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• Multiple threads modifying a collection in Java??

  - by posdef

  Hi, The project I am working on requires a whole bunch of queries towards a database. In principle there are two types of queries I am using: read from excel file, check for a couple of parameters and do a query for hits in the database. These hits are then registered as a series of custom classes. Any hit may (and most likely will) occur more than once so this part of the code checks and updates the occurrence in a custom list implementation that extends ArrayList. for each hit found, do a detail query and parse the output, so that the classes created in (I) get detailed info. I figured I would use multiple threads to optimize time-wise. However I can't really come up with a good way to solve the problem that occurs with the collection these items are stored in. To elaborate a little bit; throughout the execution objects are supposed to be modified by both (I) and (II). I deliberately didn't c/p any code, as it would be big chunks of code to make any sense.. I hope it make some sense with the description above. Thanks,

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• How do I write a J2EE/EJB Singleton?

  - by Bears will eat you

  A day ago my application was one EAR, containing one WAR, one EJB JAR, and a couple of utility JAR files. I had a POJO singleton class in one of those utility files, it worked, and all was well with the world: EAR |--- WAR |--- EJB JAR |--- Util 1 JAR |--- Util 2 JAR |--- etc. Then I created a second WAR and found out (the hard way) that each WAR has its own ClassLoader, so each WAR sees a different singleton, and things break down from there. This is not so good. EAR |--- WAR 1 |--- WAR 2 |--- EJB JAR |--- Util 1 JAR |--- Util 2 JAR |--- etc. So, I'm looking for a way to create a Java singleton object that will work across WARs (across ClassLoaders?). The @Singleton EJB annotation seemed pretty promising until I found that JBoss 5.1 doesn't seem to support that annotation (which was added as part of EJB 3.1). Did I miss something - can I use @Singleton with JBoss 5.1? Upgrading to JBoss AS 6 is not an option right now. Alternately, I'd be just as happy to not have to use EJB to implement my singleton. What else can I do to solve this problem? Basically, I need a semi-application-wide* hook into a whole bunch of other objects, like various cached data, and app config info. As a last resort, I've already considered merging my two WARs into one, but that would be pretty hellish. *Meaning: available basically anywhere above a certain layer; for now, mostly in my WARs - the View and Controller (in a loose sense).

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• Polymorphic Queue

  - by metdos

  Hello Everyone, I'm trying to implement a Polymorphic Queue. Here is my trial: QQueue <Request *> requests; while(...) { QString line = QString::fromUtf8(client->readLine()).trimmed(); if(...)){ Request *request=new Request(); request->tcpMessage=line.toUtf8(); request->decodeFromTcpMessage(); //this initialize variables in request using tcpMessage if(request->requestType==REQUEST_LOGIN){ LoginRequest loginRequest; request=&loginRequest; request->tcpMessage=line.toUtf8(); request->decodeFromTcpMessage(); requests.enqueue(request); } //Here pointers in "requests" do not point to objects I created above, and I noticed that their destructors are also called. LoginRequest *loginRequest2=dynamic_cast<LoginRequest *>(requests.dequeue()); loginRequest2->decodeFromTcpMessage(); } } Unfortunately, I could not manage to make work Polymorphic Queue with this code because of the reason I mentioned in second comment.I guess, I need to use smart-pointers, but how? I'm open to any improvement of my code or a new implementation of polymorphic queue. Thanks.

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• C#/LINQ: How to define generically a keySelector for a templated class before calling OrderBy

  - by PierrOz

  Hi Folks, I have the following class defined in C# class myClass<T,U> { public T PropertyOne { get; set; } public U PropertyTwo { get; set; } } I need to write a function that reorder a list of myClass objects and takes two other parameters which define how I do this reorder: does my reordering depend on PropertyOne or PropertyTwo and is it ascending or descending. Let's say this two parameters are boolean. With my current knowledge in LINQ, I would write: public IList<myClass<T,U>> ReOrder(IList<myClass<T,U>> myList, bool usePropertyOne, bool ascending) { if (usePropertyOne) { if (ascending) { return myList.OrderBy(o => o.PropertyOne).ToList(); } else { return myList.OrderByDescending(o => o.PropertyOne).ToList(); } } else { if (ascending) { return myList.OrderBy(o => o.PropertyTwo).ToList(); } else { return myList.OrderByDescending(o => o.PropertyTwo).ToList(); } } } What could be a more efficient/elegant way to do that ? How can I declare the Func,TResult keySelector object to reuse when I call either OrderBy or OrderByDescending? I'm interesting in the answer since in my real life, I can have more than two properties.

