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  • Mise à jour du cours vidéo Python pour débutants par Pythonnerie, trois nouvelles vidéos sur les bases de données

    voici un tutoriel, destiné à des débutants en informatique, utilise la vidéo pour aider à visualiser les concepts.Cours vidéo Python pour débutantsCe tutoriel est un travail en cours, qui sera (doucement) enrichi et complété au fil du temps. Bien entendu, il n'a aucune prétention à remplacer la documentation de référence, qu'il espère simplement rendre indirectement plus accessible. Mais son auteur espère avoir confirmé le goût de l'informatique chez ceux qui l'avaient déjà et montré aux autres que la programmation n'est pas forcément rébarbative ni mystérieuse....

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  • .NET 4.0 Dynamic object used statically?

    - by Kevin Won
    I've gotten quite sick of XML configuration files in .NET and want to replace them with a format that is more sane. Therefore, I'm writing a config file parser for C# applications that will take a custom config file format, parse it, and create a Python source string that I can then execute in C# and use as a static object (yes that's right--I want a static (not the static type dyanamic) object in the end). Here's an example of what my config file looks like: // my custom config file format GlobalName: ExampleApp Properties { ExternalServiceTimeout: "120" } Python { // this allows for straight python code to be added to handle custom config def MyCustomPython: return "cool" } Using ANTLR I've created a Lexer/Parser that will convert this format to a Python script. So assume I have that all right and can take the .config above and run my Lexer/Parser on it to get a Python script out the back (this has the added benefit of giving me a validation tool for my config). By running the resultant script in C# // simplified example of getting the dynamic python object in C# // (not how I really do it) ScriptRuntime py = Python.CreateRuntime(); dynamic conf = py.UseFile("conftest.py"); dynamic t = conf.GetConfTest("test"); I can get a dynamic object that has my configuration settings. I can now get my config file settings in C# by invoking a dynamic method on that object: //C# calling a method on the dynamic python object var timeout = t.GetProperty("ExternalServiceTimeout"); //the config also allows for straight Python scripting (via the Python block) var special = t.MyCustonPython(); of course, I have no type safety here and no intellisense support. I have a dynamic representation of my config file, but I want a static one. I know what my Python object's type is--it is actually newing up in instance of a C# class. But since it's happening in python, it's type is not the C# type, but dynamic instead. What I want to do is then cast the object back to the C# type that I know the object is: // doesn't work--can't cast a dynamic to a static type (nulls out) IConfigSettings staticTypeConfig = t as IConfigSettings Is there any way to figure out how to cast the object to the static type? I'm rather doubtful that there is... so doubtful that I took another approach of which I'm not entirely sure about. I'm wondering if someone has a better way... So here's my current tactic: since I know the type of the python object, I am creating a C# wrapper class: public class ConfigSettings : IConfigSettings that takes in a dynamic object in the ctor: public ConfigSettings(dynamic settings) { this.DynamicProxy = settings; } public dynamic DynamicProxy { get; private set; } Now I have a reference to the Python dynamic object of which I know the type. So I can then just put wrappers around the Python methods that I know are there: // wrapper access to the underlying dynamic object // this makes my dynamic object appear 'static' public string GetSetting(string key) { return this.DynamicProxy.GetProperty(key).ToString(); } Now the dynamic object is accessed through this static proxy and thus can obviously be passed around in the static C# world via interface, etc: // dependency inject the dynamic object around IBusinessLogic logic = new BusinessLogic(IConfigSettings config); This solution has the benefits of all the static typing stuff we know and love while at the same time giving me the option of 'bailing out' to dynamic too: // the DynamicProxy property give direct access to the dynamic object var result = config.DynamicProxy.MyCustomPython(); but, man, this seems rather convoluted way of getting to an object that is a static type in the first place! Since the whole dynamic/static interaction world is new to me, I'm really questioning if my solution is optimal or if I'm missing something (i.e. some way of casting that dynamic object to a known static type) about how to bridge the chasm between these two universes.

