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• Dropdown sorting in django-admin

  - by Andrey

  I'd like to know how can I sort values in the Django admin dropdowns. For example, I have a model called Article with a foreign key pointing to the Users model, smth like: class Article(models.Model): title = models.CharField(_('Title'), max_length=200) slug = models.SlugField(_('Slug'), unique_for_date='publish') author = models.ForeignKey(User) body = models.TextField(_('Body')) status = models.IntegerField(_('Status')) categories = models.ManyToManyField(Category, blank=True) publish = models.DateTimeField(_('Publish date')) I edit this model in django admin: class ArticleAdmin(admin.ModelAdmin): list_display = ('title', 'publish', 'status') list_filter = ('publish', 'categories', 'status') search_fields = ('title', 'body') prepopulated_fields = {'slug': ('title',)} admin.site.register(Article, ArticleAdmin) and of course it makes the nice user select dropdown for me, but it's not sorted and it takes a lot of time to find a user by username.

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• Coroutines in Java

  - by JUST MY correct OPINION

  I would like to do some stuff in Java that would be clearer if written using concurrent routines, but for which full-on threads are serious overkill. The answer, of course, is the use of coroutines, but there doesn't appear to be any coroutine support in the standard Java libraries and a quick Google on it brings up tantalising hints here or there, but nothing substantial. Here's what I've found so far: JSIM has a coroutine class, but it looks pretty heavyweight and conflates, seemingly, with threads at points. The point of this is to reduce the complexity of full-on threading, not to add to it. Further I'm not sure that the class can be extracted from the library and used independently. Xalan has a coroutine set class that does coroutine-like stuff, but again it's dubious if this can be meaningfully extracted from the overall library. It also looks like it's implemented as a tightly-controlled form of thread pool, not as actual coroutines. There's a Google Code project which looks like what I'm after, but if anything it looks more heavyweight than using threads would be. I'm basically nervous of something that requires software to dynamically change the JVM bytecode at runtime to do its work. This looks like overkill and like something that will cause more problems than coroutines would solve. Further it looks like it doesn't implement the whole coroutine concept. By my glance-over it gives a yield feature that just returns to the invoker. Proper coroutines allow yields to transfer control to any known coroutine directly. Basically this library, heavyweight and scary as it is, only gives you support for iterators, not fully-general coroutines. The promisingly-named Coroutine for Java fails because it's a platform-specific (obviously using JNI) solution. And that's about all I've found. I know about the native JVM support for coroutines in the Da Vinci Machine and I also know about the JNI continuations trick for doing this. These are not really good solutions for me, however, as I would not necessarily have control over which VM or platform my code would run on. (Indeed any bytecode manipulation system would suffer similar problems -- it would be best were this pure Java if possible. Runtime bytecode manipulation would restrict me from using this on Android, for example.) So does anybody have any pointers? Is this even possible? If not, will it be possible in Java 7?

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• Local variables in java

  - by Mandar

  Hello , I went through local variables and class variables concept. But I had stuck at a doubt " Why is it so that we cannot declare local variables as static " ? For e.g Suppose we have a play( ) function : void play( ) { static int i=5; System.out.println(i); } It gives me error in eclipse : Illegal modifier for parameter i; I had this doubt because of the following concepts I have read : Variables inside method : scope is local i.e within that method. When variable is declared as static , it is present for the entire class i.e not to particular object. Please could anyone help me out to clarify the concept. Thanks.

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• django m2m how can i get m2m table elements in a view

  - by dana

  i have a model using m2m feature: class Classroom(models.Model): user = models.ForeignKey(User, related_name = 'classroom_creator') classname = models.CharField(max_length=140, unique = True) date = models.DateTimeField(auto_now=True) open_class = models.BooleanField(default=True) members = models.ManyToManyField(User,related_name="list of invited members", through = 'Membership') and i want to take all members of one class in a view and display them using the template system. In the view, i'm trying to take all the members from a classroom like that: def inside_classroom(request,classname): try: theclass = Classroom.objects.get(classname = classname) members = Members.objects.all() etc but it doesn't work,(though the db_table is named Classroom_Members) i guess i have to use another query for getting all the members from the classroom classname. also, i want to verify if the request.user is a member using (if request.user in members) how can i het those members? Thanks in advance!

