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• C++ visitor pattern handling templated string types?

  - by Steve the Plant

  I'm trying to use the visitor pattern to serialize the contents of objects. However one snag I'm hitting is when I'm visiting strings. My strings are of a templated type, similar to STL's basic_string. So something like: basic_string<char_type, memory_allocator, other_possible_stuff> \\ many variations possible! Since I can have very many different templated string types, I can't go and add them to my visitor interface. It would be ridiculous. But I can't add templates to my VisitString method because C++ prevents using templates parameters in virtual methods. So what are my options to work around this?

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• Python: User-Defined Exception That Proves The Rule

  - by bandana

  Python documentations states: Exceptions should typically be derived from the Exception class, either directly or indirectly. the word 'typically' leaves me in an ambiguous state. consider the code: class good(Exception): pass class bad(object): pass Heaven = good() Hell = bad() >>> raise Heaven Traceback (most recent call last): File "<pyshell#163>", line 1, in <module> raise Heaven good >>> raise Hell Traceback (most recent call last): File "<pyshell#171>", line 1, in <module> raise Hell TypeError: exceptions must be classes or instances, not bad so when reading the python docs, should i change 'typically' with ''? what if i have a class hierarchy that has nothing to do with the Exception class, and i want to 'raise' objects belonging to the hierarchy? i can always raise an exception with an argument: raise Exception, Hell This seems slightly awkward to me What's so special about the Exception class, that only its family members can be raised?

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• Database Modelling - Conceptually different entities with near identical fields

  - by Andrew Shepherd

  Suppose you have two sets of conceptual entities: MarketPriceDataSet which has multiple ForwardPriceEntries PoolPriceForecastDataSet which has multiple PoolPriceForecastEntry Both different child objects have near identical fields: ForwardPriceEntry has StartDate EndDate SimulationItemId ForwardPrice MarketPriceDataSetId (foreign key to parent table) PoolPriceForecastEntry has StartDate EndDate SimulationItemId ForecastPoolPrice PoolPriceForecastDataSetId (foreign key to parent table) If I modelled them as separate tables, the only difference would be the foreign key, and the name of the price field. There has been a debate as to whether the two near identical tables should be merged into one. Options I've thought of to model this is: Just keep them as two independent, separate tables Have both sets in the one table with an additional "type" field, and a parent_id equalling a foreign key to either parent table. This would sacrifice referential integrity checks. Have both sets in the one table with an additional "type" field, and create a complicated sequence of joining tables to maintain referential integrity. What do you think I should do, and why?

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• django getting current user id

  - by dana

  hello, i have a mini app where users can login, view their profile, and follow each other. 'Follow' is a relation like a regular 'friend' relationship in virtual communities, but it is not necessarily reciprocal, meaning that one can follow a user, without the need that the user to be following back that person who follows him. my problem is: if i am a logged in user, and i navigate to a profile X, and push the button follow, how can i take the current profile id ?(current profile meaning the profile that I, the logged in user, am viewing right now.) the view: def follow(request): if request.method == 'POST': form = FollowForm(request.POST) if form.is_valid(): new_obj = form.save(commit=False) new_obj.initiated_by = request.user u = User.objects. what here? new_obj.follow = u new_obj.save() return HttpResponseRedirect('.') else: form = FollowForm() return render_to_response('followme/follow.html', { 'form': form, }, context_instance=RequestContext(request)) thanks in advance!

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• How to store a function in a member of class? (Using function as callback)

  - by Dane

  I want to store a function as a class member and call it inside the class? Pretty much like a callback function. My class draw a document but every document must drawn differently. So I want to assign a function (written outside of the class) into one of the members of the class and then call it when I want to draw the document. This function mostly is responsible for transforming objects according to each specific document. Here is my class: class CDocument { public: CDocument(); ~CDocument(); void *TransFunc(); } void Transform() { } int main() CDocument* Doc = new CDocument(); Doc->TransFunc = Transform(); } I know that this is probably simple question, but I couldn't find the answer by googling or searching SO.

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• Adding Colours (Colors) Together like Paint (Blue + Yellow = Green, etc)

  - by glenstorey

  I'm making an iOS game using cocos2d libraries. Lets say you have two objects that have two separate colours - defined in RGB as Blue: 0,0,255 Yellow: 255,255,0 I want to add blue and yellow to make green. To over complicate things, let's say that the Blue object is bigger than the Yellow object (for the sake of argument let's say that the ratio is 2:1), I'm adding twice as much blue as yellow - how to I calculate this new (light green) colour correctly. I understand LAB * Color Space is useful for this sort of 'natural colour' kind of thing, but I'm not sure how to use it - especially in the context of a cocos2d object which (AFAIK) is limited to using RGB in its colour schemes. I'd really appreciate practical help on how to implement this. Thanks heaps!