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  • Scripting Language Sessions at Oracle OpenWorld and MySQL Connect, 2012

    - by cj
    This posts highlights some great scripting language sessions coming up at the Oracle OpenWorld and MySQL Connect conferences. These events are happening in San Francisco from the end of September. You can search for other interesting conference sessions in the Content Catalog. Also check out what is happening at JavaOne in that event's Content Catalog (I haven't included sessions from it in this post.) To find the timeslots and locations of each session, click their respective link and check the "Session Schedule" box on the top right. GEN8431 - General Session: What’s New in Oracle Database Application Development This general session takes a look at what’s been new in the last year in Oracle Database application development tools using the latest generation of database technology. Topics range from Oracle SQL Developer and Oracle Application Express to Java and PHP. (Thomas Kyte - Architect, Oracle) BOF9858 - Meet the Developers of Database Access Services (OCI, ODBC, DRCP, PHP, Python) This session is your opportunity to meet in person the Oracle developers who have built Oracle Database access tools and products such as the Oracle Call Interface (OCI), Oracle C++ Call Interface (OCCI), and Open Database Connectivity (ODBC) drivers; Transparent Application Failover (TAF); Oracle Database Instant Client; Database Resident Connection Pool (DRCP); Oracle Net Services, and so on. The team also works with those who develop the PHP, Ruby, Python, and Perl adapters for Oracle Database. Come discuss with them the features you like, your pains, and new product enhancements in the latest database technology. CON8506 - Syndication and Consolidation: Oracle Database Driver for MySQL Applications This technical session presents a new Oracle Database driver that enables you to run MySQL applications (written in PHP, Perl, C, C++, and so on) against Oracle Database with almost no code change. Use cases for such a driver include application syndication such as interoperability across a relationship database management system, application migration, and database consolidation. In addition, the session covers enhancements in database technology that enable and simplify the migration of third-party databases and applications to and consolidation with Oracle Database. Attend this session to learn more and see a live demo. (Srinath Krishnaswamy - Director, Software Development, Oracle. Kuassi Mensah - Director Product Management, Oracle. Mohammad Lari - Principal Technical Staff, Oracle ) CON9167 - Current State of PHP and MySQL Together, PHP and MySQL power large parts of the Web. The developers of both technologies continue to enhance their software to ensure that developers can be satisfied despite all their changing and growing needs. This session presents an overview of changes in PHP 5.4, which was released earlier this year and shows you various new MySQL-related features available for PHP, from transparent client-side caching to direct support for scaling and high-availability needs. (Johannes Schlüter - SoftwareDeveloper, Oracle) CON8983 - Sharding with PHP and MySQL In deploying MySQL, scale-out techniques can be used to scale out reads, but for scaling out writes, other techniques have to be used. To distribute writes over a cluster, it is necessary to shard the database and store the shards on separate servers. This session provides a brief introduction to traditional MySQL scale-out techniques in preparation for a discussion on the different sharding techniques that can be used with MySQL server and how they can be implemented with PHP. You will learn about static and dynamic sharding schemes, their advantages and drawbacks, techniques for locating and moving shards, and techniques for resharding. (Mats Kindahl - Senior Principal Software Developer, Oracle) CON9268 - Developing Python Applications with MySQL Utilities and MySQL Connector/Python This session discusses MySQL Connector/Python and the MySQL Utilities component of MySQL Workbench and explains how to write MySQL applications in Python. It includes in-depth explanations of the features of MySQL Connector/Python and the MySQL Utilities library, along with example code to illustrate the concepts. Those interested in learning how to expand or build their own utilities and connector features will benefit from the tips and tricks from the experts. This session also provides an opportunity to meet directly with the engineers and provide feedback on your issues and priorities. You can learn what exists today and influence future developments. (Geert Vanderkelen - Software Developer, Oracle) BOF9141 - MySQL Utilities and MySQL Connector/Python: Python