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• Are document-oriented databases any more suitable than relational ones for persisting objects?

  - by Owen Fraser-Green

  In terms of database usage, the last decade was the age of the ORM with hundreds competing to persist our object graphs in plain old-fashioned RMDBS. Now we seem to be witnessing the coming of age of document-oriented databases. These databases are highly optimized for schema-free documents but are also very attractive for their ability to scale out and query a cluster in parallel. Document-oriented databases also hold a couple of advantages over RDBMS's for persisting data models in object-oriented designs. As the tables are schema-free, one can store objects belonging to different classes in an inheritance hierarchy side-by-side. Also, as the domain model changes, so long as the code can cope with getting back objects from an old version of the domain classes, one can avoid having to migrate the whole database at every change. On the other hand, the performance benefits of document-oriented databases mainly appear to come about when storing deeper documents. In object-oriented terms, classes which are composed of other classes, for example, a blog post and its comments. In most of the examples of this I can come up with though, such as the blog one, the gain in read access would appear to be offset by the penalty in having to write the whole blog post "document" every time a new comment is added. It looks to me as though document-oriented databases can bring significant benefits to object-oriented systems if one takes extreme care to organize the objects in deep graphs optimized for the way the data will be read and written but this means knowing the use cases up front. In the real world, we often don't know until we actually have a live implementation we can profile. So is the case of relational vs. document-oriented databases one of swings and roundabouts? I'm interested in people's opinions and advice, in particular if anyone has built any significant applications on a document-oriented database.

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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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• Java Random Slowdowns on Mac OS cont'd

  - by javajustice

  I asked this question a few weeks ago, but I'm still having the problem and I have some new hints. The original question is here: http://stackoverflow.com/questions/1651887/java-random-slowdowns-on-mac-os Basically, I have a java application that splits a job into independent pieces and runs them in separate threads. The threads have no synchronization or shared memory items. The only resources they do share are data files on the hard disk, with each thread having an open file channel. Most of the time it runs very fast, but occasionally it will run very slow for no apparent reason. If I attach a CPU profiler to it, then it will start running quickly again. If I take a CPU snapshot, it says its spending most of its time in "self time" in a function that doesn't do anything except check a few (unshared unsynchronized) booleans. I don't know how this could be accurate because 1, it makes no sense, and 2, attaching the profiler seems to knock the threads out of whatever mode they're in and fix the problem. Also, regardless of whether it runs fast or slow, it always finishes and gives the same output, and it never dips in total cpu usage (in this case ~1500%), implying that the threads aren't getting blocked. I have tried different garbage collectors, different sizings the parts of the memory space, writing data output to non-raid drives, and putting all data output in threads separate the main worker threads. Does anyone have any idea what kind of problem this could be? Could it be the operating system (OS X 10.6.2) ? I have not been able to duplicate it on a windows machine, but I don't have one with a similar hardware configuration.

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• Using SVN post-commit hook to update only files that have been commited

  - by fondie

  I am using an SVN repository for my web development work. I have a development site set up which holds a checkout of the repository. I have set up an SVN post-commit hook so that whenever a commit is made to the repository the development site is updated: cd /home/www/dev_ssl /usr/bin/svn up This works fine but due to the size of the repository the updates take a long time (approx. 3 minutes) which is rather frustrating when making regular commits. What I'd like is to change the post-commit hook to only update those files/directories that have been committed but I don't know how to go about doing this. Updating the "lowest common directory" would probably be the best solution, e.g. If committing the follow files: /branches/feature_x/images/logo.jpg /branches/feature_x/css/screen.css It would update the directory: /branches/feature_x/ Can anyone help me create a solution that achieves this please? Thanks! Update: The repository and development site are located on the same server so network issues shouldn't be involved. CPU usage is very low, and I/O should be ok (it's running on hi-spec dedicated server) The development site is approx. 7.5GB in size and contains approx. 600,000 items, this is mainly due to having multiple branches/tags

