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• solution for an offline server

  - by dashmug

  I'm trying to setup a development server at work that will ideally be able to test drive a couple of projects in PHP, Rails, or Django (not always running at the same time). I develop the apps locally on a Mac and then I'll put the projects up on this server for testing with my actual users (non-techies) before deploying to a production server. My problem is that we have a very poor internet connection (almost negligible) at work and doing the usual apt-get/yum/ports (make, clean, install) processes for setting up servers always get their packages from online repositories somewhere. I know I could probably download the source and then compile them myself but that's going to be too much of a hassle for me. I'm thinking about two solutions: Plan A: Run a server VM on my Mac and then use this VM as the source repository for the offline server. I've read about Ubuntu's apt-proxy and it seems to be good enough though I haven't tried it yet. I'm not sure if this is possible but can I simply do apt-get install nginx --downloadonly so that the package and its dependencies will be downloaded into my VM and my server can use the VM as the source repo for apt-get? Plan B: Run a server VM on my Mac (which I can setup/update easily when I'm home) and then clone the VM to the offline development server. Maybe I should simply make the server a VM host so I can simply copy the VM over. I think this is okay for the first-time setup but subsequent updates will take too long (cloning the VM image). If I was working on Windows, I imagine it'd be easier because most services have an installer file that I can download and then run at the server. If you could suggest another way, it would be much appreciated. Update: From Michael Hampton's answer, I found a possible solution which is apt-cacher. I also found this page on Ubuntu's website. I wonder if there is a better tool than this one.

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• Open source app to manage and run commands on cloud servers? [closed]

  - by Mark Theunissen

  I'm creating a SaaS platform, and I need a component / library that can create, delete and store the connection details for cloud servers. It also needs to support executing shell commands on these servers and returning the response to the caller. I want a central database of servers and their configuration, plus the ability to reach out and manage the servers via SSH execution of bash scripts. I don't want something that needs agents on every server like Chef. For example, this command is received by the hypothetical application: CREATE USER server = server12345 name = myuser It's translated into the following set of actions and executed by the app, which knows how to connect to server12345, and how to create a user on that server: $ ssh root@server12345 $ adduser myuser And returns the output from the shell: Added user myuser. I've done research on Google and can't quite quite find something that does this already. I've found: fabric This part handles the executing of the shell commands very elegantly, and can take multiple server definitions, but it's supposed to be a deployment tool so doesn't do everything that would be required above - for example, it doesn't have a daemon mode where it listens for commands - it expects to be executed on the shell. It also can't provide the central database functionality. libcloud This library can handle the server admin (CRUD) part, but doesn't have a command interface daemon either, and doesn't let you execute commands on the servers. I guess I need something that is a combination of libcloud, fabric and django for an API. Or something else that does that same thing regardless of language. Overmind Overmind is a GUI and wrapper around libcloud, but doesn't support the command execution part. What am I missing here?

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• QT: trouble with qobject_cast

  - by weevilo

  I have derived QGraphicsItem and QGraphicsScene classes. I want the items to be able to call scene() and get a derviedGraphicsItem * instead of a QGraphicsItem *, so I reimplemented QGraphicsScene::itemAt to return a derived pointer. DerivedItem* DerivedScene::itemAt( const QPointF &position, const QTransform &dt ) const { return qobject_cast< DerivedItem * >( QGraphicsScene::itemAt(position, dt) ); } I get the following error (Qt 4.6, GCC 4.4.3 on Ubuntut 10.4) scene.cpp: In member function ‘DerivedItem* DerivedScene::itemAt(qreal, qreal, const QTransform&) const’: scene.cpp:28: error: no matching function for call to ‘qobject_cast(QGraphicsItem*)’ I then noticed QGraphicsItem doesn't inherit QObject, so I made my derived QGraphicsItem class have multiple inheritance from QObject and QGraphicsItem, and after adding the Q_OBJECT macro and rebuilding the project I get the same error. Am I going about this the wrong way? I know it's supposed to be bad design to try to cast a parent class as a child, but in this case it seems like what I want, since my derived item class has new functionality and its objects need a way to call that new functionality on items around themselves, and asking the items scene object with itemAt() seems like the best way - but I need itemAt() to return a pointer of the right type. I can get around this by having the derived items cast the QGraphicsItem * returned by QGraphicsScene::itemAt() using dynamic_cast, but I don't really understand why that works and not qobject_cast, or the benefits or disadvantages to using dynamic_cast vs. qobject_cast.