Developers, Unite! Come to this lively discussion of the MySQL Utilities component of MySQL Workbench and MySQL Connector/Python. It includes in-depth explanations of the features and dives into the code for those interested in learning how to expand or build their own utilities and connector features. This is an audience-driven session, so put on your best Python shirt and let’s talk about MySQL Utilities and MySQL Connector/Python. (Geert Vanderkelen - Software Developer, Oracle. Charles Bell - Senior Software Developer, Oracle) CON3290 - Integrating Oracle Database with a Social Network Facebook, Flickr, YouTube, Google Maps. There are many social network sites, each with their own APIs for sharing data with them. Most developers do not realize that Oracle Database has base tools for communicating with these sites, enabling all manner of information, including multimedia, to be passed back and forth between the sites. This technical presentation goes through the methods in PL/SQL for connecting to, and then sending and retrieving, all types of data between these sites. (Marcelle Kratochvil - CTO, Piction) CON3291 - Storing and Tuning Unstructured Data and Multimedia in Oracle Database Database administrators need to learn new skills and techniques when the decision is made in their organization to let Oracle Database manage its unstructured data. They will face new scalability challenges. A single row in a table can become larger than a whole database. This presentation covers the techniques a DBA needs for managing the large volume of data in a standard Oracle Database instance. (Marcelle Kratochvil - CTO, Piction) CON3292 - Using PHP, Perl, Visual Basic, Ruby, and Python for Multimedia in Oracle Database These five programming languages are just some of the most popular ones in use at the moment in the marketplace. This presentation details how you can use them to access and retrieve multimedia from Oracle Database. It covers programming techniques and methods for achieving faster development against Oracle Database. (Marcelle Kratochvil - CTO, Piction) UGF5181 - Building Real-World Oracle DBA Tools in Perl Perl is not normally associated with building mission-critical application or DBA tools. Learn why Perl could be a good choice for building your next killer DBA app. This session draws on real-world experience of building DBA tools in Perl, showing the framework and architecture needed to deal with portability, efficiency, and maintainability. Topics include Perl frameworks; Which Comprehensive Perl Archive Network (CPAN) modules are good to use; Perl and CPAN module licensing; Perl and Oracle connectivity; Compiling and deploying your app; An example of what is possible with Perl. (Arjen Visser - CEO & CTO, Dbvisit Software Limited) CON3153 - Perl: A DBA’s and Developer’s Best (Forgotten) Friend This session reintroduces Perl as a language of choice for many solutions for DBAs and developers. Discover what makes Perl so successful and why it is so versatile in our day-to-day lives. Perl can automate all those manual tasks and is truly platform-independent. Perl may not be in the limelight the way other languages are, but it is a remarkable language, it is still very current with ongoing development, and it has amazing online resources. Learn what makes Perl so great (including CPAN), get an introduction to Perl language syntax, find out what you can use Perl for, hear how Oracle uses Perl, discover the best way to learn Perl, and take away a small Perl project challenge. (Arjen Visser - CEO & CTO, Dbvisit Software Limited) CON10332 - Oracle RightNow CX Cloud Service’s Connect PHP API: Intro, What’s New, and Roadmap Connect PHP is a public API that enables developers to build solutions with the Oracle RightNow CX Cloud Service platform. This API is used primarily by developers working within the Oracle RightNow Customer Portal Cloud Service framework who are looking to gain access to data and services hosted by the Oracle RightNow CX Cloud Service platform through a backward-compatible API. Connect for PHP leverages the same data model and services as the Connect Web Services for SOAP API. Come to this session to get an introduction and learn what’s new and what’s coming up. (Mark Rhoads - Senior Principal Applications Engineer, Oracle. Mark Ericson - Sr. Principle Product Manager, Oracle) CON10330 - Oracle RightNow CX Cloud Service APIs and Frameworks Overview Oracle RightNow CX Cloud Service APIs are available in the following areas: desktop UI, Web services, customer portal, PHP, and knowledge. These frameworks provide access to Oracle RightNow CX Cloud Service’s Connect Common Object Model and custom objects. This session provides a broad overview of capabilities in all these areas. (Mark Ericson - Sr. Principle Product Manager, Oracle)

