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  • Rails Model for Playlist that can contain tracks and albums using polymorphism

    - by philk
    I struggle to find a model how to store a playlist with different type of items on it in Rails. Consider I have class Track end class Album has_many :tracks end class PlaylistItem belongs_to :playable belongs_to :playlist end class Playable belongs_to :playable, :polymorph => true end class Playlist has_many :playlist_items end I think I can use a polymorphic model "Playable" here since the Playlist can contain Tracks, Albums and maybe in the future also Movies. Also I would like to use STI for Track and Albums since they share some common attributes like title and length but also have totally different attributes. I modeled it like described here but it does not work. Anybody any idea how to model a Playlist that can contain many items of different kind?

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  • Does importing of packages change visibility of classes?

    - by Roman
    I jsut learned that A class may be declared with the modifier public, in which case that class is visible to all classes everywhere. If a class has no modifier (the default, also known as package-private), it is visible only within its own package. This is a clear statement. But this information interfere with my understanding of importing of packages (which easily can be wrong). I thought that importing a package I make classes from the imported package visible to the importing class. So, how does it work? Are public classes visible to all classes everywhere under condition that the package containing the public class is imported? Or there is not such a condition? What about the package-private classes? They are invisible no mater if the containing package was imported or not? ADDED: It seems to me that I got 2 answers which are marked as good (up-voted) and which contradict eachother.

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  • C++: How to use types that have not been defined?

    - by Jen
    C++ requires all types to be defined before they can be used, which makes it important to include header files in the right order. Fine. But what about my situation: Bunny.h: class Bunny { ... private: Reference<Bunny> parent; } The compiler complains, because technically Bunny has not been completely defined at the point where I use it in its own class definition. This is not sufficient: class Bunny; class Bunny { ... private: Reference<Bunny> parent; } Apart from re-writing my template class Reference so it takes a pointer type (in which case I can use the forward declaration of Bunny), I don't know how to solve this. Any suggestions?

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  • Threads slowing down application and not working properly

    - by Belgin
    I'm making a software renderer which does per-polygon rasterization using a floating point digital differential analyzer algorithm. My idea was to create two threads for rasterization and have them work like so: one thread draws each even scanline in a polygon and the other thread draws each odd scanline, and they both start working at the same time, but the main application waits for both of them to finish and then pauses them before continuing with other computations. As this is the first time I'm making a threaded application, I'm not sure if the following method for thread synchronization is correct: First of all, I use two global variables to control the two threads, if a global variable is set to 1, that means the thread can start working, otherwise it must not work. This is checked by the thread running an infinite loop and if it detects that the global variable has changed its value, it does its job and then sets the variable back to 0 again. The main program also uses an empty while to check when both variables become 0 after setting them to 1. Second, each thread is assigned a global structure which contains information about the triangle that is about to be rasterized. The structures are filled in by the main program before setting the global variables to 1. My dilemma is that, while this process works under some conditions, it slows down the program considerably, and also it fails to run properly when compiled for Release in Visual Studio, or when compiled with any sort of -O optimization with gcc (i.e. nothing on screen, even SEGFAULTs). The program isn't much faster by default without threads, which you can see for yourself by commenting out the #define THREADS directive, but if I apply optimizations, it becomes much faster (especially with gcc -Ofast -march=native). N.B. It might not compile with gcc because of fscanf_s calls, but you can replace those with the usual fscanf, if you wish to use gcc. Because there is a lot of code, too much for here or pastebin, I created a git repository where you can view it. My questions are: Why does adding these two threads slow down my application? Why doesn't it work when compiling for Release or with optimizations? Can I speed up the application with threads? If so, how? Thanks in advance.

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  • How to remove hyperlink but keep text for an array of links?

    - by Keith Donegan
    My question is fairly similar to this question: Remove hyperlink but keep text? but, I can't seem to workout how I can feed an array of class names and do this in one go? For Example <a class="unwrap" href="#">Blah</a> <a class="unwrap" href="#">Blah</a> <a href="#">Blah</a> <a class="unwrap" href="#">Blah</a> I would just like the links with the unwrap class to be modified.