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• Jquery - xml parsing

  - by lmkk

  I have the following xml: <?xml version="1.0" encoding="utf-8"?> <Area xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Scenes> <Scene Index="1" Name="Scene1" /> <Scene Index="2" Name="Scene2" /> </Scenes> </Area> Which i am trying to parse with jquery: <script> $(document).ready(function(){ $.ajax({ type: "GET", url: "list.xml", dataType: "xml", success: function(xml) { $(xml).find('scenes').each(function(){ $(this).find('scene').each(function(){ var name = $(this).attr('name'); $('<div class="items" ></div>').html('<p>'+name+'</p>').appendTo('#page-wrap'); }); }); } }); }); </script> Why is this not working? Help!! first attempt at javascript/jquery This is based on a example I found, but have so far been unable to adapt it to my usage. / Lars

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• Special technology needed for browser based chat?

  - by orokusaki

  On this post, I read about the usage of XMPP. Is this sort of thing necessary, and more importantly, my main question expanded: Can a chat server and client be built efficiently using only standard HTTP and browser technologies (such as PHP and JS, or RoR and JS, etc)? Or, is it best to stick with old protocols like XMPP find a way to integrate them with my application? I looked into CampFire via LiveHTTPHeaders and Firebug for about 5 minutes, and it appears to use Ajax to send a request which is never answered until another chat happens. Is this just CampFire opening a new thread on the server to listen for an update and then returning a response to the request when the thread hears an update? I noticed that they're requesting on a specific port (8043 if memory serves me) which makes me think that they're doing something more complex than just what I mentioned. Also, the URL requested started with /tcp/ which I found interesting. Note: I don't expect to ever have more than 150 users live-chatting in all the rooms combined at the same time. I understand that if I was building a hosted pay for chat service like CampFire with thousands of concurrent users, it would behoove me to invest time in researching special technologies vs trying to reinvent the wheel in a simple way in my app. Also, if you're going to do it with server polling, how often would you personally poll to maximize response without slamming the server?

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• What would you write in a consitution (law book) for a programmers' country?

  - by Developer Art

  After we have got our great place to talk about professional matters and sozialize online - on SO, I believe the next logical step would be to found our own country! I invite you all to participate and bring together your available resources. We will buy an island, better even a group of island so that we could establish states like .NET territories, Java land, Linux republic etc. We will build a society of programmers (girls - we need you too). To the organizational side, we're going to need some constitution or a law book. I suggest we write it together. I make it a wiki as it should be a cooperative effort. I'll open the work. Section 1. Programmers' rights. Every citizen has a right to an Internet connection 24/7. Every citizen can freely choose the field of interest Section 2. Programmers' obligations. Every citizen must embrace the changing nature of the profession and constanly educate himself Section 3. Law enforcement. Code duplication when can be avoided is punished by limiting the bandwith speed to 64Kbit for a period of one week. Using ugly hacks instead of refactoring code is punished by cutting the Internet connection for a period of one month. Usage of technologies older than 5/10 years is punished by restricting the web access to the sites last updated 5/10 years ago for a period of one month. Please feel free to modify and extend the list. We'll need to have it ready before we proceed formally with the country foundation. A purchase fund will be established shortly. Everyone is invited to participate.

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• Native functions throw UnsatisfiedLinkError in custom view, despite working in main activity

