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  • Comparing objects and inheritance

    - by ereOn
    Hi, In my program I have the following class hierarchy: class Base // Base is an abstract class { }; class A : public Base { }; class B : public Base { }; I would like to do the following: foo(const Base& one, const Base& two) { if (one == two) { // Do something } else { // Do something else } } I have issues regarding the operator==() here. Of course comparing an instance A and an instance of B makes no sense but comparing two instances of Base should be possible. (You can't compare a Dog and a Cat however you can compare two Animals) I would like the following results: A == B = false A == A = true or false, depending on the effective value of the two instances B == B = true or false, depending on the effective value of the two instances My question is: is this a good design/idea ? Is this even possible ? What functions should I write/overload ? My apologies if the question is obviously stupid or easy, I have some serious fever right now and my thinking abilities are somewhat limited :/ Thank you.

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  • Django/jquery: Address forms - dyamically adding state drop down list if country is United States?

    - by User
    I have a django html form for address information. There is standard street, city, state/province, postal code, country fields. The country field is a drop down list. How can I make the state/province field a drop down list if the selected country is united states and a free form text box if the country is anything else? I'd prefer not to have to do a round trip to the server so probably through jquery?

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  • How to stop an event for raising

    - by Akshay
    Hi, I have Two fields, one textbox nad one Div element. I have onblur event for textbox, and onclick event for div element. when i click the div element the textbox's onblur event occurs and not the onclick event of div element. how to supress the onblur event when i click on the div element Thanks in advance

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  • CodeModel help needed for right-hand singleton.getinstance() assignment.

    - by antarti
    I've been able to generate 99% of what I need with the CodeModel API, but I am stumped here... Using the various "directXX" methods does not add import statements to the generated code, and I can work without the "directXXX" type of methods except for one place in a generated class. Suppose I desire a generated method like: /** * Copies data from this Value-Obj instance, to the returned PERSON instance. * * @return PERSON * */ public PERSON mapVOToPERSON() throws MappingException { Mapper mapper = (com.blah.util.MapperSingleton.getMapperInstance()); return mapper.map(this, PERSON.class); } You can see the right hand of the Mapper assignment in parens. Emitting the entire package+class was the only way I could find to just declare "SomeSingleton.someMethod()" on the right hand side and have the generated code compile. Without the MapperSingleton being added to the object model, there is no import generated... Questions: 1) Is there a way to force an import to be generated? 2) How to declare an expression that gives me the right side of the Mapper assignment within the object model (so that an import of MapperSingleton gets generated. Any help appreciated...

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  • Handling very large lists of objects without paging?

    - by user246114
    Hi, I have a class which can contain many small elements in a list. Looks like: public class Farm { private ArrayList<Horse> mHorses; } just wondering what will happen if the mHorses array grew to something crazy like 15,000 elements. I'm assuming that trying to write and read this from the datastore would be crazy, because I'd get killed on the serialization process. It's important that I can get the entire array in one shot without paging, and each Horse element may only have two string properties in it, so they are pretty lightweight: public class Horse { private String mId; private String mName; } I don't need these horses indexed at all. Does it sound reasonable to just store the mHorse array as a raw Text field, and force my clients to do the deserialization? Something like: public class Farm { private Text mHorsesSerialized; } then whenever the client receives a Farm instance, it has to take the raw string of horses, and split it in order to reinstantiate the list, something like: // GWT client perhaps Farm farm = rpcCall.getMyFarm(); String horsesSerialized = farm.getHorses(); String[] horseBlocks = horsesSerialized.split(","); for (int i = 0; i < horseBlocks.length; i++) { // .. continue deserializing the individual objects ... } yeah... so hopefully it would be quick to read a Farm instance from the datastore, and the serialization penalty is paid by the client, Thanks

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  • dynamic inheritance without touching classes

    - by Jasper
    I feel like the answer to this question is really simple, but I really am having trouble finding it. So here goes: Suppose you have the following classes: class Base; class Child : public Base; class Displayer { public: Displayer(Base* element); Displayer(Child* element); } Additionally, I have a Base* object which might point to either an instance of the class Base or an instance of the class Child. Now I want to create a Displayer based on the element pointed to by object, however, I want to pick the right version of the constructor. As I currently have it, this would accomplish just that (I am being a bit fuzzy with my C++ here, but I think this the clearest way) object->createDisplayer(); virtual void Base::createDisplayer() { new Displayer(this); } virtual void Child::createDisplayer() { new Displayer(this); } This works, however, there is a problem with this: Base and Child are part of the application system, while Displayer is part of the GUI system. I want to build the GUI system independently of the Application system, so that it is easy to replace the GUI. This means that Base and Child should not know about Displayer. However, I do not know how I can achieve this without letting the Application classes know about the GUI. Am I missing something very obvious or am I trying something that is not possible?