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• How to Link VS2010 Database Project and LINQ to SQL

  - by Jason

  As I am working with the new database projects in VS2010, and as I am learning LINQ to SQL, I am curious as to the best way to link the two groups of information so that when I update one, the other updates along with it. From my research here at SO, as well as in Google, it appears the general rule of thumb is: "Build the database, and then create your LINQ to SQL classes." Of course, if I make a change in my database, the LINQ to SQL doesn't update automatically and I have to do it by hand. This is fairly simple right now as my database is small, but I am curious if there is an easier way for this to happen. In addition, the LINQ to SQL tool is pretty nice. The ability to create tables, add associations, and even create inheritance is very simple. As my second question, I am curious as to whether or not VS2010 can work the other way - I design the database in the DBLM file and then link it back to my database project. I appreciate any help with either of these two questions. I'm really interested in making this as easy as possible to reduce errors during development and improve the speed at which changes can be made.

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• Mac gcc non-virtual thunk error

  - by fret

  I'm getting these non-virtual thunk errors only in the Deployment build of my app. It uses a private framework called Lgi. Building on 10.5.8 using XCode 3.1.4 (latest for leopard?) The error looks like this: Ld /Users/matthew/Code/Scribe-Branches/v2.00/build/Development/Scribe.app/Contents/MacOS/Scribe normal i386 cd /Users/matthew/Code/Scribe-Branches/v2.00 /Developer/usr/bin/g++-4.0 -arch i386 -L/Users/matthew/Code/Scribe-Branches/v2.00/build/Development -F/Users/matthew/Code/Scribe-Branches/v2.00/build/Development -F/Users/matthew/Code/Lgi/build -F/Users/matthew/Code/Scribe-Branches/v2.00/../../Lgi/build/Development -F/Users/matthew/Code/Scribe-Branches/v2.00/../../Lgi/build/Development -F/Users/matthew/Code/Scribe-Branches/v2.00/../../Lgi/build/Deployment -F/Users/matthew/Code/Scribe-Branches/v2.00/../../Lgi/build/Development -F/Users/matthew/Code/Scribe-Branches/v2.00/../../Lgi/build/Deployment -filelist /Users/matthew/Code/Scribe-Branches/v2.00/build/Scribe.build/Development/Scribe.build/Objects-normal/i386/Scribe.LinkFileList -framework Carbon -framework Lgi -o /Users/matthew/Code/Scribe-Branches/v2.00/build/Development/Scribe.app/Contents/MacOS/Scribe Undefined symbols: "non-virtual thunk to GWindow::OnDrop(char*, GVariant*, GdcPt2, int)", referenced from: vtable for ScribeWndin ScribeApp.o vtable for GShutdownin ScribeApp.o vtable for CalendarUiin Calendar.o vtable for CalendarViewWndin CalendarView.o vtable for CalendarConfigin CalendarView.o vtable for ScribeExportin Exp_Scribe.o vtable for GNewMailDlgin GNewMailDlg.o ....etc for lots of classes.... Anyway I know I'm not leaving those undefined because it does in fact link and run fine in the development build. Now after googling the issue the first thing to try is changing the optimization setting, which I did... and no dice. Some link error. So these virtual functions are initially defined in GDragDropTarget, and GWindow's inheritance looks like this: class LgiClass GWindow : public GView #ifndef WIN32 , public GDragDropTarget #endif (LgiClass being for __declspec export/import on win32) Any ideas on what to try next? Maybe I need to provide more info.

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• Relation between [[Prototype]] and prototype in JavaScript

  - by Claudiu

  From http://www.jibbering.com/faq/faq_notes/closures.html : Note: ECMAScript defines an internal [[prototype]] property of the internal Object type. This property is not directly accessible with scripts, but it is the chain of objects referred to with the internal [[prototype]] property that is used in property accessor resolution; the object's prototype chain. A public prototype property exists to allow the assignment, definition and manipulation of prototypes in association with the internal [[prototype]] property. The details of the relationship between to two are described in ECMA 262 (3rd edition) and are beyond the scope of this discussion. What are the details of the relationship between the two? I've browsed through ECMA 262 and all I've read there is stuff like: The constructor’s associated prototype can be referenced by the program expression constructor.prototype, Native ECMAScript objects have an internal property called [[Prototype]]. The value of this property is either null or an object and is used for implementing inheritance. Every built-in function and every built-in constructor has the Function prototype object, which is the initial value of the expression Function.prototype Every built-in prototype object has the Object prototype object, which is the initial value of the expression Object.prototype (15.3.2.1), as the value of its internal [[Prototype]] property, except the Object prototype object itself. From this all I gather is that the [[Prototype]] property is equivalent to the prototype property for pretty much any object. Am I mistaken?

