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• how do I get eclipse to use a different compiler version for Java?

  - by codeman73

  It seems like this should be a simple task, with the options in the Preferences menu for different JREs and the ability to set different compiler and build paths per project. However, it also seems to simply not work. For example, I have my JAVA_HOME set to a jre for Java 1.6. It's still not clear to me how Eclipse uses this, but it appears to be defaulting to this and not taking the project overrides. I have also installed Java 1.5, and added a JRE for this in eclipse in the Java-Installed JREs section. In my project, I've set the compiler compliance level to 1.5. In the build path for the project, I've added the System Library for the Java 1.5 JRE. However, I'm getting compile errors for a class that implements PreparedStatement for not implementing abstract methods that only exist in Java 1.6 PreparedStatement. Specifically, the methods setAsciiStream(int, InputStream, long) and setAsciiStream(int, InputStream) Strangely enough, it worked when we were compiling it against Java 1.4, which it was originally written for. We added the JREs for Java 1.4 and referenced that system library in the project, and set the project's compiler level to 1.4, and it works fine. But when I do the same changes to try to point to Java 1.5, it instead uses 1.6. Any ideas why?

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• Can I stop the dbml designer from adding a connection string to the dbml file?

  - by drs9222

  We have a custom function AppSettings.GetConnectionString() which is always called to determine the connection string that should be used. How this function works is unimportant to the discussion. It suffices to say that it returns a connection string and I have to use it. I want my LINQ to SQL DataContext to use this so I removed all connection string informatin from the dbml file and created a partial class with a default constructor like this: public partial class SampleDataContext { public SampleDataContext() : base(AppSettings.GetConnectionString()) { } } This works fine until I use the designer to drag and drop a table into the diagram. The act of dragging a table into the diagram will do several unwanted things: A settings file will be created A app.config file will be created My dbml file will have the connection string embedded in it All of this is done before I even save the file! When I save the diagram the designer file is recreated and it will contain its own default constructor which uses the wrong connection string. Of course this means my DataContext now has two default constructors and I can't build anymore! I can undo all of these bad things but it is annoying. I have to manually remove the connection string and the new files after each change! Is there anyway I can stop the designer from making these changes without asking? EDIT The requirement to use the AppSettings.GetConnectionString() method was imposed on me rather late in the game. I used to use something very similar to what it generates for me. There are quite a few places that call the default constructor. I am aware that change them all to create the data context in another way (using a different constructor, static method, factory, ect..). That kind of change would only be slightly annoying since it would only have to be done once. However, I feel, that it is sidestepping the real issue. The dbml file and configuration files would still contain an incorrect, if unused, connection string which at best could confuse other developers.

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• Login with Kohana auth module - what am I doing wrong?

  - by keithjgrant

  I'm trying to login with the following controller action, but my login attempt keeps failing (I get the 'invalid username and/or password' message). What am I doing wrong? I also tried the other method given in the examples in the auth documentation, Auth::instance()->login($user->username, $form->password);, but I get the same result. Kohana version is 2.3.4. public function login() { $auth = Auth::instance(); if ($auth->logged_in()) { url::redirect('/account/summary'); } $view = new View('login'); $view->username = ''; $view->password = ''; $post = $this->input->post(); $form = new Validation($post); $form->pre_filter('trim', 'username') ->pre_filter('trim', 'password') ->add_rules('username', 'required'); $failed = false; if (!empty($post) && $form->validate()) { $login = array( 'username' => $form->username, 'password' => $form->password, ); if (ORM::factory('user')->login($login)) { url::redirect('/accounts/summary'); } else { $view->username = $form->username; $view->message = in_array('required', $form->errors()) ? 'Username and password are required.' : 'Invalid username and/or password.'; } } $view->render(true); }

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• Determining the color of a pixel in a bitmap using C# in a WPF app