  - by Mark Ingram

  For some reason I can only call native functions from my main activity and not any custom views that I've created. Here is an example file (I followed a tutorial, but renamed the classes http://mindtherobot.com/blog/452/android-beginners-ndk-setup-step-by-step/) See the usage of the native function "getNewString". package com.example.native; import android.app.Activity; import android.app.AlertDialog; import android.content.Context; import android.graphics.Bitmap; import android.graphics.Canvas; import android.os.Bundle; import android.view.View; public class NativeTestActivity extends Activity { static { System.loadLibrary("nativeTest"); } private native String getNewString(); @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); this.setContentView(new BitmapView(this)); String hello = getNewString(); // This line works fine new AlertDialog.Builder(this).setMessage(hello).show(); } } class BitmapView extends View { static { System.loadLibrary("nativeTest"); } private native String getNewString(); public BitmapView(Context context) { super(context); String hello = getNewString(); // This line throws the UnsatisfiedLinkError new AlertDialog.Builder(this.getContext()).setMessage(hello).show(); } } How can I call native functions in my custom views? I've built the application as an Android 2.2 app. I'm running the application on my HTC Desire. I have the latest SDK (9) and latest NDK (r5).

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• How is a referencing environment generally implemented for closures?

  - by Alexandr Kurilin

  Let's say I have a statically/lexically scoped language with deep binding and I create a closure. The closure will consist of the statements I want executed plus the so called referencing environment, or, to quote this post, the collection of variables which can be used. What does this referencing environment actually look like implementation-wise? I was recently reading about ObjectiveC's implementation of blocks, and the author suggests that behind the scenes you get a copy of all of the variables on the stack and also of all the references to heap objects. The explanation claims that you get a "snapshot" of the referencing environment at the point in time of the closure's creation. Is that more or less what happens, or did I misread that? Is anything done to "freeze" a separate copy of the heap objects, or is it safe to assume that if they get modified between closure creation and the closure executing, the closure will no longer be operating on the original version of the object? If indeed there's copying being made, are there memory usage considerations in situations where one might want to create plenty of closures and store them somewhere? I think that misunderstanding of some of these concepts might lead to tricky issues like the ones Eric Lippert mentions in this blog post. It's interesting because you'd think that it wouldn't make sense to keep a reference to a value type that might be gone by the time the closure is called, but I'm guessing that in C# the compiler will figure out that the variable is needed later and put it into the heap instead. It seems that in most memory-managed languages everything is a reference and thus ObjectiveC is a somewhat unique situation with having to deal with copying what's on the stack.

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• Sending and receiving IM messages via controller in Rails

  - by Grnbeagle

  Hi, I need a way to handle XMPP communication in my Rails app. My requirements are: Keep an instance of XMPP client running and logged in as one specific user (my bot user) Trigger an event from a controller to send a message and wait for a reply. The message is sent to another machine equipped with a bot so that the reply is supposed to be returned quickly. I installed xmpp4r and backgrounDrb similar to what's described here, but backgrounDrb seems to have evolved and I couldn't get it to wait for a reply. If it has to happen asynchronously, I am willing to use a server-push technology to notify the browser when the reply arrives. To give you a better idea, here are snippets of my code: (In controller) class ServicesController < ApplicationController layout 'simple' def index render :text => "index" end def show @my_service = Service.find(params[:id]) worker = MiddleMan.worker(:jabber_agent_worker) worker.send_request(:arg => {:jid => "someuser@someserver", :cmd => "help"}) render :text => "testing" end end (In worker script) require 'xmpp4r' require 'logger' class JabberAgentWorker < BackgrounDRb::MetaWorker set_worker_name :jabber_agent_worker def create(args = nil) jid = Jabber::JID.new('myagent@myserver') @client = Jabber::Client.new(jid) @client.connect @client.auth('pass') @client.send(Jabber::Presence.new.set_show(:chat).set_status('BackgrounDRb')) @client.add_message_callback do |message| logger.info("**** messaged received: #{message}") # never reaches here end end def send_request(args = nil) to_jid = Jabber::JID.new(args[:jid]) message = Jabber::Message::new(to_jid, args[:cmd]).set_type(:normal).set_id('1') @client.send(message) end end If anyone can tell me any of the following, I'd much appreciate it: issue with my backgrounDrb usage other background process alternatives appropriate for XMPP interactions other ways of achieving this Thanks in advance.

