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  • 3-row layout, expanding middle, min-height:100% so footer is at bottom when there is minimal content

    - by David Lawson
    How would I change this to make the middle div expand vertically to fill the white space? <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title></title> <style type="text/css"> body,td,th { font-family: Tahoma, Geneva, Verdana, sans-serif; } html,body { margin:0; padding:0; height:100%; /* needed for container min-height */ } #container { position:relative; /* needed for footer positioning*/ margin:0 auto; /* center, not in IE5 */ width:100%; height:auto !important; /* real browsers */ height:100%; /* IE6: treaded as min-height*/ min-height:100%; /* real browsers */ } #header { height: 150px; border-bottom: 2px solid #ff8800; position: relative; background-color: #c97c3e; } #middle { padding-right: 90px; padding-left: 90px; padding-top: 35px; padding-bottom: 43px; background-color: #0F9; } #footer { border-top: 2px solid #ff8800; background-color: #ffd376; position:absolute; width:100%; bottom:0; /* stick to bottom */ } </style> </head> <body> <div id="container"> <div id="header"> Header </div> <div id="middle"> Middle </div> <div id="footer"> Footer </div> </div> </body> </html>

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  • Becoming a professional programmer / software engineer

    - by Matt
    This isn't strictly about programming, more about being a programmer, so I'm sorry if its not the right kind of question to ask on this forum (mod, please delete if it isn't) I'm a computer tech in the US Army, and once I'm out I'll have eight years on the job. I'm about to start a degree through an online school (the only way I can get the army to pay for it while I'm still in), and I'm seriously looking at getting a computer science degree. I'm great with computers. I can take one apart and put it back together with my eyes closed. I'm A+ and Network+ certified and I'm getting a couple other CompTIA certs before I get out. I can work Windows as well as anyone on this planet and I'm not terrible with Linux. A job in computers is something I've always wanted. But, aside from being a computer technician, it seems that every job in the field requires programming ability. I like programming as a hobby. I programmed TI BASIC in high school and I'm teaching myself Python, but that's as far as my experience goes. That sort of brings me to my questions: I've always heard that the first language is the most difficult, and once you learn it well then all the others sort of fall into place for you. Is that true? Like, if I spend the next eight months mastering Python, will I pretty much be able to pick up at least fair proficiency in any other OO language within a month of studying it or whatever? How easy is it to burn out? the biggest thing I'm afraid of is just burning out on programming. I can go all day long if I'm programming strictly for my own personal desire, but I can imagine it being really easy to burn out after a few years of programming to deadlines and certain specifications. Especially if its a big project involving a dozen different designers. From what I told you about myself, would I already be qualified to work as a regular technician (geek squad type or maybe running a computer repair shop). Is Python a good base to learn from? I've heard that it makes you hate other languages because they feel more convoluted when learning, but also that its a great beginner language. If you're a professional programmer, did you have any of the same fears? Would you recommend that I stick to computer repair and Python rather than try to get into corporate programming? (just from what you've read in this thread, anyway) Thanks for taking the time to read all this and answer (if you did)

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  • Problem with jQuery.ajax with 'delete' method in ie

    - by Max Williams
    I have a page where the user can edit various content using buttons and selects that trigger ajax calls. In particular, one action causes a url to be called remotely, with some data and a 'put' request, which (as i'm using a restful rails backend) triggers my update action. I also have a delete button which calls the same url but with a 'delete' request. The 'update' ajax call works in all browsers but the 'delete' one doesn't work in IE. I've got a vague memory of encountering something like this before...can anyone shed any light? here's my ajax calls: //update action - works in all browsers jQuery.ajax({ async:true, data:data, dataType:'script', type:'put', url:"/quizzes/"+quizId+"/quiz_questions/"+quizQuestionId, success: function(msg){ initializeQuizQuestions(); setPublishButtonStatus(); } }); //delete action - fails in ie function deleteQuizQuestion(quizQuestionId, quizId){ //send ajax call to back end to change the difficulty of the quiz question //back end will then refresh the relevant parts of the page (progress bars, flashes, quiz status) jQuery.ajax({ async:true, dataType:'script', type:'delete', url:"/quizzes/"+quizId+"/quiz_questions/"+quizQuestionId, success: function(msg){ alert("success"); initializeQuizQuestions(); setSelectStatus(quizQuestionId, true); jQuery("tr[id*='quiz_question_"+quizQuestionId+"']").removeClass('selected'); }, error: function(msg){ alert("error:" + msg); } }); } I put the alerts in success and error in the delete ajax just to see what happens, and the 'error' part of the ajax call is triggered, but WITH NO CALL BEING MADE TO THE BACK END (i know this by watching my back end server logs). So, it fails before it even makes the call. I can't work out why - the 'msg' i get back from the error block is blank. Any ideas anyone? Is this a known problem? I've tested it in ie6 and ie8 and it doesn't work in either. thanks - max EDIT - the solution - thanks to Nick Craver for pointing me in the right direction. Rails (and maybe other frameworks?) has a subterfuge for the unsupported put and delete requests: a post request with the parameter "_method" (note the underscore) set to 'put' or 'delete' will be treated as if the actual request type was that string. So, in my case, i made this change - note the 'data' option': jQuery.ajax({ async:true, data: {"_method":"delete"}, dataType:'script', type:'post', url:"/quizzes/"+quizId+"/quiz_questions/"+quizQuestionId, success: function(msg){ alert("success"); initializeQuizQuestions(); setSelectStatus(quizQuestionId, true); jQuery("tr[id*='quiz_question_"+quizQuestionId+"']").removeClass('selected'); }, error: function(msg){ alert("error:" + msg); } }); } Rails will now treat this as if it were a delete request, preserving the REST system. The reason my PUT example worked was just because in this particular case IE was happy to send a PUT request, but it officially does not support them so it's best to do this for PUT requests as well as DELETE requests.

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  • Stack and queue operations on the same array.