  - by DanM

  The only way I found so far is System.Drawing.Bitmap.GetPixel(), but Microsoft has warnings for System.Drawing that are making me wonder if this is the "old way" to do it. Are there any alternatives? Here's what Microsoft says about the System.Drawing namespace. I also noticed that the System.Drawing assembly was not automatically added to the references when I created a new WPF project. System.Drawing Namespace The System.Drawing namespace provides access to GDI+ basic graphics functionality. More advanced functionality is provided in the System.Drawing.Drawing2D, System.Drawing.Imaging, and System.Drawing.Text namespaces. The Graphics class provides methods for drawing to the display device. Classes such as Rectangle and Point encapsulate GDI+ primitives. The Pen class is used to draw lines and curves, while classes derived from the abstract class Brush are used to fill the interiors of shapes. Caution Classes within the System.Drawing namespace are not supported for use within a Windows or ASP.NET service. Attempting to use these classes from within one of these application types may produce unexpected problems, such as diminished service performance and run-time exceptions. - http://msdn.microsoft.com/en-us/library/system.drawing.aspx

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• Zend Framework: Zend_DB Error

  - by Sergio E.

  I'm trying to learn ZF, but got strange error after 20 minutes :) Fatal error: Uncaught exception 'Zend_Db_Adapter_Exception' with message 'Configuration array must have a key for 'dbname' that names the database instance' What does this error mean? I got DB information in my config file: resources.db.adapter=pdo_mysql resources.db.host=localhost resources.db.username=name resources.db.password=pass resources.db.dbname=name Any suggestions? EDIT: This is my model file /app/models/DbTable/Bands.php: class Model_DbTable_Bands extends Zend_Db_Table_Abstract { protected $_name = 'zend_bands'; } Index controller action: public function indexAction() { $albums = new Model_DbTable_Bands(); $this->view->albums = $albums->fetchAll(); } EDIT All codes: bootstrap.php protected function _initAutoload() { $autoloader = new Zend_Application_Module_Autoloader(array( 'namespace' => '', 'basePath' => dirname(__FILE__), )); return $autoloader; } protected function _initDoctype() { $this->bootstrap('view'); $view = $this->getResource('view'); $view->doctype('XHTML1_STRICT'); } public static function setupDatabase() { $config = self::$registry->configuration; $db = Zend_Db::factory($config->db); $db->query("SET NAMES 'utf8'"); self::$registry->database = $db; Zend_Db_Table::setDefaultAdapter($db); Zend_Db_Table_Abstract::setDefaultAdapter($db); } IndexController.php class IndexController extends Zend_Controller_Action { public function init() { /* Initialize action controller here */ } public function indexAction() { $albums = new Model_DbTable_Bands(); $this->view->albums = $albums->fetchAll(); } } configs/application.ini, changed database and provided password: [development : production] phpSettings.display_startup_errors = 1 phpSettings.display_errors = 1 db.adapter = PDO_MYSQL db.params.host = localhost db.params.username = root db.params.password = pedro db.params.dbname = test models/DbTable/Bands.php class Model_DbTable_Bands extends Zend_Db_Table_Abstract { protected $_name = 'cakephp_bands'; public function getAlbum($id) { $id = (int)$id; $row = $this->fetchRow('id = ' . $id); if (!$row) { throw new Exception("Count not find row $id"); } return $row->toArray(); } }

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• How to avoid multiple, unused has_many associations when using multiple models for the same entity (

  - by mikep

  Hello, I'm looking for a nice, Ruby/Rails-esque solution for something. I'm trying to split up some data using multiple tables, rather than just using one gigantic table. My reasoning is pretty much to try and avoid the performance drop that would come with having a big table. So, rather than have one table called books, I have multiple tables: books1, books2, books3, etc. (I know that I could use a partition, but, for now, I've decided to go the 'multiple tables' route.) Each user has their books placed into a specific table. The actual book table is chosen when the user is created, and all of their books go into the same table. The goal is to try and keep each table pretty much even -- but that's a different issue. One thing I don't particularly want to have is a bunch of unused associations in the User class. Right now, it looks like I'd have to do the following: class User < ActiveRecord::Base has_many :books1, :books2, :books3, :books4, :books5 end class Books1 < ActiveRecord::Base belongs_to :user end class Books2 < ActiveRecord::Base belongs_to :user end First off, for each specific user, only one of the book tables would be usable/applicable, since all of a user's books are stored in the same table. So, only one of the associations would be in use at any time and any other has_many :bookX association that was loaded would be a waste. I don't really know Ruby/Rails does internally with all of those has_many associations though, so maybe it's not so bad. But right now I'm thinking that it's really wasteful, and that there may just be a better, more efficient way of doing this. Is there's some sort of special Ruby/Rails methodology that could be applied here to avoid having to have all of those has_many associations? Also, does anyone have any advice on how to abstract the fact that there's multiple book tables behind a single books model/class?