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• Using MongoDB's map/reduce to "group by" two fields

  - by ibz

  I need something slightly more complex than the examples in the MongoDB docs and I can't seem to be able to wrap my head around it. Say I have a collection of objects of the form {date: "2010-10-10", type: "EVENT_TYPE_1", user_id: 123, ...} Now I want to get something similar to a SQL GROUP BY query, grouping over both date and type. That is, I want the number of events of each type in each day. Also, I'd like to make it unique by user_id, ie. if a user has more events in the same day, count it only once. I'm trying to do this with map/reduce. I do db.logs.mapReduce(function() { emit(this.type, 1); }, function(k, vals) { var total = 0; for (var i = 0; i < vals.length; i++) total += vals[i]; return total; }}) which nicely groups by type, but now, how can I group by date at the same time? Seems the key in emit() can't be an array (I thought about doing emit([this.date, this.type], 1)). Also, how can I ensure the per-user uniqueness? I'm just starting with MongoDB and I'm still having trouble grasping the basic concepts. Also, there is not much documentation available out there. Any help from more experienced users is appreciated. Thanks!

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• Cast errors with IXmlSerializable

  - by Nathan

  I am trying to use the IXmlSerializable interface to deserialize an Object (I am using it because I need specific control over what gets deserialized and what does not. See my previous question for more information). However, I'm stumped as to the error message I get. Below is the error message I get (I have changed some names for clarity): An unhandled exception of type 'System.InvalidCastException' occurred in App.exe Additional information: Unable to cast object of type 'System.Xml.XmlNode[]' to type 'MyObject'. MyObject has all the correct methods defined for the interface, and regardless of what I put in the method body for ReadXml() I still get this error. It doesn't matter if it has my implementation code or if it's just blank. I did some googling and found an error that looks similar to this involving polymorphic objects that implement IXmlSerializable. However, my class does not inherit from any others (besides Object). I suspected this may be an issue because I never reference XmlNode any other time in my code. Microsoft describes a solution to the polymorphism error: https://connect.microsoft.com/VisualStudio/feedback/details/422577/incorrect-deserialization-of-polymorphic-type-that-implements-ixmlserializable?wa=wsignin1.0#details The code the error occurs at is as follows. The object to be read back in is an ArrayList of "MyObjects" IO::FileStream ^fs = gcnew IO::FileStream(filename, IO::FileMode::Open); array<System::Type^>^ extraTypes = gcnew array<System::Type^>(1); extraTypes[0] = MyObject::typeid; XmlSerializer ^xmlser = gcnew XmlSerializer(ArrayList::typeid, extraTypes); System::Object ^obj; obj = xmlser->Deserialize(fs); fs->Close(); ArrayList ^al = safe_cast<ArrayList^>(obj); MyObject ^objs; for each(objs in al) //Error occurs here { //do some processing } Thanks for reading and for any help.

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• Recommendations of a high volume log event viewer in a Java enviroment

  - by Thorbjørn Ravn Andersen

  I am in a situation where I would like to accept a LOT of log events controlled by me - notably the logging agent I am preparing for slf4j - and then analyze them interactively. I am not as such interested in a facility that presents formatted log files, but one that can accept log events as objects and allow me to sort and display on e.g. threads and timelines etc. Chainsaw could maybe be an option but is currently not compatible with logback which I use for technical reasons. Is there any project with stand alone viewers or embedded in an IDE which would be suitable for this kind of log handling. I am aware that I am approaching what might be suitable for a profiler, so if there is a profiler projekt suitable for this kind of data acquisition and display where I can feed the event pipe, I would like to hear about it). Thanks for all feedback Update 2009-03-19: I have found that there is not a log viewer which allows me to see what I would like (a visual display of events with coordinates determined by day and time, etc), so I have decided to create a very terse XML format derived from the log4j XMLLayout adapted to be as readable as possible while still being valid XML-snippets, and then use the Microsoft LogParser to extract the information I need for postprocessing in other tools.

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• what kind of relationship is there between a common wall and the rooms that located next to it?