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  • PHP Magic methods not working

    - by user991047
    I am trying to create a registry class with magic __set and __get my class looks like class Registry { private $vars = array(); public function __set($key, $value) { $this->vars[$key] = $value; dump($key, $value); } public function __get($index) { $this->vars[$index]; } } but if i try to save some variable in registry class in gets only the $key the $value is alway NULL. here is the sample code how I am try to call this class $registry = new registry; $registry->router = $router; $registry->title = "Welcome ";

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  • Escaping if/else in Jade template

    - by Collin Estes
    So I have a simply block of html in my jade template with a loop: each dude, i in dudes div(class='someClass') div.otherStuff span.someContent #{name} I want to apply a data attribute to my top most div when a certain looping condition is met, in this case the first dude, I set it up like this each dude, i in dudes if i == 0 div(class='someClass, data-someAttr='first dude') else div(class='someClass') div.otherstuff span.someContent Setup like this it causes the div.otherStuff div and the span.someContent to only display on the else condition. I've moved the tab spaces around on those items but I can't get it escape that else and give the div.otherStuff and span.someContent to both the first dude and the subsequent dudes after that. I've also tried setting that data attr to a variable and trying to apply it that way but without any success. What I end up doing to get around it is this: each dude, i in dudes if i == 0 div(class='someClass, data-someAttr='first dude') div.otherstuff span.someContent else div(class='someClass') div.otherstuff span.someContent How do I escape that if/else so I dont have to duplicate the div.otherStuff and span.someContent?

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  • Should the name of my classes begin with 'Q' in Qt?

    - by Venemo
    Hello Everyone, When I first started working with Qt, it was extremely annoying that every class has a name beginning with 'Q', but now I've got used to it. I'm using Qt Creator, and it highlights code quite well. However, it only highlights class names beginning with 'Q'. And it highlights everything beginning with 'Q' even if there is no such type. It doesn't highlight custom class names. That makes me wonder, should I also begin all my class names with 'Q'? Or at least the reusable ones? (I mean, those that I put in a class library, or reuse in another app.) I've seen several places where they named their classes this way. Is it a good thing? I found this page about Qt's naming conventions, but it doesn't deal with this question. Also, I don't understand why Qt doesn't use namespaces.

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  • jQuery slideUp and slideDwon issues

    - by Alex
    I need the classes 'two and three' to be hidden as soon as the page load and than be able to click again on the menu to slide it down, I am having probles with the following code: $(document).ready(function() { $('.two, .three').slideUp('slow'); $('.active_wrapper').click(function(){ $('.two, .three').slideDown('slow'); }); }); HTML <div class="nav_wrapper"> <div class="active_wrapper one"><a class="active" href="">home</a></div> <div class="two"><a href="about.html">about</a></div> <div class="three"><a href="project.html">project</a></div> </div>

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  • jQuery append div to a specific

    - by ip
    Hi How do I append a element a specific index of the children elements using jQuery append e.g. if I have: <div class=".container"> <div class="item"><div> <div class="item"><div> <div class="item"><div> <div class="item"><div> </div> and I want to append another item between the second and third item?

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  • JPA 2.1 Schema Generation (TOTD #187)