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• java - powermock whenNew doesnt seem to work, calls the actual constructor

  - by user1331243

  I have two final classes that are used in my unit test. I am trying to use whenNew on the constructor of a final class, but I see that it calls the actual constructor. The code is @PrepareForTest({A.class, B.class, Provider.class}) @Test public void testGetStatus() throws Exception { B b = mock(B.class); when(b.getStatus()).thenReturn(1); whenNew(B.class).withArguments(anyString()).thenReturn(b); Provider p = new Provider(); int val = p.getStatus(); assertTrue((val == 1)); } public class Provider { public int getStatus() { B b = new B("test"); return b.getStatus(); } } public final class A { private void init() { // ...do soemthing } private static A a; private A() { } public static A getInstance() { if (a == null) { a = new A(); a.init(); } return a; } } public final class B { public B() { } public B(String s) { this(A.getInstance(), s); } public B(A a, String s) { } public int getStatus() { return 0; } } On debug, I find that its the actual class B instance created and not the mock instance that is returned for new usage and assertion fails. Any pointers on how to get this working. Thanks

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• Failure remediation strategy for File I/O

  - by Brett

  I'm doing buffered IO into a file, both read and write. I'm using fopen(), fseeko(), standard ANSI C file I/O functions. In all cases, I'm writing to a standard local file on a disk. How often do these file I/O operations fail, and what should the strategy be for failures? I'm not exactly looking for stats, but I'm looking for a general purpose statement on how far I should go to handle error conditions. For instance, I think everyone recognizes that malloc() could and probably will fail someday on some user's machine and the developer should check for a NULL being returned, but there is no great remediation strategy since it probably means the system is out of memory. At least, this seems to be the approach taken with malloc() on desktop systems, embedded systems are different. Likewise, is it worth reattempting a file I/O operation, or should I just consider a failure to be basically unrecoverable, etc. I would appreciate some code samples demonstrating proper usage, or a library guide reference that indicates how this is to be handled. Any other data is, of course, welcome.

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• Programming style question on how to code functions

  - by shawnjan

  Hey all! So, I was just coding a bit today, and I realized that I don't have much consistency when it comes to a coding style when programming functions. One of my main concerns is whether or not its proper to code it so that you check that the input of the user is valid OUTSIDE of the function, or just throw the values passed by the user into the function and check if the values are valid in there. Let me sketch an example: I have a function that lists hosts based on an environment, and I want to be able to split the environment into chunks of hosts. So an example of the usage is this: listhosts -e testenv -s 2 1 This will get all the hosts from the "testenv", split it up into two parts, and it is displaying part one. In my code, I have a function that you pass it in a list, and it returns a list of lists based on you parameters for splitting. BUT, before I pass it a list, I first verify the parameters in my MAIN during the getops process, so in the main I check to make sure there are no negatives passed by the user, I make sure the user didnt request to split into say, 4 parts, but asking to display part 5 (which would not be valid), etc. tl;dr: Would you check the validity of a users input the flow of you're MAIN class, or would you do a check in your function itself, and either return a valid response in the case of valid input, or return NULL in the case of invalid input? Obviously both methods work, I'm just interested to hear from experts as to which approach is better :) Thanks for any comments and suggestions you guys have!

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• What Javascript graphing package will let me plot points against a user-selected coordinate system?

  - by wes

  My customer has some specific requirements for a graph to show in our web app. We use HighCharts elsewhere in the app for more traditional graphing, but it doesn't seem to work for this situation. Their requirements: Allow the user to select a background image, set the scale and origin of the coordinate system. We'll graph our points against the user-defined coordinates. Points can be color coded Mouse-over boxes show more detail about the points Support for zooming and panning, scaling the background appropriately Less importantly: Support for drawing vectors off the points Some of this seems basic, but looking around at different graph packages, I was unable to find any with an example of this kind of usage. I've entertained the thought of just hacking it together in canvas myself, but I've never worked with canvas before so I don't think it would be cost effective. The basics of plotting points with a scaled coordinate system against an image background wouldn't be too hard, but the mouse-over details, zooming and panning sound much more daunting to me. More info: Right now we use jQuery, HighCharts, and ExtJS for our app. We tried flot in the past but switched to HighCharts after flot didn't meet our needs.

