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  • Basic Defensive Database Programming Techniques

    We can all recognise good-quality database code: It doesn't break with every change in the server's configuration, or on upgrade. It isn't affected by concurrent usage, or high workload. In an extract from his forthcoming book, Alex explains just how to go about producing resilient TSQL code that works, and carries on working.

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  • Throwing exception from a property when my object state is invalid

    - by Rumi P.
    Microsoft guidelines say: "Avoid throwing exceptions from property getters", and I normally follow that. But my application uses Linq2SQL, and there is the case where my object can be in invalid state because somebody or something wrote nonsense into the database. Consider this toy example: [Table(Name="Rectangle")] public class Rectangle { [Column(Name="ID", IsPrimaryKey = true, IsDbGenerated = true)] public int ID {get; set;} [Column(Name="firstSide")] public double firstSide {get; set;} [Column(Name="secondSide")] public double secondSide {get; set;} public double sideRatio { get { return firstSide/secondSide; } } } Here, I could write code which ensures that my application never writes a Rectangle with a zero-length side into the database. But no matter how bulletproof I make my own code, somebody could open the database with a different application and create an invalid Rectangle, especially one with a 0 for secondSide. (For this example, please forget that it is possible to design the database in a way such that writing a side length of zero into the rectangle table is impossible; my domain model is very complex and there are constraints on model state which cannot be expressed in a relational database). So, the solution I am gravitating to is to change the getter to: get { if(firstSide > 0 && secondSide > 0) return firstSide/secondSide; else throw new System.InvalidOperationException("All rectangle sides should have a positive length"); } The reasoning behind not throwing exceptions from properties is that programmers should be able to use them without having to make precautions about catching and handling them them. But in this case, I think that it is OK to continue to use this property without such precautions: if the exception is thrown because my application wrote a non-zero rectangle side into the database, then this is a serious bug. It cannot and shouldn't be handled in the application, but there should be code which prevents it. It is good that the exception is visibly thrown, because that way the bug is caught. if the exception is thrown because a different application changed the data in the database, then handling it is outside of the scope of my application. So I can't do anything about it if I catch it. Is this a good enough reasoning to get over the "avoid" part of the guideline and throw the exception? Or should I turn it into a method after all? Note that in the real code, the properties which can have an invalid state feel less like the result of a calculation, so they are "natural" properties, not methods.

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  • Updating an Entity through a Service

    - by GeorgeK
    I'm separating my software into three main layers (maybe tiers would be a better term): Presentation ('Views') Business logic ('Services' and 'Repositories') Data access ('Entities' (e.g. ActiveRecords)) What do I have now? In Presentation, I use read-only access to Entities, returned from Repositories or Services, to display data. $banks = $banksRegistryService->getBanksRepository()->getBanksByCity( $city ); $banksViewModel = new PaginatedList( $banks ); // some way to display banks; // example, not real code I find this approach quite efficient in terms of performance and code maintanability and still safe as long as all write operations (create, update, delete) are preformed through a Service: namespace Service\BankRegistry; use Service\AbstractDatabaseService; use Service\IBankRegistryService; use Model\BankRegistry\Bank; class Service extends AbstractDatabaseService implements IBankRegistryService { /** * Registers a new Bank * * @param string $name Bank's name * @param string $bik Bank's Identification Code * @param string $correspondent_account Bank's correspondent account * * @return Bank */ public function registerBank( $name, $bik, $correspondent_account ) { $bank = new Bank(); $bank -> setName( $name ) -> setBik( $bik ) -> setCorrespondentAccount( $correspondent_account ); if( null === $this->getBanksRepository()->getDefaultBank() ) $this->setDefaultBank( $bank ); $this->getEntityManager()->persist( $bank ); return $bank; } /** * Makes the $bank system's default bank * * @param Bank $bank * @return IBankRegistryService */ public function setDefaultBank( Bank $bank ) { $default_bank = $this->getBanksRepository()->getDefaultBank(); if( null !== $default_bank ) $default_bank->setDefault( false ); $bank->setDefault( true ); return $this; } } Where am I stuck? I'm struggling about how to update certain fields in Bank Entity. Bad solution #1: Making a series of setters in Service for each setter in Bank; - seems to be quite reduntant, increases Service interface complexity and proportionally decreases it's simplicity - something to avoid if you care about code maitainability. I try to follow KISS and DRY principles. Bad solution #2: Modifying Bank directly through it's native setters; - really bad. If you'll ever need to move modification into the Service, it will be pain. Business logic should remain in Business logic layer. Plus, there are plans on logging all of the actions and maybe even involve user permissions (perhaps, through decorators) in future, so all modifications should be made only through the Service. Possible good solution: Creating an updateBank( Bank $bank, $array_of_fields_to_update) method; - makes the interface as simple as possible, but there is a problem: one should not try to manually set isDefault flag on a Bank, this operation should be performed through setDefaultBank method. It gets even worse when you have relations that you don't want to be directly modified. Of course, you can just limit the fields that can be modified by this method, but how do you tell method's user what they can and cannot modify? Exceptions?