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• Compare base class part of sub class instance to another base class instance

  - by Anders Abel

  I have number of DTO classes in a system. They are organized in an inheritance hierarchy. class Person { public int Id { get; set; } public string FirstName { get; set; } public string ListName { get; set; } } class PersonDetailed : Person { public string WorkPhone { get; set; } public string HomePhone { get; set; } public byte[] Image { get; set; } } The reason for splitting it up is to be able to get a list of people for e.g. search results, without having to drag the heavy image and phone numbers along. Then the full PersonDetail DTO is loaded when the details for one person is selected. The problem I have run into is comparing these when writing unit tests. Assume I have Person p1 = myService.GetAPerson(); PersonDetailed p2 = myService.GetAPersonDetailed(); // How do I compare the base class part of p2 to p1? Assert.AreEqual(p1, p2); The Assert above will fail, as p1 and p2 are different classes. Is it possible to somehow only compare the base class part of p2 to p1? Should I implement IEquatable<> on Person? Other suggestions?

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• How to get rank from full-text search query with Linq to SQL?

  - by Stephen Jennings

  I am using Linq to SQL to call a stored procedure which runs a full-text search and returns the rank plus a few specific columns from the table Article. The rank column is the rank returned from the SQL function FREETEXTTABLE(). I've added this sproc to the data model designer with return type Article. This is working to get the columns I need; however, it discards the ranking of each search result. I'd like to get this information so I can display it to the user. So far, I've tried creating a new class RankedArticle which inherits from Article and adds the column Rank, then changing the return type of my sproc mapping to RankedArticle. When I try this, an InvalidOperationException gets thrown: Data member 'Int32 ArticleID' of type 'Heap.Models.Article' is not part of the mapping for type 'RankedArticle'. Is the member above the root of an inheritance hierarchy? I can't seem to find any other questions or Google results from people trying to get the rank column, so I'm probably missing something obvious here.

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• JPA Lookup Hierarchy Mapping

  - by Andy Trujillo

  Given a lookup table: | ID | TYPE | CODE | DESCRIPTION | | 1 | ORDER_STATUS | PENDING | PENDING DISPOSITION | | 2 | ORDER_STATUS | OPEN | AWAITING DISPOSITION | | 3 | OTHER_STATUS | OPEN | USED BY OTHER ENTITY | If I have an entity: @MappedSuperclass @Table(name="LOOKUP") @Inheritance(strategy=InheritanceType.SINGLE_TABLE) @DiscriminatorColumn(name="TYPE", discriminatorType=DiscriminatorType.STRING) public abstract class Lookup { @Id @Column(name="ID") int id; @Column(name="TYPE") String type; @Column(name="CODE") String code; @Column(name="DESC") String description; ... } Then a subclass: @Entity @DiscriminatorValue("ORDER_STATUS") public class OrderStatus extends Lookup { } The expectation is to map it: @Entity @Table(name="ORDERS") public class OrderVO { ... @ManyToOne @JoinColumn(name="STATUS", referencedColumnName="CODE") OrderStatus status; ... } So that the CODE is stored in the database. I expected that if I wrote: OrderVO o = entityManager.find(OrderVO.class, 123); the SQL generated using OpenJPA would look something like: SELECT t0.id, ..., t1.CODE, t1.TYPE, t1.DESC FROM ORDERS t0 LEFT OUTER JOIN LOOKUP t1 ON t0.STATUS = t1.CODE AND t1.TYPE = 'ORDER_STATUS' WHERE t0.ID = ? But the actual SQL that gets generated is missing the AND t1.TYPE = 'ORDER_STATUS' This causes a problem when the CODE is not unique. Is there a way to have the discriminator included on joins or am I doing something wrong here?