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• How do JVM's implicit memory barriers behave when chaining constructors

  - by Joonas Pulakka

  Referring to my earlier question on incompletely constructed objects, I have a second question. As Jon Skeet pointed out, there's an implicit memory barrier in the end of a constructor that makes sure that final fields are visible to all threads. But what if a constructor calls another constructor; is there such a memory barrier in the end of each of them, or only in one being called from outside? That is, when the "wrong" solution is: public class ThisEscape { public ThisEscape(EventSource source) { source.registerListener( new EventListener() { public void onEvent(Event e) { doSomething(e); } }); } } And the correct one would be a factory method version: public class SafeListener { private final EventListener listener; private SafeListener() { listener = new EventListener() { public void onEvent(Event e) { doSomething(e); } } } public static SafeListener newInstance(EventSource source) { SafeListener safe = new SafeListener(); source.registerListener(safe.listener); return safe; } } Would the following work too, or not? public class MyListener { private final EventListener Listener; private MyListener() { listener = new EventListener() { public void onEvent(Event e) { doSomething(e); } } } public MyListener(EventSource source) { this(); source.register(listener); } }

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• Why are my Fluent NHibernate SubClass Mappings generating redundant columns?

  - by Brook

  I'm using Fluent NHibernate 1.x build 694, built against NH 3.0 I have the following entities public abstract class Card { public virtual int Id { get; set; } public virtual string Name { get; set; } public virtual string Description { get; set; } public virtual Product Product { get; set; } public virtual Sprint Sprint { get; set; } } public class Story:Card { public virtual double Points { get; set; } public virtual int Priority { get; set; } public virtual IList<Task> Tasks { get; set; } } And the following mappings public class CardMap:ClassMap<Card> { public CardMap() { Id(c => c.Id) .Index("Card_Id"); Map(c => c.Name) .Length(50) .Not.Nullable(); Map(c => c.Description) .Length(1024) .Not.Nullable(); References(c=>c.Product) .Not.Nullable(); References(c=>c.Sprint) .Nullable(); } } public class StoryMap : SubclassMap<Story> { public StoryMap() { Map(s => s.Points); Map(s => s.Priority); HasMany(s => s.Tasks); } } When I generate my Schema, the tables are created as follows Card --------- Id Name Description Product_id Sprint_id Story ------------ Card_id Points Priority Product_id Sprint_id What I would have expected would have been to see the columns Product_id and Sprint_id ONLY in the Card table, not the Story table. What am I doing wrong or misunderstanding?

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• Should a new language compiler target the JVM?

  - by Pindatjuh

  I'm developing a new language. My initial target was to compile to native x86 for the Windows platform, but now I am in doubt. I've seen some new languages target the JVM (most notable Scala and Clojure). Ofcourse it's not possible to port every language easily to the JVM; to do so, it may lead to small changes to the language and it's design. So that's the reason behind this doubt, and thus this question: Is targetting the JVM a good idea, when creating a compiler for a new language? Or should I stick with x86? I have experience in generating JVM bytecode. Are there any workarounds to JVM's GC? The language has deterministic implicit memory management. How to produce JIT-compatible bytecode, such that it will get the highest speedup? Is it similar to compiling for IA-32, such as the 4-1-1 muops pattern on Pentium? I can imagine some advantages (please correct me if I'm wrong): JVM bytecode is easier than x86. Like x86 communicates with Windows, JVM communicates with the Java Foundation Classes. To provide I/O, Threading, GUI, etc. Implementing "lightweight"-threads.I've seen a very clever implementation of this at http://www.malhar.net/sriram/kilim/. Most advantages of the Java Runtime (portability, etc.) The disadvantages, as I imagined, are: Less freedom? On x86 it'll be more easy to create low-level constructs, while JVM has a higher level (more abstract) processor. Most disadvantages of the Java Runtime (no native dynamic typing, etc.)

