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  • How to dispose NHibernate ISession in an ASP.NET MVC App

    - by Joe Young
    I have NHibernate hooked up in my asp.net mvc app. Everything works fine, if I DON'T dispose the ISession. I have read however that you should dispose, but when I do, I get random "Session is closed" exceptions. I am injecting the ISession into my other objects with Windsor. Here is my current NHModule: public class NHibernateHttpModule : IHttpModule { public void Init(HttpApplication context) { context.BeginRequest += context_BeginRequest; context.EndRequest += context_EndRequest; } static void context_EndRequest(object sender, EventArgs e) { CurrentSessionContext.Unbind(MvcApplication.SessionFactory); } static void context_BeginRequest(object sender, EventArgs e) { CurrentSessionContext.Bind(MvcApplication.SessionFactory.OpenSession()); } public void Dispose() { // do nothing } } Registering the ISession: container .Register(Component.For<ISession>() .UsingFactoryMethod(() => MvcApplication.SessionFactory.GetCurrentSession()).LifeStyle.Transient); The error happens when I tack the Dispose on the unbind in the module. Since I keep getting the session is closed error I assume this is not the correct way to do this, so what is the correct way? Thanks, Joe

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  • Numeric Data Entry in WPF

    - by Matt Hamilton
    How are you handling the entry of numeric values in WPF applications? Without a NumericUpDown control, I've been using a TextBox and handling its PreviewKeyDown event with the code below, but it's pretty ugly. Has anyone found a more graceful way to get numeric data from the user without relying on a third-party control?private void NumericEditPreviewKeyDown(object sender, KeyEventArgs e) { bool isNumPadNumeric = (e.Key >= Key.NumPad0 && e.Key <= Key.NumPad9) || e.Key == Key.Decimal; bool isNumeric = (e.Key >= Key.D0 && e.Key <= Key.D9) || e.Key == Key.OemPeriod; if ((isNumeric || isNumPadNumeric) && Keyboard.Modifiers != ModifierKeys.None) { e.Handled = true; return; } bool isControl = ((Keyboard.Modifiers != ModifierKeys.None && Keyboard.Modifiers != ModifierKeys.Shift) || e.Key == Key.Back || e.Key == Key.Delete || e.Key == Key.Insert || e.Key == Key.Down || e.Key == Key.Left || e.Key == Key.Right || e.Key == Key.Up || e.Key == Key.Tab || e.Key == Key.PageDown || e.Key == Key.PageUp || e.Key == Key.Enter || e.Key == Key.Return || e.Key == Key.Escape || e.Key == Key.Home || e.Key == Key.End); e.Handled = !isControl && !isNumeric && !isNumPadNumeric; }

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  • Actionscript 3.0 - drag and throw with easing

    - by Joe Hamilton
    I'm creating a map in flash and I would like to have a smooth movement similar to this: http://www.conceptm.nl/ I have made a start but I'm having trouble taking it to the next stage. My code currently throws the movieclip after the mouse is release but there is no easing while the mouse button is down. Any tips on how I would achieve this? Here is my current code: // Vars var previousPostionX:Number; var previousPostionY:Number; var throwSpeedX:Number; var throwSpeedY:Number; var isItDown:Boolean; // Event Listeners addEventListener(MouseEvent.MOUSE_DOWN, clicked); addEventListener(MouseEvent.MOUSE_UP, released); // Event Handlers function clicked(theEvent:Event) { isItDown =true; addEventListener(Event.ENTER_FRAME, updateView); } function released(theEvent:Event) { isItDown =false; } function updateView(theEvent:Event) { if (isItDown==true){ throwSpeedX = mouseX - previousPostionX; throwSpeedY = mouseY - previousPostionY; mcTestMovieClip.x = mouseX; mcTestMovieClip.y = mouseY; } else{ mcTestMovieClip.x += throwSpeedX; mcTestMovieClip.y += throwSpeedY; throwSpeedX *=0.9; throwSpeedY *=0.9; } previousPostionX= mcTestMovieClip.x; previousPostionY= mcTestMovieClip.y; }

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  • write client ip in iis 7.0 log over firewalls

    - by Guy Bertental
    Hi, I a solution for IIS 7.0 which runs on windows server 2008 64bit to write my clients IP to IIS logs while the server is behind firewalls and proxies (Pass X-Forwarded-For header value). I've tried to install the an ISAPI Filter written by Joe Pruitt. it works great on Windows Server 2003 32bit IIS 6.0, but seems to do nothing at all on windows server 2008 64bit IIS 7.0. Did anyone try this ISAPI filter on this version of OS? or have another solution? link to the Joe Pruitt's (from F5) ISAPI filter: http://devcentral.f5.com/weblogs/Joe/archive/2009/08/19/x_forwarded_for_log_filter_for_windows_servers.aspx best regards, guy bertental

