMillis() - callbackStart); } System.gc(); } System.out.println("Avg. callback: " + (totalCallback / iterations)); System.out.println("Avg. tryGet(): " + (totalTryGet / iterations)); } On my first attempt, I got 50% worse performance for callback than for tryGet(), which really surprised me. But, on a hunch, I added some garbage collection, and the performance penalty vanished. This fits with my instinct, which is that we're basically talking about taking the same number of method calls, conditional checks, etc. and rearranging them. But then, I wrote the code, so I might well have written a suboptimal or subconsicously penalized tryGet() implementation. Thoughts?

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