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  • How to switch from VARCHAR to TEXT in SQL 2000?

    - by MatthewMartin
    What do I need to consider before I switch a bunch of fields from VARCHAR(bignumber) to TEXT? Aside from performance, and sometime in the far future TEXT will be deprecated, and aside from the fact that it looks like I need to drop and recreate the table to alter the column's data type? This is for SQL 2000-- I can't do VARCHAR(max) and VARCHAR(8000) isn't large enough.

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  • SQLAlchemy: an efficient/better select by primary keys?

    - by hadrien
    Yet another newbie question.. Let's say I have an user table in declarative mode: class User(Base): __tablename__ = 'user' id = Column(u'id', Integer(), primary_key=True) name = Column(u'name', String(50)) When I have a list of users identifiers, I fetch them from db with: user_ids = [1, 2, 3, 4, 5] users = Session.query(User).filter(User.id.in_(user_ids)).all() I dislike using in_ because I think I learned it has bad performance on indexed fields (is that true/false?). Anyway, is there a better way doing that query? Thanks!

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  • IE7 and IE8: Float clearing without adding empty elements

    - by tk-421
    Hello, I'm having a problem similar to the one described here (without a resolution): http://stackoverflow.com/questions/2467745/ie7-float-and-clear-on-the-same-element The following HTML renders as intended in Firefox but not in (both) IE7 and IE8: <html> <head> <style> ul { list-style-type: none; } li { clear: both; padding: 5px; } .left { clear: left; float: left; } .middle { clear: none; float: left; } .right { clear: right; float: left; } </style> </head> <body> <ul> <li>1</li> <li class="left">2</li> <li class="right">3</li> <li class="left">4</li> <li class="middle">5</li> <li class="right">6</li> <li>7</li> </ul> </body> </html> This is a form layout, and in Firefox the results appear like: 1 2 3 4 5 6 7 That's what I'm going for. In IE7 and IE8 however, the results are: 1 2 3 5 6 4 7 [Note: I don't want to float anything to the right because I want the fields on my form to left-align correctly, without a giant space in-between the floated fields to account for the parent container's width.] Apparently I need a full clear, and can probably add an empty list-item element to the list to force clearing, but that seems like a dumb solution and sort of defeats the purpose. Any ideas? I've spent a few hours reading and trying different options without success.

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  • Saving a Django form to a csv file

    - by Oli
    I have a Django form that is working fine. I'd like to save the data it submits to a CSV file. Is there a "best practice" way to do this? I need to include blank fields in the CSV file where the user has not filled in a "required=False" field

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  • Changing pointer of self

    - by rob5408
    I have an object that I alloc/init like normal just to get a instance. Later in my application I want to load state from disk for that object. I figure I could unarchive my class (which conforms to NSCoding) and just swap where my instance points to. To this end I use this code... NSString* pathForDataFile = [self pathForDataFile]; if([[NSFileManager defaultManager] fileExistsAtPath:pathForDataFile] == YES) { NSLog(@"Save file exists"); NSData *data = [[NSMutableData alloc] initWithContentsOfFile:pathForDataFile]; NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data]; [data release]; Person *tempPerson = [unarchiver decodeObjectForKey:@"Person"]; [unarchiver finishDecoding]; [unarchiver release]; if (tempPerson) { [self release]; self = [tempPerson retain]; } } Now when I sprinkled some NSLogs throughout my application I noticed self.person: <Person: 0x3d01a10> (After I create the object with alloc/init) self: <Person: 0x3d01a10> (At the start of this method) tempPerson: <Person: 0x3b1b880> (When I create the tempPerson) self: <Person: 0x3b1b880> (after i point self to the location of the tempPerson) self.person: <Person: 0x3d01a10> (After the method back in the main program) What am I missing?