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  • How do you update your twitter status using YQL?

    - by waterfallrain
    This is the code example I am following: VALUES ('tweeting from yql!', '@your_consumer_key', '@your_consumer_secret', '@your_access_token', '@your_access_secret'); I understand the consumer key and secret part however I dont understand what to put in for the your_access_token and your_access_secret part. Are these urls I was given what I need to add for the last two items? http://twitter.com/oauth/request_token

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  • Is there a jQuery plugin for error messages at top like Twitter?

    - by sami
    I'm looking for a jquery plugin that would create an errors div like what twitter has. The div gets added by the plugin, it stays hidden while it doesn't have content, then when a message gets added to it, it appears at the top (with either a close button option or automatic disappear after an x number of seconds). It's not too difficult to write, but there would be no reason to write it if it's already been done before. Anyone knows of a plugin like that?

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  • Does jQuery have a plugin to display a "message bar" like the Twitter "wrong password" bar at the to

    - by Jian Lin
    Twitter will pop down a message bar at the top of the screen say "Wrong password" and after 10 seconds, it will slide up and disappear. Chrome also shows "Do you want to save the password" message box using such a way. Does jQuery have a plug in to do that already? Does it also work in IE 6? Because usually, the display of relative to the viewport (using position: fixed) will not work on IE 6. thanks.

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  • possible to fetch @mentions thru Facebook API (like thru Twitter API?)

    - by db
    I'm looking to implement a feature where I am able to collect @mentions through the facebook API in a similar fashion to the twitter API. Specifically, if I run a group called foo, and other people on facebook mention @foo in their wall posts, I'd like to fetch and collect the text of that particular @foo mention. I can't find any relevant documentation on Facebook....

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  • How to use Rx to asynchronously query Twitter search ?

    - by Jalfp
    Hi, I'm thinking about using Rx (Reactive Framework) in order to asynchronously query Twitter search API on a given keyword. The sample app I'd like to build should be able to display new tweets in the console. Do you think it is possible to do that ? Would it be simpler than using standard programming techniques ? How would you do that ? Thank ! Jeremy

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  • Supporting twitter-like user page urls with apache/php?

    - by user246114
    Hi, I'm using php on apache with mysql. I want to let users enter a url into their browser to see a custom user page for themselves, just like twitter does. For example, they could enter urls like: www.mysite.com/johndoe www.mysite.com/janedoe and see that user's page. How could I do this with php and apache? I don't want to create a folder on disk for every user like above, I'd instead kind of like to catch the url and generate the page on the fly for them, Thanks

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  • Get a specific entry by group in SQL

    - by Jensen
    Hi, I've a database who contain some datas in that form: icon(name, size, tag) (myicon.png, 16, 'twitter') (myicon.png, 32, 'twitter') (myicon.png, 128, 'twitter') (myicon.png, 256, 'twitter') (anothericon.png, 32, 'facebook') (anothericon.png, 128, 'facebook') (anothericon.png, 256, 'facebook') So as you see it, the name field is not uniq I can have multiple icons with the same name and they are separated with the size field. Now in PHP I have a query that get ONE icon set, for example : mysql_query("SELECT * FROM icon WHERE tag='".$tag."' ORDER BY size LIMIT 0, 10"); With this example if $tag contain 'twitter' it will show ONLY the first SQL data entry with the tag 'twitter', so it will be : (myicon.png, 16, 'twitter') This is what I want, but I would prefer the '128' size by default. Is this possible to tell SQL to send me only the 128 size when existing and if not another size ? Thanks !

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  • ASP.NET MVC ....or.... PHP, Python, Ruby, Java...?

    - by Muaz Khan
    I’m using ASP.NET MVC in C# and jQuery as well as Ajax. A lot of other web technologies confuse me: PHP, Python, Ruby, Java (or C++) etc. What is your opinion about ASP.NET MVC? Should I choose something else? Today, everyone says, “PHP” is worldly used language..!! And that’s true!!! I’m confused, much confused about my future career. I’m worried I’m not going in right direction! Or for making my future brighter, whether I should choose something else other than ASP.NET MVC and C#. And what would that something else be? I want to be a web developer that can do everything with web (and for web). I’m worried if I’m wasting my time with ASP.NET MVC!!!

