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• Passing optional parameter by reference in c++

  - by Moomin

  I'm having a problem with optional function parameter in C++ What I'm trying to do is to write function with optional parameter which is passed by reference, so that I can use it in two ways (1) and (2), but on (2) I don't really care what is the value of mFoobar. I've tried such a code: void foo(double &bar, double &foobar = NULL) { bar = 100; foobar = 150; } int main() { double mBar(0),mFoobar(0); foo(mBar,mFoobar); // (1) cout << mBar << mFoobar; mBar = 0; mFoobar = 0; foo(mBar); // (2) cout << mBar << mFoobar; return 0; } but it crashes at void foo(double &bar, double &foobar = NULL) with message : error: default argument for 'double& foobar' has type 'int' Is it possible to solve it without function overloading? Thanks in advance for any suggestions. Pawel

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• Initial capacity of collection types, i.e. Dictionary, List

  - by Neil N

  Certain collection types in .Net have an optional "Initial Capacity" constructor param. i.e. Dictionary<string, string> something = new Dictionary<string,string>(20); List<string> anything = new List<string>(50); I can't seem to find what the default initial capacity is for these objects on MSDN. If I know I will only be storing 12 or so items in a dictionary, doesn't it make sense to set the initial capacity to something like 20? My reasoning is, assuming the capacity grows like it does for a StringBuiler, which doubles each time the capacity is hit, and each re-allocation is costly, why not pre-set the size to something you know will hold your data, with some extra room just in case? If the initial capacity is 100, and I know I will only need a dozen or so, it seems as though the rest of that allocated RAM is allocated for nothing. Please spare me the "premature optimization" speil for the O(n^n)th time. I know it won't make my apps any faster or save any meaningful amount of memory, this is mostly out of curiosity.

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• Transform RSS-Feed into another "standard" XML-Format with PHP

  - by ChrisBenyamin

  Hey friends, quick question: I need to transform a default RSS Structure into another XML-format. The RSS File is like.... Name des RSS Feed Feed Beschreibung de http://xml-rss.de Sat, 1 Jan 2000 00:00:00 GMT Titel der Nachricht Die Nachricht an sich http://xml-rss.de/link-zur-nachricht.htm Sat, 1. Jan 2000 00:00:00 GMT 01012000-000000 Titel der Nachricht Die Nachricht an sich http://xml-rss.de/link-zur-nachricht.htm Sat, 1. Jan 2000 00:00:00 GMT 01012000-000000 Titel der Nachricht Die Nachricht an sich http://xml-rss.de/link-zur-nachricht.htm Sat, 1. Jan 2000 00:00:00 GMT 01012000-000000 ...and I want to extract only the item-elements (with childs and attributes) XML like: <?xml version="1.0" encoding="ISO-8859-1"?> <item> <title>Titel der Nachricht</title> <description>Die Nachricht an sich</description> <link>http://xml-rss.de/link-zur-nachricht.htm</link> <pubDate>Sat, 1. Jan 2000 00:00:00 GMT</pubDate> <guid>01012000-000000</guid> </item> ... It hasn't to be stored into a file. I need just the output. I tried different approaches with DOMNode, SimpleXML, XPath, ... but without success. Thanks chris