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• Castle Windsor with ASP.NET MVC 2 Areas

  - by Doug Shontz

  Been lurking for a few months and decided to jump in with a question. I am very new to Windsor and IoC in general. I can get Windsor to work with my MVC2 project with no problem. The project I am working on is a "portal" of multiple applications under one MVC2 project using the new Areas concept. In this scenario, each Area will actually be a separate application inside the "portal". We are doing this to effectively share a LOT of common code, views, authentication, and cross-application functionality. Many of our apps link to one another, so it made sense after discussing it to combine them into one project. What I am wondering how to do is actually allow different Areas to inject different concrete classes? In my limited understanding, the Application_Start is governing building the container and assigning it as the controller factory. I don't necessarily want to do all the injection at the application level. We have a config system where we have a config.xml at the root of every Area and those settings override any root settings. I would like to continue that trend by having the injections for each Area be read by the Area's config.xml (an inheritance similar to Webforms web.config where the config in a lower folder overrides settings in a parent folder). Example: I would have an ILogHandler which would need a different concrete implementation depending on which Area of the application I am in. So I would need to inject something different depending on where I am at in the application. I can easily do this using factories since each area could have it's own set of factories, but I am attempting to take this opportunity to learn about IoC and what the benefits/drawbacks are. Any help would be appreciated.

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• JPA : many-to-many - only one foreign key in the association table

  - by Julien

  Hi, I mapped two classes in a ManyToMany association with these annotations : @Entity @Inheritance(strategy=InheritanceType.TABLE_PER_CLASS) public abstract class TechnicalItem extends GenericBusinessObject implements Resumable{ @SequenceGenerator(name="TECHNICAL_ITEM_ID_GEN", sequenceName="TECHNICAL_ITEM_ID_SEQ") @Id @Column(name = "\"ID\"", nullable = false) @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "TECHNICAL_ITEM_ID_GEN") private int id; @ManyToMany(mappedBy = "referencePerformanceItems", fetch=FetchType.LAZY) private List testingRates; } @Entity @DiscriminatorValue("T") public class TestingRate extends Rate { @ManyToMany(fetch=FetchType.LAZY) @JoinTable(name="ecc.\"TESTING_RATE_TECHNICAL_ITEM\"", joinColumns = {@JoinColumn(name = "\"TESTING_RATE_ID\"")}, inverseJoinColumns = {@JoinColumn(name = "\"TECHNICAL_ITEM_ID\"")}) //@ManyToMany(mappedBy = "testingRates", fetch=FetchType.LAZY) private List referencePerformanceItems; } The sql generated for the association table creation is : create table ecc."TESTING_RATE_TECHNICAL_ITEM" ( "TESTING_RATE_ID" int4 not null, "TECHNICAL_ITEM_ID" int4 not null ); alter table ecc."TESTING_RATE_TECHNICAL_ITEM" add constraint FKC5D64DF6A2FE2698 foreign key ("TESTING_RATE_ID") references ecc."RATE"; There is no mention of the second foreign key "TECHNICAL_ITEM_ID" (the second part of the composite foreign key which should be in the association table). Is it a normal behaviour ? What should I do in the mapping if I want my 2 columns are 2 foreign keys referencing the primary keys of my 2 concerned tables. I use a PostGreSQL database and Hibernate as JPA provider. Thanks, Julien

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• Authlogic with nested attributes and polymorphic associations

  - by ferparra

  Hi all! I'm having trouble with the following code: User < AR acts_as_authentic belongs_to :owner, :polymorphic => true end Worker < AR has_one :user, :as => :owner accepts_nested_attributes_for :user end Employer < AR has_one :user, :as => :owner accepts_nested_attributes_for :user end I'd like to create registration forms based on user types, and to include authentication fields such as username and password. I currently do this: UserRegistrationController < AC #i.e. a new Employer def new @employer = Employer.new @employer.build_user end ... end I then include User fields with fields_for. All views render fine, but here's the catch: I cannot build a User, it tells me :password is a wrong method, so I guess the authentication logic was bypassed. What should I do? Am I doing it wrong altogether? Should I drop polymorphic associations in favor of Single Table Inheritance? Whatever I do, I have to make sure it plays nicely with Authlogic.