  - by siamak

  I want to know whats the Relationship between a common wall (that are located In an adjoining room ) and the rooms. As i know the relationship between a room and its walls is Composition not Aggregation (am i right ?) And according to the definition of Composition the contained object can't be shared between two containers, whereas in aggregation it is possible. now i am confused that whats the best modeling approach to represent the relationship between a common wall and the rooms located next to it ? It would be highly Appreciated if you could provide your advices with some code. |--------|--------| Approch1: (wall class ---- room class) /Composition Approach2: wall class ----- room class /Aggregation Approch3: we have a wall class and a Common wall class , Common wall class inherits from wall class adjoining room class ---- (1) Common wall class /Aggregation adjoining room class ---- (6) wall class / composition Approach4: I am a developer not a designer :) so this is my idea : class Room { private wall _firstwall ; private wall _secondtwall; private wall _thirdwall ; private wall _commonwall ; public Room( CommonWall commonwall) { _firstwall=new Wall(); _secondtwall=new Wall(); _thirdwall=new Wall(); _commonwall=commonwall; } } Class CommonWall:Wall { //... } // in somewher : static void main() { Wall _commonWall=new Wall(); Room room1=new Room(_commonWall); Room room2=new Room(_commonWall); Room [] adjacentRoom =new Room[2]{room1,room2}; } Edit 1: I think this is a clear question but just for more clarification : The point of the question is to find out whats the best pattern or approach to model a relationship for an object that is a component of two other objects in the same time. and about my example : waht i mean by a "room" ?,surely i mean an enclosed square room with 4 walls and one door.but in this case one of these walls is a common wall and is shared between two adjacent rooms.

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• Facebook SDK Comment Deleting

  - by mwoodworth

  Working with the Facebook php SDK's, I am having a lot of trouble figuring out how to delete comments, given its id and xid. At first I was using the REST API, where you can call 'comments_remove($xid, $id);' to delete a comment. The problem with this method came when the xid parameter only accepts alphanumeric characters and underscores. Based on the documentation (http://developers.facebook.com/docs/reference/fbml/comments ) a valid XID can be the result of any url_encode. Now I am testing my luck with the new GRAPH api. Looking at http://developers.facebook.com/docs/api under 'Deleting Objects', It seems that comment deleting is definitely supported. However, I have tried sending a DELETE request, and I have also tried sending POST and GET to the object url with the argument 'method=delete'. No matter how I try it, I always get the same error: {"error":{"type":"GraphMethodException","message":"Unsupported delete request."}} I am sending the access token as a parameter as well. The access token that I am sending is the access token saved in the facebook cookie from the single sign on javascript cookie. These are all comments made on my application. Does this happen to anyone else, or am I simply not doing this right? Any help or guidance is GREATLY appreciated.

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• XmlSerialize a custom collection with an Attribute

  - by roomaroo

  I've got a simple class that inherits from Collection and adds a couple of properties. I need to serialize this class to XML, but the XMLSerializer ignores my additional properties. I assume this is because of the special treatment that XMLSerializer gives ICollection and IEnumerable objects. What's the best way around this? Here's some sample code: using System.Collections.ObjectModel; using System.IO; using System.Xml.Serialization; namespace SerialiseCollection { class Program { static void Main(string[] args) { var c = new MyCollection(); c.Add("Hello"); c.Add("Goodbye"); var serializer = new XmlSerializer(typeof(MyCollection)); using (var writer = new StreamWriter("test.xml")) serializer.Serialize(writer, c); } } [XmlRoot("MyCollection")] public class MyCollection : Collection<string> { [XmlAttribute()] public string MyAttribute { get; set; } public MyCollection() { this.MyAttribute = "SerializeThis"; } } } This outputs the following XML (note MyAttribute is missing in the MyCollection element): <?xml version="1.0" encoding="utf-8"?> <MyCollection xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <string>Hello</string> <string>Goodbye</string> </MyCollection> What I want is <MyCollection MyAttribute="SerializeThis" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <string>Hello</string> <string>Goodbye</string> </MyCollection> Any ideas? The simpler the better. Thanks.

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• javascript pausing consistently. How do I find what is causing it to pause?