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• Django Initial for a ManyToMany Field

  - by gramware

  I have a form that edits an instance of my model. I would like to use the form to pass all the values as hidden with an inital values of username defaulting to the logged in user so that it becomes a subscribe form. The problem is that the normal initial={'field':value} doesn't seem to work for manytomany fields. how do i go about it? my views.py @login_required def event_view(request,eventID): user = UserProfile.objects.get(pk=request.session['_auth_user_id']) event = events.objects.get(eventID = eventID) if request.method == 'POST': form = eventsSusbcribeForm( request.POST,instance=event) if form.is_valid(): form.save() return HttpResponseRedirect('/events/') else: form = eventsSusbcribeForm(instance=event) return render_to_response('event_view.html', {'user':user,'event':event, 'form':form},context_instance = RequestContext( request )) my forms.py class eventsSusbcribeForm(forms.ModelForm): eventposter = forms.ModelChoiceField(queryset=UserProfile.objects.all(), widget=forms.HiddenInput()) details = forms.CharField(widget=forms.Textarea(attrs={'cols':'50', 'rows':'5'}),label='Enter Event Description here') date = forms.DateField(widget=SelectDateWidget()) class Meta: model = events exclude = ('deleted') def __init__(self, *args, **kwargs): super(eventsSusbcribeForm, self).__init__(*args, **kwargs) self.fields['username'].initial = (user.id for user in UserProfile.objects.filter())

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• is there a way to get a "subtree" from hclust ? (R)

  - by Tal Galili

  Hello all, I wish to create a "subtree" from an hclust object. For example, let's say I have the following object: a <- list() # initialize empty object a$merge <- matrix(c(-1, -2, -3, -4, 1, 2, -5,-6, 3,4), nc=2, byrow=TRUE ) a$height <- c(1, 1.5, 3,4,4.5) # define merge heights a$order <- 1:6 # order of leaves(trivial if hand-entered) a$labels <- 1:6# LETTERS[1:4] # labels of leaves class(a) <- "hclust" # make it an hclust object plot(a) # look at the result Now I wish the extract from it the following subtree: a <- list() # initialize empty object a$merge <- matrix(c(-1, -2, -3, -4, 1, 2 ), nc=2, byrow=TRUE ) a$height <- c(1, 1.5, 3) # define merge heights a$order <- 1:4 # order of leaves(trivial if hand-entered) a$labels <- 1:4# LETTERS[1:4] # labels of leaves class(a) <- "hclust" # make it an hclust object plot(a) # look at the result How could I access it? (I know that cutree could get me the objects of the sub tree, but not create an actual hclust object) Thanks for any help, Tal

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• How does multiple implementing multiple COM interfaces work in C++?

  - by Martin

  I am trying to understand this example code regarding Browser Helper Objects. Inside, the author implements a single class which exposes multiple interfaces (IObjectWithSite, IDispatch). His QueryInterface function performs the following: if(riid == IID_IUnknown) *ppv = static_cast<BHO*>(this); else if(riid == IID_IObjectWithSite) *ppv = static_cast<IObjectWithSite*>(this); else if (riid == IID_IDispatch) *ppv = static_cast<IDispatch*>(this); I have learned that from a C perspective, interface pointers are just pointers to VTables. So I take it to mean that C++ is capable of returning the VTable of any implemented interface using static_cast. Does this mean that a class constructed in this way has a bunch of VTables in memory (IObjectWithSite, IDispatch, etc)? What does C++ do with the name collisions on the different interfaces (they each have a QueryInterface, AddRef and Release function), can I implement different methods for each of these?

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• Are Python properties broken?