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  • Sending keyboard commands to Ubuntu through Python. Remote for my Blackberry

    - by Rudi Strydom
    I am trying to build a remote control application to control media on my Ubuntu. Does anyone know a way in order to accomplish this. The media keys in particular. Thank you. EDIT 1: I have tried using XTE, but is seems python in truncating the input or there is a limit or something which means that you can't do Ctrl + Key key presses, which wont suit my needs. I also tried uinput, but alas you need to run it as root, which also will not quite my needs. Now I am looking at EVDEV which seems promicing, that is if I can get it working.

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  • Should data structures be integrated into the language (as in Python) or be provided in the standard library (as in Java)?

    - by Anto
    In Python, and most likely many other programming languages, common data structures can be found as an integrated part of the core language with their own dedicated syntax. If we put LISP's integrated list syntax aside, I can't think of any other languages that I know which provides some kind of data structure above the array as an integrated part of their syntax, though all of them (but C, I guess) seem to provide them in the standard library. From a language design perspective, what are your opinions on having a specific syntax for data structures in the core language? Is it a good idea, and does the purpose of the language (etc.) change how good this could be of a choice? Edit: I'm sorry for (apparently) causing some confusion about which data structures I mean. I talk about the basic and commonly used ones, but still not the most basic ones. This excludes trees (too complex, uncommon), stacks (too seldom used), arrays (too simple) but includes e.g. sets, lists and hashmaps.

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  • What will be a good python script (or your favorite language goes here) to test a system's performance and capabilities?

    - by dassouki
    Let's say you're in a computer store looking at 10 laptops, you want to really compare the system's capabilities. What will be an efficient "your fav language goes here" script that will allow you to do this? As an example, when I go to the store I usually open a macbook and a pro's terminal and write an equation in python, iterate it a million or so times, and time them. I like to compare the difference in time. What would be an ideal and simple script that can efficiently compare systems?

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  • How to move to Java enterprise development after Python and Ruby?

    - by rdasxy
    I used to develop in Django/Python and Rails/Ruby (and before that C/C++ and C#), and I'm now at a job where we do enterprise Java development (Spring, Hibernate, RESTEasy, Maven, etc.) for web applications and web services. Coming from the Convention over Configuration world, what's the best way to get up to speed doing enterprise Java web services development? I know Java (the language) well, and I've written GUIs in Swing and basic JSP before, but nothing of the kind I'm doing now. Are there any recommended tutorials to get up to speed on popular Java enterprise development tutorials?

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  • Plongée dans les entrailles de l'outil Person Finder de Google, une API open-source codée en Python

    Plongée dans les entrailles de l'outil Person Finder de Google, une API open-source codée en Python Mise à jour du 14.03.2011 par Katleen Comme indiqué dans la news précédente, Google a lancé son outil Person Finder à destination des personnes concernées par le drame survenu le 11.03.2011 au Japon (victimes et entourage de victimes). Ce service a déjà servi auparavant, lors des sinistres de Haiti ou de Christchurch par exemple. En fait, il est né à l'initiative de la firme comme projet sur Google.org, dans le cadre du secteur Google Crisis Response qui y a été lancé en janvier 2010 (séisme d'Haïti), en réponse ...

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  • Notable programs/games made in C/C++/Java/Python? [closed]

    - by ThePlan
    What are some famous programs or video games that were written in the following languages? C C++ Java Python I'm asking this particularly so I know how powerful impact did those languages have on our lives. I believe Windows was also written in C/C++ but I'm not sure if fully. Also if you are kind enough you can mention some other language impacts besides programs/video games. These languages are by far the most common so that's why I've picked them. Besides the impact on our lives I'd also like to see the power these languages have. I'm studying programming and I've learned bits of all those languages and I think if I knew some famous examples of programs written in those languages I could understand the power of them, as well as inspire me further in my career.