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  • Google Top Geek E07

    Google Top Geek E07 In Spanish! Noticias: 1. Gráfico de conocimiento ahora en español y varios idiomas más. Totalmente localizado. 2. Nueva versión de Snapseed para iOS y Android. Gmail para Android y la versión 2.0 para iOS. Nuevo estilo para YouTube. 3. 500Millones de usuarios en Google+ y una nueva característica: comunidades. Las búsquedas de la semana y lo más visto en YouTube. Recomendamos Picket, una app para Android que funciona en México y te da la cartelera en cines. Noticias para desarrolladores: 1. Mejores mapas para apps de Android, nuevo API. 2. Una imagen dice más que mil palabras: Place Photos y Radar Search Ligas y más información en el blog: programa-con-google.blogspot.com From: GoogleDevelopers Views: 80 11 ratings Time: 18:09 More in Science & Technology

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  • Senior Developers vs. Junior

    - by huwyss
    I like the following quote which I found on codinghorror:[As Steve points out this is one key difference between junior and senior developers:] In the old days, seeing too much code at once quite frankly exceeded my complexity threshold, and when I had to work with it I'd typically try to rewrite it or at least comment it heavily. Today, however, I just slog through it without complaining (much). When I have a specific goal in mind and a complicated piece of code to write, I spend my time making it happen rather than telling myself stories about it [in comments].

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  • Best way to render card images

    - by user1065145
    I have high-quality SVG card images, but they drastically lose their quality when I downsize them. I have tried two ways of rendering cards (using Inkscape and Imagemagics): 1) Render SVG to high-res PNG and resize it then; 2) Render SVG to image of proper size at once. Both approaches generate blurry card images, which looks even worse than old Windows cards. What are the best way to generate smaller card images from SVG sources and not to loose their quality a lot?

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  • Google I/O 2012 - Dart - A Modern Web Language

    Google I/O 2012 - Dart - A Modern Web Language Lars Bak, Kasper Lund The two creators of Dart will discuss the rationale behind Dart's design and its impact on web scalability and performance. They'll also present how Dart helps developers innovate by increasing their productivity without breaking backwards compatibility. For all I/O 2012 sessions, go to developers.google.com From: GoogleDevelopers Views: 2066 36 ratings Time: 01:03:40 More in Science & Technology

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  • SharpDOM, view engine for ASP.NET MVC

    Sharp DOM is a view engine for ASP.NET MVC platform allowing developers to design extendable and maintenable dynamic HTML layouts using C# 4.0 language. It is also possible to use Sharp DOM project to generate HTML layouts outisde of MVC framework.

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  • How do I get localized names of application in python?

    - by Mystic-Mirage
    This code gives me only English application name if .desktop file does not have "Name[*]" options (like in totem.desktop) but only "X-Ubuntu-Gettext-Domain: totem": from gi.repository import Gio app = Gio.app_info_get_default_for_type('video/x-flv', True) print app.get_name() This like code gives me proper result for vlc.desktop. Ubuntu Dash shows proper localized names for all applications. How do I get localized names of application in python? Sorry for my English.

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  • can't update nvida having error near the end of the install

