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  • C# - Advantages/Disadvantages of different implementations for Comparing Objects

    - by Kevin Crowell
    This questions involves 2 different implementations of essentially the same code. First, using delegate to create a Comparison method that can be used as a parameter when sorting a collection of objects: class Foo { public static Comparison<Foo> BarComparison = delegate(Foo foo1, Foo foo2) { return foo1.Bar.CompareTo(foo2.Bar); }; } I use the above when I want to have a way of sorting a collection of Foo objects in a different way than my CompareTo function offers. For example: List<Foo> fooList = new List<Foo>(); fooList.Sort(BarComparison); Second, using IComparer: public class BarComparer : IComparer<Foo> { public int Compare(Foo foo1, Foo foo2) { return foo1.Bar.CompareTo(foo2.Bar); } } I use the above when I want to do a binary search for a Foo object in a collection of Foo objects. For example: BarComparer comparer = new BarComparer(); List<Foo> fooList = new List<Foo>(); Foo foo = new Foo(); int index = fooList.BinarySearch(foo, comparer); My questions are: What are the advantages and disadvantages of each of these implementations? What are some more ways to take advantage of each of these implementations? Is there a way to combine these implementations in such a way that I do not need to duplicate the code? Can I achieve both a binary search and an alternative collection sort using only 1 of these methods?

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  • Encapsulating user input of data for a class (C++)

    - by Dr. Monkey
    For an assignment I've made a simple C++ program that uses a superclass (Student) and two subclasses (CourseStudent and ResearchStudent) to store a list of students and print out their details, with different details shown for the two different types of students (using overriding of the display() method from Student). My question is about how the program collects input from the user of things like the student name, ID number, unit and fee information (for a course student) and research information (for research students): My implementation has the prompting for user input and the collecting of that input handled within the classes themselves. The reasoning behind this was that each class knows what kind of input it needs, so it makes sense to me to have it know how to ask for it (given an ostream through which to ask and an istream to collect the input from). My lecturer says that the prompting and input should all be handled in the main program, which seems to me somewhat messier, and would make it trickier to extend the program to handle different types of students. I am considering, as a compromise, to make a helper class that handles the prompting and collection of user input for each type of Student, which could then be called on by the main program. The advantage of this would be that the student classes don't have as much in them (so they're cleaner), but also they can be bundled with the helper classes if the input functionality is required. This also means more classes of Student could be added without having to make major changes to the main program, as long as helper classes are provided for these new classes. Also the helper class could be swapped for an alternative language version without having to make any changes to the class itself. What are the major advantages and disadvantages of the three different options for user input (fully encapsulated, helper class or in the main program)?

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  • Executing untrusted code

    - by MainMa
    Hi, I'm building a C# application which uses plug-ins. The application must guarantee to the user that plug-ins will not do whatever they want on the user machine, and will have less privileges that the application itself (for example, the application can access its own log files, whereas plug-ins cannot). I considered three alternatives. Using System.AddIn. I tried this alternative first, because it seamed much powerful, but I'm really disappointed by the need of modifying the same code seven times in seven different projects each time I want to modify something. Besides, there is a huge number of problems to solve even for a simple Hello World application. Using System.Activator.CreateInstance(assemblyName, typeName). This is what I used in the preceding version of the application. I can't use it nevermore, because it does not provide a way to restrict permissions. Using System.Activator.CreateInstance(AppDomain domain, [...]). That's what I'm trying to implement now, but it seems that the only way to do that is to pass through ObjectHandle, which requires serialization for every used class. Although plug-ins contain WPF UserControls, which are not serializable. So is there a way to create plug-ins containing UserControls or other non serializable objects and to execute those plug-ins with a custom PermissionSet ?

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  • Is DB logging more secure than file logging for my PHP web app?

    - by iama
    I would like to log errors/informational and warning messages from within my web application to a log. I was initially thinking of logging all of these onto a text file. However, my PHP web app will need write access to the log files and the folder housing this log file may also need write access if log file rotation is desired which my web app currently does not have. The alternative is for me to log the messages to the MySQL database since my web app is already using the MySQL database for all its data storage needs. However, this got me thinking that going with the MySQL option is much better than the file option since I already have a configuration file with the database access information protected using file system permissions. If I now go with the log file option I need to tinker the file and folder access permissions and this will only make my application less secure and defeats the whole purpose of logging. Is this correct? I am using XAMPP for development and am a newbie to LAMP. Please let me know your recommendations for logging. Thanks.