    - by arungupta
    This blog explained some of the key features of JPA 2.1 earlier. Since then Schema Generation has been added to JPA 2.1. This Tip Of The Day (TOTD) will provide more details about this new feature in JPA 2.1. Schema Generation refers to generation of database artifacts like tables, indexes, and constraints in a database schema. It may or may not involve generation of a proper database schema depending upon the credentials and authorization of the user. This helps in prototyping of your application where the required artifacts are generated either prior to application deployment or as part of EntityManagerFactory creation. This is also useful in environments that require provisioning database on demand, e.g. in a cloud. This feature will allow your JPA domain object model to be directly generated in a database. The generated schema may need to be tuned for actual production environment. This usecase is supported by allowing the schema generation to occur into DDL scripts which can then be further tuned by a DBA. The following set of properties in persistence.xml or specified during EntityManagerFactory creation controls the behaviour of schema generation. Property Name Purpose Values javax.persistence.schema-generation-action Controls action to be taken by persistence provider "none", "create", "drop-and-create", "drop" javax.persistence.schema-generation-target Controls whehter schema to be created in database, whether DDL scripts are to be created, or both "database", "scripts", "database-and-scripts" javax.persistence.ddl-create-script-target, javax.persistence.ddl-drop-script-target Controls target locations for writing of scripts. Writers are pre-configured for the persistence provider. Need to be specified only if scripts are to be generated. java.io.Writer (e.g. MyWriter.class) or URL strings javax.persistence.ddl-create-script-source, javax.persistence.ddl-drop-script-source Specifies locations from which DDL scripts are to be read. Readers are pre-configured for the persistence provider. java.io.Reader (e.g. MyReader.class) or URL strings javax.persistence.sql-load-script-source Specifies location of SQL bulk load script. java.io.Reader (e.g. MyReader.class) or URL string javax.persistence.schema-generation-connection JDBC connection to be used for schema generation javax.persistence.database-product-name, javax.persistence.database-major-version, javax.persistence.database-minor-version Needed if scripts are to be generated and no connection to target database. Values are those obtained from JDBC DatabaseMetaData. javax.persistence.create-database-schemas Whether Persistence Provider need to create schema in addition to creating database objects such as tables, sequences, constraints, etc. "true", "false" Section 11.2 in the JPA 2.1 specification defines the annotations used for schema generation process. For example, @Table, @Column, @CollectionTable, @JoinTable, @JoinColumn, are used to define the generated schema. Several layers of defaulting may be involved. For example, the table name is defaulted from entity name and entity name (which can be specified explicitly as well) is defaulted from the class name. However annotations may be used to override or customize the values. The following entity class: @Entity public class Employee {    @Id private int id;    private String name;     . . .     @ManyToOne     private Department dept; } is generated in the database with the following attributes: Maps to EMPLOYEE table in default schema "id" field is mapped to ID column as primary key "name" is mapped to NAME column with a default VARCHAR(255). The length of this field can be easily tuned using @Column. @ManyToOne is mapped to DEPT_ID foreign key column. Can be customized using JOIN_COLUMN. In addition to these properties, couple of new annotations are added to JPA 2.1: @Index - An index for the primary key is generated by default in a database. This new annotation will allow to define additional indexes, over a single or multiple columns, for a better performance. This is specified as part of @Table, @SecondaryTable, @CollectionTable, @JoinTable, and @TableGenerator. For example: @Table(indexes = {@Index(columnList="NAME"), @Index(columnList="DEPT_ID DESC")})@Entity public class Employee {    . . .} The generated table will have a default index on the primary key. In addition, two new indexes are defined on the NAME column (default ascending) and the foreign key that maps to the department in descending order. @ForeignKey - It is used to define foreign key constraint or to otherwise override or disable the persistence provider's default foreign key definition. Can be specified as part of JoinColumn(s), MapKeyJoinColumn(s), PrimaryKeyJoinColumn(s). For example: @Entity public class Employee {    @Id private int id;    private String name;    @ManyToOne    @JoinColumn(foreignKey=@ForeignKey(foreignKeyDefinition="FOREIGN KEY (MANAGER_ID) REFERENCES MANAGER"))    private Manager manager;     . . . } In this entity, the employee's manager is mapped by MANAGER_ID column in the MANAGER table. The value of foreignKeyDefinition would be a database specific string. A complete replay of Linda's talk at JavaOne 2012 can be seen here (click on CON4212_mp4_4212_001 in Media). These features will be available in GlassFish 4 promoted builds in the near future. JPA 2.1 will be delivered as part of Java EE 7. The different components in the Java EE 7 platform are tracked here. JPA 2.1 Expert Group has released Early Draft 2 of the specification. Section 9.4 and 11.2 provide all details about Schema Generation. The latest javadocs can be obtained from here. And the JPA EG would appreciate feedback.

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  • How to enable a Web portal-based enterprise platform on different domains and hosts without customization [on hold]

    - by S.Jalali
    At Coscend, a cloud and communications software product company, we have built a Web portal-based collaboration platform that we like to host on five different Windows- and Linux-based servers in different hosting environments that run Web servers. Each of these Windows and Linux servers has a different host name and domain name (and IP address). Our team would appreciate your guidance on: (1) Is there a way to implement this Web portal-based platform on these Linux and Windows servers without customizing the host name, domain name and IP address for each individual instance? (2) Is there a way to create some variables using JavaScript for host name and domain name and call them from the different implementations? If a reference to the host/domain names occurs on hundreds of our pages, the variables or objects would replace that. (3) This is part of making these JavaScript modules portable and re-usable for different environments and instances. The portal is written in JavaScript that is embedded in HTML5 and padded with CSS3. Other technologies include Flash, Flex, PostgreSQL and MySQL.

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  • What is the best way to "override" enums?

    - by Tyler
    I have a number of classes which extend an abstract class. The abstract parent class defines an enum with a set of values. Some of the subclasses inherit the parent class's enum values, but some of the subclasses need the enum values to be different. Is there any way to somehow override the enum for these particular subclasses, and if not, what is a good way to achieve what I'm describing? class ParentClass { private MyEnum m_EnumVal; public virtual MyEnum EnumVal { get { return m_EnumVal; } set { m_EnumVal = value; } } public enum MyEnum { a, b, c }; } class ChildClass : ParentClass { private MyEnum m_EnumVal; public virtual MyEnum EnumVal { get { return m_EnumVal; } set { m_EnumVal = value; } } public enum MyEnum { d, e, f }; }

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  • Deserializing only select properties of an Entity using JDOQL query string?