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• How to reset parent child relationship between nested div

  - by Shantanu Gupta

  I am new to CSS designing and not aware of most of the properties of CSS. I am creating a layout for a web page. I am using div in my layout. My structure is somewhat like this <div id="content1_bg"> <div> <div class="content1_title_img_div"></div> <div class="content1_title_txt_div"></div> <div class="content1_dvider_div"></div> <div class="content1_content_div"></div> </div> <div></div> <div></div> </div> For this my CSS is #content1_bg div{width:250px;height:220px;float:left;border:3px solid blue; margin:20px;} .content1_title_img_div{width:50px;height:100px;} .content1_title_txt_div{width:150px;height:100px;} .content1_dvider_div{width:100%;height:10%;clear:both;} .content1_content_div{width:100%;height:50%;clear:both;} For this layout i was expecting my design to be like ---------------- |BOX1 BOX2 | ---------------- | BOX 3 | ---------------- | BOX 4 | ---------------- But on using my css layout is somewhat like this -------------------- | | | | | |BOX1| | BOX2| | | | | | | -------------------- | | |BOX3| | | -------------------- | | |BOX4| | | Basically i want my inner div's not to inherit the properties of outer div. How can i remove this inheritance relationship between parent div and child div

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• UDK SettingsScene variable

  - by Ricket

  I am in the process of porting a script from UT3 to UDK. The script is for class ZOUIFrontEnd_MainMenu extends UTUIFrontEnd_MainMenu. I'm getting the following compiler error: C:\UDK\UDK-2010-03\Development\Src\FixIt\Classes\ZOUIFrontEnd_MainMenu.uc(18) : Error, Bad or missing expression in Call to 'OpenSceneByName', parameter 1 The referenced line is as follows: OpenSceneByName(SettingsScene); Okay, so I figured the OpenSceneByName function changed in UDK. Tracing the path of inheritance all the way up to UDKUIScene.uc, I found the definition: function UIScene OpenSceneByName(string SceneToOpen, bool bSkipAnimation=false, optional delegate<OnSceneActivated> SceneDelegate=None) Assuming SettingsScene is a string, everything looks fine, right? So I figured I would find SettingsScene to make sure it's a string. Well doing a search for "SettingsScene" in all files turned up only one other line; UTGameReplicationInfo.uc line 334: UTPC.OpenUIScene(class'UTUIFrontEnd_MainMenu'.default.SettingsScene); But UTUIFrontEnd_MainMenu doesn't have a SettingsScene variable in it! Just to check, I changed my line of code to match: OpenSceneByName(class'UTUIFrontEnd_MainMenu'.default.SettingsScene); And indeed, I get the following compile error now: C:\UDK\UDK-2010-03\Development\Src\FixIt\Classes\ZOUIFrontEnd_MainMenu.uc(18) : Error, Unknown Property 'SettingsScene' in 'Class UTGame.UTUIFrontEnd_MainMenu' How does UTGameReplicationInfo.uc successfully compile? Where is the SettingsScene variable?

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• Big problem with regular expression in Lex (lexical analyzer)

  - by Nazgulled

  Hi, I have some content like this: author = "Marjan Mernik and Viljem Zumer", title = "Implementation of multiple attribute grammar inheritance in the tool LISA", year = 1999 author = "Manfred Broy and Martin Wirsing", title = "Generalized Heterogeneous Algebras and Partial Interpretations", year = 1983 author = "Ikuo Nakata and Masataka Sassa", title = "L-Attributed LL(1)-Grammars are LR-Attributed", journal = "Information Processing Letters" And I need to catch everything between double quotes for title. My first try was this: ^(" "|\t)+"title"" "*=" "*"\"".+"\"," Which catches the first example, but not the other two. The other have multiple lines and that's the problem. I though about changing to something with \n somewhere to allow multiple lines, like this: ^(" "|\t)+"title"" "*=" "*"\""(.|\n)+"\"," But this doesn't help, instead, it catches everything. Than I though, "what I want is between double quotes, what if I catch everything until I find another " followed by ,? This way I could know if I was at the end of the title or not, no matter the number of lines, like this: ^(" "|\t)+"title"" "*=" "*"\""[^"\""]+"," But this has another problem... The example above doesn't have it, but the double quote symbol (") can be in between the title declaration. For instance: title = "aaaaaaa \"X bbbbbb", And yes, it will always be preceded by a backslash (\). Any suggestions to fix this regexp?