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• Problem with UITextView

  - by user367039

  I have a strange problem with trying to pass a string from one viewcontroller to another view controller if the string originates from a UITextview instead of UITextfield. Both UITextview.text and UITextfield.text are of type NSString. The following code takes either Textfield.text or Textview.text depending on the fieldType and puts it into a string called aString. NSString *aString = [[NSString alloc] init]; if (fieldType == 3) { aString = textView.text; } else { aString = textField.text; } When I examine aString on either cases, I can see that it has successfully assigned the text into aString. I then pass the string to the other view controller using this code. [delegate updateSite:aString :editedFieldKey :fieldType]; [self.navigationController popViewControllerAnimated:YES]; This works fine if aString originated from textfield.text but nothing happens except the view controller is popped if aString was from textview.text This is the code that takes aString and does stuff with it, however it doesn't even execute the first line of code "NSLog(@"Returned object: %@, field type:%@", aString,editedFieldKey);" if aString was from textview.text Any help will be appreciated. -(void)updateSite:(NSString *)aString :(NSString *)editedFieldKey :(int)fieldType { NSLog(@"Returned object: %@, field type:%@", aString,editedFieldKey); switch (fieldType) { case 0: //string [aDiveSite setValue:aString forKey:editedFieldKey] ; NSLog(@"String set %@",[aDiveSite valueForKey:editedFieldKey] ); break; case 1: //int [aDiveSite setValue:[NSNumber numberWithInt:aString.intValue] forKey:editedFieldKey]; NSLog(@"Integer set"); break; case 2: //float NSLog(@"Saving floating value"); [aDiveSite setValue:[NSNumber numberWithFloat:aString.floatValue] forKey:editedFieldKey]; NSLog(@"Float set"); break; case 3: //Text view [aDiveSite setValue:aString forKey:editedFieldKey]; NSLog(@"Textview text saved"); default: break; } [self.tableView reloadData]; }

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• entity framework vNext wish list

  - by Fred Yang

  I have been intensively studying and use ef4 in my project. I do feel the improvement that it has over version 1. But I found that I have something I cannot get around easily. Here is a list I want it to be better in ef vNext. the model designer should allow multiple view of the same model, so that I don't need cram all my entity into a single view. respect user's manual edit of edmx. Currently, the some database view object simply can not be imported to the model because the designer "smartly" think that the view does not have a primary key, so that I have to manually edit the edmx to correct designer's behavior. But in the next "update from database" task, designer will revert my customization. For now, I simply fallback to manually edit the edmx file at all, or I have to use compare tool to keep the new update, and rollback and put the new update into my old edmx file manually. Designer should be improved to allow default behavior and user's manual control. I want control not to let the designer refresh the change of imported object. support user defined table function. linq is about Composability, stored proc dos not support composability. I wish I could use user defined table function which support this. What are you wishes for EF vNext?

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• lighten background color on button click per binding

  - by one of two

  I want to lighten a buttons background on click. So I did the following: <converter:ColorLightConverter x:Key="colorLightConverter" /> ... <Style BasedOn="{StaticResource default}" TargetType="{x:Type controls:Button}"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="{x:Type controls:Button}"> <ControlTemplate.Triggers> <Trigger Property="IsPressed" Value="True"> <Setter Property="Background"> <Setter.Value> <SolidColorBrush Color="{Binding Path=Background.Color, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource colorLightConverter}}" /> </Setter.Value> </Setter> </Trigger> </ControlTemplate.Triggers> <Border Background="{TemplateBinding Background}" BorderBrush="Transparent" BorderThickness="0"> ... </Border> </ControlTemplate> </Setter.Value> </Setter> </Style> The converter: class ColorLightConverter : IValueConverter { public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { Color color = (Color)value; System.Drawing.Color lightColor = ControlPaint.Light(System.Drawing.Color.FromArgb(color.A, color.R, color.G, color.B)); return Color.FromArgb(lightColor.A, lightColor.R, lightColor.G, lightColor.B); } public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) { throw new NotImplementedException(); } } But the converter isn't called when I click the button. I think there is anything wrong with the binding, but I can't see the error... Can you help me? Maybe I'm completely wrong. What I basically want to do: When clicking the button, take the current background color and lighten it. Not more...

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• How to patch an S4 method in an R package?