    - by user246114
    Hi, I have a rather large class stored in the datastore, for example a User class with lots of fields (I'm using java, omitting all decorations below example for clarity): @PersistenceCapable class User { private String username; private String city; private String state; private String country; private String favColor; } For some user queries, I only need the favColor property, but right now I'm doing this: SELECT FROM " + User.class.getName() + " WHERE username == 'bob' which should deserialize all of the entity properties. Is it possible to do something instead like: SELECT username, favColor FROM " + User.class.getName() + " WHERE username == 'bob' and then in this case, all of the returned User instances will only spend time deserializing the username and favColor properties, and not the city/state/country properties? If so, then I suppose all the other properties will be null (in the case of objects) or 0 for int/long/float? Thank you

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  • Where can I get a definition of how the code is laid out in VB.NET 2010?

    - by ByteWorker
    I am just starting out learning Visual Basic 2010. I have books and videos. The books all seem to be written for people who have some programming experience, even the books that say they are for beginners. The videos were great until they started talking about variables. I got the basics of them but they started into complicated variables and I don’t see the need for them right away. Where can I go to see code for fairly intricate applications written out, with an over lay of definitions of which part of the code is a method as opposed to a class and so on? Also, I am working at a company that does not use SQL. So I need to use Access 2007 for all of my tables. Is there much of a difference to the coding?

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  • Can't append to second container

    - by George Katsanos
    I have the following script: (function($) { $.fn.easyPaginate = function(options){ var defaults = { step: 4, delay: 100, numeric: true, nextprev: true, controls: 'pagination', current: 'current' }; var options = $.extend(defaults, options); var step = options.step; var lower, upper; var children = $(this).children(); var count = children.length; var obj, next, prev; var page = 1; var timeout; var clicked = false; function show(){ clearTimeout(timeout); lower = ((page-1) * step); upper = lower+step; $(children).each(function(i){ var child = $(this); child.hide(); if(i>=lower && i<upper){ setTimeout(function(){ child.fadeIn('fast') }, ( i-( Math.floor(i/step) * step) )*options.delay ); } if(options.nextprev){ if(upper >= count) { next.addClass('stop'); } else { next.removeClass('stop'); }; if(lower >= 1) { prev.removeClass('stop'); } else { prev.addClass('stop'); }; }; }); $('li','#'+ options.controls).removeClass(options.current); $('li[data-index="'+page+'"]','#'+ options.controls).addClass(options.current); if(options.auto){ if(options.clickstop && clicked){}else{ timeout = setTimeout(auto,options.pause); }; }; }; function auto(){ if(upper <= count){ page++; show(); } else { page--; show(); } }; this.each(function(){ obj = this; if(count>step){ var pages = Math.floor(count/step); if((count/step) > pages) pages++; var ol = $('<ol id="'+ options.controls +'" class="pagin"></ol>').insertAfter(obj); if(options.nextprev){ prev = $('<li class="prev">prev</li>') .appendTo(ol) .bind('click', function() { //check to see if there are any more pages in the negative direction if (page > 1) { clicked = true; page--; show(); } }); } if(options.numeric){ for(var i=1;i<=pages;i++){ $('<li data-index="'+ i +'">'+ i +'</li>') .appendTo(ol) .click(function(){ clicked = true; page = $(this).attr('data-index'); show(); }); }; }; if(options.nextprev){ next = $('<li class="next">next</li>') .appendTo(ol) .bind('click', function() { //check to see if there are any pages in the positive direction if (page < (count / 4)) { clicked = true; page++; show(); } }); } show(); }; }); }; })(jQuery); jQuery(function($){ $('ul.news').easyPaginate({step:4}); }); which is a carousel-like plugin that produces this html structure for the navigation: <ol id="pagination" class="pagin"><li class="prev">prev</li><li data-index="1" class="">1</li><li data-index="2" class="">2</li><li data-index="3" class="current">3</li><li class="next stop">next</li></ol> And all I want is to enclose this list in a div. Seems simple, but appendTo doesn't want to cooperate with me, or I'm doing something wrong (I'd appreciate if you would help me understand what that is..) So I'm modifying as such: var ol = $('<ol id="'+ options.controls +'" class="pagin"></ol>'); var tiv = $('<div id="lala"></div>'); ol.appendTo('#lala'); tiv.insertAfter(obj); I know how to chain, but I'm in "debugging" mode trying to understand why I don't get the result I imagine I would get: <div id="lala> <ol id="pagination><li>...... </li></ol> </div> I tried putting some console.log's to see the status of my variables but couldn't find something useful.. I guess there's something with DOM insertion I don't get.