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• Importing hibernate configuration file into Spring applicationContext

  - by Himanshu Yadav

  I am trying to integrate Hibernate 3 with Spring 3.1.0. The problem is that application is not able to find mapping file which declared in hibernate.cfg.xml file. Initially hibernate configuration has datasource configuration, hibernate properties and mapping hbm.xml files. Master hibernate.cfg.xml file exist in src folder. this is how Master file looks: <hibernate-configuration> <session-factory> <!-- Mappings --> <mapping resource="com/test/class1.hbm.xml"/> <mapping resource="/class2.hbm.xml"/> <mapping resource="com/test/class3.hbm.xml"/> <mapping resource="com/test/class4.hbm.xml"/> <mapping resource="com/test/class5.hbm.xml"/> Spring config is: <bean id="sessionFactoryEditSolution" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <property name="dataSource" ref="data1"/> <property name="mappingResources"> <list> <value>/master.hibernate.cfg.xml</value> </list> </property> <property name="hibernateProperties"> <props> <prop key="hibernate.dialect">org.hibernate.dialect.SQLServerDialect</prop> <prop key="hibernate.cache.use_second_level_cache">true</prop> </props> </property> </bean>

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• How to build a sequence in the method calls of a fluent interface

  - by silverfighter

  Hi I would like to build a fluent interface for creating am object some sort of factory or builder. I understand that I have to "return this" in order to make the methods chainable. public class CarBuilder { public CarBuilder() { car = new Car(); } private Car car; public CarBuilder AddEngine(IEngineBuilder engine) { car.Engine = engine.Engine(); return this; } public CarBuilder AddWheels(IWheelsBuilder wheels) { car.Wheels = wheels.Wheels(); return this; } public CarBuilder AddFrame(IFrameBuilder frame) { car.Frame = frame.Frame(); return this; } public Car BuildCar() { return car; } } with this I could build a car like that: Car c = builder.AddFrame(fBuilder).AddWheels(wBuilder).AddEngine(eBuilder).BuildCar(); But what I need is a special sequence or workflow: I can only build the wheels on top of the frame and when the wheels exist then I'll be able to build up the engine. So instead of offering every method of the car builder I want to be able to add only the frame to the builder and then only the wheels to the frame and then the engine on top of that... And how would it be or what would be a good implementation if the EngineBuilder itself has a fluent api like eBuilder.Cylinders(12).WithPistons().... Would it be possible to have something like this Car c = builder.AddFrame(fBuilder).AddWheels(wBuilder).AddEngine(x=>x.WithCylinders(12).WithPistons()).BuildCar(); So in sum how to structure the flow of the fluent interface and how to nest fluent Interfaces?

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• Discriminator based on joined property

  - by Andrew

  Suppose I have this relationship: abstract class Base { int Id; int JoinedId; ... } class Joined { int Id; int Discriminator; ... } class Sub1 : Base { ... } class Sub2 : Base { ... } for the following tables: table Base ( Id int, JoinedId int, ... ) table Joined ( Id int, Discriminator int, ... ) I would like to set up a table-per-hierarchy inheritance mapping for the Base, Sub1, Sub2 relationships, but using the Disciminator property from the Joined class as the discriminator. Here's the general idea for the mapping file: <class name="Base" table="Base"> <id name="Id"><generator class="identity"/></id> <discriminator /> <!-- ??? or <join> or <many-to-one>? --> <subclass name="Sub1" discriminator-value="1">...</subclass> <subclass name="Sub2" discriminator-value="2">...</subclass> </class> Is there any way of accomplishing something like this with the <discriminator>, <join>, or <many-to-one>? NHiberante seems to assume the discriminator is a column on the given table (which makes sense to me.. I know this is unorthodox). Thanks.

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• PHP: tips/resources/patterns for learning to implement a basic ORM

  - by BoltClock

  I've seen various MVC frameworks as well as standalone ORM frameworks for PHP, as well as other ORM questions here; however, most of the questions ask for existing frameworks to get started with, which is not what I'm looking for. (I have also read this SO question but I'm not sure what to make of it, and the answers are vague.) Instead, I figured I'd learn best by getting my hands dirty and actually writing my own ORM, even a simple one. Except I don't really know how to get started, especially since the code I see in other ORMs is so complicated. With my PHP 5.2.x (this is important) MVC framework I have a basic custom database abstraction layer, that has: Very simple methods like connect($host, $user, $pass, $base), query($sql, $binds), etc Subclasses for each DBMS that it supports A class (and respective subclasses) to represent SQL result sets But does not have: Active Record functionality, which I assume is an ORM thing (correct me if I'm wrong) I've read up a little about ORM, and from my understanding they provide a means to further abstract data models from the database itself by representing data as nothing more than PHP-based classes/objects; again, correct me if I am wrong or have missed out in any way. Still, I'd like some simple tips from anyone else who's dabbled more or less with ORM frameworks. Is there anything else I need to take note of, simple example code for me to refer to, or resources I can read? Thanks a lot in advance!