  - by Richie Cotton

  If you find a bug in a package, it's usually possible to patch the problem with fixInNamespace, e.g. fixInNamespace("mean.default", "base"). For S4 methods, I'm not sure how to do it though. The method I'm looking at is in the gWidgetstcltk package. You can see the source code with getMethod(".svalue", c("gTabletcltk", "guiWidgetsToolkittcltk")) I can't find the methods with fixInNamespace. fixInNamespace(".svalue", "gWidgetstcltk") Error in get(subx, envir = ns, inherits = FALSE) : object '.svalue' not found I thought setMethod might do the trick, but setMethod(".svalue", c("gTabletcltk", "guiWidgetsToolkittcltk"), definition = function (obj, toolkit, index = NULL, drop = NULL, ...) { widget = getWidget(obj) sel <- unlist(strsplit(tclvalue(tcl(widget, "selection")), " ")) if (length(sel) == 0) { return(NA) } theChildren <- .allChildren(widget) indices <- sapply(sel, function(i) match(i, theChildren)) inds <- which(visible(obj))[indices] if (!is.null(index) && index == TRUE) { return(inds) } if (missing(drop) || is.null(drop)) drop = TRUE chosencol <- tag(obj, "chosencol") if (drop) return(obj[inds, chosencol, drop = drop]) else return(obj[inds, ]) }, where = "package:gWidgetstcltk" ) Error in setMethod(".svalue", c("gTabletcltk", "guiWidgetsToolkittcltk"), : the environment "gWidgetstcltk" is locked; cannot assign methods for function ".svalue" Any ideas?

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• PHP.ini Settings Are Ignored By PHP5.3.5 Running With Windows 7 And Apache 2.2.15

  - by Andy

  I did an install of PHP5.3.5 on Windows 7 Home Premium using the MSI installer download. I got it to overwrite a previous version of PHP5 in C:\php5\ When first testing it, the server failed to start. I fixed this by adding the path to PHP in the Apache2.2 httpd file where the installer had inserted 2 lines of coded pointing to the ini file directory and the PHP DLL but had left out the directory path. After doing this, the server starts ok and I can run phpinfo to view the PHP settings in my web browser on local host. In the phpinfo it states that the loaded configuration file is C:\php5\php.ini as expected. But if I make any changes to the settings, and reboot the server, none of the changes are reflected in phpinfo. Yes, I do refresh the browser window. If I rename the php.ini to something else to make it invisible phpinfo then correctly identifies that there is no php.ini file loaded. So the settings in php.ini are being ignored and some default settings are being used (but I have no idea where these are derived from). As far as I can tell, there are no other php.ini files on my computer. In phpinfo it states that the Configuration File (php.ini) Path is C:\Windows but this is the same as on a Windows XP computer that I work on. And in the windows folder I don't see any php.ini file. In the windows registry, there is no mention of PHP5, and the PATH environment variable starts with C:\php5\; So hopefully someone can suggest how I can get PHP5 to take notice of the C:\php5\php.ini settings. :)

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• Generic cast type to primitive.

  - by Nix

  Is there a way to do the below? Imagine a generic result wrapper class. Where you have a type and an associated error list. When there is no result to return to the user we will use boolean to indicate success failure. I want to create a constructor that takes in an error list, and if the list is null or count 0, AND the type is a bool/Boolean i want to set it to true.... Seemingly simple, but amazingly not possible. public class Result<T>{ private T valueObject { get;set;} private List<Error> errors{ get;set;} public Result(T valueObj, List<Error> errorList){ this.valueObject = valueObj; this.errors = errorList; } public Result(List<Error> errors) { this.valueObject = default(ReturnType); if (valueObject is Boolean) { //Wont work compile //(valueObject as Boolean) = ((errors == null) || errors.Count == 0); //Compiles but detaches reference //bool temp = ((bool)(valueObject as object)) ; //temp = ((errors == null) || errors.Count == 0); } this.errors = errors; } } } Am I missing something simple? And in general I would prefer to do it without reflection.