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• Rendering a control generates security exception in .Net 4

  - by Jason Short

  I am having a problem with code that worked fine in .Net 2 giving this error under .Net 4. Build (web): Inheritance security rules violated while overriding member: 'Controls.RelatedPosts.RenderControl(System.Web.UI.HtmlTextWriter)'. Security accessibility of the overriding method must match the security accessibility of the method being overriden. This is in DotNetBlogEngine. There were several other security demands in the code that .Net 4 didn't seem to like. I followed some of the advice I found on blogs (and here) and got rid of all the other errors. But this one still eludes me. The Main blogengine core dll is not set for security demands anylonger and is compiled for .Net 4 as well. This error is in the website side attempting to use the dll. There are controls that call a RenderControl method taking an HtmlTextWriter. Apparently the text writer now has some soft of security attributes set on it. Each of the controls implements a custom interface ( public interface ICustomFilter ), there are no security permissions present or demands. The site is running full trust on my local dev machine.

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• Simple Xml list parsing problem

  - by Hubidubi

  I have this xml: <root> <fruitlist> <apple>4</apple> <apple>5</apple> <orange>2</orange> <orange>6</orange> </fruitlist> </root> I'm writing a parser class, although I can't figure out how to deal with multiple node types. I can easily parse a list that contains only one node type (eg. just apples, not oranges) @ElementList(name = "fruitlist") private List<Apple> exercises; with more than one node type it also wants so parse non Apple nodes which doesn't work. I also tried to make another list for oranges, but it doen't work, I can't use fruitlist name more than once. @ElementList(name = "fruitlist", entry = "orange") private List<Orange> exercises; The ideal would be two seperate list for both node types. Hubi EDIT: After more searching & fiddling this question is a duplicate: Inheritance with Simple XML Framework

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• PostgreSQL: Auto-partition a table

  - by Adam Matan

  Hi, I have a huge database which holds pairs of numbers (A,B), each ranging from 0 to 10,000 and stored as floats. e.g., (1, 9984.4), (2143.44, 124.243), (0.55, 0), ... Since the PostgreSQL table which stores these pairs grew quite large, I have decided to partition it into inheriting sub-tables. I intend to create 100 such tables, each storing a range of 1000x1000. The problem is that these numbers tend to come in large chunks of nearby numbers. It means that in the future, some tables will be nearly empty and some will hold a very large portion of the database. Unfortunately, the distribution of future pairs is yet unknown. I am looking for a way to automatically repartition my table. That means that if a certain subtable holds more than a specific number of pairs, it will be automatically partitioned into four sub-sub tables, and so on. My questions are: Is recursive partitioning and inheritance possible in PostgreSQL 8.3? Will indexes and query plans understand it? What's the best way to split a subtable once it grew too large? I should point out that this isn't a live database, so a downtime of few hours every week is totally acceptable. Thanks in advance, Adam

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• Question about functional OOP style in JavaScript

  - by valums

  I prefer to use functional OOP style for my code (similar to the module pattern) because it helps me to avoid the "new" keyword and all problems with the scope of "this" keyword in callbacks. But I've run into a few minor issues with it. I would like to use the following code to create a class. namespace.myClass = function(){ var self = {}, somePrivateVar1; // initialization code that would call // private or public methods privateMethod(); self.publicMethod(); // sorry, error here function privateMethod(){} self.publicMethod = function(){}; return self; } The problem is that I can't call public methods from my initialization code, as these functions are not defined yet. The obvious solution would be to create an init method, and call it before "return self" line. But maybe you know a more elegant solution? Also, how do you usually handle inheritance with this pattern? I use the following code, butI would like to hear your ideas and suggestions. namespace.myClass2 = function(){ var self = namespace.parentClass(), somePrivateVar1; var superMethod = self.someMethod; self.someMethod = function(){ // example shows how to overwrite parent methods superMethod(); }; return self; } Edit. For those who asked what are the reasons for choosing this style of OOP, you can look into following questions: http://stackoverflow.com/questions/1557386/prototypal-vs-functional-oop-in-javascript http://stackoverflow.com/questions/383402/is-javascript-s-new-keyword-considered-harmful

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• What is a good standard exercise to learn the OO features of a language?