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  • Attributes in XML subtree that belong to the parent

    - by Bart van Heukelom
    Say I have this XML <doc:document> <objects> <circle radius="10" doc:colour="red" /> <circle radius="20" doc:colour="blue" /> </objects> </doc:document> And this is how it is parsed (pseudo code): // class DocumentParser public Document parse(Element edoc) { doc = new Document(); doc.objects = ObjectsParser.parse(edoc.getChild("objects")); for ( ...?... ) { doc.objectColours.put(object, colour); } return doc; } ObjectsParser is responsible for parsing the objects bit, but is not and should not be aware of the existence of documents. However, in Document colours are associated with objects by use of a Map. What kind of pattern would you recommend to give the colour settings back to DocumentParser.parse from ObjectsParser.parse so it can associate it with the objects they belong to in a map? The alternative would be something like this: <doc:document> <objects> <circle id="1938" radius="10" /> <circle id="6398" radius="20" /> </objects> <doc:objectViewSettings> <doc:objectViewSetting object="1938" colour="red" /> <doc:objectViewSetting object="6398" colour="blue" /> </doc:objectViewSettings> </doc:document> Ugly!

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  • Database design - table relationship question

    - by iama
    I am designing schema for a simple quiz application. It has 2 tables - "Question" and "Answer Choices". Question table has 'question ID', 'question text' and 'answer id' columns. "Answer Choices" table has 'question ID', 'answer ID' and 'answer text' columns. With this simple schema it is obvious that a question can have multiple answer choices & hence the need for the answer choices table. However, a question can have only one correct answer and hence the need for the 'answer ID' in the question table. However, this 'answer ID' column in the question table provides a illusion as though there can be multiple questions for a single answer which is not correct. The other alternative to eliminate this illusion is to have another table just for correct answer that will have just 2 columns namely the question ID and the answer ID with a 1-1 relationship between the two tables. However, I think this is redundant. Any recommendation on how best to design this thereby enforcing the rules that a question can have multiple answer choices but only one correct answer? Many Thanks.

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  • Do database engines other than SQL Server behave this way?

    - by Yishai
    I have a stored procedure that goes something like this (pseudo code) storedprocedure param1, param2, param3, param4 begin if (param4 = 'Y') begin select * from SOME_VIEW order by somecolumn end else if (param1 is null) begin select * from SOME_VIEW where (param2 is null or param2 = SOME_VIEW.Somecolumn2) and (param3 is null or param3 = SOME_VIEW.SomeColumn3) order by somecolumn end else select somethingcompletelydifferent end All ran well for a long time. Suddenly, the query started running forever if param4 was 'Y'. Changing the code to this: storedprocedure param1, param2, param3, param4 begin if (param4 = 'Y') begin set param2 = null set param3 = null end if (param1 is null) begin select * from SOME_VIEW where (param2 is null or param2 = SOME_VIEW.Somecolumn2) and (param3 is null or param3 = SOME_VIEW.SomeColumn3) order by somecolumn end else select somethingcompletelydifferent And it runs again within expected parameters (15 seconds or so for 40,000+ records). This is with SQL Server 2005. The gist of my question is this particular "feature" specific to SQL Server, or is this a common feature among RDBMS' in general that: Queries that ran fine for two years just stop working as the data grows. The "new" execution plan destroys the ability of the database server to execute the query even though a logically equivalent alternative runs just fine? This may seem like a rant against SQL Server, and I suppose to some degree it is, but I really do want to know if others experience this kind of reality with Oracle, DB2 or any other RDBMS. Although I have some experience with others, I have only seen this kind of volume and complexity on SQL Server, so I'm curious if others with large complex databases have similar experience in other products.