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• Forcing Kernel::method_name to be called in Ruby

  - by Peter

  I want to add a foo method to Ruby's Kernel module, so I can write foo(obj) anywhere and have it do something to obj. Sometimes I want a class to override foo, so I do this: module Kernel private # important; this is what Ruby does for commands like 'puts', etc. def foo x if x.respond_to? :foo x.foo # use overwritten method. else # do something to x. end end end this is good, and works. but, what if I want to use the default Kernel::foo in some other object that overwrites foo? Since I've got an instance method foo, I've lost the original binding to Kernel::foo. class Bar def foo # override behaviour of Kernel::foo for Bar objects. foo(3) # calls Bar::foo, not the desired call of Kernel::foo. Kernel::foo(3) # can't call Kernel::foo because it's private. # question: how do I call Kernel::foo on 3? end end Is there any clean way to get around this? I'd rather not have two different names, and I definitely don't want to make Kernel::foo public.

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• Django IntegrityError: foreign key violation upon delete

  - by Lukasz Korzybski

  I have Order and Shipment model. Shipment has a foreign key to Order. class Order(...): ... class Shipment() order = m.ForeignKey('Order') ... Now in one of my views I want do delete order object along with all related objects. So I invoke order.delete(). I have Django 1.0.4, PostgreSQL 8.4 and I use transaction middleware, so whole request is enclosed in single transaction. The problem is that upon order.delete() I get: ... File "/usr/local/lib/python2.6/dist-packages/django/db/backends/__init__.py", line 28, in _commit return self.connection.commit() IntegrityError: update or delete on table "main_order" violates foreign key constraint "main_shipment_order_id_fkey" on table "main_shipment" DETAIL: Key (id)=(45) is still referenced from table "main_shipment". I checked in connection.queries that proper queries are executed in proper order. First shipment is deleted, after that django executes delete on order row: {'time': '0.000', 'sql': 'DELETE FROM "main_shipment" WHERE "id" IN (17)'}, {'time': '0.000', 'sql': 'DELETE FROM "main_order" WHERE "id" IN (45)'} Foreign key have ON DELETE NO ACTION (default) and is initially deferred. I don't know why I get foreign key constraint violation. I also tried to register pre_delete signal and manually delete shipment objects before delete on order is called, but it resulted in the same error. I can change ON DELETE behaviour for this key in Postgres but it would be just a hack, I wonder if anyone has a better idea what's going on here. There is also a small detail, my Order model inherits from Cart model, so it actually doesn't have id field but cart_ptr_id and after DELETE on order is executed there is also DELETE on cart, but it seems unrelated? to the shipment-order problem so I simplified it in the example.

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• Class library reference problem

  - by Anindya Chatterjee

  I am building a class library and using its default namespace as "System". There suppose I am creating a generic data structure say PriorityQueue and putting it under System.Collections.Generic namespace. Now when I am referencing that library from another project, I can't see PriorityQueue under "System.Collections.Generic" namespace anymore. Though the library is referenced in that project I can not access any of the classes in it. My question was mscorlib and System.dll share similar namespaces, but still classes from both the assembly is accessible, but why can't mine? If I put a public class under System.Collections.Generic namespace in my class library and refer that library in a project and use a statement like "using System.Collections.Generic", still why I can't access my class there? This was an experimentation I did, I know using System namespace is not encouraged in custom class library, but I want to know the reason behind why I can't access my class in this special case? Please someone shed some light on it. PS: Last time I asked similar question but put it wrongly, so people got misunderstood and I didn't get my answer. This time I am trying to put it correctly as far as I can. Sorry for the misunderstanding.

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• select option clears when page loads in php

  - by user79685

  Hey guys, the scenario is this: see select below <form name="limit"> <select name="limiter" onChange="limit(this.value)"> <option selected="selected">&nbsp;</option> <option value="5">5</option> <option value="10">10</option> <option value="15">15</option> </select> </form> I want whenever any option is selected for 3 things to happen: 1.) js limit() function is called which all it does its takes current url, adds new query parameter 'limit' with the user selected value eg: http://localhost/blahblah/apps/category.php?pg=1&catId=3021&limit=5 (this will cause the category.php page to be hit and # of product displayed limited to the value selected by user) 2.)Once the url is hit, it reloads but i DONT want the value selected to reset back to the default (which it currently does). I want it to reflect the users selection after page reload. 3.) Also, when i move to the next page (pagination), i would like the state to be carried ova to the next page (ie. remembering the user selection).