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• Instantiating and starting a Scala Actor in a Map

  - by Bruce Ferguson

  I'm experimenting with a map of actors, and would like to know how to instantiate them and start them in one fell swoop... import scala.actors.Actor import scala.actors.Actor._ import scala.collection.mutable._ abstract class Message case class Update extends Message object Test { val groupings = "group1" :: "group2" :: "group3":: Nil val myActorMap = new HashMap[String,MyActor] def main(args : Array[String]) { groupings.foreach(group => myActorMap += (group -> new MyActor)) myActorMap("group2").start myActorMap("group2") ! Update } } class MyActor extends Actor { def act() { loop { react { case Update => println("Received Update") case _ => println("Ignoring event") } } } } The line: myActorMap("group2").start will grab the second instance, and let me start it, but I would like to be able to do something more like: groupings.foreach(group => myActorMap += (group -> (new MyActor).start)) but no matter how I wrap the new Actor, the compiler complains with something along the lines of: type mismatch; found : scala.actors.Actor required: com.myCompany.test.MyActor or various other complaints. I know it must be something simple to do with anonymous classes, but I can't see it right now. Any suggestions? Thanks in advance!!

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• Forward declaration of derived inner class

  - by Loom

  I ran into problem implementing some variations of factory method. // from IFoo.h struct IFoo { struct IBar { virtual ~IBar() = 0; virtual void someMethod() = 0; }; virtual IBar *createBar() = 0; }; // from Foo.h struct Foo : IFoo { // implementation of Foo, Bar in Foo.cpp struct Bar : IBar { virtual ~Bar(); virtual void someMethod(); }; virtual Bar *createBar(); // implemented in Foo.cpp }; I'd like to place declaration of Foo::Bar in Foo.cpp. For now I cannot succeed: struct Foo : IFoo { //struct Bar; //1. error: invalid covariant return type // for ‘virtual Foo::Bar* //struct Bar : IBar; //2. error: expected ‘{’ before ‘;’ token virtual Bar *createBar(); // virtual IBar *createBar(); // Is not acceptable by-design }; Is there a trick to have just forward declaration of Boo in Foo.hpp and to have full declaration in Foo.cpp?

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• Hibernate: deletes not cascading for self-referencing entities

  - by jwaddell

  I have the following (simplified) Hibernate entities: @Entity @Table(name = "package") public abstract class Package { protected Content content; @ManyToOne(cascade = {javax.persistence.CascadeType.ALL}) @JoinColumn(name = "content_id") @Fetch(value = FetchMode.JOIN) public Content getContent() { return content; } public void setContent(Content content) { this.content = content; } } @Entity @Table(name = "content") public class Content { private Set<Content> subContents = new HashSet<Content>(); @ManyToMany(fetch = FetchType.EAGER) @JoinTable(name = "subcontents", joinColumns = {@JoinColumn(name = "content_id")}, inverseJoinColumns = {@JoinColumn(name = "elt")}) @Cascade(value = {org.hibernate.annotations.CascadeType.DELETE, org.hibernate.annotations.CascadeType.REPLICATE}) @Fetch(value = FetchMode.SUBSELECT) public Set<Content> getSubContents() { return subContents; } public void setSubContents(Set<Content> subContents) { this.subContents = subContents; } } So a Package has a Content, and a Content is self-referencing in that it has many sub-Contents (which may contain sub-Contents of their own etc). The relationships are required to be ManyToOne (Package to Content) and ManyToMany (Content to sub-Contents) but for the case I am currently testing each sub-Content only relates to one Package or Content. The problem is that when I delete a Package and flush the session, I get a Hibernate error stating that I'm violating a foreign key constraint on table subcontents, with a particular content_id still referenced from table subcontents. I've tried specifically (recursively) deleting the Contents before deleting the Package but I get the same error. Is there a reason why this entity tree is not being deleted properly?