  - by jacob

  How can it be that this test case import unittest class PropTest(unittest.TestCase): def test(self): class C(): val = 'initial val' def get_p(self): return self.val def set_p(self, prop): if prop == 'legal val': self.val = prop prop=property(fget=get_p, fset=set_p) c=C() self.assertEqual('initial val', c.prop) c.prop='legal val' self.assertEqual('legal val', c.prop) c.prop='illegal val' self.assertNotEqual('illegal val', c.prop) fails as below? Failure Traceback (most recent call last): File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/unittest.py", line 279, in run testMethod() File "/Users/jacob/aau/admissions_proj/admissions/plain_old_unit_tests.py", line 24, in test self.assertNotEqual('illegal val', c.prop) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/unittest.py", line 358, in failIfEqual (msg or '%r == %r' % (first, second)) AssertionError: 'illegal val' == 'illegal val'

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• c++ queue template

  - by Dalton Conley

  ALright, pardon my messy code please. Below is my queue class. #include <iostream> using namespace std; #ifndef QUEUE #define QUEUE /*---------------------------------------------------------------------------- Student Class # Methods # Student() // default constructor Student(string, int) // constructor display() // out puts a student # Data Members # Name // string name Id // int id ----------------------------------------------------------------------------*/ class Student { public: Student() { } Student(string iname, int iid) { name = iname; id = iid; } void display(ostream &out) const { out << "Student Name: " << name << "\tStudent Id: " << id << "\tAddress: " << this << endl; } private: string name; int id; }; // define a typedef of a pointer to a student. typedef Student * StudentPointer; template <typename T> class Queue { public: /*------------------------------------------------------------------------ Queue Default Constructor Preconditions: none Postconditions: assigns default values for front and back to 0 description: constructs a default empty Queue. ------------------------------------------------------------------------*/ Queue() : myFront(0), myBack(0) {} /*------------------------------------------------------------------------ Copy Constructor Preconditions: requres a reference to a value for which you are copying Postconditions: assigns a copy to the parent Queue. description: Copys a queue and assigns it to the parent Queue. ------------------------------------------------------------------------*/ Queue(const T & q) { myFront = myBack = 0; if(!q.empty()) { // copy the first node myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } /*------------------------------------------------------------------------ Destructor Preconditions: none Postconditions: deallocates the dynamic memory for the Queue description: deletes the memory stored for a Queue. ------------------------------------------------------------------------*/ ~Queue() { NodePointer prev = myFront, ptr; while(prev != NULL) { ptr = prev->next; delete prev; prev = ptr; } } /*------------------------------------------------------------------------ Empty() Preconditions: none Postconditions: returns a boolean value. description: returns true/false based on if the queue is empty or full. ------------------------------------------------------------------------*/ bool empty() const { return (myFront == NULL); } /*------------------------------------------------------------------------ Enqueue Preconditions: requires a constant reference Postconditions: allocates memory and appends a value at the end of a queue description: ------------------------------------------------------------------------*/ void enqueue(const T & value) { NodePointer newNodePtr = new Node(value); if(empty()) { myFront = myBack = newNodePtr; newNodePtr->next = NULL; } else { myBack->next = newNodePtr; myBack = newNodePtr; newNodePtr->next = NULL; } } /*------------------------------------------------------------------------ Display