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• Modify XML existing content in C#

  - by Nano HE

  Purpose: I plan to Create a XML file with XmlTextWriter and Modify/Update some Existing Content with XmlNode SelectSingleNode(), node.ChildNode[?].InnerText = someting, etc. After I created the XML file with XmlTextWriter as below. XmlTextWriter textWriter = new XmlTextWriter("D:\\learning\\cs\\myTest.xml", System.Text.Encoding.UTF8); I practiced the code below. But failed to save my XML file. XmlDocument doc = new XmlDocument(); doc.Load("D:\\learning\\cs\\myTest.xml"); XmlNode root = doc.DocumentElement; XmlNode myNode; myNode= root.SelectSingleNode("descendant::books"); .... textWriter.Close(); doc.Save("D:\\learning\\cs\\myTest.xml"); I found it is not good to produce like my way. Is there any suggestion about it? I am not clear about the concepts and usage of both XmlTextWriter and XmlNode in the same project. Thank you for reading and replies.

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• Winsock WSAAsyncSelect sending without an infinite buffer

  - by Xexr

  Hi, This is more of a design question than a specific code question, I'm sure I am missing the obvious, I just need another set of eyes. I am writing a multi-client server based on WSAAsyncSelect, each connection is made into an object of a connection class I have written which contains associated settings and buffers etc. My question concerns FD_WRITE, I understand how it operates: One FD_WRITE is sent immediately after a connection is established. Thereafter, you should send until WSAEWOULDBLOCK is received at which point you store what is left to send in a buffer, and wait to be told that it is ok to send again. This is where I have a problem, how large do I make this holding buffer within each connections object? The amount of time until a new FD_WRITE is received is unknown, I could be attempting to send a lot of stuff during this period, all the time adding to my outgoing buffer. If I make the buffer dynamic, memory usage could spiral out of control if for whatever reason, I am unable to send() and reduce the buffer. So my question is how do you generally handle this situation? Note I am not talking about the network buffer itself which winsock uses, but one of my own creation used to "queue" up sends. Hope I explained that well enough, thanks all!

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• Is it right that Strophe.addHandler reads only first node from response?

  - by markcial

  I'm starting to learn strophe library usage and when i use addHandler to parse response it seems to read only first node of xml response so when i receive a xml like that : <body xmlns='http://jabber.org/protocol/httpbind'> <presence xmlns='jabber:client' from='test2@localhost' to='test2@localhost' type='avaliable' id='5593:sendIQ'> <status/> </presence> <presence xmlns='jabber:client' from='test@localhost' to='test2@localhost' xml:lang='en'> <status /> </presence> <iq xmlns='jabber:client' from='test2@localhost' to='test2@localhost' type='result'> <query xmlns='jabber:iq:roster'> <item subscription='both' name='test' jid='test@localhost'> <group>test group</group> </item> </query> </iq> </body> With the handler testHandler used like that : connection.addHandler(testHandler,null,"presence"); function testHandler(stanza){ console.log(stanza); } It only logs : <presence xmlns='jabber:client' from='test2@localhost' to='test2@localhost' type='avaliable' id='5593:sendIQ'> <status/> </presence> What i am missing? is it a right behaviour? Should i add more handlers to get the other stanzas? Thanks for advance

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• Null Pointer Exception in Primavera P6 8.1