    - by Passonate Learner
    Hi. I've been thinking about a program logic, but I cannot draw a conclusion to my problem. Here, I've implemented stack and queue operations to a fixed array. int A[1000]; int size=1000; int top; int front; int rear; bool StackIsEmpty() { return (top==0); } bool StackPush( int x ) { if ( top >= size ) return false; A[top++] = x; return true; } int StackTop( ) { return A[top-1]; } bool StackPop() { if ( top <= 0 ) return false; A[--top] = 0; return true; } bool QueueIsEmpty() { return (front==rear); } bool QueuePush( int x ) { if ( rear >= size ) return false; A[rear++] = x; return true; } int QueueFront( ) { return A[front]; } bool QueuePop() { if ( front >= rear ) return false; A[front++] = 0; return true; } It is presumed(or obvious) that the bottom of the stack and the front of the queue is pointing at the same location, and vice versa(top of the stack points the same location as rear of the queue). For example, integer 1 and 2 is inside an array in order of writing. And if I call StackPop(), the integer 2 will be popped out, and if I call QueuePop(), the integer 1 will be popped out. My problem is that I don't know what happens if I do both stack and queue operations on the same array. The example above is easy to work out, because there are only two values involved. But what if there are more than 2 values involved? For example, if I call StackPush(1); QueuePush(2); QueuePush(4); StackPop(); StackPush(5); QueuePop(); what values will be returned in the order of bottom(front) from the final array? I know that if I code a program, I would receive a quick answer. But the reason I'm asking this is because I want to hear a logical explanations from a human being, not a computer.

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  • Adding OutputCache to an ASP.NET WebForm crashes my site :(

    - by Pure.Krome
    Hi folks, When I add either one of these ... <%@ OutputCache Duration="600" Location="Any" VaryByParam="*" %> or <%@ OutputCache CacheProfile="CmsArticlesListOrItem" %> (.. and this into the web.config file...) <caching> <outputCacheSettings> <outputCacheProfiles> <add name="CmsArticlesListOrItem" duration="600" varyByParam="*" /> </outputCacheProfiles> </outputCacheSettings> <sqlCacheDependency ........ ></sqlCacheDependency </caching> my page/site crashes with the following error:- Source: System.Web ---------------------------------------------------------------------------- TargetSite: System.Web.DirectoryMonitor FindDirectoryMonitor(System.String, Boolean, Boolean) ---------------------------------------------------------------------------- Message:System.Web.HttpException: Directory 'C:\Web Sites\My Site Foo - Main Site\Controls\InfoAdvice' does not exist. Failed to start monitoring file changes. at System.Web.FileChangesMonitor.FindDirectoryMonitor(String dir, Boolean addIfNotFound, Boolean throwOnError) at System.Web.FileChangesMonitor.StartMonitoringPath(String alias, FileChangeEventHandler callback, FileAttributesData& fad) at System.Web.Caching.CacheDependency.Init(Boolean isPublic, String[] filenamesArg, String[] cachekeysArg, CacheDependency dependency, DateTime utcStart) at System.Web.Caching.CacheDependency..ctor(Int32 dummy, String[] filenames, DateTime utcStart) at System.Web.Hosting.MapPathBasedVirtualPathProvider.GetCacheDependency(String virtualPath, IEnumerable virtualPathDependencies, DateTime utcStart) at System.Web.ResponseDependencyList.CreateCacheDependency(CacheDependencyType dependencyType, CacheDependency dependency) at System.Web.HttpResponse.CreateCacheDependencyForResponse(CacheDependency dependencyVary) at System.Web.Caching.OutputCacheModule.InsertResponse(HttpResponse response, HttpContext context, String keyRawResponse, HttpCachePolicySettings settings, CachedVary cachedVary, CachedRawResponse memoryRawResponse) at System.Web.Caching.OutputCacheModule.OnLeave(Object source, EventArgs eventArgs) at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) Ok .. so for some reason, the OutputCache wants a folder/file to be there? Well, i've had this site live for around 3 years and i'm pretty sure that the folders \Controls and \Controls\InfoAdvice doesn't exist on my production server. On my localhost, it sure does .. and contains a large list of ascx controls. But they don't exist on my live server. So ... what is going on here? Can anyone please help? Oh :) Before someone suggests I create those two folders and even stick a random file in those folders .. and have some random text in those random files .. i've done that and it doesn't seem to work, still :( Please Help !

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  • function parameter used to store value

    - by user248247
    Hi, I have to define an interface. The API in my homework is stated below: int generate_codes(char * ssn, char * student_id); int denotes 0 or 1 for pass or fail. studentid is an output param should return a 6 digit id. ssn is a 9 digit input param they school program will take ssn's and use my code to generate the student id. now from an API perspective should I not be using const char * for both parameters. should the studentid not be passed in by reference? rather than by pointer? can someone tell me how i can easily use the pointer in my test app which uses my api to get the pointer such that it prints a std::string from a char *? my app code looks something like const char * ssn = "987098765" const char * studnt_id = new char [7]; int value = -1; value = generate_codes(ssn,studnt_id); std::string test(studnt_id); std::cout<<"student id= "<<test<<" Pass/fail= "<<value<<std::endl; delete [] studnt_id; return 0; I basically got an error about << not being compatible with the right hand side of the operand. When i changed the code to std::cout<<"student id= "<<test.c_str()<<" Pass/fail= "<<value<<std::endl; then it worked but i get garbage for the value. not sure how to do get the value form the pointer. THe value inside the function prints just fine. but when i try to print it outside of the function it prints garbage. Inside the above function I do set the studndt_id like so std::string str_studnt_id = studnt_id; should that make the address of the str_studnt point to the address of studnt_id and thus any changes I make to the value that its pointing to it should reflect outside the function?

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  • Saving a reference to a int.