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  • Is this a problem typically solved with IOC?

    - by Dirk
    My current application allows users to define custom web forms through a set of admin screens. it's essentially an EAV type application. As such, I can't hard code HTML or ASP.NET markup to render a given page. Instead, the UI requests an instance of a Form object from the service layer, which in turn constructs one using a several RDMBS tables. Form contains the kind of classes you would expect to see in such a context: Form= IEnumerable<FormSections>=IEnumerable<FormFields> Here's what the service layer looks like: public class MyFormService: IFormService{ public Form OpenForm(int formId){ //construct and return a concrete implementation of Form } } Everything works splendidly (for a while). The UI is none the wiser about what sections/fields exist in a given form: It happily renders the Form object it receives into a functional ASP.NET page. A few weeks later, I get a new requirement from the business: When viewing a non-editable (i.e. read-only) versions of a form, certain field values should be merged together and other contrived/calculated fields should are added. No problem I say. Simply amend my service class so that its methods are more explicit: public class MyFormService: IFormService{ public Form OpenFormForEditing(int formId){ //construct and return a concrete implementation of Form } public Form OpenFormForViewing(int formId){ //construct and a concrete implementation of Form //apply additional transformations to the form } } Again everything works great and balance has been restored to the force. The UI continues to be agnostic as to what is in the Form, and our separation of concerns is achieved. Only a few short weeks later, however, the business puts out a new requirement: in certain scenarios, we should apply only some of the form transformations I referenced above. At this point, it feels like the "explicit method" approach has reached a dead end, unless I want to end up with an explosion of methods (OpenFormViewingScenario1, OpenFormViewingScenario2, etc). Instead, I introduce another level of indirection: public interface IFormViewCreator{ void CreateView(Form form); } public class MyFormService: IFormService{ public Form OpenFormForEditing(int formId){ //construct and return a concrete implementation of Form } public Form OpenFormForViewing(int formId, IFormViewCreator formViewCreator){ //construct a concrete implementation of Form //apply transformations to the dynamic field list return formViewCreator.CreateView(form); } } On the surface, this seems like acceptable approach and yet there is a certain smell. Namely, the UI, which had been living in ignorant bliss about the implementation details of OpenFormForViewing, must possess knowledge of and create an instance of IFormViewCreator. My questions are twofold: Is there a better way to achieve the composability I'm after? (perhaps by using an IoC container or a home rolled factory to create the concrete IFormViewCreator)? Did I fundamentally screw up the abstraction here?

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  • Django admin - remove field if editing an object

    - by John McCollum
    I have a model which is accessible through the Django admin area, something like the following: # model class Foo(models.Model): field_a = models.CharField(max_length=100) field_b = models.CharField(max_length=100) # admin.py class FooAdmin(admin.ModelAdmin): pass Let's say that I want to show field_a and field_b if the user is adding an object, but only field_a if the user is editing an object. Is there a simple way to do this, perhaps using the fields attribute? If if comes to it, I could hack a JavaScript solution, but it doesn't feel right to do that at all!

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  • Android: ListAdapter populating image (icon) source

    - by user117701
    I'm populating a list from the DB, and i have a image field in the DB which contains a URL to a image file. ListAdapter adapter=new SimpleCursorAdapter(this, R.layout.row, constantsCursor, new String[] {"title", "subtitle", "image"}, new int[] {R.id.value, R.id.title, R.id.icon}); However, the other fields are populated, but the image remains empty. Why?

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  • open a text file only if not opened alread (open in NotePad)

    - by Mr_Green
    In my project, I am trying to open a text file. Well the below code works but when the user click the button again and again, many files are being opened. (which I dont want) System.Diagnostics.Process.Start(filePath); I also tried Link , File.Open and File.OpenText which are not opening the text file and also not showing any error (tried with try catch block) File.Open(filePath); (or) File.OpenText(filePath); (or) FileStream fileStream = new FileStream(filePath, FileMode.Open); I also tried this: (ERROR : Cannot be accessed with instance reference qualify with a type name instead) System.Diagnostics.Process proc = new System.Diagnostics.Process(); proc.Start(filePath); /*red scribbles here*/ proc.WaitForExit(); How to show only one instance of the Text file(.txt). am I doing something wrong in my attempts? please suggest. EDIT: I want to open other text files afterwards but not the same and also the application should be accessible after opening a text file(or many). I have only one form.