  - by FarmBoy

  When I'm learning a new language, I often program some mathematical functions to get used to the control flow syntax. After that, I like to implement some sorting algorithms to get used to the array/list constructs. But I don't have a standard exercise for exploring the languages OO features. Does anyone have a stock exercise for this? A good answer would naturally lend to inheritance, polymorphism, etc., for a programmer already comfortable with these concepts. An ideal answer would be one that could be communicated in a few words, without ambiguity, in the way that "implement mergesort" is completely unambiguous. (As an example, answering "design a game" is so vague as to be useless.) Any ideas? EDIT: I have to remark that the results here are somewhat ironic. 10 upvotes and (originally) 5 favorites suggest that this is a question others are interested in. Yet the most upvoted answer is one that says there is no good answer. Oh well. I think I'll look at the textbook below, I've found games useful in the past for OO.

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• What is the best practice for using lock within inherited classes

  - by JDMX

  I want to know if one class is inheriting from another, is it better to have the classes share a lock object that is defined at the base class or to have a lock object defined at each inheritance level. A very simple example of a lock object on each level of the class public class Foo { private object thisLock = new object(); private int ivalue; public int Value { get { lock( thisLock ) { return ivalue; } } set { lock( thisLock ) { ivalue= value; } } } } public class Foo2: Foo { private object thisLock2 = new object(); public int DoubleValue { get { lock( thisLock2 ) { return base.Value * 2; } } set { lock( thisLock2 ) { base.Value = value / 2; } } } } public class Foo6: Foo2 { private object thisLock6 = new object(); public int TripleDoubleValue { get { lock( thisLock6 ) { return base.DoubleValue * 3; } } set { lock( thisLock6 ) { base.DoubleValue = value / 3; } } } } A very simple example of a shared lock object public class Foo { protected object thisLock = new object(); private int ivalue; public int Value { get { lock( thisLock ) { return ivalue; } } set { lock( thisLock ) { ivalue= value; } } } } public class Foo2: Foo { public int DoubleValue { get { lock( thisLock ) { return base.Value * 2; } } set { lock( thisLock ) { base.Value = value / 2; } } } } public class Foo6: Foo2 { public int TripleDoubleValue { get { lock( thisLock ) { return base.DoubleValue * 3; } } set { lock( thisLock ) { base.DoubleValue = value / 3; } } } } Which example is the preferred way to manage locking within an inherited class?

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• Why are all objects in this extension of usercontrol null at runtime?

  - by csciguy

  All, I have a simple class. public class Container : UserControl { public bool IsClickable { get; set; } } I have a class that extends this class. public class ScrollingContainer : Container { public void Draw() { } public void Update() { } } I have a custom class, that then extends ScrollingContainer. public partial class MaskContainer : ScrollingContainer { public MaskContainer() { InitializeComponent(); } } XAML <local:ScrollingContainer x:Class="Test.Types.MaskContainer" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:local="clr-namespace:GameObjects;assembly=GameObjects" mc:Ignorable="d" > </local:ScrollingContainer> In my mainpage.xaml, I have the following. <types:MaskContainer x:Name="maskContainer" Canvas.ZIndex="1" Width="Auto" Height="Auto"> <Canvas x:Name="maskCanvas"> <Button x:Name="button1" Content="test button"/> </Canvas> </types:MaskContainer> Why, at runtime, are both maskCanvas and button1 null? maskContainer is not null. The inheritance should be straightforward here. Container inherits usercontrol. Scrollable container inherits container. Mask Container inherits scrollable container. Why am I losing the fucntionality of the original base class at this level? Is it incorrect to add the element (button1) to the maskcontainer inside of the main.xaml? My end goal is to create a container that is reusable, but inherits all properties/methods that I've specified throughout the chain. Any help is appreciated.

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• executing stored procedure from Spring-Hibernate using Annotations