Preconditions: requires a reference of type ostream Postconditions: returns the ostream value (for chaining) description: outputs the contents of a queue. ------------------------------------------------------------------------*/ void display(ostream & out) const { NodePointer ptr; ptr = myFront; while(ptr != NULL) { out << ptr->data << " "; ptr = ptr->next; } out << endl; } /*------------------------------------------------------------------------ Front Preconditions: none Postconditions: returns a value of type T description: returns the first value in the parent Queue. ------------------------------------------------------------------------*/ T front() const { if ( !empty() ) return (myFront->data); else { cerr << "*** Queue is empty -- returning garbage value ***\n"; T * temp = new(T); T garbage = * temp; delete temp; return garbage; } } /*------------------------------------------------------------------------ Dequeue Preconditions: none Postconditions: removes the first value in a queue ------------------------------------------------------------------------*/ void dequeue() { if ( !empty() ) { NodePointer ptr = myFront; myFront = myFront->next; delete ptr; if(myFront == NULL) myBack = NULL; } else { cerr << "*** Queue is empty -- " "can't remove a value ***\n"; exit(1); } } /*------------------------------------------------------------------------ pverloaded = operator Preconditions: requires a constant reference Postconditions: returns a const type T description: this allows assigning of queues to queues ------------------------------------------------------------------------*/ Queue<T> & operator=(const T &q) { // make sure we arent reassigning ourself // e.g. thisQueue = thisQueue. if(this != &q) { this->~Queue(); if(q.empty()) { myFront = myBack = NULL; } else { myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } return *this; } private: class Node { public: T data; Node * next; Node(T value, Node * first = 0) : data(value), next(first) {} }; typedef Node * NodePointer; NodePointer myFront, myBack, queueSize; }; /*------------------------------------------------------------------------ join Preconditions: requires 2 queue values Postconditions: appends queue2 to the end of queue1 description: this function joins 2 queues into 1. ------------------------------------------------------------------------*/ template <typename T> Queue<T> join(Queue<T> q1, Queue<T> q2) { Queue<T> q1Copy(q1), q2Copy(q2); Queue<T> jQueue; while(!q1Copy.empty()) { jQueue.enqueue(q1Copy.front()); q1Copy.dequeue(); } while(!q2Copy.empty()) { jQueue.enqueue(q2Copy.front()); q2Copy.dequeue(); } cout << jQueue << endl; return jQueue; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a Queue of type T Postconditions: returns the ostream (for chaining) description: this function is overloaded for outputing a queue with << ----------------------------------------------------------------------------*/ template <typename T> ostream & operator<<(ostream &out, Queue<T> &s) { s.display(out); return out; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of type Student Postconditions: none description: this function is overloaded for outputing an object of type Student. ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, Student &s) { s.display(out); } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of a pointer to a Student object. Postconditions: none description: this function is overloaded for outputing pointers to Students ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, StudentPointer &s) { s->display(out); } #endif Now I'm having some issues with it. For one, when I add 0 to a queue and then I output the queue like so.. Queue<double> qdub; qdub.enqueue(0); cout << qdub << endl; That works, it will output 0. But for example, if I modify that queue in any way.. like.. assign it to a different queue.. Queue<double> qdub1; Queue<double> qdub2; qdub1.enqueue(0; qdub2 = qdub1; cout << qdub2 << endl; It will give me weird values for 0 like.. 7.86914e-316. Help on this would be much appreciated!