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• URL naming conventions

  - by LookitsPuck

  So, this may be a can of worms. But I'm curious what your practices are? For example, let's say your website consists of the following needs (very basic): A landing page An information page for an event (static) A listing of places for that event (dynamic) An information page for each place With that said, how would you design your URLs? Typically, I'd do something like the following: www.domain.com/ - landing page [also accessible via www.domain.com/home] www.domain.com/event - event information page www.domain.com/places - listing of all places www.domain.com/places/{id} - place information page Now, here's a question. Just grammatically speaking, I have a hangup of referring to a given place in a url as being plural. Shouldn't it make more sense to go with this: www.domain.com/place/{id} as opposed to www.domain.com/places/{id} In some frameworks, you have a convention to follow (for example, ASP.NET MVC) by default. Yes, you can define custom routes to have /place/{id} route to the PlacesController. However, I'm just trying to keep this a bit abstract in discussion. With that being said, let's see for instance on another page of your site, you have a link, that when clicked, would open a modal popup populated with place information. Where you place that information? We could go with something like this: www.domain.com/ajax/places/{id} OR www.domain.com/places/{id} and serve based on the request header (that is, if requesting JSON, return JSON?}. Finally, for SEO reasons, typically I use a slug associated with a given resource. So, something like such: www.domain.com/ajax/places/{id}/london Where london is only there to add decoration to the link for SEO reasons. Is this sound? I ask all of these questions, because these are practices that I've been using for awhile, and I'd just like to see what other developers are doing or if I'm approaching things incorrectly. Thanks!

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• Designing a general database interface in PHP

  - by lamas

  I'm creating a small framework for my web projects in PHP so I don't have to do the basic work over and over again for every new website. It is not my goal to create a second CakePHP or Codeigniter and I'm also not planning to build my websites with any of the available frameworks as I prefer to use things I've created myself in general. I have no problems in designing that framework when it comes to parts like the core structure, request handling, and so on but I'm getting stuck with designing the database interface for my modules. I've already thought about using the MVC pattern but thought that it would be a bit of a overkill. So the exact problem I'm facing is how my frameworks modules (viewCustomers could be a module, for example) should interact with the database. Is it a good idea to write SQL directly in PHP (mysql_query( 'SELECT firstname, lastname(.....))? How could I abstract a query like SELECT firstname, lastname FROM customers WHERE id=X Would MySQL helper functions like $this->db->get( array('firstname', 'lastname'), array('id'=>X) ) be a good idea? I suppose not because they actually make everything more complicated by requiring arrays to be created and passed. Is the Model pattern from MVC my only real option?

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• hibernate c3p0 broken pipe

  - by raven_arkadon

  Hi, I'm using hibernate 3 with c3p0 for a program which constantly extracts data from some source and writes it to a database. Now the problem is, that the database might become unavailable for some reasons (in the simplest case: i simply shut it down). If anything is about to be written to the database there should not be any exception - the query should wait for all eternity until the database becomes available again. If I'm not mistaken this is one of the things the connection pool could do for me: if there is a problem with the db, just retry to connect - in the worst case for infinity. But instead i get a broken pipe exception, sometimes followed by connection refused and then the exception is passed to my own code, which shouldn't happen. Even if I catch the exception, how could i cleanly reinitialize hibernate again? (So far without c3p0 i simply built the session factory again, but i wouldn't be surprised if that could leak connections (or is it ok to do so?)). The database is Virtuoso open source edition. My hibernate.xml.cfg c3p0 config: <property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property> <property name="hibernate.c3p0.breakAfterAcquireFailure">false</property> <property name="hibernate.c3p0.acquireRetryAttempts">-1</property> <property name="hibernate.c3p0.acquireRetryDelay">30000</property> <property name="hibernate.c3p0.automaticTestTable">my_test_table</property> <property name="hibernate.c3p0.initialPoolSize">3</property> <property name="hibernate.c3p0.minPoolSize">3</property> <property name="hibernate.c3p0.maxPoolSize">10</property> btw: The test table is created and i get tons of debug output- so it seems it actually reads the config.