  - by HanuAthena

  I'm trying to execute a simple stored procedure with Spring/Hibernate using Annotations. Here are my code snippets: DAO class: public class UserDAO extends HibernateDaoSupport { public List selectUsers(final String eid){ return (List) getHibernateTemplate().execute(new HibernateCallback() { public Object doInHibernate(Session session) throws HibernateException, SQLException { Query q = session.getNamedQuery("SP_APPL_USER"); System.out.println(q); q.setString("eid", eid); return q.list(); } }); } } my entity class: @Entity @Table(name = "APPL_USER") @Inheritance(strategy = InheritanceType.SINGLE_TABLE) @DiscriminatorFormula(value = "SUBSCRIBER_IND") @DiscriminatorValue("N") @NamedQuery(name = "req.all", query = "select n from Requestor n") @org.hibernate.annotations.NamedNativeQuery(name = "SP_APPL_USER", query = "call SP_APPL_USER(?, :eid)", callable = true, readOnly = true, resultClass = Requestor.class) public class Requestor { @Id @Column(name = "EMPL_ID") public String getEmpid() { return empid; } public void setEmpid(String empid) { this.empid = empid; } @Column(name = "EMPL_FRST_NM") public String getFirstname() { return firstname; } ... } public class Test { public static void main(String[] args) { ApplicationContext ctx = new ClassPathXmlApplicationContext( "applicationContext.xml"); APFUser user = (APFUser)ctx.getBean("apfUser"); List selectUsers = user.getUserDAO().selectUsers("EMP456"); System.out.println(selectUsers); } } and the stored procedure: create or replace PROCEDURE SP_APPL_USER (p_cursor out sys_refcursor, eid in varchar2) as empId varchar2(8); fname varchar2(50); lname varchar2(50); begin empId := null; fname := null; lname := null; open p_cursor for select l.EMPL_ID, l.EMPL_FRST_NM, l.EMPL_LST_NM into empId, fname, lname from APPL_USER l where l.EMPL_ID = eid; end; If i enter invalid EID, its returning empty list which is OK. But when record is there, following exception is thrown: Exception in thread "main" org.springframework.jdbc.BadSqlGrammarException: Hibernate operation: could not execute query; bad SQL grammar [call SP_APPL_USER(?, ?)]; nested exception is java.sql.SQLException: Invalid column name Do I need to modify the entity(Requestor.class) ? How will the REFCURSOR be converted to the List? The stored procedure is expected to return more than one record.

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• Can the Diamond Problem be really solved?

  - by Mecki

  A typical problem in OO programming is the diamond problem. I have parent class A with two sub-classes B and C. A has an abstract method, B and C implement it. Now I have a sub-class D, that inherits of B and C. The diamond problem is now, what implementation shall D use, the one of B or the one of C? People claim Java knows no diamond problem. I can only have multiple inheritance with interfaces and since they have no implementation, I have no diamond problem. Is this really true? I don't think so. See below: [removed vehicle example] Is a diamond problem always the cause of bad class design and something neither programmer nor compiler needs to solve, because it shouldn't exist in the first place? Update: Maybe my example was poorly chosen. See this image Of course you can make Person virtual in C++ and thus you will only have one instance of person in memory, but the real problem persists IMHO. How would you implement getDepartment() for GradTeachingFellow? Consider, he might be student in one department and teach in another one. So you can either return one department or the other one; there is no perfect solution to the problem and the fact that no implementation might be inherited (e.g. Student and Teacher could both be interfaces) doesn't seem to solve the problem to me.

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• How to implement or emulate an "abstract" OCUnit test class?

  - by Quinn Taylor

  I have a number of Objective-C classes organized in an inheritance hierarchy. They all share a common parent which implements all the behaviors shared among the children. Each child class defines a few methods that make it work, and the parent class raises an exception for the methods designed to be implemented/overridden by its children. This effectively makes the parent a pseudo-abstract class (since it's useless on its own) even though Objective-C doesn't explicitly support abstract classes. The crux of this problem is that I'm unit testing this class hierarchy using OCUnit, and the tests are structured similarly: one test class that exercises the common behavior, with a subclass corresponding to each of the child classes under test. However, running the test cases on the (effectively abstract) parent class is problematic, since the unit tests will fail in spectacular fashion without the key methods. (The alternative of repeating the common tests across 5 test classes is not really an acceptable option.) The non-ideal solution I've been using is to check (in each test method) whether the instance is the parent test class, and bail out if it is. This leads to repeated code in every test method, a problem that becomes increasingly annoying if one's unit tests are highly granular. In addition, all such tests are still executed and reported as successes, skewing the number of meaningful tests that were actually run. What I'd prefer is a way to signal to OCUnit "Don't run any tests in this class, only run them in its child classes." To my knowledge, there isn't (yet) a way to do that, something similar to a +(BOOL)isAbstractTest method I can implement/override. Any ideas on a better way to solve this problem with minimal repetition? Does OCUnit have any ability to flag a test class in this way, or is it time to file a Radar? Edit: Here's a link to the test code in question. Notice the frequent repetition of if (...) return; to start a method, including use of the NonConcreteClass() macro for brevity.

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