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• Access Controller Context/ TempData from business objects

  - by thanikkal

  I am trying to build a session/tempdata provider that can be swapped. The default provider will work on top of asp.net mvc and it needed to access the .net mvc TempData from the business object class. I know the tempdata is available through the controller context, but i cant seem to find if that is exposed through HttpContext or something. I dont really want to pass the Controller context as an argument as that would dilute my interface definition since only asp.net based session provider needs this, other (using NoSQL DB etc) doesn't care about Controller Context. To clarify further, adding little more code here. my ISession interface look like this. and when this code goes to production, the session/tempdata is expected to work using NoSql db. But i also like to have another implementation that works on top of asp.net mvc session/tempdata for my dev testing etc. public interface ISession { T GetTempData<T>(string key); void PutTempData<T>(string key, T value); T GetSessiondata<T>(string key); void PutSessiondata<T>(string key, T value); }

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• Spring security or BCrypt algorithm which one is good for accounts like project?

  - by Ranjith Kumar Nethaji

  I am using spring security for hashing my password.And is it safe ,because am using spring security for first time. my code here <security:http auto-config="true"> <security:intercept-url pattern="/welcome*" access="ROLE_USER" /> <security:form-login login-page="/login" default-target-url="/welcome" authentication-failure-url="/loginfailed" /> <security:logout logout-success-url="/logout" /> </security:http> authentication-failure-url="/loginfailed" /> <security:logout logout-success-url="/logout" /> </security:http> <authentication-manager> <authentication-provider> <password-encoder hash="sha" /> <user-service> <user name="k" password="7c4a8d09ca3762af61e59520943dc26494f8941b" authorities="ROLE_USER" /> </user-service> </authentication-provider> </authentication-manager> .And I havnt used bcrypt algorithm.what is your feedback for both?any recommendation?

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• How could I cache images that I'm pulling from a magento database through ajax?

  - by wes

  Here's script being called through ajax: <?php require_once '../app/Mage.php'; umask(0); /* not Mage::run(); */ Mage::app('default'); $cat_id = ($_POST['cat_id']) ? $_POST['cat_id'] : NULL; try { $category = new Mage_Catalog_Model_Category(); $category->load($cat_id); $collection = $category->getProductCollection(); $output = '<ul>'; foreach ($collection as $product) { $cProduct = Mage::getModel('catalog/product'); $cProduct->load($product->getId()); $output .= '<li><img id="'.$product->getId().'" src="' . (string)Mage::helper('catalog/image')->init($cProduct, 'small_image')->resize(75) . '" class="thumb" /></li>'; } $output .= '</ul>'; echo $output; } catch (Exception $e) { echo 'Caught exception: ', $e->getMessage(), "\n"; } I'm just passing in the Category ID, which I've tacked onto the navigation links, then doing some work to eventually just pass back all product images in that category. I'm using this on a drag and drop build-a-bracelet type of application, and the amount of images returned is sometimes in the 500s. So it get's pretty held up during transmission, sometimes 10 seconds or so. I know I'd do good by caching them some way, just not sure how to go about it. Any help is much appreciated. Thanks. -Wes

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• What is happening in Crockford's object creation technique?