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• Passing IDisposable objects through constructor chains

  - by Matt Enright

  I've got a small hierarchy of objects that in general gets constructed from data in a Stream, but for some particular subclasses, can be synthesized from a simpler argument list. In chaining the constructors from the subclasses, I'm running into an issue with ensuring the disposal of the synthesized stream that the base class constructor needs. Its not escaped me that the use of IDisposable objects this way is possibly just dirty pool (plz advise?) for reasons I've not considered, but, this issue aside, it seems fairly straightforward (and good encapsulation). Codes: abstract class Node { protected Node (Stream raw) { // calculate/generate some base class properties } } class FilesystemNode : Node { public FilesystemNode (FileStream fs) : base (fs) { // all good here; disposing of fs not our responsibility } } class CompositeNode : Node { public CompositeNode (IEnumerable some_stuff) : base (GenerateRaw (some_stuff)) { // rogue stream from GenerateRaw now loose in the wild! } static Stream GenerateRaw (IEnumerable some_stuff) { var content = new MemoryStream (); // molest elements of some_stuff into proper format, write to stream content.Seek (0, SeekOrigin.Begin); return content; } } I realize that not disposing of a MemoryStream is not exactly a world-stopping case of bad CLR citizenship, but it still gives me the heebie-jeebies (not to mention that I may not always be using a MemoryStream for other subtypes). It's not in scope, so I can't explicitly Dispose () it later in the constructor, and adding a using statement in GenerateRaw () is self-defeating since I need the stream returned. Is there a better way to do this? Preemptive strikes: yes, the properties calculated in the Node constructor should be part of the base class, and should not be calculated by (or accessible in) the subclasses I won't require that a stream be passed into CompositeNode (its format should be irrelevant to the caller) The previous iteration had the value calculation in the base class as a separate protected method, which I then just called at the end of each subtype constructor, moved the body of GenerateRaw () into a using statement in the body of the CompositeNode constructor. But the repetition of requiring that call for each constructor and not being able to guarantee that it be run for every subtype ever (a Node is not a Node, semantically, without these properties initialized) gave me heebie-jeebies far worse than the (potential) resource leak here does.

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• Which is the better C# class design for dealing with read+write versus readonly

  - by DanM

  I'm contemplating two different class designs for handling a situation where some repositories are read-only while others are read-write. (I don't foresee any need to a write-only repository.) Class Design 1 -- provide all functionality in a base class, then expose applicable functionality publicly in sub classes public abstract class RepositoryBase { protected virtual void SelectBase() { // implementation... } protected virtual void InsertBase() { // implementation... } protected virtual void UpdateBase() { // implementation... } protected virtual void DeleteBase() { // implementation... } } public class ReadOnlyRepository : RepositoryBase { public void Select() { SelectBase(); } } public class ReadWriteRepository : RepositoryBase { public void Select() { SelectBase(); } public void Insert() { InsertBase(); } public void Update() { UpdateBase(); } public void Delete() { DeleteBase(); } } Class Design 2 - read-write class inherits from read-only class public class ReadOnlyRepository { public void Select() { // implementation... } } public class ReadWriteRepository : ReadOnlyRepository { public void Insert() { // implementation... } public void Update() { // implementation... } public void Delete() { // implementation... } } Is one of these designs clearly stronger than the other? If so, which one and why? P.S. If this sounds like a homework question, it's not, but feel free to use it as one if you want :)

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• Is there a way to get number of connections in Signalr hub group?

  - by pajo

  Here is my problem, I want to track if user is online or offline and notify other clients about it. I'm using hubs and implemented both IConnected and IDisconnect interfaces. My idea was to send notification to all clients when hub detects connect or disconnect. By default when user refreshes page he will get new connection id and eventually previous connection will call disconnect notifying other clients user is offline even though he's actually online. I tired to use my own ConnectionIdFactory returning username for connection id but with multiple tabs opened at some point it will detect user connectionid disconnected and after that client side hub will try to unsuccessfully connect to the hub in endless loop wasting memory and cpu making browser almost unusable. I needed to fix it fast so I removed my factory and now I add every new connection to the group using username, so I can easily notify single user on all connections, but then I have problem of detecting if user is online or offline as I don't know how many active connection user is having. So I'm wondering is there a way to get number of connections in one group? Or if anybody has some better idea how to track when user goes offline? I'm using Signalr 0.4

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• Why am I having this InstantiationException in Java when accessing final local variables?