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  • Handling form from different view and passing form validation through session in django

    - by Mo J. Mughrabi
    I have a requirement here to build a comment-like app in my django project, the app has a view to receive a submitted form process it and return the errors to where ever it came from. I finally managed to get it to work, but I have doubt for the way am using it might be wrong since am passing the entire validated form in the session. below is the code comment/templatetags/comment.py @register.inclusion_tag('comment/form.html', takes_context=True) def comment_form(context, model, object_id, next): """ comment_form() is responsible for rendering the comment form """ # clear sessions from variable incase it was found content_type = ContentType.objects.get_for_model(model) try: request = context['request'] if request.session.get('comment_form', False): form = CommentForm(request.session['comment_form']) form.fields['content_type'].initial = 15 form.fields['object_id'].initial = 2 form.fields['next'].initial = next else: form = CommentForm(initial={ 'content_type' : content_type.id, 'object_id' : object_id, 'next' : next }) except Exception as e: logging.error(str(e)) form = None return { 'form' : form } comment/view.py def save_comment(request): """ save_comment: """ if request.method == 'POST': # clear sessions from variable incase it was found if request.session.get('comment_form', False): del request.session['comment_form'] form = CommentForm(request.POST) if form.is_valid(): obj = form.save(commit=False) if request.user.is_authenticated(): obj.created_by = request.user obj.save() messages.info(request, _('Your comment has been posted.')) return redirect(form.data.get('next')) else: request.session['comment_form'] = request.POST return redirect(form.data.get('next')) else: raise Http404 the usage is by loading the template tag and firing {% comment_form article article.id article.get_absolute_url %} my doubt is if am doing the correct approach or not by passing the validated form to the session. Would that be a problem? security risk? performance issues? Please advise Update In response to Pol question. The reason why I went with this approach is because comment form is handled in a separate app. In my scenario, I render objects such as article and all I do is invoke the templatetag to render the form. What would be an alternative approach for my case? You also shared with me the django comment app, which am aware of but the client am working with requires a lot of complex work to be done in the comment app thats why am working on a new one.

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  • Is there a JSON library that can serialize Proxy objects?

    - by gmoore
    Using ActiveObjects as my ORM and Gson as my JSON processor. Ran into a problem going toJson from persisted objects. The problem is that my persisted class is actually an Interface and AO is proxying that object under the hood. Here's some sample code: Venue venue = manager.get(Venue.class, id); gson.toJson(venue); Comes up with this exception: java.lang.UnsupportedOperationException: Expecting parameterized type, got interface java.lang.reflect.InvocationHandler. Are you missing the use of TypeToken idiom? See http://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and... Because venue.getClass().getName() gives: $Proxy228 I've tried a few solutions in various combinations: gsonBuilder.registerTypeAdapter(Venue.class, newVenueSerializer()); Type listType = new TypeToken<Venue>() {}.getType(); Nothing has worked so far and I'm using a wonky field-by-field workaround. Any suggestions? I'm not married to Gson, so if there's an alternative library that can do this I'd be happy to use it.

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  • Get the last checked checkboxes...

    - by Sara
    Hi everyone, I'm not sure how to accomplish this issue which has been confusing me for a few days. I have a form that updates a user record in MySQL when a checkbox is checked. Now, this is how my form does this: if (isset($_POST['Update'])) { $paymentr = $_POST['paymentr']; //put checkboxes array into variable $paymentr2 = implode(', ', $paymentr); //implode array for mysql $query = "UPDATE transactions SET paymentreceived=NULL"; $result = mysql_query($query); $query = "UPDATE transactions SET paymentdate='0000-00-00'"; $result = mysql_query($query); $query = "UPDATE transactions SET paymentreceived='Yes' WHERE id IN ($paymentr2)"; $result = mysql_query($query); $query = "UPDATE transactions SET paymentdate=NOW() WHERE id IN ($paymentr2)"; $result = mysql_query($query); foreach ($paymentr as $v) { //should collect last updated records and put them into variable for emailing. $query = "SELECT id, refid, affid FROM transactions WHERE id = '$v'"; $result = mysql_query($query) or die("Query Failed: ".mysql_errno()." - ".mysql_error()."<BR>\n$query<BR>\n"); $trans = mysql_fetch_array($result, MYSQL_ASSOC); $transactions .= '<br>User ID:'.$trans['id'].' -- '.$trans['refid'].' -- '.$trans['affid'].'<br>'; } } Unfortunately, it then updates ALL the user records with the latest date which is not what I want it to do. The alternative I thought of was, via Javascript, giving the checkbox a value that would be dynamically updated when the user selected it. Then, only THOSE checkboxes would be put into the array. Is this possible? Is there a better solution? I'm not even sure I could wrap my brain around how to do that WITH Javascript. Does the answer perhaps lie in how my mysql code is written? Thanks - I sincerely appreciate it!!!