  - by Chris Noe

  There are only 3 lines of code, and yet I'm having trouble fully grasping this: Object.create = function (o) { function F() {} F.prototype = o; return new F(); }; newObject = Object.create(oldObject); (from Prototypal Inheritance) 1) Object.create() starts out by creating an empty function called F. I'm thinking that a function is a kind of object. Where is this F object being stored? Globally I guess. 2) Next our oldObject, passed in as o, becomes the prototype of function F. Function (i.e., object) F now "inherits" from our oldObject, in the sense that name resolution will route through it. Good, but I'm curious what the default prototype is for an object, Object? Is that also true for a function-object? 3) Finally, F is instantiated and returned, becoming our newObject. Is the "new" operation strictly necessary here? Doesn't F already provide what we need, or is there a critical difference between function-objects and non-function-objects? Clearly it won't be possible to have a constructor function using this technique. What happens the next time Object.create() is called? Is global function F overwritten? Surely it is not reused, because that would alter previously configured objects. And what happens if multiple threads call Object.create(), is there any sort of synchronization to prevent race conditions on F?

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• error while reading Excel sheet

  - by Lalit

  Hi, I have code to read Excel from c3 language : DataTable dtChildrenData = new DataTable(); OdbcConnection oConn = null; try { if (File.Exists(strSheetPath)) { oConn = new OdbcConnection(); oConn.ConnectionString = @"DSN=Excel Files;DBQ=" + strSheetPath + @";DriverId=1046;FIL=excel 12.0;MaxBufferSize=2048;PageTimeout=5;"; OdbcCommand oComm = new OdbcCommand(); oComm.Connection = oConn; oComm.CommandText = "Select * From [Sheet1$]"; DataSet ds = new DataSet(); OdbcDataAdapter oAdapter = new OdbcDataAdapter(oComm); oConn.Open(); oAdapter.Fill(ds); dtChildrenData = ds.Tables[0]; } } finally { oConn.Close(); } return dtChildrenData; But getting this error when i deploy the web application on IIS. Wherere as it is running fine locally. ERROR [IM002] [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified How to solve this. Please let me know if any information required to answer this question (about configuration)

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• Problem registering a COM server written for Excel registered on client machine (can't set full path

  - by toytrains

  In this previous question <How to get COM Server for Excel written in VB.NET installed and registered in Automation Servers list? there is an example of how to create the full path to a registry key using VS 2008. Everything in the previous answer works correctly except the full path that I am setting (using the registry editor in VS) for mscoree.dll is not working (meaning it seems to do nothing). The full registry path is: HKEY_CLASSES_ROOT\CLSID{my_GUID}\InprocServer32(default) and the value I am setting is: [SystemFolder]mscoree.dll I can put anything (including hardcoding the full path) but the setting does not seem to matter and the registry always contains mscoree.dll without any path. I have tried adding another value to the registry path via VS and that works correctly including having the full path as specified by [SystemFolder]. The reason I need the full path (as explained in the previous question) is that without the path, Excel generates an error when the automation server is selected as it cannot find mscoree.dll (interestingly even though I receive an error the registration works OK). I am doing the install via a setup project which otherwise works fine. I am installing on a VISTA*64 system but have gotten the same error on other OS's. Does anyone know what I am doing wrong?

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• How do I serialise a graph in Java without getting StackOverflowException?

  - by Tim Cooper

  I have a graph structure in java, ("graph" as in "edges and nodes") and I'm attempting to serialise it. However, I get "StackOverflowException", despite significantly increasing the JVM stack size. I did some googling, and apparently this is a well known limitation of java serialisation: that it doesn't work for deeply nested object graphs such as long linked lists - it uses a stack record for each link in the chain, and it doesn't do anything clever such as a breadth-first traversal, and therefore you very quickly get a stack overflow. The recommended solution is to customise the serialisation code by overriding readObject() and writeObject(), however this seems a little complex to me. (It may or may not be relevant, but I'm storing a bunch of fields on each edge in the graph so I have a class JuNode which contains a member ArrayList<JuEdge> links;, i.e. there are 2 classes involved, rather than plain object references from one node to another. It shouldn't matter for the purposes of the question). My question is threefold: (a) why don't the implementors of Java rectify this limitation or are they already working on it? (I can't believe I'm the first person to ever want to serialise a graph in java) (b) is there a better way? Is there some drop-in alternative to the default serialisation classes that does it in a cleverer way? (c) if my best option is to get my hands dirty with low-level code, does someone have an example of graph serialisation java source-code that can use to learn how to do it?