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• How to configure a has_many association with non-ActiveRecord model

  - by Callmeed

  My Rails app has a normal ActiveRecord "Account" model stored in the database. The model will store the URL to a remote XML file which defines some other objects. For example, the Account has_many :galleries but the Gallery model is simply defined by nodes in the XML document. So how do I get /accounts/1/galleries to show the galleries from that account's XML? How do I setup this relationship? I know how to do basic non-AR models, but I'm not sure how to define the association or if I need to create a Gallery model at all.

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• VS 2010 Entity Repository Error Class member EntityBase.id is unmapped.

  - by Steve

  In my project I have it set up so that all the tables in the DB has the property "id" and then I have the entity objects inherit from the EntityBase class using a repository pattern. I then set the inheritance modifier for "id" property in the dbml file o/r designer to "overrides" Public MustInherit Class EntityBase MustOverride Property id() As Integer End Class Public MustInherit Class RepositoryBase(Of T As EntityBase) Protected _Db As New DataClasses1DataContext Public Function GetById(ByVal Id As Integer) As T Return (From a In _Db.GetTable(Of T)() Where a.id = Id).SingleOrDefault End Function End Class Partial Public Class Entity1 Inherits EntityBase End Class Public Class TestRepository Inherits RepositoryBase(Of Entity1) End Class the line Return (From a In _Db.GetTable(Of T)() Where a.id = Id).SingleOrDefault however produces the error "Class member EntityBase.id is unmapped" when i use VS 2010 using the 4.0 framework but I never received that error with the old one. Any help would be greatly appreciated. Thanks in advance.

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• does a switch idiom make sense in this case?

  - by the ungoverned

  I'm writing a parser/handler for a network protocol; the protocol is predefined and I am writing an adapter, in python. In the process of decoding the incoming messages, I've been considering using the idiom I've seen suggested elsewhere for "switch" in python: use a hash table whose keys are the field you want to match on (a string in this case) and whose values are callable expressions: self.switchTab = { 'N': self.handleN, 'M': self.handleM, ... } Where self.handleN, etc., are methods on the current class. The actual switch looks like this: self.switchTab[selector]() According to some profiling I've done with cProfile (and Python 2.5.2) this is actually a little bit faster than a chain of if..elif... statements. My question is, do folks think this is a reasonable choice? I can't imagine that re-framing this in terms of objects and polymorphism would be as fast, and I think the code looks reasonably clear to a reader.

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• Linq to SQL Azure generating Error "Specified cast is not valid."

  - by Rabbi

  B"H I have an application that has been working for months using Linq to SQL connecting to a SQLExpress. I tried migrating it to SQL Azure. I copied the structure and data using the Sync Framework. I viewed the data in SQL Azure using SSMS 2008 R2 and it seams to be exactly what I have in my Sql Server. However when I try to use Linq to SQL against it I get an error "Specified cast is not valid." I seams to be happening any time I get child records. i.e. whenever I fill (the first time I access) an entity set. It seams to be happening after the data returns and when Linq tries to put it into the objects. Remember, the application is working perfectly against sqlexpress, even when accessed across the internet or vpn.

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• JAVA: 500 Worker Threads, what kind of thread pool?

  - by Submerged

  I am wondering if this is the best way to do this. I have about 500 threads that run indefinitely, but Thread.sleep for a minute when done one cycle of processing. ExecutorService es = Executors.newFixedThreadPool(list.size()+1); for (int i = 0; i < list.size(); i++) { es.execute(coreAppVector.elementAt(i)); //coreAppVector is a vector of extends thread objects } I do need a separate threads for each running task, so changing the architecture isn't an option. I tried making my threadPool size equal to Runtime.getRuntime().availableProcessors() which attempted to run all 500 threads, but only let 8 (4xhyperthreading) of them execute. The other threads wouldn't surrender and let other threads have their turn. I tried putting in a wait() and notify(), but still no luck. If anyone has a simple example or some tips, I would be grateful!

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• Custom keys for Google App Engine models (Python)

  - by Cameron

  First off, I'm relatively new to Google App Engine, so I'm probably doing something silly. Say I've got a model Foo: class Foo(db.Model): name = db.StringProperty() I want to use name as a unique key for every Foo object. How is this done? When I want to get a specific Foo object, I currently query the datastore for all Foo objects with the target unique name, but queries are slow (plus it's a pain to ensure that name is unique when each new Foo is created). There's got to be a better way to do this! Thanks.