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  • Significance in R

    - by Gemsie
    Ok, this is quite hard to explain, but I'm at a complete loss what to do. I'm a relative newcomer to R and although I can completely admire how powerful it is, I'm not too good at actually using it.... Basically, I have some very contrived data that I need to analyse (it wasn't me who chose this, I can assure you!). I have the right and left hand lengths of lots of people, as well as some numeric data that shows their sociability. Now I would like to know if people who have significantly different lengths of hand are more or less sociable than those who have the same (leading into the research that 'symmetrical' people are more sociable and intelligent, etc. I have got as far as loading the data into R, then I have no idea where to go from there. How on Earth do I start to separate those who are close to symmetrical to those who aren't to then start to do the analysis? Ok, using Sasha's great advice, I did the cor.test and got the following: Pearson's product-moment correlation data: measurements$l.hand - measurements$r.hand and measurements$sociable t = 0.2148, df = 150, p-value = 0.8302 alternative hypothesis: true correlation is not equal to 0 95 percent confidence interval: -0.1420623 0.1762437 sample estimates: cor 0.01753501 I have never used this test before, so am unsure how to intepret it...you wouldn't think I was on my fourth Scientific degree would you?! :(

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  • What's a reasonable way to mutate a primitive variable from an anonymous Java class?

    - by Steve
    I would like to write the following code: boolean found = false; search(new SearchCallback() { @Override void onFound(Object o) { found = true; } }); Obviously this is not allowed, since found needs to be final. I can't make found a member field for thread-safety reasons. What is the best alternative? One workaround is to define final class MutableReference<T> { private T value; MutableReference(T value) { this.value = value; } T get() { return value; } void set(T value) { this.value = value; } } but this ends up taking a lot of space when formatted properly, and I'd rather not reinvent the wheel if at all possible. I could use a List<Boolean> with a single element (either mutating that element, or else emptying the list) or even a Boolean[1]. But everything seems to smell funny, since none of the options are being used as they were intended. What is a reasonable way to do this?

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  • How to justify using a scripting language as part of a project

    - by sylvanaar
    I have a specific project in which I want to use either a scripting language + C, or as an alternative a 100% Java solution. The program adapts a legacy system for use with other moderns systems. Basically, I have few choices as to what language I can use. I have C/C++, Java 1.4, and I have also compiled the Lua for this environment. The program does 'screen scraping' and has to deal with alot of strings. That part of the code is highly variable. Most of the developers at my company use C, so - my original design was to write some portions in C, and use Lua for the part that dealt with strings and changed freqently. I was told 'You have to justify your use of the scripting language.' So i reworked my design using 100% Java, and was told - Java wont have enough performance. You should do the whole thing in C. I'm not controlling lasers or doing image processing - just some screen scraping. I still have to provide justification for using anything but C - so what justification can I provide?

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  • routing mvc on the web

    - by generic_noob
    Hi, I was wondering if anyone could possibly provide me some advice on how i could improve the routing (and/or architecture) to each 'section' of my application. (I'm writing in PHP5, and trying to use strict MVC) Basically, I have a generic index page for the app, and that will spew out boilerplate stuff like jquery and the css etc. and it also generates the main navidation for the entire site, but i'm unsure about the best approach to connect the 'main menu' items(hyperlinks) with their associated controllers. Up until now I have been appending strings into the url and using a 'switch' statement to branch to the correct controller(and view) by extracting the strings back out of '$GET[]' to let it execute the code for the corrosponding action. for instance if i had a basic crud system for customer data, the url to edit a customers details would look like 'www.example.com/index.php?page=customer&action=edit&id=4'. I'm worried that there is a security concern by doing it this way, and i'm not sure of an alternative to branch the main 'index.php' file to the correct controller for each action once the user has clicked the link. Would it be better to use mod_rewrite to disguise the controllers names? or to create a similar system to the ASP MVC framework, where there is a seperate routing system where each url is filtered to get the associated controller? Cheers!