  - by pedalpete

  I've got a fairly ajax heavy site and I'm trying to tune the performance. I have a function that runs between 20 & 200 times, depending on the user. I'm outputting the time the function takes to execute via console.time in firefox. The function takes about 4-6ms to complete. The strange thing is that on my larger test with 200 or runs through that function, it runs through the first 31, then seems to pause for almost a second before completing the last 170 or so. However, that 'pause' doesn't show up in the console.time logs, and I'm not running any other functions, and the object that gets passed to the function looks the same as all other objects that get passed in. The function is called like this for (var s in thisGroup.events){ showEvent(thisGroup.events[s]) } so, I don't see how or why it would suddenly pause near the beginning. but only pause once and then continue through. The pause ALWAYS happens on the 31st time through the function. I've taken a close look at the 'thisGroup.events[s]' that it is being run through, and it looks like this for #31 "eventId":"5106", "sid":"68", "gid":"29", "uid":"70","type":"event", "startDate":"2010-03-22","startTime":"6:00 PM","endDate":"2010-03-22","endTime":"11:00 PM","durationLength":"5", "durationTime":"5:00", "note":"", "desc":"event" The event immediately after the pause, #32 looks like this "eventId":"5111", "sid":"68", "gid":"29", "uid":"71","type":"event", "startDate":"2010-03-22","startTime":"6:00 PM","endDate":"2010-03-22","endTime":"11:00 PM","durationLength":"5", "durationTime":"5:00", "note":"", "desc":"event" another event that runs through no problem looks like this "eventId":"5113", "sid":"68", "gid":"29", "uid":"72","type":"event", "startDate":"2010-03-22","startTime":"4:30 PM","endDate":"2010-03-22","endTime":"11:00 PM","durationLength":"6.5", "durationTime":"6:30", "note":"", "desc":"event" From the console outputs, it doesn't appear as there is anything hanging or taking up time in the function itself, as the console.time for each event including #31,32 is 4ms. Another strange thing here is that the total time running the for loop across the entire object is coming out as 1014ms which is right for 200 events at 4-6ms each. Any suggestions on how to find this 'pause'? I find it very interesting that it is consistently happening between #31 & #32 only!

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• Generate an ID via COM interop

  - by Erik van Brakel

  At the moment, we've got an unmaintanable ball of code which offers an interface to a third party application. The third party application has a COM assembly which MUST be used to create new entries. This process involves two steps: generate a new object (basically an ID), and update that object with new field values. Because COM interop is so slow, we only use that to generate the ID (and related objects) in the database. The actual update is done using a regular SQL query. What I am trying to figure out if it's possible to use NHibernate to do some of the heavy lifting for us, without bypassing the COM assembly. Here's the code for saving something to the database as I envision it: using(var s = sessionFactory.OpenSession()) using(var t = s.BeginTransaction()) { MyEntity entity = new MyEntity(); s.Save(entity); t.Commit(); } Regular NH code I'd say. Now, this is where it gets tricky. I think I have to supply my own implementation of NHibernate.Id.IIdentifierGenerator which calls the COM assembly in the Generate method. That's not a problem. What IS a problem is that the COM assembly requires initialisation, which does take a bit of time. It also doesn't like multiple instances in the same process, for some reason. What I would like to know is if there's a way to properly access an external service in the generator code. I'm free to use any technique I want, so if it involves something like an IoC container that's no problem. The thing I am looking for is where exactly to hook-up my code so I can access the things I need in my generator, without having to resort to using singletons or other nasty stuff.

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• reddit style voting with django

  - by dotty

  Hay i need to hand implemeneting a voting system into a model. I've had a huge helping hand from Mike DeSimone making this work in the first place, but i need to expand upon his work. Here is my current code View def show_game(request): game = Game.objects.get(pk=1) discussions = game.gamediscussion_set.filter(reply_to=None) d = { 'game':game, 'discussions':discussions } return render_to_response('show_game', d) Template <ul> {% for discussion in discussions %} {{ discussion.html }} {% endfor %} </ul> Model class GameDiscussion(models.Model): game = models.ForeignKey(Game) message = models.TextField() reply_to = models.ForeignKey('self', related_name='replies', null=True, blank=True) created_on = models.DateTimeField(blank=True, auto_now_add=True) userUpVotes = models.ManyToManyField(User, blank=True, related_name='threadUpVotes') userDownVotes = models.ManyToManyField(User, blank=True, related_name='threadDownVotes') def html(self): DiscussionTemplate = loader.get_template("inclusions/discussionTemplate") return DiscussionTemplate.render(Context({ 'discussion': self, 'replies': [reply.html() for reply in self.replies.all()] })) DiscussionTemplate <li> {{ discussion.message }} {% if replies %} <ul> {% for reply in replies %} {{ reply }} {% endfor %} </ul> {% endif %} </li> As you can see we have 2 fields userUpVotes and userDownVotes on the model, these will calculate how to order the discussions and replies. How would i implement these 2 fields to order the replies and discussions based on votes? Any help would be great!