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• .NET interview, code structure and the design

  - by j_lewis

  I have been given the below .NET question in an interview. I don’t know why I got low marks. Unfortunately I did not get a feedback. Question: The file hockey.csv contains the results from the Hockey Premier League. The columns ‘For’ and ‘Against’ contain the total number of goals scored for and against each team in that season (so Alabama scored 79 goals against opponents, and had 36 goals scored against them). Write a program to print the name of the team with the smallest difference in ‘for’ and ‘against’ goals. the structure of the hockey.csv looks like this (it is a valid csv file, but I just copied the values here to get an idea) Team - For - Against Alabama 79 36 Washinton 67 30 Indiana 87 45 Newcastle 74 52 Florida 53 37 New York 46 47 Sunderland 29 51 Lova 41 64 Nevada 33 63 Boston 30 64 Nevada 33 63 Boston 30 64 Solution: class Program { static void Main(string[] args) { string path = @"C:\Users\<valid csv path>"; var resultEvaluator = new ResultEvaluator(string.Format(@"{0}\{1}",path, "hockey.csv")); var team = resultEvaluator.GetTeamSmallestDifferenceForAgainst(); Console.WriteLine( string.Format("Smallest difference in ‘For’ and ‘Against’ goals > TEAM: {0}, GOALS DIF: {1}", team.Name, team.Difference )); Console.ReadLine(); } } public interface IResultEvaluator { Team GetTeamSmallestDifferenceForAgainst(); } public class ResultEvaluator : IResultEvaluator { private static DataTable leagueDataTable; private readonly string filePath; private readonly ICsvExtractor csvExtractor; public ResultEvaluator(string filePath){ this.filePath = filePath; csvExtractor = new CsvExtractor(); } private DataTable LeagueDataTable{ get { if (leagueDataTable == null) { leagueDataTable = csvExtractor.GetDataTable(filePath); } return leagueDataTable; } } public Team GetTeamSmallestDifferenceForAgainst() { var teams = GetTeams(); var lowestTeam = teams.OrderBy(p => p.Difference).First(); return lowestTeam; } private IEnumerable<Team> GetTeams() { IList<Team> list = new List<Team>(); foreach (DataRow row in LeagueDataTable.Rows) { var name = row["Team"].ToString(); var @for = int.Parse(row["For"].ToString()); var against = int.Parse(row["Against"].ToString()); var team = new Team(name, against, @for); list.Add(team); } return list; } } public interface ICsvExtractor { DataTable GetDataTable(string csvFilePath); } public class CsvExtractor : ICsvExtractor { public DataTable GetDataTable(string csvFilePath) { var lines = File.ReadAllLines(csvFilePath); string[] fields; fields = lines[0].Split(new[] { ',' }); int columns = fields.GetLength(0); var dt = new DataTable(); //always assume 1st row is the column name. for (int i = 0; i < columns; i++) { dt.Columns.Add(fields[i].ToLower(), typeof(string)); } DataRow row; for (int i = 1; i < lines.GetLength(0); i++) { fields = lines[i].Split(new char[] { ',' }); row = dt.NewRow(); for (int f = 0; f < columns; f++) row[f] = fields[f]; dt.Rows.Add(row); } return dt; } } public class Team { public Team(string name, int against, int @for) { Name = name; Against = against; For = @for; } public string Name { get; private set; } public int Against { get; private set; } public int For { get; private set; } public int Difference { get { return (For - Against); } } } Output: Smallest difference in for' andagainst' goals TEAM: Boston, GOALS DIF: -34 Can someone please review my code and see anything obviously wrong here? They were only interested in the structure/design of the code and whether the program produces the correct result (i.e lowest difference). Much appreciated. "P.S - Please correct me if the ".net-interview" tag is not the right tag to use"

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• Input not firing in jsp page

  - by GigaPr

  Hi, i have been using the spring mvc frameworks lately for a university project. Could you tell me why this work <FORM METHOD=POST ACTION="SaveName.jsp"> <input type="image" class="floatR marginTMinus10" src="images/delete.png" name="image" value="${rssItem.id}" alt="Delete"/> </FORM> while this not <input type="image" class="floatR marginTMinus10" src="images/delete.png" name="image" value="${rssItem.id}" alt="Delete"/> does it mean a button has to be in a form to work? Can i use a button? if yes how do i handle the event in the controller? thanks

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• JSF inner datatable not respecting rendered condition of outer table.