    - by Scott Chamberlain
    Here is a much simplified version of what I am trying to do static void Main(string[] args) { int test = 0; int test2 = 0; Test A = new Test(ref test); Test B = new Test(ref test); Test C = new Test(ref test2); A.write(); //Writes 1 should write 1 B.write(); //Writes 1 should write 2 C.write(); //Writes 1 should write 1 Console.ReadLine(); } class Test { int _a; public Test(ref int a) { _a = a; //I loose the reference here } public void write() { var b = System.Threading.Interlocked.Increment(ref _a); Console.WriteLine(b); } } In my real code I have a int that will be incremented by many threads however where the threads a called it will not be easy to pass it the parameter that points it at the int(In the real code this is happening inside a IEnumerator). So a requirement is the reference must be made in the constructor. Also not all threads will be pointing at the same single base int so I can not use a global static int either. I know I can just box the int inside a class and pass the class around but I wanted to know if that is the correct way of doing something like this? What I think could be the correct way: static void Main(string[] args) { Holder holder = new Holder(0); Holder holder2 = new Holder(0); Test A = new Test(holder); Test B = new Test(holder); Test C = new Test(holder2); A.write(); //Writes 1 should write 1 B.write(); //Writes 2 should write 2 C.write(); //Writes 1 should write 1 Console.ReadLine(); } class Holder { public Holder(int i) { num = i; } public int num; } class Test { Holder _holder; public Test(Holder holder) { _holder = holder; } public void write() { var b = System.Threading.Interlocked.Increment(ref _holder.num); Console.WriteLine(b); } } Is there a better way than this?

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  • List of Django model instance foreign keys losing consistency during state changes.

    - by Joshua
    I have model, Match, with two foreign keys: class Match(model.Model): winner = models.ForeignKey(Player) loser = models.ForeignKey(Player) When I loop over Match I find that each model instance uses a unique object for the foreign key. This ends up biting me because it introduces inconsistency, here is an example: >>> def print_elo(match_list): ... for match in match_list: ... print match.winner.id, match.winner.elo ... print match.loser.id, match.loser.elo ... >>> print_elo(teacher_match_list) 4 1192.0000000000 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 >>> teacher_match_list[0].winner.elo = 3000 >>> print_elo(teacher_match_list) 4 3000 # Object 4 2 1192.0000000000 5 1208.0000000000 2 1192.0000000000 5 1208.0000000000 4 1192.0000000000 # Object 4 >>> I solved this problem like so: def unify_refrences(match_list): """Makes each unique refrence to a model instance non-unique. In cases where multiple model instances are being used django creates a new object for each model instance, even if it that means creating the same instance twice. If one of these objects has its state changed any other object refrencing the same model instance will not be updated. This method ensure that state changes are seen. It makes sure that variables which hold objects pointing to the same model all hold the same object. Visually this means that a list of [var1, var2] whose internals look like so: var1 --> object1 --> model1 var2 --> object2 --> model1 Will result in the internals being changed so that: var1 --> object1 --> model1 var2 ------^ """ match_dict = {} for match in match_list: try: match.winner = match_dict[match.winner.id] except KeyError: match_dict[match.winner.id] = match.winner try: match.loser = match_dict[match.loser.id] except KeyError: match_dict[match.loser.id] = match.loser My question: Is there a way to solve the problem more elegantly through the use of QuerySets without needing to call save at any point? If not, I'd like to make the solution more generic: how can you get a list of the foreign keys on a model instance or do you have a better generic solution to my problem? Please correct me if you think I don't understand why this is happening.

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  • Saxon XSLT-Transformation: How to change serialization of an empty tag from <x/> to <x></x>?

    - by Ben
    Hello folks! I do some XSLT-Transformation using Saxon HE 9.2 with the output later being unmarshalled by Castor 1.3.1. The whole thing runs with Java at the JDK 6. My XSLT-Transformation looks like this: <xsl:transform version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:ns="http://my/own/custom/namespace/for/the/target/document"> <xsl:output method="xml" encoding="UTF-8" indent="no" /> <xsl:template match="/"> <ns:item> <ns:property name="id"> <xsl:value-of select="/some/complicated/xpath" /> </ns:property> <!-- ... more ... --> </xsl:template> So the thing is: if the XPath-expression /some/complicated/xpath evaluates to an empty sequence, the Saxon serializer writes <ns:property/> instead of <ns:property></ns:property>. This, however, confuses the Castor unmarshaller, which is next in the pipeline and which unmarshals the output of the transformation to instances of XSD-generated Java-code. So my question is: How can I tell the Saxon-serializer to output empty tags not as standalone tags? Here is what I am proximately currently doing to execute the transformation: import net.sf.saxon.s9api.*; import javax.xml.transform.*; import javax.xml.transform.sax.SAXSource; // ... // read data XMLReader xmlReader = XMLReaderFactory.createXMLReader(); // ... there is some more setting up the xmlReader here ... InputStream xsltStream = new FileInputStream(xsltFile); InputStream inputStream = new FileInputStream(inputFile); Source xsltSource = new SAXSource(xmlReader, new InputSource(xsltStream)); Source inputSource = new SAXSource(xmlReader, new InputSource(inputStream)); XdmNode input = processor.newDocumentBuilder().build(inputSource); // initialize transformation configuration Processor processor = new Processor(false); XsltCompiler compiler = processor.newXsltCompiler(); compiler.setErrorListener(this); XsltExecutable executable = compiler.compile(xsltSource); Serializer serializer = new Serializer(); serializer.setOutputProperty(Serializer.Property.METHOD, "xml"); serializer.setOutputProperty(Serializer.Property.INDENT, "no"); serializer.setOutputStream(output); // execute transformation XsltTransformer transformer = executable.load(); transformer.setInitialContextNode(input); transformer.setErrorListener(this); transformer.setDestination(serializer); transformer.setSchemaValidationMode(ValidationMode.STRIP); transformer.transform(); I'd appreciate any hint pointing in the direction of a solution. :-) In case of any unclarity I'd be happy to give more details. Nightly greetings from Germany, Benjamin

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  • Iterator failure while moving over equal_range in Boost MultiIndex container