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• django hidden field error

  - by dana

  hi, there, i'm building a message system for a virtual community, but i can't take the userprofile id i have in views.py def save_message(request): if request.method == 'POST': form = MessageForm(request.POST) if form.is_valid(): new_obj = form.save(commit=False) new_obj.sender = request.user u = UserProfile.objects.get(request.POST['userprofile_id']) new_obj.owner = u new_obj.save() return HttpResponseRedirect('.') else: form = MessageForm() return render_to_response('messages/messages.html', { 'form': form, }, context_instance=RequestContext(request)) and the template: {% block primary %} <form action="." method="post"> {{ form.as_p }} <p><input type="hidden" value="{{ userprofile.id }}" name = "owner" /></p> <p><input type="submit" value="Send Message!" /></p> </form> {% endblock %} forms.py: class MessageForm(ModelForm): class Meta: model = Messages fields = ['message'] models.py: class Messages(models.Model): message = models.CharField(max_length = 300) read = models.BooleanField(default=False) owner = models.ForeignKey(UserProfile) sender = models.ForeignKey(User) I don't figure out why i get this error,since i'm just trying to get the profileId of a user, using a hiddeen field. the error is: Key 'UserProfile_id' not found in <QueryDict: {u'owner': [u''], u'message': [u'fdghjkl']}> and i'm getting it after i fill out the message text field. Thanks!

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• Cocoa UI Elements Not Updating

  - by spamguy

  I have a few Cocoa UI elements with outlet connexions to an object instantiated within an NSView object, which is in turn put there by an NSViewController. These elements, a definite progress bar and a text label, are not updating: the progress bar is dead and empty despite having its value change constantly, the text label does not unhide through [textLabel setHidden:NO], the text label does not change its string. What I know: There's no difference between binding values and setting them in code. Nothing changes either way. I've checked outlet connections. They're all there. I've tried [X displayIfNeeded], where X has been the UI objects themselves, the containing NSView, and the main window. No difference. [progressBar setUsesThreadedAnimation:YES] makes no difference. Interestingly, if I look at progressBar mid-program, _threadedAnimation is still NO. The object holding all these outlets and performing an import operation is in an NSOperationQueue owned by the NSViewController object. Thanks! EDIT: As suggested, I called [self performSelectorOnMainThread:@selector(updateProgress:) withObject:[NSNumber numberWithInt:myObject] waitUntilDone:NO]. (I've also tried waitUntilDone:YES.) It's still not updating. The debugger clearly shows updateProgress: taking place in the main thread, so I don't know what's missing.

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• C# reflection instantiation

  - by NickLarsen

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

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• item-not-found(404) when trying to get a node using Smackx pubsub

  - by DustMason

  I'm trying to use the latest Smackx trunk to get and then subscribe to a pubsub node. However, openfire just sends me a back an error: item not found (404). I am instantiating the java objects from ColdFusion, so my code snippets might look funny but maybe someone will be able to tell me what I've forgotten. Here's how I create the node: ftype = createObject("java", "org.jivesoftware.smackx.pubsub.FormType"); cform = createObject("java", "org.jivesoftware.smackx.pubsub.ConfigureForm").init(ftype.submit); cform.setPersistentItems(true); cform.setDeliverPayloads(true); caccess = createObject("java", "org.jivesoftware.smackx.pubsub.AccessModel"); cform.setAccessModel(caccess.open); cpublish = createObject("java", "org.jivesoftware.smackx.pubsub.PublishModel"); cform.setPublishModel(cpublish.open); cform.setMaxItems(99); manager = createObject("java", "org.jivesoftware.smackx.pubsub.PubSubManager").init(XMPPConnection); myNode = manager.createNode("subber", cform); And here's how I am trying to get to it (in a different section of code): manager = createObject("java", "org.jivesoftware.smackx.pubsub.PubSubManager").init(XMPPConnection); myNode = manager.getNode("subber"); Immediately upon creating the node I seem to be able to publish to it like so: payload = createObject("java", "org.jivesoftware.smackx.pubsub.SimplePayload").init("book","pubsub:test:book","<book xmlns='pubsub:test:book'><title>Lord of the Rings</title></book>"); item = createObject("java", "org.jivesoftware.smackx.pubsub.Item").init(payload); myNode.publish(item); However, it is the getNode() call that is causing my code to error. I have verified that the nodes are being created by checking the DB used by my openfire server. I can see them in there, properly attributed as leaf nodes, etc. Any advice? Anyone else out there doing anything with XMPP and ColdFusion? I have had great success sending and receiving messages with CF and Smack just haven't had the pubsub working yet :) Thanks!