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  • PHP File Exists Always False

    - by Joe
    I have a case where file_exists() is always returning false. My latest attempt was to just test to see if it would return true for $_SERVER["SCRIPT_FILENAME"] and then return the value of the path if it couldn't find the file which it does. The path while not necessarily relevant to solving the problem is: /Users/joe/Workspace/720/app/webroot/index.php I have obviously verified that the file is there, and am not even sure how it couldn't be there since php is serving it up. I should mention this is on an install of OS X Snow Leopard running PHP 5.3.0. Any ideas would be fantastic. CODE SAMPLE: if (!file_exists($_SERVER["SCRIPT_FILENAME"])) $errors[] = 'Cant find:'. $_SERVER["SCRIPT_FILENAME"];

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  • What version control system is best designed to *prevent* concurrent editing?

    - by Fred Hamilton
    We've been using CVS (with TortoiseCVS interface) for years for both source control and wide-ranging document control (including binaries such as Word, Excel, Framemaker, test data, simulation results, etc.). Unlike typical version control systems, 99% of the time we want to prevent concurrent editing - when a user starts editing a file, the pre-edit version of the file becomes read only to everyone else. Many of the people who will be using this are not programmers or even that computer savvy, so we're also looking for a system that let's people simply add documents to the repository, check out and edit a document (unless someone else is currently editing it), and check it back in with a minimum of fuss. We've gotten this to work reasonably well with CVS + TortoiseCVS, but we're now considering Subversion and Mercurial (and open to others if they're a better fit) for their better version tracking, so I was wondering which one supported locking files most transparently. For example, we'd like exclusive locking enabled as the default, and we want to make it as difficult as possible for someone to accidentally start editing a file that someone else has checked out. For example when someone checks out a file for editing, it checks with the master database first even if they have not recently updated their sandbox. Maybe it even won't let a user check out a document if it's off the network and can't check in with the mothership.

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  • Cucumber/Webrat: follow link by CSS class?

    - by Joe
    Hello there, is it possible to follow a link by it's class name instead of the id, text or title? Given I have (haha, cucumber insider he?) the following html code: <div id="some_information_container"> <a href="edit" class="edit_button">Translation here</a> </div> I do not want to match by text because I'd have to care about the translation values in my tests I want to have my buttons look all the same style, so I will use the CSS class. I don't want to assign a id to every single link, because some of them are perfectly identified through the container and the link class Is there anything I missed in Cucumber/Webrat? Or do you have some advices to solve this in a better way? Thanks for your help and best regards, Joe edit: I found an interesting discussion going on about this topic right here - seems to remain an open issue for now. Do you have any other solutions for this?

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  • How to compile scheme into native binary files ?

    - by Joe
    I am very new to scheme. And now I am trying to compile some scheme code into binary file which will be loaded faster into interpreter. (The interpreter is a hybrid interpreter)Some one told me that I can compile the code into native binary file and then load it into interperter. And my question is: 1. What is the native binary file? 2. How can I compile the scheme code into a native binary file? 3. How can I load native bianry file into scheme interpreter? Thanks in advance. Joe Suggested that I want to compile below code into native binary file: (define test (lambda() (display "this is a test")) And then load the bianry file into interpreter and call the function "test".

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  • Tables with no Primary Key

    - by Matt Hamilton
    I have several tables whose only unique data is a uniqueidentifier (a Guid) column. Because guids are non-sequential (and they're client-side generated so I can't use newsequentialid()), I have made a non-primary, non-clustered index on this ID field rather than giving the tables a clustered primary key. I'm wondering what the performance implications are for this approach. I've seen some people suggest that tables should have an auto-incrementing ("identity") int as a clustered primary key even if it doesn't have any meaning, as it means that the database engine itself can use that value to quickly look up a row instead of having to use a bookmark. My database is merge-replicated across a bunch of servers, so I've shied away from identity int columns as they're a bit hairy to get right in replication. What are your thoughts? Should tables have primary keys? Or is it ok to not have any clustered indexes if there are no sensible columns to index that way?