    - by Sarah
    I'm making some mistake with my iterators, but I can't see it yet. I have a Boost MultiIndex container, HostContainer hmap, whose elements are boost::shared_ptr to members of class Host. All the indices work on member functions of class Host. The third index is by Host::getHousehold(), where the household member variable is an int. Below, I'm trying to iterate over the range of Hosts matching a particular household (int hhold2) and load the corresponding private member variable Host::id into an array. I'm getting an "Assertion failed: (px != 0), function operator-, file /Applications/boost_1_42_0/boost/smart_ptr/shared_ptr.hpp, line 418" error in runtime when the household size is 2. (I can't yet tell if it happens anytime the household size is 2, or if other conditions must be met.) typedef multi_index_container< boost::shared_ptr< Host >, indexed_by< hashed_unique< const_mem_fun<Host,int,&Host::getID> >, // 0 - ID index ordered_non_unique< const_mem_fun<Host,int,&Host::getAgeInY> >, // 1 - Age index ordered_non_unique< const_mem_fun<Host,int,&Host::getHousehold> > // 2 - Household index > // end indexed_by > HostContainer; typedef HostContainer::nth_index<2>::type HostsByHH; // inside main() int numFamily = hmap.get<2>().count( hhold2 ); int familyIDs[ numFamily ]; for ( int f = 0; f < numFamily; f++ ) { familyIDs[ f ] = 0; } int indID = 0; int f = 0; std::pair< HostsByHH::iterator, HostsByHH::iterator pit = hmap.get<2().equal_range( hhold2 ); cout << "\tNeed to update households of " << numFamily << " family members (including self) of host ID " << hid2 << endl; while ( pit.first != pit.second ) { cout << "Pointing at new family member still in hhold " << ((pit.first))-getHousehold() << "; " ; indID = ((pit.first) )-getID(); familyIDs[ f ] = indID; pit.first++; f++; } What could make this code fail? The above snippet only runs when numFamily 1. (Other suggestions and criticisms are welcome too.) Thank you in advance.

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  • What could cause a Labwindows/CVI C program to hate the number 2573?

    - by Adam Bard
    Using Windows So I'm reading from a binary file a list of unsigned int data values. The file contains a number of datasets listed sequentially. Here's the function to read a single dataset from a char* pointing to the start of it: function read_dataset(char* stream, t_dataset *dataset){ //...some init, including setting dataset->size; for(i=0;i<dataset->size;i++){ dataset->samples[i] = *((unsigned int *) stream); stream += sizeof(unsigned int); } //... } Where read_dataset in such a context as this: //... char buff[10000]; t_dataset* dataset = malloc( sizeof( *dataset) ); unsigned long offset = 0; for(i=0;i<number_of_datasets; i++){ fseek(fd_in, offset, SEEK_SET); if( (n = fread(buff, sizeof(char), sizeof(*dataset), fd_in)) != sizeof(*dataset) ){ break; } read_dataset(buff, *dataset); // Do something with dataset here. It's screwed up before this, I checked. offset += profileSize; } //... Everything goes swimmingly until my loop reads the number 2573. All of a sudden it starts spitting out random and huge numbers. For example, what should be ... 1831 2229 2406 2637 2609 2573 2523 2247 ... becomes ... 1831 2229 2406 2637 2609 0xDB00000A 0xC7000009 0xB2000008 ... If you think those hex numbers look suspicious, you're right. Turns out the hex values for the values that were changed are really familiar: 2573 -> 0xA0D 2523 -> 0x9DB 2247 -> 0x8C7 So apparently this number 2573 causes my stream pointer to gain a byte. This remains until the next dataset is loaded and parsed, and god forbid it contain a number 2573. I have checked a number of spots where this happens, and each one I've checked began on 2573. I admit I'm not so talented in the world of C. What could cause this is completely and entirely opaque to me.

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  • MVVM Binding Orthogonal Aspects in Views e.g. Application Settings

    - by chibacity
    I have an application which I am developing using WPF\Prism\MVVM. All is going well and I have some pleasing MVVM implementations. However, in some of my views I would like to be able to bind application settings e.g. when a user reloads an application, the checkbox for auto-scrolling a grid should be checked in the state it was last time the user used the application. My view needs to bind to something that holds the "auto-scroll" setting state. I could put this on the view-model, but applications settings are orthogonal to the purpose of the view-model. The "auto-scroll" setting is controlling an aspect of the view. This setting is just an example. There will be quite a number of them and splattering my view-models with properties to represent application settings (so I can bind them) feels decidedly yucky. One view-model per view seems to be de rigeuer... What is best\usual practice here? Splatter my view-models with application settings? Have multiple view-models per view so settings can be represented in their own right? Split views so that controls can bind to an ApplicationSettingsViewModel? = too many views? Something else? Edit 1 To add a little more context, I am developing a UI with a tabbed interface. Each tab will host a single widget and there a variety of widgets. Each widget is a Prism composition of individual views. Some views are common amongst widgets e.g. a file picker view. Whilst each widget is composed of several views, as a whole, conceptually a widget has a single set of user settings e.g. last file selected, auto-scroll enabled, etc. These need to be persisted and retrieved\applied when the application starts again, and the widget views are created. My question is focused on the fact that conceptually a widget has a single set of user settings which is at right-angles to the fact that a widget consists of many views. Each view in the widget has it's own view-model (which works nicely and logically) but if I stick to a one view-model per view, I would have to splatter each view-model with user settings appropriate to it. This doesn't sound right ?!?

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  • Is it too early to start designing for Task Parallel Library?

    - by Joe Erickson
    I have been following the development of the .NET Task Parallel Library (TPL) with great interest since Microsoft first announced it. There is no doubt in my mind that we will eventually take advantage of TPL. What I am questioning is whether it makes sense to start taking advantage of TPL when Visual Studio 2010 and .NET 4.0 are released, or whether it makes sense to wait a while longer. Why Start Now? The .NET 4.0 Task Parallel Library appears to be well designed and some relatively simple tests demonstrate that it works well on today's multi-core CPUs. I have been very interested in the potential advantages of using multiple lightweight threads to speed up our software since buying my first quad processor Dell Poweredge 6400 about seven years ago. Experiments at that time indicated that it was not worth the effort, which I attributed largely to the overhead of moving data between each CPU's cache (there was no shared cache back then) and RAM. Competitive advantage - some of our customers can never get enough performance and there is no doubt that we can build a faster product using TPL today. It sounds fun. Yes, I realize that some developers would rather poke themselves in the eye with a sharp stick, but we really enjoy maximizing performance. Why Wait? Are today's Intel Nehalem CPUs representative of where we are going as multi-core support matures? You can purchase a Nehalem CPU with 4 cores which share a single level 3 cache today, and most likely a 6 core CPU sharing a single level 3 cache by the time Visual Studio 2010 / .NET 4.0 are released. Obviously, the number of cores will go up over time, but what about the architecture? As the number of cores goes up, will they still share a cache? One issue with Nehalem is the fact that, even though there is a very fast interconnect between the cores, they have non-uniform memory access (NUMA) which can lead to lower performance and less predictable results. Will future multi-core architectures be able to do away with NUMA? Similarly, will the .NET Task Parallel Library change as it matures, requiring modifications to code to fully take advantage of it? Limitations Our core engine is 100% C# and has to run without full trust, so we are limited to using .NET APIs.