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• ClassNotFoundException when transfer data between service and activity

  - by androider

  Hello again, I am writing an application which is composed of an underlying service and a GUI controller. The service collects data and sends to the controller, I used Messenger and put an array of parcelable objects into the bundle of the message. But when it is received at the controller side, error occurs: android.os.BadParcelableException: ClassNotFoundException in unmarshalling MyData ... I am sure that MyData implements correctly Parcelable interface. It seems I have to do something with ClassLoader? or what else? Please help me. Thank you very much!

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• how to set Custom attribute of NSManagedObject which is calculated from other attributes ?

  - by Kundan

  I am using core data framework to manage objects.i have an entity which has several attributes of decimal types. Among them is attribute which is mathematically calculated from other attributes. Ex :- @interface Marks : NSManagedObject { } @property (nonatomic, retain) NSDecimalNumber * answerGradeA; @property (nonatomic, retain) NSDecimalNumber * answerGradeB; @property (nonatomic, retain) NSDecimalNumber * answerGradeC; @property (nonatomic, retain) NSDecimalNumber * total; Here i want attribute total = 3xanswerGradeA + 2xanswerGradeB + 1xanswerGradeC if it is possible to do like this, then how ? please reply. Thanks in advance.

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• GridView items are displaying the wrong drawables sometimes.

  - by originalbryan

  I've implemented a GridView based on this tutorial. It works great unless open up the search dialog or rotate the screen then scroll around. When the search dialog and virtual keyboard appear, the drawables for each of my grid items shift. I can click on them and they do what I expect, except the drawable is wrong. The same problem happens when I go into landscape mode and scroll around. If I scroll down, up, the down again, the drawables are shuffled. For better illustration, let's say I have three objects, each with an image. Obj A shows an Apple Obj B shows a Banana Obj C shows a Cantaloupe When the shift occurs I end up with: Obj A shows an Cantaloupe Obj B shows a Banana Obj C shows a Apple The problem isn't consistent between the two causes (search dialog and screen rotate n' scroll), but each cause itself is consistent. Scrolling around repeatedly reveals a pattern as does the search dialog appearing. How can I stop this from happening?

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• MVC without ORM is not real MVC?

  - by ajsie

  at the moment im integrating ORM (doctrine) into a MVC framework (codeigniter). then it hit me that this was the obvious way of setting up a MVC: the controller calls the models that are representing database tables. look at this picture: MVC + ORM then i wondered, how can a MVC without ORM be real MVC? cause then the models are not real objects, rather aggregations of different functions that perform CRUD, then returning the result to the controller. and there is no need for a state (object properties) i guess so the functions would be all static? correct me if im wrong on this one. i guess a lot of people are using models without ORM. please share your thoughts. how do your models look like?

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• Element point map for html5 canvas element, need algorithm

  - by Artiom Chilaru

  I'm currently working on a pure html 5 canvas implementation of the "flying tag cloud sphere", which many of you have undoubtedly seen as a flash object in some pages. The tags are drawn fine, and the performance is satisfactory, but there's one thing in the canvas element that's kind of breaking this idea: you can't identify the objects that you've drawn on a canvas, as it's just a simple flat "image".. What I have to do in this case is catch the click event, and try to "guess" which element was clicked. So I have to have some kind of matrix, which stores a link to a tag object for each pixel on the canvas, AND I have to update this matrix on every redraw. Now this sounds incredibly inefficient, and before I even start trying to implement this, I want to ask the community - is there some "well known" algorithm that would help me in this case? Or maybe I'm just missing something, and the answer is right behind the corner? :)

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• Sending string from class to Form1

  - by Farstucker

  Although there are some similar questions I’m having difficulties finding an answer on how to receive data in my form from a class. I have been trying to read about instantiation and its actually one of the few things that does make sense to me :) but if I were to instantiate my form, would I not have two form objects? To simplify things, lets say I have a some data in Class1 and I would like to pass a string into a label on Form1. Is it legal to instantiate another form1? When trying to do so it looks like I can then access label1.Text but the label isn’t updating. The only thing I can think of is that the form needs to be redrawn or there is some threading issue that I’m unaware of. Any insight you could provide would be greatly appreciated.

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• KeyError this says that key(partner) is not in dict ?