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• Finding the left-most and right-most points of a list. std::find_if the right way to go?

  - by Tom

  Hi, I have a list of Point objects, (each one with x,y properties) and would like to find the left-most and right-most points. I've been trying to do it with find_if, but i'm not sure its the way to go, because i can't seem to pass a comparator instance. Is find_if the way to go? Seems not. So, is there an algorithm in <algorithm> to achieve this? Thanks in advance. #include <iostream> #include <list> #include <algorithm> using namespace std; typedef struct Point{ float x; float y; } Point; bool left(Point& p1,Point& p2) { return p1.x < p2.x; } int main(){ Point p1 ={-1,0}; Point p2 ={1,0}; Point p3 ={5,0}; Point p4 ={7,0}; list <Point> points; points.push_back(p1); points.push_back(p2); points.push_back(p3); points.push_back(p4); //Should return an interator to p1. find_if(points.begin(),points.end(),left); return 0; }

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• Schema design: many to many plus additional one to many

  - by chrisj

  Hi, I have this scenario and I'm not sure exactly how it should be modeled in the database. The objects I'm trying to model are: teams, players, the team-player membership, and a list of fees due for each player on a given team. So, the fees depend on both the team and the player. So, my current approach is the following: **teams** id name **players** id name **team_players** id player_id team_id **team_player_fees** id team_players_id amount send_reminder_on Schema layout ERD In this schema, team_players is the junction table for teams and players. And the table team_player_fees has records that belong to records to the junction table. For example, playerA is on teamA and has the fees of $10 and $20 due in Aug and Feb. PlayerA is also on teamB and has the fees of $25 and $25 due in May and June. Each player/team combination can have a different set of fees. Questions: Are there better ways to handle such a scenario? Is there a term for this type of relationship? (so I can google it) Or know of any references with similar structures?

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• Why is creating a ring buffer shared by different processes so hard (in C++), what I am doing wrong?

  - by recipriversexclusion

  I am being especially dense about this but it seems I'm missing an important, basic point or something, since what I want to do should be common: I need to create a fixed-size ring buffer object from a manager process (Process M). This object has write() and read() methods to write/read from the buffer. The read/write methods will be called by independent processes (Process R and W) I have implemented the buffer, SharedBuffer<T&>, it allocates buffer slots in SHM using boost::interprocess and works perfectly within a single process. I have read the answers to this question and that one on SO, as well as asked my own, but I'm still in the dark about how to have different processes access methods from a common object. The Boost doc has an example of creating a vector in SHM, which is very similar to what I want, but I want to instantiate my own class. My current options are: Use placement new, as suggested by Charles B. to my question; however, he cautions that it's not a good idea to put non-POD objects in SHM. But my class needs the read/write methods, how can I handle those? Add an allocator to my class definition, e.g. have SharedBuffer<T&, Alloc> and proceed similarly to the vector example given in boost. This sounds really complicated. Change SharedBuffer to a POD class, i.e. get rid of all the methods. But then how to synchronize reading and writing between processes? What am I missing? Fixed-length ring buffers are very common, so either this problem has a solution or else I'm doing something wrong.

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• CSS styles are not applied to elements added to JavaFX component tree