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  • How to count incrementally in SQL SERVER

    - by joe
    Hi Folks, I am assigned a problem which i am not sure how to write it in SQL SEVER (version 5/8) yet. Here is the simple query and its output: Select location, date_time, Item_sold From Product Location Date_time Item_sold VA 12/10/2010 1:30:00 PM Candy VA 12/10/2010 3:30:00 PM Chips VA 12/13/2010 12:50:00 AM Wine DC 12/13/2010 8:00:00 AM Gum DC 12/13/2010 12:30:00 PM Bags DC 12/13/2010 1:16:00 PM Cheese DC 12/13/2010 12:00:00 AM Hotdog NJ 12/15/2010 12:00:00 AM Coffee NJ 12/15/2010 1:15:00 PM Beers NJ 12/15/2010 3:45:00 AM Cream Here is my desired output, which I guess a while/for loop or a pivot function could do the job but my experience is not there yet. Basically, I need to count the number of item sold from the Item_sold column incrementally (base line date starts from 12/8 to 12/9, 12/8 to 12/10, 12/8 to 12/11, 12/8 to 12/12...) I was wondering if anyone could edcuate and solve this problem. Many thanks in advance, Joe Location 12/8 |12/8-12/9 |12/8-12/10 |12/8 - 12/11 |12/8 - 12/12 |12/8 - 12/13 VA 0 0 2 0 0 3 DC 0 0 0 0 0 4

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  • Twig Template For loop Results

    - by user981480
    I am trying to print out a the contents of an array but am not getting the expected results. any help is much appreciated: PHP code: $list[1]['first_name'] = 'Joe'; $list[1]['last_name'] = 'Smith'; $list[2]['first_name'] = 'John'; $list[2]['last_name'] = 'brand'; $data = array( 'customer' => $list ); echo $template->render($data); Template Markup: <html> <head><title>My first Twig template!</title></head> <body> {% for person in customer %} {{ person.first_name }} {% endfor %} </body> RESULTS: Array ( [first_name] = Joe [last_name] = Smith ) first_name Joe Array ( [first_name] = John [last_name] = brand ) first_name John

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  • I'm not sure if I should use a redirect

    - by Joe
    Hi there, I have an affiliate link on my webpage. When you click on the link it follows the href value which is as follows: www.site_name.com/?refer=my_affiliate_id This would be fine, except that the site offers no tracking for the ads, so I can't tell how many clicks I am getting. I could easily implement my own tracking by changing the original link href value to a php script which increments some click stats in a database and then redirects the user to the original page. But I have read some articles that say that using redirects may be seen by google as a sign of 'blackhat' techniques and they might rank me lower, unindex my site or even hurt the site that I'm redirecting too. Does anybody know if this is true, or have any idea of the best way I could go about this? Many thanks in advance Joe

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  • OWL inferencing question

    - by user439170
    I am using the Jena semantic web framework version 2.6.3. I have code that creates a model with owl inferencing and then adds the following triples: [:bnode-3 rdf:type owl:Restriction] [:bnode-3 owl:onProperty :offspringOf] [:bnode-3 owl:someValuesFrom :Person] [:bnode-3 rdfs:subClassOf :Person] bnode-3 is supposed to be a restriction class which, for example, would contain :joe if :bob is a :Person and the following triple were asserted: [:joe :offspringOf :bob]. Then, since the restriction class is a subclass of Person, :joe would also be a person. And, in fact, this works. Whats confusing to me is that after I assert just the 4 triples at the top of this post, the inferencer creates a blank node which is a Person. In other words, the following triple is now in the model: [_:b0 rdf:type :Person] I don't understand why it would do this. Any help in understanding this would be greatly appreciated. Thanks. Kent.

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  • Cannot access implict object from within method in custom JSP tag file

    - by David Hamilton
    I'm attempting to create a custom jsp tag. Everything is working fine, except for the fact that I the request seems to be out-of-scope for my custom function. Here is the relevant bit from the .tag file: <%! private String process(String age, BigDecimal amount) { //Attempting to access request here results in an compile time error trying to: String url=request.getURL; } %> I'm very new to JSP so I'm sure I'm missing something obvious..but I can't seem to figure out what. Any help is appreciated.

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  • Do you like languages that let you put the "then" before the "if"?

    - by Matt Hamilton
    I was reading through some C# code of mine today and found this line: if (ProgenyList.ItemContainerGenerator.Status != System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated) return; Notice that you can tell without scrolling that it's an "if" statement that works with ItemContainerGenerator.Status, but you can't easily tell that if the "if" clause evaluates to "false" the method will return at that point. Realistically I should have moved the "return" statement to a line by itself, but it got me thinking about languages that allow the "then" part of the statement first. If C# permitted it, the line could look like this: return if (ProgenyList.ItemContainerGenerator.Status != System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated); This might be a bit "argumentative", but I'm wondering what people think about this kind of construct. It might serve to make lines like the one above more readable, but it also might be disastrous. Imagine this code: return 3 if (x > y); Logically we can only return if x y, because there's no "else", but part of me looks at that and thinks, "are we still returning if x <= y? If so, what are we returning?" What do you think of the "then before the if" construct? Does it exist in your language of choice? Do you use it often? Would C# benefit from it?