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  • IronRuby 1.0 et IronPython 2.6.1, les implémentations de Ruby et de Python pour .NET sont disponible

    IronRuby 1.0 et IronPython 2.6.1 Les implémentations de Ruby et de Python pour .NET sont disponibles L'univers de .NET s'enrichit encore un peu plus avec l'arrivée de IronRuby 1.0. Comme l'explique très bien Thibaut Barrère sur son blog Développez, « IronRuby, c'est tout simplement ?Ruby pour .Net? » ou plus exactement « une implémentation de Ruby s'appuyant sur le runtime .Net. Le but affiché de ce projet est de fournir une implémentation de qualité, compatible Ruby 1.8.x, tout en permettant un bon niveau d'inter-opérabilité avec les librairies .Net ». Longtemps en projet, IronRuby 1.0 vient donc de sortir officiellement aujourd'hui en deux versions différent...

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  • I know Python, but I don't know how the hell I'm supposed to make my program do stuff [on hold]

    - by Relentless Pursuit
    Look, I know how to operate sets, open files, create algorithms, optimize my code, use for loops, while loops, etc btu I don't know how to do anything USEFUL NO BOOK HAS TAUGHT ME HOW TO BE USEFUL. ALL MY PROGRAMS ARE NOTHING BUT LINES OF PYTHON / C++ CODE WITH NO GUI, NO FUNCTIONALITY . nothing :( Is their some sort of secret? How do I go from command line interface, to actual GUI applications that can do useful stuff, I've heard the term being thrown around alot 'api' does that api have anything to do with this? ~A frustrated programmer

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  • for ps aux what are Ss Sl Ssl proccess types UNIX

    - by JiminyCricket
    when doing a "ps aux" command I get some process listed as Ss, Ssl and Sl what do these mean? root 24653 0.0 0.0 2256 8 ? Ss Apr12 0:00 /bin/bash -c /usr/bin/python /var/python/report_watchman.py root 24654 0.0 0.0 74412 88 ? Sl Apr12 0:01 /usr/bin/python /var/python/report_watchman.py root 21976 0.0 0.0 2256 8 ? Ss Apr14 0:00 /bin/bash -c /usr/bin/python /var/python/report_watchman.py root 21977 0.0 0.0 73628 88 ? Sl Apr14 0:01 /usr/bin/python /var/python/report_watchman.py

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  • Using LINQ Distinct: With an Example on ASP.NET MVC SelectListItem