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• Django: Determining if a user has voted or not

  - by TheLizardKing

  I have a long list of links that I spit out using the below code, total votes, submitted by, the usual stuff but I am not 100% on how to determine if the currently logged in user has voted on a link or not. I know how to do this from within my view but do I need to alter my below view code or can I make use of the way templates work to determine it? I have read http://stackoverflow.com/questions/1528583/django-vote-up-down-method but I don't quite understand what's going on ( and don't need any ofjavascriptery). Models (snippet): class Link(models.Model): category = models.ForeignKey(Category, blank=False, default=1) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) modified = models.DateTimeField(auto_now=True) url = models.URLField(max_length=1024, unique=True, verify_exists=True) name = models.CharField(max_length=512) def __unicode__(self): return u'%s (%s)' % (self.name, self.url) class Vote(models.Model): link = models.ForeignKey(Link) user = models.ForeignKey(User) created = models.DateTimeField(auto_now_add=True) def __unicode__(self): return u'%s vote for %s' % (self.user, self.link) Views (snippet): def hot(request): links = Link.objects.select_related().annotate(votes=Count('vote')).order_by('-created') for link in links: delta_in_hours = (int(datetime.now().strftime("%s")) - int(link.created.strftime("%s"))) / 3600 link.popularity = ((link.votes - 1) / (delta_in_hours + 2)**1.5) if request.user.is_authenticated(): try: link.voted = Vote.objects.get(link=link, user=request.user) except Vote.DoesNotExist: link.voted = None links = sorted(links, key=lambda x: x.popularity, reverse=True) links = paginate(request, links, 15) return direct_to_template( request, template = 'links/link_list.html', extra_context = { 'links': links, }) The above view actually accomplishes what I need but in what I believe to be a horribly inefficient way. This causes the dreaded n+1 queries, as it stands that's 33 queries for a page containing just 29 links while originally I got away with just 4 queries. I would really prefer to do this using Django's ORM or at least .extra(). Any advice?

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• Storing values in the DataValueField and DataTextField of a dropdownlist using a linq query

  - by user1318369

  I have a website for dance academy where Users can register and add/drop dance classes. In the web page to drop a particular dance, for a particular user, the dropdown displays her registered dances. Now I want to delete one of the dances from the list. So I'll remove the row from the table and also from the dropdownlist. The problem is that everytime the item with the lowest ID (index) is getting deleted, no matter which one the user selects. I think I am storing the DataTextField and DataValueField for the dropdown incorrectly. The code is: private void PopulateDanceDropDown() { // Retrieve the username MembershipUser currentUser = Membership.GetUser(); var username = currentUser.UserName; // Retrive the userid of the curren user var dancerIdFromDB = from d in context.DANCER where d.UserName == username select d.UserId; Guid dancerId = new Guid(); var first = dancerIdFromDB.FirstOrDefault(); if (first != null) { dancerId = first; } dances.DataSource = (from dd in context.DANCER_AND_DANCE where dd.UserId == dancerId select new { Text = dd.DanceName, Value = dd.DanceId }).ToList(); dances.DataTextField = "Text"; dances.DataValueField = "Value"; dances.DataBind(); } protected void dropthedance(object o, EventArgs e) { String strDataValueField = dances.SelectedItem.Value; int danceIDFromDropDown = Convert.ToInt32(strDataValueField); var dancer_dance = from dd in context.DANCER_AND_DANCE where dd.DanceId == danceIDFromDropDown select dd; foreach (var dndd in dancer_dance) { context.DANCER_AND_DANCE.DeleteOnSubmit(dndd); } try { context.SubmitChanges(); } catch (Exception ex) { Console.WriteLine(ex); } } The problem is in the line: String strDataValueField = dances.SelectedItem.Value; The strDataValueField is always getting the minimum id from the list of dance item ids in the dropdown (which happens by default). I want this to hold the id of the dance selected by the user.