  - by gwrichard

  I am getting a null pointer exception in a Primavera P6 8.1 installation. The exception only occurs in one section of the web-client: Application settings.P6 web and the P6 API are deployed on the same WebLogic (10.3.5) node running on a Windows Server 2008 R2 installation. I have done this installation using this same software stack a dozen times and don't have this issue on any of the other installs. Exact error below: Match: beginTraversal Match: digest selected JREDesc: JREDesc[version 1.6.0_20+, heap=-1--1, args=null, href=http://java.sun.com/products/autodl/j2se, sel=false, null, null], JREInfo: JREInfo for index 0: platform is: 1.7 product is: 1.7.0_17 location is: http://java.sun.com/products/autodl/j2se path is: C:\Program Files (x86)\Java\jre7\bin\javaw.exe args is: null native platform is: Windows, x86 [ x86, 32bit ] JavaFX runtime is: JavaFX 2.2.7 found at C:\Program Files (x86)\Java\jre7\ enabled is: true registered is: true system is: true Match: ignoring maxHeap: -1 Match: ignoring InitHeap: -1 Match: digesting vmargs: null Match: digested vmargs: [JVMParameters: isSecure: true, args: ] Match: JVM args after accumulation: [JVMParameters: isSecure: true, args: ] Match: digest LaunchDesc: http://localhost:7001/p6/action/jnlp/appletsjnlp.jnlp?mainClass=com.primavera.pvapplets.adminpreferences.AdminPreferencesApplet&classPath=adminpreferences.jar,prm-applets-common.jar,forms-1.0.7.jar,prm-guisupport.jar,prm-to.jar,jide.jar,tablesupport.jar,formsupport.jar,applets-bo.jar,commons-lang.jar,prm-common.jar,resource_strings.jar,prm-img.jar,commons-logging.jar&name=AdminPreferences&version=8.1.2.0.0602 Match: digest properties: [] Match: JVM args: [JVMParameters: isSecure: true, args: ] Match: endTraversal .. Match: JVM args final: Match: Running JREInfo Version match: 1.7.0.17 == 1.7.0.17 Match: Running JVM args match: have:<> satisfy want:<> Java Plug-in 10.17.2.02 Using JRE version 1.7.0_17-b02 Java HotSpot(TM) Client VM User home directory = C:\Users\gwrichard ---------------------------------------------------- c: clear console window f: finalize objects on finalization queue g: garbage collect h: display this help message l: dump classloader list m: print memory usage o: trigger logging q: hide console r: reload policy configuration s: dump system and deployment properties t: dump thread list v: dump thread stack x: clear classloader cache 0-5: set trace level to <n> ----------------------------------------------------

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• Component based web project directory layout with git and symlinks

  - by karlthorwald

  I am planning my directory structure for a linux/apache/php web project like this: Only www.example.com/webroot/ will be exposed in apache www.example.com/ webroot/ index.php comp1/ comp2/ component/ comp1/ comp1.class.php comp1.js comp2/ comp2.class.php comp2.css lib/ lib1/ lib1.class.php the component/ and lib/ directory will only be in the php path. To make the css and js files visible in the webroot directory I am planning to use symlinks. webroot/ index.php comp1/ comp1.js (symlinked) comp2/ comp2.css (symlinked) I tried following these principles: layout by components and libraries, not by file type and not by "public' or 'non public', index.php is an exception. This is for easier development. symlinking files that need to be public for the components and libs to a public location, but still mirroring the layout. So the component and library structure is also visible in the resulting html code in the links, which might help development. git usage should be safe and always work. it would be ok to follow some procedure to add a symlink to git, but after that checking them out or changing branches should be handled safely and clean How will git handle the symlinking of the single files correctly, is there something to consider? When it comes to images I will need to link directories, how to handle that with git? component/ comp3/ comp3.class.php img/ img1.jpg img2.jpg img3.jpg They should be linked here: webroot/ comp3/ img/ (symlinked ?) If using symlinks for that has disadvantages maybe I could move images to the webroot/ tree directly, which would break the first principle for the third (git practicability). So this is a git and symlink question. But I would be interested to hear comments about the php layout, maybe you want to use the comment function for this.