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  • PHP ORM's, multiple tables and efficiency

    - by sunwukung
    Let's say I have a data mapper function that aggregates multiple tables and generates an object instance from that data. The mapper has a typical save() method which delegates to update/insert. When the mapper executes save - ideally it isolates object fields that have been modified, thus preventing the code from blanket bombing the database. How would you go about this?

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  • Same random numbers from instantiated class

    - by user1797202
    I'm learning C# and created a class within my program that holds a random number generator: class RandomNumberGenerator { Random RNG = new Random(); // A bunch of methods that use random numbers are in here } Inside this class are a few methods that use the RNG. Data gets sent here from other parts of the program, gets processed, then gets returned. One of the methods does the following: // Method works something like this int Value1 = RNG.Next(x, y); int Value2 = RNG.Next(x, y); int Value3 = RNG.Next(x, y); The x, y values are to be sent here from another class. So, I have to create an instance of the RandomNumberGenerator within that class so I can call its methods and pass the x and y values to it. class DoStuff { RandomNumberGenerator Randomizer = new RandomNumberGenerator // Here I call a bunch of Randomizer methods that give me values I need } The problem in the above method is that I get the same numbers every time for all three values. I'm not sure if it's because they're so close together and Randomizer's seed value hasn't had time to change or if I'm doing something wrong when I create a new instance of the RandomNumberGenerator class. I've gone through a bunch of answers on here already and typically problems like this are due to people creating many new Random objects when they run methods (thus setting the seed for all of them to the same value), but the only new Random object I create is within the RandomNumberGenerator class. I then instantiate that once within the other class so I can pass it data and use its methods. Why is this happening and how would I fix this?

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  • Unsure how to modify userDetailsService to allow for custom userDetails but keep datasource

    - by adam2510
    what i am trying to do is i'm following this http://www.theserverside.com/tip/-Spring-Security-Customizing-Your-User-and-Authorization-in website to attempt to customise the UserDetails so i can retrieve more fields regarding to the user... as far as implementing the UserDetails, where i am confused is the UserDetailsService at the moment i only have the code for the userDetailsService that is in the website linked above i'm just not sure on how to go about doing it

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  • Rails HTML editor to create forms

    - by Ignace
    Hey all, I'm looking for a HTML editor which can be (easiliy) integrated in a RoR app that has the possibility to create forms. Not forms per se, but I need the possibility to add radiobuttons, input fields, checkboxes and so on. I loved the smoothness of TinyMCE, but apparently this doesn't take me far enough. Does there exists such a gem/plugin? Thanks!

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  • Why would one want to use the public constructors on Boolean and similar immutable classes?

    - by Robert J. Walker
    (For the purposes of this question, let us assume that one is intentionally not using auto(un)boxing, either because one is writing pre-Java 1.5 code, or because one feels that autounboxing makes it too easy to create NullPointerExceptions.) Take Boolean, for example. The documentation for the Boolean(boolean) constructor says: Note: It is rarely appropriate to use this constructor. Unless a new instance is required, the static factory valueOf(boolean) is generally a better choice. It is likely to yield significantly better space and time performance. My question is, why would you ever want to get a new instance in the first place? It seems like things would be simpler if constructors like that were private. For example, if they were, you could write this with no danger (even if myBoolean were null): if (myBoolean == Boolean.TRUE) It'd be safe because all true Booleans would be references to Boolean.TRUE and all false Booleans would be references to Boolean.FALSE. But because the constructors are public, someone may have used them, which means that you have to write this instead: if (Boolean.TRUE.equals(myBoolean)) But where it really gets bad is when you want to check two Booleans for equality. Something like this: if (myBooleanA == myBooleanB) ...becomes this: if ( (myBooleanA == null && myBooleanB == null) || (myBooleanA == null && myBooleanA.equals(myBooleanB)) ) I can't think of any reason to have separate instances of these objects which is more compelling than not having to do the nonsense above. What say you?

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