  - by Marc

  <h:dataTable cellpadding="0" cellspacing="0" styleClass="list_table" id="OuterItems" value="#{valueList.values}" var="item" border="0"> <h:column rendered="#{item.typeA"> <h:dataTable cellpadding="0" cellspacing="0" styleClass="list_table" id="InnerItems" value="#{item.options}" var="option" border="0"> <h:column > <h:outputText value="Option: #{option.displayValue}"/> </h:column> </h:dataTable> </h:column> <h:column rendered="#{item.typeB"> <h:dataTable cellpadding="0" cellspacing="0" styleClass="list_table" id="InnerItems" value="#{item.demands}" var="demand" border="0"> <h:column > <h:outputText value="Demand: #{demand.displayValue}"/> </h:column> </h:dataTable> </h:column> </h:dataTable> public class Item{ ... public boolean isTypeA(){ return this instanceof TypeA; } public boolean isTypeB(){ return this instanceof TypeB; } ... } public class typeA extends Item(){ ... public List getOptions(){ .... } ... } public class typeB extends Item(){ ... public List getDemands(){ ... } .... } I'm having an issue with JSF. I've abstracted the problem out here, and I'm hoping someone can help me understand how what I'm doing fails. I'm looping over a list of Items. These Items are actually instances of the subclasses TypeA and TypeB. For Type A, I want to display the options, for Type B I want to display the demands. When rendering the page for the first time, this works fine. However, when I post back to the page for some action, I get an error: [3/26/10 12:52:32:781 EST] 0000008c SystemErr R javax.faces.FacesException: Error getting property 'options' from bean of type TypeB at com.sun.faces.lifecycle.ApplyRequestValuesPhase.execute(ApplyRequestValuesPhase.java:89) at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java(Compiled Code)) at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:91) at com.ibm.faces.portlet.FacesPortlet.processAction(FacesPortlet.java:193) My grasp on the JSF lifecyle is very rough. At this point, i understand there is an error in the ApplyRequestValues Phases which is very early and so the previous state is restored and nothing changes. What I don't understand is that in order to fufill the condition for rendering "item.typeA" that object has to be an instance of TypeA. But here, it looks like that object passed the condition even though it was an instance of TypeB. It is like it is evaluating the inner dataTable (InnerItems) before evaluating the outer (outerItems). My working assumption is that I just don't understand how/when the rendered attribute is actually evaluated.

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• adding Form Validation Javacript of jquery???

  - by user634599

  How can I add inline Validation to make sure a choice of radio input must be selected <script type="text/javascript"> function choosePage() { if(document.getElementById('weightloss').form1_option1.checked) { window.location.replace( "http://google.com/" ); } if(document.getElementById('weightloss').form1_option2.checked) { window.location.replace( "http://yahoo.com/" ); } } </script> <form id="weightloss"> <input type="radio" id="form1_option1" name="weight-loss" value="5_day" class="plan"> <label for="form1_option1"> 5 Day - All Inclusive Price</label><br> <input type="radio" id="form1_option2" name="weight-loss" value="7_day"> <label for="form1_option2"> 7 Day - All Inclusive Price</label><br> <input type="button" value="Place Order" alt="Submit button" class="orange_btn" onclick="choosePage()"> </form>

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• Link objects as fields in UML diagram

  - by fearofawhackplanet

  I'm trying to generate a diagram for a design document. I've generated a class diagram in VS. At the moment it's just a bunch of unconnected boxes as there isn't any inheritance going on. It feels like it would be more useful if I could show how the objects interact through properties and parameters. As an example, a Boy class has a method Kiss which takes a Girl object. How can I show that Boy and Girl interact by connecting this in the diagram? Is there a notation for this in UML? Or is there another type of diagram that shows this? Can I make VS draw this connection for me somehow? Or is this a silly/useless idea? It just doesn't feel like a proper diagram unless it's got some lines on it somewhere :)

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• Beginner having a problem with classes

  - by David

  I'm working through O'Reilly's "Learning Python" and having a problem with classes. I think I understand the concept, but in practice have stumbled upon this problem. Fron page 88-89: >>> class Worker: def __innit__(self, name, pay): self.name=name self.pay=pay def lastName(self): return self.name.split()[-1] def giveRaise(self, percent): self.pay*=(1.0+percent) Then the book says "Calling the class like a function generates instances of a new type ...etc" and gives this example. bob = Worker('Bob Smith', 50000) This gives me this error: TypeError: this constructor takes no arguments. And then I start muttering profanities. So what am I doing wrong here? Thanks for the help.

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• How can you query for an object using one of its properties' id

  - by James Smith

  I have two entities, say, House and People, where multiple people can live in one house. It's a unidirectional link where each Person has a field for which House they belong to, so the Person table has a column named house_id. I need to be able to return all the Person objects who belong to a certain House, but I only have the id of the house. This can be done like this: House house = houseDAO.findById(houseId); List people = session.createCriteria(Person.class).add(Restrictions.eq("house", house)).list(); But since I don't need the house, that's adding an unnecessary query. I've tried to do: session.createCriteria(Person.class).add(Restrictions.eq("house_id", houseId)).list(); But that doesn't work because house_id is not a property, it's a database column. I could just add an sql restriction, but is there a hibernate way of doing this?