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• Problem using Lazy<T> from within a generic abstract class

  - by James Black

  I have a generic class that all my DAO classes derive from, which is defined below. I also have a base class for all my entities, but that is not generic. The method GetIdOrSave is going to be a different type than how I defined SabaAbstractDAO, as I am trying to get the primary key to fulfill the foreign key relationships, so this function goes out to either get the primary key or save the entity and then get the primary key. The last code snippet has a solution on how it will work if I get rid of the generic part, so I think this can be solved by using variance, but I can't figure out how to write an interface that will compile. public abstract class SabaAbstractDAO<T> { ... public K GetIdOrSave<K>(K item, Lazy<SabaAbstractDAO<BaseModel>> lazyitemdao) where K : BaseModel { if (item != null && item.Id.IsNull()) { var itemdao = lazyitemdao.Value; item.Id = itemdao.retrieveID(item); if (item.Id.IsNull()) { return itemdao.SaveData(item); } } return item; } } I am getting this error, when I try to compile: Argument 2: cannot convert from 'System.Lazy<ORNL.HRD.LMS.Dao.SabaCourseDAO>' to 'System.Lazy<ORNL.HRD.LMS.Dao.SabaAbstractDAO<ORNL.HRD.LMS.Models.BaseModel>>' I am trying to call it this way: GetIdOrSave(input.OfferingTemplate, new Lazy<SabaCourseDAO>( () => { return new SabaCourseDAO() { Dao = Dao }; }) ); If I change the definition to this, it works. public K GetIdOrSave<K>(K item, Lazy<SabaCourseDAO> lazyitemdao) where K : BaseModel { So, how can I get this to compile using variance (if needed) and generics, so I can have a very general method that will only work with BaseModel and AbstractDAO<BaseModel>? I expect I should only need to make the change in the method and perhaps abstract class definition, the usage should be fine.

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• What are Code Smells? What is the best way to correct them?

  - by Rob Cooper

  OK, so I know what a code smell is, and the Wikipedia Article is pretty clear in its definition: In computer programming, code smell is any symptom in the source code of a computer program that indicates something may be wrong. It generally indicates that the code should be refactored or the overall design should be reexamined. The term appears to have been coined by Kent Beck on WardsWiki. Usage of the term increased after it was featured in Refactoring. Improving the Design of Existing Code. I know it also provides a list of common code smells. But I thought it would be great if we could get clear list of not only what code smells there are, but also how to correct them. Some Rules Now, this is going to be a little subjective in that there are differences to languages, programming style etc. So lets lay down some ground rules: ** ONE SMELL PER ANSWER PLEASE! & ADVISE ON HOW TO CORRECT! ** See this answer for a good display of what this thread should be! DO NOT downmod if a smell doesn't apply to your language or development methodology We are all different. DO NOT just quickly smash in as many as you can think of Think about the smells you want to list and get a good idea down on how to work around. DO downmod answers that just look rushed For example "dupe code - remove dupe code". Let's makes it useful (e.g. Duplicate Code - Refactor into separate methods or even classes, use these links for help on these common.. etc. etc.). DO upmod answers that you would add yourself If you wish to expand, then answer with your thoughts linking to the original answer (if it's detailed) or comment if its a minor point. DO format your answers! Help others to be able to read it, use code snippets, headings and markup to make key points stand out!

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• Using PHP as template language