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  • Optimizing tasks to reduce CPU in a trading application

    - by Joel
    Hello, I have designed a trading application that handles customers stocks investment portfolio. I am using two datastore kinds: Stocks - Contains unique stock name and its daily percent change. UserTransactions - Contains information regarding a specific purchase of a stock made by a user : the value of the purchase along with a reference to Stock for the current purchase. db.Model python modules: class Stocks (db.Model): stockname = db.StringProperty(multiline=True) dailyPercentChange=db.FloatProperty(default=1.0) class UserTransactions (db.Model): buyer = db.UserProperty() value=db.FloatProperty() stockref = db.ReferenceProperty(Stocks) Once an hour I need to update the database: update the daily percent change in Stocks and then update the value of all entities in UserTransactions that refer to that stock. The following python module iterates over all the stocks, update the dailyPercentChange property, and invoke a task to go over all UserTransactions entities which refer to the stock and update their value: Stocks.py # Iterate over all stocks in datastore for stock in Stocks.all(): # update daily percent change in datastore db.run_in_transaction(updateStockTxn, stock.key()) # create a task to update all user transactions entities referring to this stock taskqueue.add(url='/task', params={'stock_key': str(stock.key(), 'value' : self.request.get ('some_val_for_stock') }) def updateStockTxn(stock_key): #fetch the stock again - necessary to avoid concurrency updates stock = db.get(stock_key) stock.dailyPercentChange= data.get('some_val_for_stock') # I get this value from outside ... some more calculations here ... stock.put() Task.py (/task) # Amount of transaction per task amountPerCall=10 stock=db.get(self.request.get("stock_key")) # Get all user transactions which point to current stock user_transaction_query=stock.usertransactions_set cursor=self.request.get("cursor") if cursor: user_transaction_query.with_cursor(cursor) # Spawn another task if more than 10 transactions are in datastore transactions = user_transaction_query.fetch(amountPerCall) if len(transactions)==amountPerCall: taskqueue.add(url='/task', params={'stock_key': str(stock.key(), 'value' : self.request.get ('some_val_for_stock'), 'cursor': user_transaction_query.cursor() }) # Iterate over all transaction pointing to stock and update their value for transaction in transactions: db.run_in_transaction(updateUserTransactionTxn, transaction.key()) def updateUserTransactionTxn(transaction_key): #fetch the transaction again - necessary to avoid concurrency updates transaction = db.get(transaction_key) transaction.value= transaction.value* self.request.get ('some_val_for_stock') db.put(transaction) The problem: Currently the system works great, but the problem is that it is not scaling well… I have around 100 Stocks with 300 User Transactions, and I run the update every hour. In the dashboard, I see that the task.py takes around 65% of the CPU (Stock.py takes around 20%-30%) and I am using almost all of the 6.5 free CPU hours given to me by app engine. I have no problem to enable billing and pay for additional CPU, but the problem is the scaling of the system… Using 6.5 CPU hours for 100 stocks is very poor. I was wondering, given the requirements of the system as mentioned above, if there is a better and more efficient implementation (or just a small change that can help with the current implemntation) than the one presented here. Thanks!! Joel

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  • Which MarkDown (WMD) javascript editor should I use?

    - by Edan Maor
    Background I'm working on an application which requires user-entered content, and I've decided to use a StackOverflow-style MarkDown editor. After researching this topic for the last few days, I realize there are numerous forks of the base WMD editor, some with a few basic enhancements and some with serious differences from the StackOverflow one. Since this will be the heart of the application, I'd like to start with the best code base I can. I'd be happy if anyone can recommend which one of the many solutions out there best fits my needs. Below is requirements, plus what I've managed to find already. I'm hoping this question will help me decide which version to go with, and maybe help me discover a port out there that's an even better fit for my needs. The requirements for my project Live Preview Multiple editors on the same page (not know how many in advance, since the user can dynamically add another editing box). Ability to extend with extra buttons (I'd like a button to upload a picture, instead of just adding an img url). Ability to dynamically show/hide the edit box (and only see the preview box). Not an absolute must, but I'd prefer to stick as close to StackOverflow's look and feel, since it's well known. Don't know if this matters, but the backend is written in Django. Editors I've looked at Here are a few of the code bases I've looked at, with thoughts. Obviously, I might be missing another solution out there. The derobins version. From what I can tell, this is the official StackOverflow version. Seems like it doesn't support multiple editors on one page. JQuery.MarkEdit. Looks very good, but is pretty different from the StackOverflow version. MooWMD. Looks like the winner right now, but I'm a little concerned since it looks less active/hackable than MarkEdit. The wmd-new version. Not sure, looks like an old codebase without much use. The SocialSite branch. Seems like it's not for public use.

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  • How to catch 'exceptions' for out of order execution in Workflow Foundation 4?