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  • Dart Can't get logging statements to compile

    - by Nate Lockwood
    I'm trying to learn how to implement logging using the examples/tutorial in: http://blog.dartwatch.com/2013/05/campaign-to-use-real-logging-instead-of.html#comment-form But having imported the libraries this line in main will not compile because the class 'PrintHandler' is not recognized and Google has not been a help in this case. My server application consists of a main and three classes. I'm new at Dart. Below I've extracted the logging code that I added. In what library is 'PrintHandler'? Is this a class I need to write? library server; import 'package:logging_handlers/logging_handlers_shared.dart'; import 'package:logging/logging.dart'; final _serverLogger = new Logger("server"); // top level logger void main() { Logger.root.onRecord.listen(new PrintHandler()); // default PrintHandler _serverLogger.fine("Server created"); } class A { } class B { } class C { }

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  • are Hierarchical SIngletons in Java possible?

    - by Zach H
    I've been toying with an interesting idea (No idea if I'll include it in any code, but it's fun to think about) Let's say we have a program that requires a large number of classes, all of a certain subclass. And those classes all need to be singletons. Now, we could write the singleton pattern for each of those classes, but it seems wasteful to write the same code over and over, and we already have a common base class. It would be really nice to create a getSingleton method of A that when called from a subclass, returns a singleton of the B class (cast to class A for simplicity) class A{ public A getSingleton(){ //Wizardry } } class B extends A{ } A blargh = B.getSingleton() A gish = B.getSingleton() if(A == B) System.out.println("It works!") It seems to me that the way to do this would be to recognize and call B's default constructor (assuming we don't need to pass anything in.) I know a little of the black magic of reflection in Java, but i'm not sure if this can be done. Anyone interested in puzzling over this?

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  • Guice child injector override binding

    - by Roman
    Hi All I am trying to to override a binding in a child injector that was already configured in a base injector. like that : public class PersistenceModule extends Abstract{ @Override protected void configure() { bind(IProductPersistenceHelper.class).to(ProductPersistenceHelper.class); } } then : Injector injector = Guice.createInjector(new PersistenceModule()); injector.createChildInjector(new AbstractModule(){ @Override protected void configure() { bind(IProductPersistenceHelper.class).to(MockProductPersistenceHelper.class); } }) Guice is complaining that it has already a binding for that. Are there any patterns or best practices for that problem ?

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  • using static methods and classes

    - by vedant1811
    I know that static methods/variables are associated with the class and not the objects of the class and are useful in situations when we need to keep count of, say the number of objects of the class that were created. Non-static members on the other hand may need to work on the specific object (i.e. to use the variables initialized by the constructor) My question what should we do when we need neither of the functionalities? Say I just need a utility function that accepts value(s) and returns a value besed solely on the values passed. I want to know whether such methods should be static or not. How is programming efficiency affected and which is a better coding practice/convention and why. PS: I don't want to spark off a debate, I just want a subjective answer and/or references.

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  • Java Inheritance Concept Understanding

    - by Nirmal
    Hello All.... I am just refreshing the oops features of the java. So, I have a little confusion regarding inheritance concept. For that I have a following sample code : class Super{ int index = 5; public void printVal(){ System.out.println("Super"); } } class Sub extends Super{ int index = 2; public void printVal(){ System.out.println("Sub"); } } public class Runner { public static void main(String args[]){ Super sup = new Sub(); System.out.println(sup.index+","); sup.printVal(); } } Now above code is giving me output as : 5,Sub. Here, we are overriding printVal() method, so that is understandable that it is accessing child class method only. But I could not understand why it's accessing the value of x from Super class... Thanks in advance....

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  • getting hidden elements

    - by Emin
    Say I have the following unordered list <ul class="container"> <li class="item" style="display: none;">first item</li> <li class="item">second item</li> <li class="item">third item</li> <li class="item">forth item</li> </ul> how can I carry out a task only if all the items in the container are hidden? regards...

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  • Performance side effect with static internal Util classes?

    - by Fostah
    For a util class that contains a bunch of static functionality that's related to the same component, but has different purposes, I like to use static internal classes to organize the functionality, like so: class ComponentUtil { static class Layout { static int calculateX(/* ... */) { // ... } static int calculateY(/* ... */) { // ... } } static class Process { static int doThis(/* ... */) { // ... } static int doThat(/* ... */) { // ... } } } Is there any performance degradation using these internal classes vs. just having all the functionality in the Util class?

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