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• When should I open and close a connection to SQL Server

  - by Martin

  I have a simple static class with a few methods in it. Each of those methods open a SqlConnection, query the database and close the connection. This way, I am sure that I always close the connection to the database, but on the other hand, I don't like to always open and close connection. Below is an example of what my methods look like. public static void AddSomething(string something) { using (SqlConnection connection = new SqlConnection("...")) { connection.Open(); // ... connection.Close(); } } Considering that the methods are inside a static class, should I have a static member containing a single SqlConnection? How and when should I drop it? What are the best practices?

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• Unable to create unmanaged object using new keyword in managed C++

  - by chair79

  Hi all, I've created a class with a boost::unordered_map as a member, Linkage.h #ifndef LINKAGE_H #define LINKAGE_H #include <boost/unordered_map.hpp> class Linkage { private: boost::unordered_map<int, int> m_IOMap; public: .... }; Linkage.cpp #include "stdafx.h" ... // methods and in the managed side of C++, I try to create the pointer of the obj: private: System::Void Form1_Load(System::Object^ sender, System::EventArgs^ e) { Linkage* m_pLink = new Linkage(); ..... } However this produces errors: Error 4 error LNK2005: "private: static unsigned int const boost::detail::type_with_alignment_imp<4>::found" (?found@?$type_with_alignment_imp@$03@detail@boost@@$$Q0IB) already defined in Proj_Test.obj Linkage.obj ..... Error 7 fatal error LNK1169: one or more multiply defined symbols found Could anyone explain to me pls? Thanks.

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• Lua: Why changing value on one variable changes value on an other one too?

  - by user474563

  I think that running this code you will get excactly what I mean. I want to register 5 names to a register(people). I loop 5 times and in each loop I have a variable newPerson which is supposed to save all information about a person and then be added to the people register. In this example only the names of the people are being registered for simplicity. The problem is that in the end all people turn to have the same name: "Petra". I playied a bit with this but can't get a reasonable reason for this behaviour. Help appreciated! local people={} local person={ name="Johan", lastName="Seferidis", class="B" } local names={"Markus", "Eva", "Nikol", "Adam", "Petra"} --people to register for i=1, 5 do --register 5 people local newPerson=person local name=names[i] for field=1, 3 do --for each field(name, lastname, class) if field==1 then newPerson["name"]=name end --register name end people[i]=newPerson end print("First person name: " ..people[1]["name"]) print("Second person name: "..people[2]["name"]) print("Third person name: " ..people[3]["name"])

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• user defined Copy ctor, and copy-ctors further down the chain - compiler bug ? programmers brainbug