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• How do I restart mysql and where is my.cnf file

  - by dorelal

  I am using snow leopard mac. I installed mysql on my machine using instructions mentioned here. Everything works great. However I have two questions. 1) Where is my.cnf file? I searched the whole file system and result is empty. Is it possible that there is no my.cnf and mysql works with default values. If yes then probably I should create my.inf at /etc/mysql. Is that right? 2) How do I restar server. I know it gets started when I restart my machine. Here is what plist looks like. mysqld_safe does not let me restart server. <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>KeepAlive</key> <true/> <key>Label</key> <string>com.mysql.mysqld</string> <key>Program</key> <string>/usr/local/mysql/bin/mysqld_safe</string> <key>RunAtLoad</key> <true/> <key>UserName</key> <string>mysql</string> <key>WorkingDirectory</key> <string>/usr/local/mysql</string> </dict> </plist>

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• Is memory allocation in linux non-blocking?

  - by Mark

  I am curious to know if the allocating memory using a default new operator is a non-blocking operation. e.g. struct Node { int a,b; }; ... Node foo = new Node(); If multiple threads tried to create a new Node and if one of them was suspended by the OS in the middle of allocation, would it block other threads from making progress? The reason why I ask is because I had a concurrent data structure that created new nodes. I then modified the algorithm to recycle the nodes. The throughput performance of the two algorithms was virtually identical on a 24 core machine. However, I then created an interference program that ran on all the system cores in order to create as much OS pre-emption as possible. The throughput performance of the algorithm that created new nodes decreased by a factor of 5 relative the the algorithm that recycled nodes. I'm curious to know why this would occur. Thanks. *Edit : pointing me to the code for the c++ memory allocator for linux would be helpful as well. I tried looking before posting this question, but had trouble finding it.

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• How to write this snippet in Python?

  - by morpheous

  I am learning Python (I have a C/C++ background). I need to write something practical in Python though, whilst learning. I have the following pseudocode (my first attempt at writing a Python script, since reading about Python yesterday). Hopefully, the snippet details the logic of what I want to do. BTW I am using python 2.6 on Ubuntu Karmic. Assume the script is invoked as: script_name.py directory_path import csv, sys, os, glob # Can I declare that the function accepts a dictionary as first arg? def getItemValue(item, key, defval) return !item.haskey(key) ? defval : item[key] dirname = sys.argv[1] # declare some default values here weight, is_male, default_city_id = 100, true, 1 # fetch some data from a database table into a nested dictionary, indexed by a string curr_dict = load_dict_from_db('foo') #iterate through all the files matching *.csv in the specified folder for infile in glob.glob( os.path.join(dirname, '*.csv') ): #get the file name (without the '.csv' extension) code = infile[0:-4] # open file, and iterate through the rows of the current file (a CSV file) f = open(infile, 'rt') try: reader = csv.reader(f) for row in reader: #lookup the id for the code in the dictionary id = curr_dict[code]['id'] name = row['name'] address1 = row['address1'] address2 = row['address2'] city_id = getItemValue(row, 'city_id', default_city_id) # insert row to database table finally: f.close() I have the following questions: Is the code written in a Pythonic enough way (is there a better way of implementing it)? Given a table with a schema like shown below, how may I write a Python function that fetches data from the table and returns is in a dictionary indexed by string (name). How can I insert the row data into the table (actually I would like to use a transaction if possible, and commit just before the file is closed) Table schema: create table demo (id int, name varchar(32), weight float, city_id int); BTW, my backend database is postgreSQL

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