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  • Program to format every media in c++

    - by AtoMerZ
    Problem: I'm trying to write a program that formats any type of media. So far I've managed to format Hard disk partitions, flash memories, SDRAM, RDX. But there's this last type of media (DVD-RAM) I need to format. My program fails to format this media. I'm using the FormatEx function in fmifs.dll. I had absolutely no idea how to use this function Except for its name and that it resides in fmifs.dll. with the help of this I managed to find a simple program that uses this library. Yet still it doesn't give complete information about how to use it. What I've tried: I'm looking for a full documentation about FormatEx, its parameters, and exactly what values each parameter can take. I tried searching on google and MSDN. This is what I found. First of all this isn't the function I'm working with. But even putting that aside there's not enough information on how to use the function (Like which headers/libraries to use). EDIT: I don't have to use FormatEx if there's an alternative to use please tell.

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  • What does it mean for an OS to "execute within user processes"? Do any modern OS's use that approach

    - by Chris Cooper
    I have recently become interested in operating system, and a friend of mine lent me a book called Operating Systems: Internals and Design Principles (I have the third edition), published in 1998. It's been a very interesting book so far, but I have come to the part dealing with process control, and it's using UNIX System V as one of its examples of an operating system that executes within user processes. This concept has struck me as a little strange. First of all, does this mean that OS instructions and data are stored in each user of the processes? Probably not, because that would be an absurdly redundant scheme. But if not, then what does it mean to "execute within" a user process? Do any modern operating systems use this approach? It seems much more logical to have the operating system execute as its own process, or even independently of all processes, if you're short on memory. All the inter-accessiblilty of process data required for this layout seems to greatly complicate things. (But maybe that's just because I don't quite get the concept ;D) Here is what the book says: "Execution within User Processes: An alternative that is common with operation systems on smaller machines is to execute virtually all operating system software in the context of a user process. ... "

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  • Iterating through Event Log Entry Collection, IndexOutOutOfBoundsException

    - by fjdumont
    Hello, in a service application I am iterating through the Windows application event log to parse Events in order react depanding on the entry message. In the case that the event log is full (Windows usually makes sure there is enough space by deleting old entries - this is configurable in the eventvwr.exe settings), the service always runs into an IndexOutOfBoundsException while iterating through the EventLog.Entries collection. No matter how I iterate (for-loop, using the collections enumerator, copying the collection into an array, ...), I can't seem to get rid of this ´bug´. Currently, I ensure that the log is not full in order to keep the service running by regularly deleting the last few item by parsing the event log file and deleting the last few nodes (Don't beat me up, I couldn't find a better alternative...). How can I iterate through the collection without trying to access already deleted entries? Is there probably a more elegant method? I am only trying to acces the logs written during the last x seconds (even LINQ failed to select those when the log is full - same exception), could this help? Thanks for any advice and hints Frank Edit: I forgot to mention that my assumption is the loops are accessing entries which are being deleted during iteration by Windows. Basically that is why I tried to clone the collection. Is there perhaps a way to lock the collection for a small amount of time for just my application?

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  • Changing default compiler in Linux, using SCons

    - by ereOn
    On my Linux platform, I have several versions of gcc. Under usr/bin I have: gcc34 gcc44 gcc Here are some outputs: $ gcc --version gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48) $ gcc44 --version gcc44 (GCC) 4.4.0 20090514 (Red Hat 4.4.0-6) I need to use the 4.4 version of gcc however the default seems to the 4.1 one. I there a way to replace /usr/bin/gcc and make gcc44 the default compiler not using a symlink to /usr/bin/gcc44 ? The reason why I can't use a symlink is because my code will have to be shipped in a RPM package using mock. mock creates a minimal linux installation from scratch and just install the specified dependencies before compiling my code in it. I cannot customize this "minimal installation". Ideally, the perfect solution would be to install an official RPM package that replaces gcc with gcc44 as the default compiler. Is there such a package ? Is this even possible/good ? Additional information I have to use SCons (a make alternative) and it doesn't let me specify the binary to use for gcc. I will also accept any answer that will tell me how to specify the gcc binary in my SConstruct file.