    - by Joe Mayo
    One of the things that might be surprising in the LINQ Distinct standard query operator is that it doesn’t automatically work properly on custom classes. There are reasons for this, which I’ll explain shortly. The example I’ll use in this post focuses on pulling a unique list of names to load into a drop-down list. I’ll explain the sample application, show you typical first shot at Distinct, explain why it won’t work as you expect, and then demonstrate a solution to make Distinct work with any custom class. The technologies I’m using are  LINQ to Twitter, LINQ to Objects, Telerik Extensions for ASP.NET MVC, ASP.NET MVC 2, and Visual Studio 2010. The function of the example program is to show a list of people that I follow.  In Twitter API vernacular, these people are called “Friends”; though I’ve never met most of them in real life. This is part of the ubiquitous language of social networking, and Twitter in particular, so you’ll see my objects named accordingly. Where Distinct comes into play is because I want to have a drop-down list with the names of the friends appearing in the list. Some friends are quite verbose, which means I can’t just extract names from each tweet and populate the drop-down; otherwise, I would end up with many duplicate names. Therefore, Distinct is the appropriate operator to eliminate the extra entries from my friends who tend to be enthusiastic tweeters. The sample doesn’t do anything with the drop-down list and I leave that up to imagination for what it’s practical purpose could be; perhaps a filter for the list if I only want to see a certain person’s tweets or maybe a quick list that I plan to combine with a TextBox and Button to reply to a friend. When the program runs, you’ll need to authenticate with Twitter, because I’m using OAuth (DotNetOpenAuth), for authentication, and then you’ll see the drop-down list of names above the grid with the most recent tweets from friends. Here’s what the application looks like when it runs: As you can see, there is a drop-down list above the grid. The drop-down list is where most of the focus of this article will be. There is some description of the code before we talk about the Distinct operator, but we’ll get there soon. This is an ASP.NET MVC2 application, written with VS 2010. Here’s the View that produces this screen: <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<TwitterFriendsViewModel>" %> <%@ Import Namespace="DistinctSelectList.Models" %> <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">     Home Page </asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">     <fieldset>         <legend>Twitter Friends</legend>         <div>             <%= Html.DropDownListFor(                     twendVM => twendVM.FriendNames,                     Model.FriendNames,                     "<All Friends>") %>         </div>         <div>             <% Html.Telerik().Grid<TweetViewModel>(Model.Tweets)                    .Name("TwitterFriendsGrid")                    .Columns(cols =>                     {                         cols.Template(col =>                             { %>                                 <img src="<%= col.ImageUrl %>"                                      alt="<%= col.ScreenName %>" />                         <% });                         cols.Bound(col => col.ScreenName);                         cols.Bound(col => col.Tweet);                     })                    .Render(); %>         </div>     </fieldset> </asp:Content> As shown above, the Grid is from Telerik’s Extensions for ASP.NET MVC. The first column is a template that renders the user’s Avatar from a URL provided by the Twitter query. Both the Grid and DropDownListFor display properties that are collections from a TwitterFriendsViewModel class, shown below: using System.Collections.Generic; using System.Web.Mvc; namespace DistinctSelectList.Models { /// /// For finding friend info on screen /// public class TwitterFriendsViewModel { /// /// Display names of friends in drop-down list /// public List FriendNames { get; set; } /// /// Display tweets in grid /// public List Tweets { get; set; } } } I created the TwitterFreindsViewModel. The two Lists are what the View consumes to populate the DropDownListFor and Grid. Notice that FriendNames is a List of SelectListItem, which is an MVC class. Another custom class I created is the TweetViewModel (the type of the Tweets List), shown below: namespace DistinctSelectList.Models { /// /// Info on friend tweets /// public class TweetViewModel { /// /// User's avatar /// public string ImageUrl { get; set; } /// /// User's Twitter name /// public string ScreenName { get; set; } /// /// Text containing user's tweet /// public string Tweet { get; set; } } } The initial Twitter query returns much more information than we need for our purposes and this a special class for displaying info in the View.  Now you know about the View and how it’s constructed. Let’s look at the controller next. The controller for this demo performs authentication, data retrieval, data manipulation, and view selection. I’ll skip the description of the authentication because it’s a normal part of using OAuth with LINQ to Twitter. Instead, we’ll drill down and focus on the Distinct operator. However, I’ll show you the entire controller, below,  so that you can see how it all fits together: using System.Linq; using System.Web.Mvc; using DistinctSelectList.Models; using LinqToTwitter; namespace DistinctSelectList.Controllers { [HandleError] public class HomeController : Controller { private MvcOAuthAuthorization auth; private TwitterContext twitterCtx; /// /// Display a list of friends current tweets /// /// public ActionResult Index() { auth = new MvcOAuthAuthorization(InMemoryTokenManager.Instance, InMemoryTokenManager.AccessToken); string accessToken = auth.CompleteAuthorize(); if (accessToken != null) { InMemoryTokenManager.AccessToken = accessToken; } if (auth.CachedCredentialsAvailable) { auth.SignOn(); } else { return auth.BeginAuthorize(); } twitterCtx = new TwitterContext(auth); var friendTweets = (from tweet in