    - by Alex Key
    Hi, I am attempting to model a worklfow using a "WCF Workflow Service" in .net / vs 2010 that needs to handle out of order execution gracefully (but not allow it - if thath makes sense!?) For example I have 2 receive activities one called Initialize and the other called GetValue inside a FlowChart. In most cases Initialize should be called first and GetValue after (as modled in the flow chart). However if GetValue is executed before Initialize I do not want to return an "out of order" exception (although when I look at the WCF test client, I can't actually see an exception). But instead a custom exception saying something like "you must initialize first". In theory I could model this with lots of parallel activities and conditions to check if Initialized / Running / Terminated etc. But the business process I am modelling if very very similar to a state machine... except it must handle people executing things in the wrong order. Ideally I would like to catch the "out of order" exception (thought I don't think it's really an exception as such), check the 'exception' to see which function was attempted to run and then handle it. I have done some research around enabling AllowBufferedReceive. However I don't want to be able to execute out of order (I don't think), but instead give a detailed response if it does happen. I've looked at the new beta state machine template for WF 4 - but i'm not sure if it does what i'm after? I'm not sure if I have the wrong end of the stick, so any help would be greatly appreciated. [EDIT] To help clarify... Sorry it's a tricky one to explain. The standard I am trying to implement (the e-learning standard SCORM RTE) is structured like a state machine i.e. certain functions can only be executed in certain states. However the standard specifies that if the calling clients tries to execute a function that it is not meant to, then a warning should be issued... for example "you cannot use GetValue(), because you have not yet Initialized". Ideally I'd like to structure the workflow as the theoretical state machine and not need to have to use multiple if/else's to handle all the scenarios where something could be executed out-of-order. I'd like to catch a out-of-order exception (but I don't think there is such an exception - as it's not in the debugger) and rethrow it.

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  • Feeding PDF through IInternetSession to WebBrowser control - Error

    - by Codesleuth
    As related to my previous question, I have developed a temporary asynchronous pluggable protocol with the specific aim to be able to serve PDF documents directly to a WebBrowser control via a database. I need to do this because my limitations include not being able to access the disk other than IsolatedStorage; and a MemoryStream would be far better for serving up PDF documents that average around 31kb. Unfortunately the code doesn't work, and I'm getting an error from the WebBrowser control (i.e. IE): Unable to download . Unable to open this Internet site. The requested site is either unavailable or cannot be found. Please try again later. The line in my code where this occurs is within the following: pOIProtSink.ReportData(BSCF.BSCF_LASTDATANOTIFICATION, (uint)_stream.Length, (uint)_stream.Length); However, if you download the project and run it, you will be able to see the stream is successfully read and passed to the browser, so it seems like there's a problem somewhere to do with the end of reading the data: public uint Read(IntPtr pv, uint cb, out uint pcbRead) { var bytesToRead = Math.Min(cb, _streamBuffer.Length); pcbRead = (uint)_stream.Read(_streamBuffer, 0, (int)bytesToRead); Marshal.Copy(_streamBuffer, 0, pv, (int)pcbRead); return (pcbRead == 0 || pcbRead < cb) ? HRESULT.S_FALSE : HRESULT.S_OK; } Here is the entire sample project: InternetSessionSample.zip (VS2010) I will leave this up for as long as I can to help other people in the future If anyone has any ideas why I might be getting this message and can shed some light on the problem, I would be grateful for the assistance. EDIT: A friend suggested inserting a line that calls the IInternetProtocolSink.ReportProgress with BINDSTATUS_CACHEFILENAMEAVAILABLE pointing at the original file. This prevents it from failing now and shows the PDF in the Adobe Reader control, but means it defeats the purpose of this by having Adobe Reader simply load from the cache file (which I can't provide). See below: pOIProtSink.ReportProgress(BINDSTATUS.BINDSTATUS_CACHEFILENAMEAVAILABLE, @"D:\Visual Studio Solutions\Projects\InternetSessionSample\bin\Debug\sample.pdf"); pOIProtSink.ReportData(BSCF.BSCF_LASTDATANOTIFICATION, (uint)_stream.Length, (uint)_stream.Length); This is progress though, I guess.

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  • Function Point Analysis -- a seriously over-estimating technique?

    - by kizzx2
    I know questions about FPA has been asked numerous times before, but this time I'm taking a more analytical angle at it, backed up with data. 1. First, some data This question is based on a tutorial. He had a "Sample Count" section where he demonstrated it step by step. You can see some screenshots of his sample application here. In the end, he calculated the unadjusted FP to be 99. There is another article on InformIT with industry data on typical hour/FP. It ranges from 2 hours/FP to 27.4 hours/FP. Let's try to stick with 2 for the moment (since SO readers are probably the more efficient crowd :p). 2. Reality check!? Now just check out the screenshots again. Do a little math here 99 * 2 = 198 hours 198 hours / 40 hours per week = 5 weeks Seriously? That sample application is going to take 5 weeks to implement? Is it just my feeling that it wouldn't take any decent programmer longer than one week to have it completed? Now let's try estimating the cost of the project. We'll use New York's minimum wage at the moment (Wikipedia), which is $7.25 198 * 7.25 = $1435.5 From what I could see from the screenshots, this application is a small excel-improvement app. I could have bought MS Office Pro for 200 bucks which gives me greater interoperability (.xls files) and flexibility (spreadsheets). (For the record, that same Web site has another article discussing productivity. It seems like they typically use 4.2 hours/FP, which gives us even more shocking stats: 99 * 4.2 = 415 hours = 10 weeks = almost 3 whopping months! 415 hours * $7.25 = $3000 zomg (That's even assuming that all our poor coders get the minimum wage!) 3. Am I missing something here? Right now, I could come up with several possible explanation: FPA is really only suited for bigger projects (1000+ FPs) so it becomes extremely inaccurate at smaller scale. The hours/FP metric fluctuates abruptly from team to team, project to project. For a small project like this, we could have used something like 0.5 hour/FP or something. (Now this kind of makes the whole estimation thing pointless, unless my firm does the same type of projects for several years with the same team, not really common.) From my experience with several software metrics, Function Point is really not a lightweight metric. If the hour/FP thing fluctuates so much, then what's the point, maybe I could have gone with User Story Points which is a lot faster to get and arguably almost as uncertain. What would be the FP experts' answers to this?