  - by Kunal

  I wrote up this quick class to do templating via PHP -- I was wondering if this is easily exploitable if I were ever to open up templating to users (not the immediate plan, but thinking down the road). class Template { private $allowed_methods = array( 'if', 'switch', 'foreach', 'for', 'while' ); private function secure_code($template_code) { $php_section_pattern = '/\<\?(.*?)\?\>/'; $php_method_pattern = '/([a-zA-Z0-9_]+)[\s]*\(/'; preg_match_all($php_section_pattern, $template_code, $matches); foreach (array_unique($matches[1]) as $index => $code_chunk) { preg_match_all($php_method_pattern, $code_chunk, $sub_matches); $code_allowed = true; foreach ($sub_matches[1] as $method_name) { if (!in_array($method_name, $this->allowed_methods)) { $code_allowed = false; break; } } if (!$code_allowed) { $template_code = str_replace($matches[0][$index], '', $template_code); } } return $template_code; } public function render($template_code, $params) { extract($params); ob_start(); eval('?>'.$this->secure_code($template_code).'<?php '); $result = ob_get_contents(); ob_end_clean(); return $result; } } Example usage: $template_code = '<?= $title ?><? foreach ($photos as $photo): ?><img src="<?= $photo ?>"><? endforeach ?>'; $params = array('title' => 'My Title', 'photos' => array('img1.jpg', 'img2.jpg')); $template = new Template; echo $template->render($template_code, $params); The idea here is that I'd store the templates (PHP code) in the database, and then run it through the class which uses regular expressions to only allow permitted methods (if, for, etc.). Anyone see an obvious way to exploit this and run arbitrary PHP? If so, I'll probably go the more standard route of a templating language such as Smarty...

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• Question about WeakHashMap

  - by michael

  Hi, In the Javadoc of "http://java.sun.com/j2se/1.4.2/docs/api/java/util/WeakHashMap.html", it said "Each key object in a WeakHashMap is stored indirectly as the referent of a weak reference. Therefore a key will automatically be removed only after the weak references to it, both inside and outside of the map, have been cleared by the garbage collector." And then Note that a value object may refer indirectly to its key via the WeakHashMap itself; that is, a value object may strongly refer to some other key object whose associated value object, in turn, strongly refers to the key of the first value object. But should not both Key and Value should be used weak reference in WeakHashMap? i.e. if there is low on memory, GC will free the memory held by the value object (since the value object most likely take up more memory than key object in most cases)? And if GC free the Value object, the Key Object can be free as well? Basically, I am looking for a HashMap which will reduce memory usage when there is low memory (GC collects the value and key objects if necessary). Is it possible in Java? Thank you.

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• Point data structure for a sketching application

  - by bebraw

  I am currently developing a little sketching application based on HTML5 Canvas element. There is one particular problem I haven't yet managed to find a proper solution for. The idea is that the user will be able to manipulate existing stroke data (points) quite freely. This includes pushing point data around (ie. magnet tool) and manipulating it at whim otherwise (ie. altering color). Note that the current brush engine is able to shade by taking existing stroke data in count. It's a quick and dirty solution as it just iterates the points in the current stroke and checks them against a distance rule. Now the problem is how to do this in a nice manner. It is extremely important to be able to perform efficient queries that return all points within given canvas coordinate and radius. Other features, such as space usage, should be secondary to this. I don't mind doing some extra processing between strokes while the user is not painting. Any pointers are welcome. :)

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• Catch a thread's exception in the caller thread in Python

  - by Mikee

  Hi Everyone, I'm very new to Python and multithreaded programming in general. Basically, I have a script that will copy files to another location. I would like this to be placed in another thread so I can output "...." to indicate that the script is still running. The problem that I am having is that if the files cannot be copied it will throw an exception. This is ok if running in the main thread; however, having the following code does not work: try: threadClass = TheThread(param1, param2, etc.) threadClass.start() ##### **Exception takes place here** except: print "Caught an exception" In the thread class itself, I tried to re-throw the exception, but it does not work. I have seen people on here ask similar questions, but they all seem to be doing something more specific than what I am trying to do (and I don't quite understand the solutions offered). I have seen people mention the usage of sys.exc_info(), however I do not know where or how to use it. All help is greatly appreciated! EDIT: The code for the thread class is below: class TheThread(threading.Thread): def __init__(self, sourceFolder, destFolder): threading.Thread.__init__(self) self.sourceFolder = sourceFolder self.destFolder = destFolder def run(self): try: shul.copytree(self.sourceFolder, self.destFolder) except: raise

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