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  • I Cannot retrieve ARPINSTALLLOCATION so we know where to install a new version [WIX]

    - by Birkoff
    I am trying to retrieve the ARPINSTALLLOCATION during the installation of a Major Upgrade version of the software. Following this info I managed to set the ARPINSTALLLOCATION to the custom path. However, retrieving it again isn't working. I've tried many things over the past days but it keeps defaulting back to the default installation path instead of the custom one. <InstallUISequence> <AppSearch After="FindRelatedProducts"/> ... </InstallUISequence> <Property Id="WIXUI_INSTALLDIR" Value="APPROOTDIRECTORY"> <RegistrySearch Id="FindInstallLocation" Root="HKLM" Key="Software\Microsoft\Windows\CurrentVersion\Uninstall\[OLDERVERSIONBEINGUPGRADED]" Name="InstallLocation" Type="raw" /> </Property> In the custom WixUI_InstallDir UI I have this in the CustomInstallDirDlg <Control Id="Folder" Type="PathEdit" X="20" Y="90" Width="260" Height="18" Property="WIXUI_INSTALLDIR" Indirect="yes" /> The alternative install path is in the registry, but it isn't retrieved and shown in the control. What am I doing wrong here? -Birkoff

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  • mimic a table using css

    - by user357523
    I'm trying to display a grid of items, with each item having a photo on the left and a description on the right, something like this: ---------------------------- | photo | item description | ---------------------------- I want to display these items in a 3x3 grid on the page. I have the grid part worked out, what I'm having trouble with is alignment of the photo and description. When the height of the description exceeds the height of the photo, I don't want the text to wrap under the photo. I essentially want to maintain two separate columns. I have tried this: .item{ padding-left: 60px; // size of photo + 5px margin background-position: 5px 0px; } <div class="item" style="background-image: url('/img/photo123.jpg');"> Here is the item description </div> That has worked very well. the markup is clean and I don't have to mess around with absolute/relative, however, now I can't add a border to the image. Can anyone suggest a workaround or alternative?

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  • Observer Design Pattern - multiple event types

    - by David
    I'm currently implementing the Observer design pattern and using it to handle adding items to the session, create error logs and write messages out to the user giving feedback on their actions (e.g. You've just logged out!). I began with a single method on the subject called addEvent() but as I added more Observers I found that the parameters required to detail all the information I needed for each listener began to grow. I now have 3 methods called addMessage(), addStorage() and addLog(). These add data into an events array that has a key related to the event type (e.g. log, message, storage) but I'm starting to feel that now the subject needs to know too much about the listeners that are attached. My alternative thought is to go back to addEvent() and pass an event type (e.g. USER_LOGOUT) along with the data associated and each Observer maintains it's own list of event handles it is looking for (possibly in a switch statement), but this feels cumbersome. Also, I'd need to check that sufficient data had also been passed along with the event type. What is the correct way of doing this? Please let me know if I can explain any parts of this further. I hope you can help and see the problem I'm battling with.

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  • Circular Reference exception with JSON Serialisation with MVC3 and EF4 CTP5w

    - by nakchak
    Hi I'm having problems with a circular reference when i try and serialise an object returned via EF4 CTP5. Im using the code first approach and simple poco's for my model. I have added [ScriptIgnore] attributes to any properties that provide a back references to an object and annoyingly every seems to work fine if i manually instantiate the poco's, i.e. they serialise to JSON fine, and the scriptignore attribute is acknowledged. However when i try and serialise an object returned from the DAL i get the circular reference exception "A circular reference was detected while serializing an object of type 'System.Data.Entity.DynamicProxies.xxxx'" I have tried several ways of retreiving the data but they all get stuck with this error: public JsonResult GetTimeSlot(int id) { TimeSlotDao tsDao = new TimeSlotDao(); TimeSlot ts = tsDao.GetById(id); return Json(ts); } The method below works slightly better as rather than the timeslot dynamic proxied object causing the circular refference its the appointment object. public JsonResult GetTimeSlot(int id) { TimeSlotDao tsDao = new TimeSlotDao(); var ts = from t in tsDao.GetQueryable() where t.Id == id select new {t.Id, t.StartTime, t.Available, t.Appointment}; return Json(ts); } Any ideas or solutions to this problem? Update I would prefer to use the out of the box serialiser if possible although Json.Net via nuget is ok as an alternative i would hope its possible to use it as I intended as well...