    - by user94843
    I had just got Ubuntu (first timer to Ubuntu so be very descriptive). I think there a problem with my Nvida update it won't let me update it. This is the name of the update in update manager NVIDIA binary xorg driver, kernel module and VDPAU library. When i attempt to install it, it starts out fine but near the end i get a window titaled package operation failed with these under the details installArchives() failed: Setting up nvidia-current (295.40-0ubuntu1) ... update-initramfs: deferring update (trigger activated) INFO:Enable nvidia-current DEBUG:Parsing /usr/share/nvidia-common/quirks/put_your_quirks_here DEBUG:Parsing /usr/share/nvidia-common/quirks/dell_latitude DEBUG:Parsing /usr/share/nvidia-common/quirks/lenovo_thinkpad DEBUG:Processing quirk Latitude E6530 DEBUG:Failure to match Gigabyte Technology Co., Ltd. with Dell Inc. DEBUG:Quirk doesn't match DEBUG:Processing quirk ThinkPad T420s DEBUG:Failure to match Gigabyte Technology Co., Ltd. with LENOVO DEBUG:Quirk doesn't match Removing old nvidia-current-295.40 DKMS files... Loading new nvidia-current-295.40 DKMS files... Error! DKMS tree already contains: nvidia-current-295.40 You cannot add the same module/version combo more than once. dpkg: error processing nvidia-current (--configure): subprocess installed post-installation script returned error exit status 3 Processing triggers for bamfdaemon ... Rebuilding /usr/share/applications/bamf.index... Processing triggers for initramfs-tools ... update-initramfs: Generating /boot/initrd.img-3.2.0-31-generic Warning: No support for locale: en_US.utf8 Errors were encountered while processing: nvidia-current Error in function: Setting up nvidia-current (295.40-0ubuntu1) ... update-initramfs: deferring update (trigger activated) INFO:Enable nvidia-current DEBUG:Parsing /usr/share/nvidia-common/quirks/put_your_quirks_here DEBUG:Parsing /usr/share/nvidia-common/quirks/dell_latitude DEBUG:Parsing /usr/share/nvidia-common/quirks/lenovo_thinkpad DEBUG:Processing quirk Latitude E6530 DEBUG:Failure to match Gigabyte Technology Co., Ltd. with Dell Inc. DEBUG:Quirk doesn't match DEBUG:Processing quirk ThinkPad T420s DEBUG:Failure to match Gigabyte Technology Co., Ltd. with LENOVO DEBUG:Quirk doesn't match Removing old nvidia-current-295.40 DKMS files... Loading new nvidia-current-295.40 DKMS files... Error! DKMS tree already contains: nvidia-current-295.40 You cannot add the same module/version combo more than once. dpkg: error processing nvidia-current (--configure): subprocess installed post-installation script returned error exit status 3 Processing triggers for bamfdaemon ... Rebuilding /usr/share/applications/bamf.index... Processing triggers for initramfs-tools ... update-initramfs: Generating /boot/initrd.img-3.2.0-31-generic Warning: No support for locale: en_US.utf8

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  • Migrate ldap to another server

    - by user3215
    I have ubuntu(8.10) ldap server running. I am migrating from my old servers to ubuntu 10.04.2 server and I have set up almost all freshly on the new servers. How could I perfectly migrate ldap to the new server after installing ldap?. I found the following to export and import ldap in the google: slapcat -l master.ldif slapadd -c -l master.ldif Is there anything I've to do before/after using those commands?. Any precautions?

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  • Dartisans ep 12 - Dart + Web Components

    Dartisans ep 12 - Dart + Web Components Web Components are ushering in the "declarative renaissance" for modern web development. Watch this episode of Dartisans to learn how you can build Web Components with Dart, and compile them into JavaScript to run across the modern web. Learn more about Dart at www.dartlang.org From: GoogleDevelopers Views: 2 0 ratings Time: 46:17 More in Science & Technology

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  • Google I/O 2012 - SQL vs NoSQL: Battle of the Backends

    Google I/O 2012 - SQL vs NoSQL: Battle of the Backends Ken Ashcraft, Alfred Fuller Google App Engine now offers both SQL and NoSQL data storage -- but which is right for your application? Advocates of each try to settle the issue once and for all, and show some of the tricks for getting the most out of each. For all I/O 2012 sessions, go to developers.google.com From: GoogleDevelopers Views: 2394 38 ratings Time: 43:09 More in Science & Technology

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  • Prompted to type password (for installation purpose) AFTER I removed my password. What to do?

    - by Matiss Janis Aboltinš
    I just installed Ubuntu and one of the 1st things that I did was - remove my password. I went into settings - user accounts, clicked on the unlock icon and changed the password to nothing, made it so it doesn't require me to log in, but yet, when I try to install some software I get prompted to type in my password. I tried using nothing and my old password - neither of them work. What should I do to fix this? Do I really have to re-install Ubuntu?

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  • Twazzup and App Engine

    Twazzup and App Engine An interview with the developers behind twazzup.com on how App Engine helps them run their application. From: GoogleDevelopers Views: 1298 7 ratings Time: 08:37 More in Science & Technology

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  • Is there a modern tutorial for setting up SSL on apache2?

    - by John Baber
    I've been running apache2 for ages on my ubuntu server without SSL. Now that I want to have some directories delivered by SSL, I can't find any straightforward tutorials that were written recently. The best I've found is http://vanemery.com/Linux/Apache/apache-SSL.html but it tells me to put stuff in /etc/httpd/conf I don't want to guess that that should translate to /etc/apache2/conf because guessing based on old tutorials has ruined my web serving before.

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