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  • Why is Func<T> ambiguous with Func<IEnumerable<T>>?

    - by Matt Hamilton
    This one's got me flummoxed, so I thought I'd ask here in the hope that a C# guru can explain it to me. Why does this code generate an error? class Program { static void Main(string[] args) { Foo(X); // the error is on this line } static String X() { return "Test"; } static void Foo(Func<IEnumerable<String>> x) { } static void Foo(Func<String> x) { } } The error in question: Error 1 The call is ambiguous between the following methods or properties: 'ConsoleApplication1.Program.Foo(System.Func<System.Collections.Generic.IEnumerable<string>>)' and 'ConsoleApplication1.Program.Foo(System.Func<string>)' C:\Users\mabster\AppData\Local\Temporary Projects\ConsoleApplication1\Program.cs 12 13 ConsoleApplication1 It doesn't matter what type I use - if you replace the "String" declarations with "int" in that code you'll get the same sort of error. It's like the compiler can't tell the difference between Func<T> and Func<IEnumerable<T>>. Can someone shed some light on this?

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  • C++ STL map.find() not finding my stuff

    - by Joe
    Hello, I have constructed a map and loaded it with data. If I iterate over all the elements I see they are all valid. However, the find method doesn't find my item. I'm sure it's something stupid I am doing. Here is snippet: // definitions // I am inserting a person class and using the firstname as the key typedef std::map<char*,Person *> mapType; mapType _myMap; mapType::iterator _mapIter; ... Person *pers = new Person(FirstName, LastName, Address, Phone); _myMap.insert(make_pair(pers->firstName, pers); ... ...later.... _mapIter = _myMap.find(firstName); // returns map.end _mapIter = _myMap.find("joe"); // returns map.end and I have no idea why :(

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  • phpunit - generate tests for all the classes from a directory

    - by joe
    Hi! I have a directoy structure, and all the classes of the business logic are placed in the app_dir/lib/ directory. I would like to generate unit tests for all the classes from this lib/ folder. The problem is, that I haven't found any option to specify the source directory, only the source file: from app_dir: phpunit --skeleton-class lib/ Error: "lib/.php" could not be opened. Is it the only solution to write my own php script, which iterates through the /lib folder and calls the skeleton generator for every file found? And how can I specify the output folder, where all the generated test files are placed? Thanx, Joe

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  • How do I find the Recaptcha ID?

    - by Joe
    I've been stuck on something for the past day. I'm building a RoR bot, and part of it involves signing up for an email account with mail.com. I've automated all the filling out of the form, apart from the captcha (Recaptcha). I'll be using the deathbycaptcha Ruby gem. However, in order to have the captcha solved, I'll need to get either its ID or its URL. While this shows up when I "enable form details" with the Firefox Web Developer toolbar, it doesn't seem to be in the source. How can I find it out? I'm using Watir. Thanks! Joe

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  • What's the best approach to printing/reporting from WPF?

    - by Matt Hamilton
    I have an upcoming project which will have to be able to print simple reports from its data. It'll be WPF-based, and I'm wondering which way to go. I know that WPF introduces its own printing technology (based on XPS) which looks quite easy to use. However, part of me wonders whether it would just be easier to use the ReportViewer control and embed it in a Windows Forms host control, since that will give users the ability to export to a variety of formats as well as print. Has anyone had any experience with printing/reporting from WPF? Which direction would you recommend?

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  • Customer count map (Google maps?)

    - by David Hamilton
    I have a two column list consisting of a US zipcode and a count (number of customers in this case). I want to put this data onto a map. Would Google maps API be a good fit for this? It seems like this would be a common enough type of problem to already have an existing (preferably Java based) solution without having to re-invent the wheel. Any suggestions?

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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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  • I can't boot into Ubuntu "Try (hd0,0): NTFS5: No ang0" Error Message

    - by Joe
    I recently installed Ubuntu 12.04 alongside windows 7. It was working fine but now when I try to boot with ubuntu after the operating system choice screen I get this. Boot Error Message Try (hd0,0): NFTS5: No ang0 Try (hd0,1): NTFS5: No ang0 Try (hd0,2): NTFS5: No ang0 Try (hd0,3): Extended: Try (hd0,4): NTFS5: No ang0 Try (hd0,5): Extended: Try (hd0,5): EXT2: And when I press ctrl+alt+del it restarts the computer and if I chose to boot with ubuntu same thing happens again. But windows works fine.. How do I resolve this problem? Thanks.

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