  - by J.Colmsee

  Hi. i have a little problem, and I am not sure if it's a compiler bug, or stupidity on my side. I have this struct : struct BulletFXData { int time_next_fx_counter; int next_fx_steps; Particle particles[2];//this is the interesting one ParticleManager::ParticleId particle_id[2]; }; The member "Particle particles[2]" has a self-made kind of smart-ptr in it (resource-counted texture-class). this smart-pointer has a default constructor, that initializes to the ptr to 0 (but that is not important) I also have another struct, containing the BulletFXData struct : struct BulletFX { BulletFXData data; BulletFXRenderFunPtr render_fun_ptr; BulletFXUpdateFunPtr update_fun_ptr; BulletFXExplosionFunPtr explode_fun_ptr; BulletFXLifetimeOverFunPtr lifetime_over_fun_ptr; BulletFX( BulletFXData data, BulletFXRenderFunPtr render_fun_ptr, BulletFXUpdateFunPtr update_fun_ptr, BulletFXExplosionFunPtr explode_fun_ptr, BulletFXLifetimeOverFunPtr lifetime_over_fun_ptr) :data(data), render_fun_ptr(render_fun_ptr), update_fun_ptr(update_fun_ptr), explode_fun_ptr(explode_fun_ptr), lifetime_over_fun_ptr(lifetime_over_fun_ptr) { } /* //USER DEFINED copy-ctor. if it's defined things go crazy BulletFX(const BulletFX& rhs) :data(data),//this line of code seems to do a plain memory-copy without calling the right ctors render_fun_ptr(render_fun_ptr), update_fun_ptr(update_fun_ptr), explode_fun_ptr(explode_fun_ptr), lifetime_over_fun_ptr(lifetime_over_fun_ptr) { } */ }; If i use the user-defined copy-ctor my smart-pointer class goes crazy, and it seems that calling the CopyCtor / assignment operator aren't called as they should. So - does this all make sense ? it seems as if my own copy-ctor of struct BulletFX should do exactly what the compiler-generated would, but it seems to forget to call the right constructors down the chain. compiler bug ? me being stupid ? Sorry about the big code, some small example could have illustrated too. but often you guys ask for the real code, so well - here it is :D EDIT : more info : typedef ParticleId unsigned int; Particle has no user defined copyctor, but has a member of type : Particle { .... Resource<Texture> tex_res; ... } Resource is a smart-pointer class, and has all ctor's defined (also asignment operator) and it seems that Resource is copied bitwise. EDIT : henrik solved it... data(data) is stupid of course ! it should of course be rhs.data !!! sorry for huge amount of code, with a very little bug in it !!! (Guess you shouldn't code at 1 in the morning :D )

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• Inheritance classes in Scheme

  - by DreamWalker

  Now I research OOP-part of Scheme. I can define class in Scheme like this: (define (create-queue) (let ((mpty #t) (the-list '())) (define (enque value) (set! the-list (append the-list (list value))) (set! mpty #f) the-list) (define (deque) (set! the-list (cdr the-list)) (if (= (length the-list) 0) (set! mpty #t)) the-list) (define (isEmpty) mpty) (define (ptl) the-list) (define (dispatch method) (cond ((eq? method 'enque) enque) ((eq? method 'deque) deque) ((eq? method 'isEmpty) isEmpty) ((eq? method 'print) ptl))) dispatch)) (Example from css.freetonik.com) Can I implement class inheritance in Scheme?

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• Does std::multiset guarntee insertion order?

  - by Naveen

  I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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• Multiple classes in a Python module

  - by ralphL

  I'm very new to Python (I'm coming from a JAVA background) and I'm wondering if anyone could help me with some of the Python standards. Is it a normal or "proper" practice to put multiple class in a module? I have been working with Django and started with the tutorials and they place their database model classes in the same module. Is this something that is normally done or should I stick with 1 class per module? Is their a reason I would do one over the other? Hope I'm being clear and not to generic. Thanks to everyone in advance!

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• Django says the "id may not be NULL" but why is it?

  - by Oli

  I'm going crazy today. I just tried to insert a new record and it threw back a "post_blogpost.id may not be NULL" error. Here's my model: class BlogPost(models.Model): title = models.CharField(max_length=100) slug = models.SlugField(max_length=100) who = models.ForeignKey(User, default=1) when = models.DateTimeField() intro = models.TextField(blank=True, null=True) content = models.TextField(blank=True, null=True) counter = models.PositiveIntegerField(default=0) published = models.BooleanField(default=False) css = models.TextField(blank=True, null=True) class Meta: ordering = ('-when', 'id') There are a number of functions beneath the model too but I won't include them in full here. Their names are: content_cache_key, clear_cache, __unicode__, reads, read, processed_content. I'm adding through the admin... And I'm running out of hair.

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• C# two classes with static members referring to each other

  - by Jerry

  Hi, I wonder why this code doesn't end up in endless recursion. I guess it's connected to the automatic initialization of static members to default values, but can someone tell me "step by step" how does 'a' get the value of 2 and 'b' of 1? public class A { public static int a = B.b + 1; } public class B { public static int b = A.a + 1; } static void Main(string[] args) { Console.WriteLine("A.a={0}, B.b={1}", A.a, B.b); //A.a=2, B.b=1 Console.Read(); }

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