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  • crazy asp.net error

    - by dominic
    Hi I am having a problem debugging an issue on a website. Everything works locally, the local and server databases are the same The strange thing about the error is that it points to my local dev machine in the error stack. Is that crazy or what, The files are published and being hosted on a server machine and the error is pointing to a line of code on my local dev box. I feel like I am losing the plot. Can someone pls help be clear the air here because this is very weird Error in '/' Application. Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace: [ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index] System.Collections.ArrayList.get_Item(Int32 index) +10066148 System.Collections.Specialized.NameObjectCollectionBase.BaseGet(Int32 index) +17 System.Web.HttpFileCollection.get_Item(Int32 index) +9 System.Web.HttpFileCollectionWrapper.get_Item(Int32 index) +18 PitchPortal.Web.Binders.DocumentModelBinder.ValidateAndAssignPostedFile(ControllerContext controllerContext, ModelBindingContext bindingContext, Document doc) in C:\Users\Bich Vu\Documents\Visual Studio 2008\Projects\PitchPortal\PitchPortal.Web\Binders\DocumentModelBinder.cs:73 PitchPortal.Web.Binders.DocumentModelBinder.BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) in C:\Users\Bich Vu\Documents\Visual Studio 2008\Projects\PitchPortal\PitchPortal.Web\Binders\DocumentModelBinder.cs:45 System.Web.Mvc.ControllerActionInvoker.GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor) +404 System.Web.Mvc.ControllerActionInvoker.GetParameterValues(ControllerContext controllerContext, ActionDescriptor actionDescriptor) +140 System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +658084 System.Web.Mvc.Controller.ExecuteCore() +125 System.Web.Mvc.<c_DisplayClass8.b_4() +48 System.Web.Mvc.Async.<c_DisplayClass1.b_0() +21 System.Web.Mvc.Async.<c__DisplayClass81.<BeginSynchronous>b__7(IAsyncResult _) +15 System.Web.Mvc.Async.WrappedAsyncResult1.End() +85 System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +51 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +454 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +263

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  • dojo layout tutorial dor version 1.7 doesn't work for 1.7.2

    - by Sheena
    This is sortof a continuation to dojo1.7 layout acting screwy. So I made some working widgets and tested them out, i then tried altering my work using the tutorial at http://dojotoolkit.org/documentation/tutorials/1.7/dijit_layout/ to make the layout nice. After failing at that in many interesting ways (thus my last question) I started on a new path. My plan is now to implement the layout tutorial example and then stick in my widgets. For some reason even following the tutorial wont work... everything loads then disappears and I'm left with a blank browser window. Any ideas? It just struck me that it could be browser compatibility issues, I'm working on Firefox 13.0.1. As far as I know Dojo is supposed to be compatible with this... anyway, have some code: HTML: <body class="claro"> <div id="appLayout" class="demoLayout" data-dojo-type="dijit.layout.BorderContainer" data-dojo-props="design: 'headline'"> <div class="centerPanel" data-dojo-type="dijit.layout.ContentPane" data-dojo-props="region: 'center'"> <div> <h4>Group 1 Content</h4> <p>stuff</p> </div> <div> <h4>Group 2 Content</h4> </div> <div> <h4>Group 3 Content</h4> </div> </div> <div class="edgePanel" data-dojo-type="dijit.layout.ContentPane" data-dojo-props="region: 'top'"> Header content (top) </div> <div id="leftCol" class="edgePanel" data-dojo-type="dijit.layout.ContentPane" data-dojo-props="region: 'left', splitter: true"> Sidebar content (left) </div> </div> </body> Dojo Configuration: var dojoConfig = { baseUrl: "${request.static_url('mega:static/js')}", //this is in a mako template tlmSiblingOfDojo: false, packages: [ { name: "dojo", location: "libs/dojo" }, { name: "dijit", location: "libs/dijit" }, { name: "dojox", location: "libs/dojox" }, ], parseOnLoad: true, has: { "dojo-firebug": true, "dojo-debug-messages": true }, async: true }; other js stuff: require(["dijit/layout/BorderContainer", "dijit/layout/TabContainer", "dijit/layout/ContentPane", "dojo/parser"]); css: html, body { height: 100%; margin: 0; overflow: hidden; padding: 0; } #appLayout { height: 100%; } #leftCol { width: 14em; }

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  • Is there a path of least resistance that a newcomer to graphics-technology-adoption can take at this point in the .NET graphics world?

    - by Rao
    For the past 5 months or so, I've spent time learning C# using Andrew Troelsen's book and getting familiar with stuff in the .NET 4 stack... bits of ADO.NET, EF4 and a pinch of WCF to taste. I'm really interested in graphics development (not for games though), which is why I chose to go the .NET route when I decided choose from either Java or .NET to learn... since I heard about WPF and saw some sexy screenshots and all. I'm even almost done with the 4 WPF chapters in Troelsen's book. Now, all of a sudden I saw some post on a forum about how "WPF was dead" in the face of something called Silverlight. I searched more and saw all the confusion going on at present... even stuff like "Silverlight is dead too!" wrt HTML5. From what I gather, we are in a delicate period of time that will eventually decide which technology will stabilize, right? Even so, as someone new moving into UI & graphics development via .NET, I wish I could get some guidance from people more experienced people. Maybe I'm reading too much? Maybe I have missed some pieces of information? Maybe a path exists that minimizes tears of blood? In any case, here is a sample vomiting of my thoughts on which I'd appreciate some clarification or assurance or spanking: My present interest lies in desktop development. But on graduating from college, I wish to market myself as a .NET developer. The industry seems to be drooling for web stuff. Can Silverlight do both equally well? (I see on searches that SL works "out of browser"). I have two fair-sized hobby projects planned that will have hawt UIs with lots of drag n drop, sliding animations etc. These are intended to be desktop apps that will use reflection, database stuff using EF4, networking over LAN, reading-writing of files... does this affect which graphics technology can be used? At some laaaater point, if I become interested in doing a bit of 3D stuff in .NET, will that affect which technologies can be used? Or what if I look up to the heavens, stick out my middle finger, and do something crazy like go learn HTML5 even though my knowledge of it can be encapsulated in 2 sentences? Sorry I seem confused so much, I just want to know if there's a path of least resistance that a newcomer to graphics-technology-adoption can take at this point in the graphics world.

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  • Who calls the Destructor of the class when operator delete is used in multiple inheritance.