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  • Calculating distance from latitude, longitude and height using a geocentric co-ordinate system

    - by Sarge
    I've implemented this method in Javascript and I'm roughly 2.5% out and I'd like to understand why. My input data is an array of points represented as latitude, longitude and the height above the WGS84 ellipsoid. These points are taken from data collected from a wrist-mounted GPS device during a marathon race. My algorithm was to convert each point to cartesian geocentric co-ordinates and then compute the Euclidean distance (c.f Pythagoras). Cartesian geocentric is also known as Earth Centred Earth Fixed. i.e. it's an X, Y, Z co-ordinate system which rotates with the earth. My test data was the data from a marathon and so the distance should be very close to 42.26km. However, the distance comes to about 43.4km. I've tried various approaches and nothing changes the result by more than a metre. e.g. I replaced the height data with data from the NASA SRTM mission, I've set the height to zero, etc. Using Google, I found two points in the literature where lat, lon, height had been transformed and my transformation algorithm is matching. What could explain this? Am I expecting too much from Javascript's double representation? (The X, Y, Z numbers are very big but the differences between two points is very small). My alternative is to move to computing the geodesic across the WGS84 ellipsoid using Vincenty's algorithm (or similar) and then calculating the Euclidean distance with the two heights but this seems inaccurate. Thanks in advance for your help!

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  • Constructor Overloading

    - by Mark Baker
    Normally when I want to create a class constructor that accepts different types of parameters, I'll use a kludgy overloading principle of not defining any args in the constructor definition: e.g. for an ECEF coordinate class constructor, I want it to accept either $x, $y and $z arguments, or to accept a single array argument containg x, y and z values, or to accept a single LatLong object I'd create a constructor looking something like: function __construct() { // Identify if any arguments have been passed to the constructor if (func_num_args() > 0) { $args = func_get_args(); // Identify the overload constructor required, based on the datatype of the first argument $argType = gettype($args[0]); switch($argType) { case 'array' : // Array of Cartesian co-ordinate values $overloadConstructor = 'setCoordinatesFromArray'; break; case 'object' : // A LatLong object that needs converting to Cartesian co-ordinate values $overloadConstructor = 'setCoordinatesFromLatLong'; break; default : // Individual Cartesian co-ordinate values $overloadConstructor = 'setCoordinatesFromXYZ'; break; } // Call the appropriate overload constructor call_user_func_array(array($this,$overloadConstructor),$args); } } // function __construct() I'm looking at an alternative: to provide a straight constructor with $x, $y and $z as defined arguments, and to provide static methods of createECEFfromArray() and createECEFfromLatLong() that handle all the necessary extraction of x, y and z; then create a new ECEF object using the standard constructor, and return that Which option is cleaner from an OO purists perspective?

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  • Index an array expression directly in PostgreSQL

    - by wich
    I'm trying to insert data into a table from a template table. I need to rewrite one of the columns for which I wanted to use a directly indexed array expression, but I can't seem to find how to do this, if it is even possible. The scenario: create table template ( id integer, index integer, foo integer); insert into template values (0, 1, 23), (0, 2, 18), (0, 3, 16), (0, 4, 7), (1, 1, 17), (1, 2, 26), (1, 3, 11), (1, 4, 3); create table data ( data_id integer, foo integer); Now what I'd like to do is the following: insert into data select (array[3,7,5,2])[index], foo from template where id = 1; But this doesn't work, the (array[3,7,5,2])[index] syntax isn't valid. I tried a few variants, but was unable to get anything working and wasn't able to find the correct syntax in the docs, nor even whether this is at all possible or not. As a current workaround I've devised the following, but it is less than ideal, from an elegance perspective at least, but it may also be a performance hit, I haven't looked into that yet. insert into data select arr[index], foo from template, (select array[3,7,5,2] as arr) as q where id = 1; If anyone could suggest a (better) alternative to accomplish this I'd like to hear that as well.

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