twitterCtx.Status where tweet.Type == StatusType.Friends select new TweetViewModel { ImageUrl = tweet.User.ProfileImageUrl, ScreenName = tweet.User.Identifier.ScreenName, Tweet = tweet.Text }) .ToList(); var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct() .ToList(); var twendsVM = new TwitterFriendsViewModel { Tweets = friendTweets, FriendNames = friendNames }; return View(twendsVM); } public ActionResult About() { return View(); } } } The important part of the listing above are the LINQ to Twitter queries for friendTweets and friendNames. Both of these results are used in the subsequent population of the twendsVM instance that is passed to the view. Let’s dissect these two statements for clarification and focus on what is happening with Distinct. The query for friendTweets gets a list of the 20 most recent tweets (as specified by the Twitter API for friend queries) and performs a projection into the custom TweetViewModel class, repeated below for your convenience: var friendTweets = (from tweet in twitterCtx.Status where tweet.Type == StatusType.Friends select new TweetViewModel { ImageUrl = tweet.User.ProfileImageUrl, ScreenName = tweet.User.Identifier.ScreenName, Tweet = tweet.Text }) .ToList(); The LINQ to Twitter query above simplifies what we need to work with in the View and the reduces the amount of information we have to look at in subsequent queries. Given the friendTweets above, the next query performs another projection into an MVC SelectListItem, which is required for binding to the DropDownList.  This brings us to the focus of this blog post, writing a correct query that uses the Distinct operator. The query below uses LINQ to Objects, querying the friendTweets collection to get friendNames: var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct() .ToList(); The above implementation of Distinct seems normal, but it is deceptively incorrect. After running the query above, by executing the application, you’ll notice that the drop-down list contains many duplicates.  This will send you back to the code scratching your head, but there’s a reason why this happens. To understand the problem, we must examine how Distinct works in LINQ to Objects. Distinct has two overloads: one without parameters, as shown above, and another that takes a parameter of type IEqualityComparer<T>.  In the case above, no parameters, Distinct will call EqualityComparer<T>.Default behind the scenes to make comparisons as it iterates through the list. You don’t have problems with the built-in types, such as string, int, DateTime, etc, because they all implement IEquatable<T>. However, many .NET Framework classes, such as SelectListItem, don’t implement IEquatable<T>. So, what happens is that EqualityComparer<T>.Default results in a call to Object.Equals, which performs reference equality on reference type objects.  You don’t have this problem with value types because the default implementation of Object.Equals is bitwise equality. However, most of your projections that use Distinct are on classes, just like the SelectListItem used in this demo application. So, the reason why Distinct didn’t produce the results we wanted was because we used a type that doesn’t define its own equality and Distinct used the default reference equality. This resulted in all objects being included in the results because they are all separate instances in memory with unique references. As you might have guessed, the solution to the problem is to use the second overload of Distinct that accepts an IEqualityComparer<T> instance. If you were projecting into your own custom type, you could make that type implement IEqualityComparer<T>, but SelectListItem belongs to the .NET Framework Class Library.  Therefore, the solution is to create a custom type to implement IEqualityComparer<T>, as in the SelectListItemComparer class, shown below: using System.Collections.Generic; using System.Web.Mvc; namespace DistinctSelectList.Models { public class SelectListItemComparer : EqualityComparer { public override bool Equals(SelectListItem x, SelectListItem y) { return x.Value.Equals(y.Value); } public override int GetHashCode(SelectListItem obj) { return obj.Value.GetHashCode(); } } } The SelectListItemComparer class above doesn’t implement IEqualityComparer<SelectListItem>, but rather derives from EqualityComparer<SelectListItem>. Microsoft recommends this approach for consistency with the behavior of generic collection classes. However, if your custom type already derives from a base class, go ahead and implement IEqualityComparer<T>, which will still work. EqualityComparer is an abstract class, that implements IEqualityComparer<T> with Equals and GetHashCode abstract methods. For the purposes of this application, the SelectListItem.Value property is sufficient to determine if two items are equal.   Since SelectListItem.Value is type string, the code delegates equality to the string class. The code also delegates the GetHashCode operation to the string class.You might have other criteria in your own object and would need to define what it means for your object to be equal. Now that we have an IEqualityComparer<SelectListItem>, let’s fix the problem. The code below modifies the query where we want distinct values: var friendNames = (from tweet in friendTweets select new SelectListItem { Text = tweet.ScreenName, Value = tweet.ScreenName }) .Distinct(new SelectListItemComparer()) .ToList(); Notice how the code above passes a new instance of SelectListItemComparer as the parameter to the Distinct operator. Now, when you run the application, the drop-down list will behave as you expect, showing only a unique set of names. In addition to Distinct, other LINQ Standard Query Operators have overloads that accept IEqualityComparer<T>’s, You can use the same techniques as shown here, with SelectListItemComparer, with those other operators as well. Now you know how to resolve problems with getting Distinct to work properly and also have a way to fix problems with other operators that require equality comparisons. @JoeMayo

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