  - by Oscar Reyes

  I was playing with some code to make a "closure like" construct ( not working btw ) Everything looked fine but when I tried to access a final local variable in the code, the exception InstantiationException is thrown. If I remove the access to the local variable either by removing it altogether or by making it class attribute instead, no exception happens. The doc says: InstantiationException Thrown when an application tries to create an instance of a class using the newInstance method in class Class, but the specified class object cannot be instantiated. The instantiation can fail for a variety of reasons including but not limited to: - the class object represents an abstract class, an interface, an array class, a primitive type, or void - the class has no nullary constructor What other reason could have caused this problem? Here's the code. comment/uncomment the class attribute / local variable to see the effect (lines:5 and 10 ). import javax.swing.*; import java.awt.event.*; import java.awt.*; class InstantiationExceptionDemo { //static JTextField field = new JTextField();// works if uncommented public static void main( String [] args ) { JFrame frame = new JFrame(); JButton button = new JButton("Click"); final JTextField field = new JTextField();// fails if uncommented button.addActionListener( new _(){{ System.out.println("click " + field.getText()); }}); frame.add( field ); frame.add( button, BorderLayout.SOUTH ); frame.pack();frame.setVisible( true ); } } class _ implements ActionListener { public void actionPerformed( ActionEvent e ){ try { this.getClass().newInstance(); } catch( InstantiationException ie ){ throw new RuntimeException( ie ); } catch( IllegalAccessException ie ){ throw new RuntimeException( ie ); } } } Is this a bug in Java? edit Oh, I forgot, the stacktrace ( when thrown ) is: Caused by: java.lang.InstantiationException: InstantiationExceptionDemo$1 at java.lang.Class.newInstance0(Class.java:340) at java.lang.Class.newInstance(Class.java:308) at _.actionPerformed(InstantiationExceptionDemo.java:25)

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• Concurrent WCF calls via shared channel

  - by Kent Boogaart

  I have a web tier that forwards calls onto an application tier. The web tier uses a shared, cached channel to do so. The application tier services in question are stateless and have concurrency enabled. But they are not being called concurrently. If I alter the web tier to create a new channel on every call, then I do get concurrent calls onto the application tier. But I wanted to avoid that cost since it is functionally unnecessary for my scenario. I have no session state, and nor do I need to re-authenticate the caller each time. I understand that the creation of the channel factory is far more expensive than than the creation of the channels, but it is still a cost I'd like to avoid if possible. I found this article on MSDN that states: While channels and clients created by the channels are thread-safe, they might not support writing more than one message to the wire concurrently. If you are sending large messages, particularly if streaming, the send operation might block waiting for another send to complete. Firstly, I'm not sending large messages (just a lot of small ones since I'm doing load testing) but am still seeing the blocking behavior. Secondly, this is rather open-ended and unhelpful documentation. It says they "might not" support writing more than one message but doesn't explain the scenarios under which they would support concurrent messages. Can anyone shed some light on this?

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• How to bundle extension methods requiring configuration in a library

  - by Greg

  Hi, I would like to develop a library that I can re-use to add various methods involved in navigating/searching through a graph (nodes/relationships, or if you like vertexs/edges). The generic requirements would be: There are existing classes in the main project that already implement the equivalent of the graph class (which contains the lists of nodes / relationships), node class and relationship class (which links nodes together) - the main project likely already has persistence mechanisms for the info (e.g. these classes might be built using Entity Framework for persistance) Methods would need to be added to each of these 3 classes: (a) graph class - methods like "search all nodes", (b) node class - methods such as "find all children to depth i", c) relationship class - methods like "return relationship type", "get parent node", "get child node". I assume there would be a need to inform the library with the extending methods the class names for the graph/node/relationships table (as different project might use different names). To some extent it would need to be like how a generics collection works (where you pass the classes to the collection so it knows what they are). Need to be a way to inform the library of which node property to use for equality checks perhaps (e.g. if it were a graph of webpages the equality field to use might be the URI path) I'm assuming that using abstract base classes wouldn't really work as this would tie usage down to have to use the same persistence approach, and same class names etc. Whereas really I want to be able to, for a project that has "graph-like" characteristics, the ability to add graph searching/walking methods to it.

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