    - by dicaprio-leonard
    This question may sound too silly, however , I don't find concrete answer any where else. With little knowledge on how late binding works and virtual keyword used in inheritance. As in the code sample, when in case of inheritance where a base class pointer pointing to a derived class object created on heap and delete operator is used to deallocate the memory , the destructor of the of the derived and base will be called in order only when the base destructor is declared virtual function. Now my question is : 1) When the destructor of base is not virtual, why the problem of not calling derived dtor occur only when in case of using "delete" operator , why not in the case given below: derived drvd; base *bPtr; bPtr = &drvd; //DTOR called in proper order when goes out of scope. 2) When "delete" operator is used, who is reponsible to call the destructor of the class? The operator delete will have an implementation to call the DTOR ? or complier writes some extra stuff ? If the operator has the implementation then how does it looks like , [I need sample code how this would have been implemented]. 3) If virtual keyword is used in this example, how does operator delete now know which DTOR to call? Fundamentaly i want to know who calls the dtor of the class when delete is used. Sample Code class base { public: base() { cout<<"Base CTOR called"<<endl; } virtual ~base() { cout<<"Base DTOR called"<<endl; } }; class derived:public base { public: derived() { cout<<"Derived CTOR called"<<endl; } ~derived() { cout<<"Derived DTOR called"<<endl; } }; I'm not sure if this is a duplicate, I couldn't find in search. int main() { base *bPtr = new derived(); delete bPtr;// only when you explicitly try to delete an object return 0; }

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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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  • Loading the last related record instantly for multiple parent records using Entity framework

    - by Guillaume Schuermans
    Does anyone know a good approach using Entity Framework for the problem described below? I am trying for our next release to come up with a performant way to show the placed orders for the logged on customer. Of course paging is always a good technique to use when a lot of data is available I would like to see an answer without any paging techniques. Here's the story: a customer places an order which gets an orderstatus = PENDING. Depending on some strategy we move that order up the chain in order to get it APPROVED. Every change of status is logged so we can see a trace for statusses and maybe even an extra line of comment per status which can provide some extra valuable information to whoever sees this order in an interface. So an Order is linked to a Customer. One order can have multiple orderstatusses stored in OrderStatusHistory. In my testscenario I am using a customer which has 100+ Orders each with about 5 records in the OrderStatusHistory-table. I would for now like to see all orders in one page not using paging where for each Order I show the last relevant Status and the extra comment (if there is any for this last status; both fields coming from OrderStatusHistory; the record with the highest Id for the given OrderId). There are multiple scenarios I have tried, but I would like to see any potential other solutions or comments on the things I have already tried. Trying to do Include() when getting Orders but this still results in multiple queries launched on the database. Each order triggers an extra query to the database to get all orderstatusses in the history table. So all statusses are queried here instead of just returning the last relevant one, plus 100 extra queries are launched for 100 orders. You can imagine the problem when there are 100000+ orders in the database. Having 2 computed columns on the database: LastStatus, LastStatusInformation and a regular Linq-Query which gets those columns which are available through the Entity-model. The problem with this approach is the fact that those computed columns are determined using a scalar function which can not be changed without removing the formula from the computed column, etc... In the end I am very familiar with SQL and Stored procedures, but since the rest of the data-layer uses Entity Framework I would like to stick to it as long as possible, even though I have my doubts about performance. Using the SQL approach I would write something like this: WITH cte (RN, OrderId, [Status], Information) AS ( SELECT ROW_NUMBER() OVER (PARTITION BY OrderId ORDER BY Id DESC), OrderId, [Status], Information FROM OrderStatus ) SELECT o.Id, cte.[Status], cte.Information AS StatusInformation, o.* FROM [Order] o INNER JOIN cte ON o.Id = cte.OrderId AND cte.RN = 1 WHERE CustomerId = @CustomerId ORDER BY 1 DESC; which returns all orders for the customer with the statusinformation provided by the Common Table Expression. Does anyone know a good approach using Entity Framework?

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  • iPhone memory management

    - by Prazi
    I am newbie to iPhone programming. I am not using Interface Builder in my programming. I have some doubt about memory management, @property topics in iPhone. Consider the following code @interface LoadFlag : UIViewController { UIImage *flag; UIImageView *preview; } @property (nonatomic, retain) UIImageView *preview; @property (nonatomic, retain) UIImage *flag; @implementation @synthesize preview; @synthesize flag; - (void)viewDidLoad { flag = [UIImage imageNamed:@"myImage.png"]]; NSLog(@"Preview: %d\n",[preview retainCount]); //Count: 0 but shouldn't it be 1 as I am retaining it in @property in interface file preview=[[UIImageView alloc]init]; NSLog(@"Count: %d\n",[preview retainCount]); //Count: 1 preview.frame=CGRectMake(0.0f, 0.0f, 100.0f, 100.0f); preview.image = flag; [self.view addSubview:preview]; NSLog(@"Count: %d\n",[preview retainCount]); //Count: 2 [preview release]; NSLog(@"Count: %d\n",[preview retainCount]); //Count: 1 } When & Why(what is the need) do I have to set @property with retain (in above case for UIImage & UIImageView) ? I saw this statement in many sample programs but didn't understood the need of it. When I declare @property (nonatomic, retain) UIImageView *preview; statement the retain Count is 0. Why doesn't it increase by 1 inspite of retaining it in @property. Also when I declare [self.view addSubview:preview]; then retain Count increments by 1 again. In this case does the "Autorelease pool" releases for us later or we have to take care of releasing it. I am not sure but I think that the Autorelease should handle it as we didn't explicitly retained it so why should we worry of releasing it. Now, after the [preview release]; statement my count is 1. Now I don't need UIImageView anymore in my program so when and where should I release it so that the count becomes 0 and the memory gets deallocated. Again, I am not sure but I think that the Autorelease should handle it as we didn't explicitly retained it so why should we worry of releasing it. What will happen if I release it in -(void) dealloc method In the statement - flag = [UIImage imageNamed:@"myImage.png"]]; I haven't allocated any memory to flag but how can I still use it in my program. In this case if I do not allocate memory then who allocates & deallocates memory to it or is the "flag" just a reference pointing to - [UIImage imageNamed:@"myImage.png"]];. If it is a reference only then do i need to release it. Thanks in advance.

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