  - by pazabo

  I have applied CSS style to JavaFX components and it looks like everything is working fine except one situation: when I add JavaFX components to component tree on-the-fly their CSS styles are not applied. For example following code: package test; import javafx.stage.Stage; import javafx.scene.Scene; import javafx.scene.shape.Rectangle; import javafx.scene.input.MouseEvent; import javafx.util.Math; import javafx.scene.paint.Color; function getRect(): Rectangle { return Rectangle { x: 230 * Math.random() y: 60 * Math.random() width: 20, height: 20 styleClass: "abc" } } def stage: Stage = Stage { scene: Scene { width: 250, height: 80 stylesheets: "{__DIR__}main.css" content: [ Rectangle { x: 0, y: 0, width: 250, height: 80 fill: Color.WHITE onMouseClicked: function (evt: MouseEvent): Void { insert getRect() into stage.scene.content; } } getRect() ] } } with following stylesheet: .abc { fill: red; } in main.css file (both in test package) display red square on white background, but after clicking the main rectangle black (not red) squares are added to scene. I noticed that: Components added dynamically look just like style information was not applied. If you set their style in JavaFX code then everything works fine. After changing stylesheets property (so that it points to another valid stylesheet) the objects already added render properly. Does anyone know the solution to this problem? I could of course put all the properties into JavaFX code or provide another stylesheet (for every existing stylesheed) that would contain the same data and change stylesheet right after adding any component, but I would like to find some elegant solution. Thanks in advance.

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

  - by CJM

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

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• Best way to databind a Winforms control to a nullable type?

  - by Steve Hiner

  I'm currently using winforms databinding to wire up a data editing form. I'm using the netTiers framework through CodeSmith to generate my data objects. For database fields that allow nulls it creates nullable types. I've found that using winforms databinding the controls won't bind properly to nullable types. I've seen solutions online suggesting that people create new textbox classes that can handle the nullable types but that could be a pain having to swap out the textboxes on the forms I've already created. Initially I thought it would be great to use an extension method to do it. Basically creating an extension property for the textbox class and bind to that. From my limited extension method experience and doing a bit of checking online it looks like you can't do an extension property. As far as I can tell, binding has to be through a property since it needs to be able to get or set the value so an extension method wouldn't work. I'd love to find a clean way to retrofit these forms using something like extension methods but if I have to create new textbox and combo box controls that's what I'll do. My project is currently limited to .Net 2.0 due to the requirement to run on Windows 2000. Any suggestions?

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• Django: Save data from form in DB

  - by Anry

  I have a model: class Cost(models.Model): project = models.ForeignKey(Project) cost = models.FloatField() date = models.DateField() For the model I created a class form: class CostForm(ModelForm): class Meta: model = Cost fields = ['date', 'cost'] view.py: def cost(request, offset): if request.method == 'POST': #HOW save data in DB? return HttpResponseRedirect('/') else: form = CostForm() In the template file determined: <form action="/cost/{{ project }}/" method="post" accept-charset="utf-8"> <label for="date">Date:</label><input type="text" name="date" value={{ current_date }} id="date" /> <label for="cost">Cost:</label><input type="text" name="cost" value="0" id="cost" /> <p><input type="submit" value="Add"></p> </form> How save data from form in DB? P.S. offset = project name Model: class Project(models.Model): title = models.CharField(max_length=150) url = models.URLField() manager = models.ForeignKey(User) timestamp = models.DateTimeField() I tried to write: def cost(request, offset): if request.method == 'POST': form = CostForm(request.POST) if form.is_valid(): instance = form.save(commit=False) instance.project = Project.objects.filter(title=offset) instance.date = request.date instance.cost = request.cost instance.save() return HttpResponseRedirect('/') else: form = CostForm() But it does not work :(

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• Passing data between ViewControllers versus doing local Fetch in each VC

  - by Tofrizer

  Hi All, I'm developing an iPhone app using Core Data and I'm looking for some general advice and recommendations on whether its acceptable to pass data between ViewControllers versus doing a local fetch in each ViewController as you navigate to it. Ordinarily I would say it all depends on various factors (e.g. performance etc) but the passing data approach is so prevalent in my app and I'm spooked by all the stories about Apple rejecting apps because of not conforming to their standard guidelines. So let me put another way -- is it non-standard to pass data between VC's? The reason I pass data so much is because each ViewController is just another view on to data present in my object model / graph. Once I have a handle on my first object in the first view controller (which I of course do have to fetch), I can use the existing object composition / relationships to drill down into the next level of detail into data and so I just pass these objects to the next VC. Separately, one possible downside with this passing-data-to-each-VC approach is I don't benefit from (what I perceive to be) the optimisation/benefits that NSFetchedResultsController provides in terms of efficient memory usage and section handling. My app is read-only but I do have one table with 5000 rows and I'm curious if I am missing out on NSFetchedResultsController benefits. Any thoughts on this as well? Can I somehow still benefit from NSFetchedResultsController goodness without having to do a full fetch (as I would have already passed in the data from my previous VC)? Thanks a lot.

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