  - by Ansh Jain

  I am trying to make an chat application using python and django. I almost complete it and its working fine for 8-10 minutes when two persons are chatting after that certain time it shows an error. here is the traceback : - Traceback (most recent call last): File "\Django_chat\django_chat\chat\views.py", line 55, in receive message = chatSession.getMessage(request.session['partner'],request.session['uid'],afterTime) File "C:\Python26\lib\site-packages\django\contrib\sessions\backends\base.py", line 47, in __getitem__ return self._session[key] KeyError: 'partner' here is the receive module :- def receive(request): message received by this user chatSession = chat() data = request.POST afterTime = data['lastMsgTime'] try: message = chatSession.getMessage(request.session['partner'],request.session['uid'],afterTime) except: #partnerId = virtual_users.objects.get(id=request.session['uid']).partner print('there is an error in receive request') traceback.print_exc(file=open("/myapp.log","a")) msg = serializers.serialize("json", message) return HttpResponse(msg) Please Help me :( thanks Ansh J

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• Which external DSLs do you like to use?

  - by Max Toro

  The reason I'm asking is because right now there seems to be tendency to make DSLs internal. One example is LINQ in C# and VB. You can use it against in-memory objects, or you can use it as a replacement of SQL or other external DSL. Another example is HTML5 vs XHTML2. XHTML2 supported decentralized extensibility through namespaces, in other words you embed external DSL code (XForms, SVG, MathML, etc.) in your XHTML code. Sadly HTML5 doesn't seem to have such mechanism, instead new features are internal (e.g. <canvas> instead of SVG). I'd like to know what other developers think about this. Do you like using external DSLs ? Which ones ? If not, why ?

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• Store data in file system rather than SQL or Oracle database.

  - by nunu

  Hi All, As I am working on Employee Management system, I have two table (for example) in database as given below. EmployeeMaster (DB table structure) EmployeeID (PK) | EmployeeName | City MonthMaster (DB table structure) Month | Year | EmployeeID (FK) | PrenentDays | BasicSalary Now my question is, I want to store data in file system rather than storing data in SQL or ORACLE. I want my data in file system storage for Insert, Edit and Delete opration with keeping relation with objects too. I am a C# developer, Could anybody have thoughts or idea on it. (To store data in file system with keeping relations between them) Thanks in advance. Any ideas on it?

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• Pattern for null settings

  - by user21243

  Hi, I would like to hear your thoughts and ideas about this one. in my application i have controls that are binded to objects properties. but.. the controls always looks like that: a check box, label that explain the settings and then the edited control (for ex: text box) when unchecking the checkbox i disable the text box (using binding) when the checkbox is unchecked i want the property to contain null, and when it is checked i would like the property to contain the text box's text. Of course text box can be NumericUpDown, ComboBox, DatePicker etc.. Do you have any smart way of doing it using binding or do i have to do everything on code; I really would like to a build a control that supports that and re-use it all over Ideas? Thanks,

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• ORMs and Constructors

  - by Harper Shelby

  I'm looking over .NET ORM implementations, and I have a major burning question - are there any .NET ORM implemenations that don't require public properties for every field in the database? When I see examples like this, a little bell goes off in my head. I firmly believe in encapsulation, and being forced to open the kimono of my objects just to make them work nicely with persistence frameworks gives me the heebie-jeebies. Is this sort of accessibility required in all ORMs out there? If not, please point me to examples of those that don't need it!

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• How do I build a specialized JQuery Timer

  - by Sayem Ahmed

  I have an asp.net page where two grid views are available showing current stock market price updates. I need to update these two grid views every 20 seconds. So I was thinking of using JQuery to do this job. What I need is a timer which will fire every 20 seconds, send an ajax request to the servers, bring the order lists from the server using json and then update those two grid views. If a request to the server is still being served 20 seconds after it is fired, then I want the old one to be aborted without causing any trouble. I already know how to bring objects using json. I just need to figure out how to send a request every 20 seconds and cancel a request if it is still being server for 20 seconds.

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• iPhone Input with Stacked Views

  - by Forrest

  Hi, I've got a situation in an iphone application where buttons are not receiving input as I expect. Here's the setup: ViewMain - The main view full of various images and labels ViewOverlay - A HUD like overlay view with two UIButton objects. To create my scene I do the following: viewController.view = ViewMain [ViewMain addsubview:ViewOverlay] This view renders as expected, with ViewOverlay correctly rendered ontop of ViewMain. However the two buttons found inside ViewOverlay do not receive touch events and can not be pressed. Tapping them does nothing at all. I very well may be going about this in the entirely wrong direction. Any ideas?

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