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• streaming XML serialization in .net

  - by Luca Martinetti

  Hello, I'm trying to serialize a very large IEnumerable<MyObject> using an XmlSerializer without keeping all the objects in memory. The IEnumerable<MyObject> is actually lazy.. I'm looking for a streaming solution that will: Take an object from the IEnumerable<MyObject> Serialize it to the underlying stream using the standard serialization (I don't want to handcraft the XML here!) Discard the in memory data and move to the next I'm trying with this code: using (var writer = new StreamWriter(filePath)) { var xmlSerializer = new XmlSerializer(typeof(MyObject)); foreach (var myObject in myObjectsIEnumerable) { xmlSerializer.Serialize(writer, myObject); } } but I'm getting multiple XML headers and I cannot specify a root tag <MyObjects> so my XML is invalid. Any idea? Thanks

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• Attribute lost with yield

  - by Nelson

  Here's an interesting one... There is some code that I'm trying to convert from IList to IEnumerable: [Something(123)] public IEnumerable<Foo> GetAllFoos() { SetupSomething(); DataReader dr = RunSomething(); while (dr.Read()) { yield return Factory.Create(dr); } } The problem is, SetupSomething() comes from the base class and uses: Attribute.GetCustomAttribute(new StackTrace().GetFrame(1).GetMethod(), typeof(Something)) Yield ends up creating MoveNext(), MoveNext() calls SetupSomething(), and MoveNext() does not have the [Something(123)] attribute. I can't change the base class, so it appears I am forced to stay with IList or implement IEnumerable manually (and add the attribute to MoveNext()). Is there any other way to make yield work in this scenario?

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• Why does LINQ-to-SQL Paging fail inside a function?

  - by ssg

  Here I have an arbitrary IEnumerable<T>. And I'd like to page it using a generic helper function instead of writing Skip/Take pairs every time. Here is my function: IEnumerable<T> GetPagedResults<T>(IEnumerable<T> query, int pageIndex, int pageSize) { return query.Skip((pageIndex - 1) * pageSize).Take(pageSize); } And my code is: result = GetPagedResults(query, 1, 10).ToList(); This produces a SELECT statement without TOP 10 keyword. But this code below produces the SELECT with it: result = query.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList(); What am I doing wrong in the function?

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• C# Entity Framework Base Repository

  - by Andy

  I'm trying to create a base repository for use with Entity Framework 4.0 and having some trouble. In this code below, why is it not possible to do this in one line? public IEnumerable<T> GetAll<T>(Expression<Func<T, bool>> filter) { IEnumerable<T> allCustomers = this.GetAll<T>(); IEnumerable<T> result = allCustomers.Where(filter.Compile()); return result; } Won't this result in 2 SQL statements: one without a where clause that retrieves all rows, and one with a where clause that only retrieves the rows that match the predicate? How can this be done with a single SQL statement? I can't get it to compile if I try to cast the filter.Compile() to Func<Customer, bool>. Thanks, Andy

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• how VAR is determined against many options?

  - by Royi Namir

  i have this code : IEnumerable<string> q = customers /*EF entity*/ .Select (c => c.Name.ToUpper()) .OrderBy (n => n) To select entity, ObjectContext actually create ObjectQuery, which implement IQueryable. The object return from ObjectQuery, is not normal object, but EntityObject but what if i write : ( notice the var) var q = customers /*EF entity*/ .Select (c => c.Name.ToUpper()) .OrderBy (n => n) it can be determined both to ienumerable or iqueryable : because ObjectQuery Also implements IEnumerable... i dont know if there's any specific info which tell the compiler "use A and not B. A is more specific..." ( there must be...i just cant find it) any help ? how will it know to use A || B ?

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• In C#: How to declare a generic Dictionary with a type as key and an enumeration of that type as val

  - by Marcel

  Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: (Edited to follow johny g's comment) private IDictionary<Type, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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• Mvp View knows Model

  - by userbb

  I'm trying to use MVP and I notice that my View must know Model that should not happen in MVP I presume. here is example: public partial class TestForm : Form, ITestPresenter { public void LoadList(IEnumerable<AppSignature> data) { testPresenterBindingSource.DataSource = data; } } public interface ITestPresenter { event EventHandler<EventArgs> Load; void LoadList(IEnumerable<AppSignature> data); } and the problem is that in TestForm I need reference to AppSignature. In all tutorials I saw, there are some simple examples like public void LoadList(IEnumerable<String> data) where there is no need reference to model. But how i.e DataGridView can publish current row data?

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• How to create DataSource dependency property on a wpf User Control

  - by Michael Hedgpeth

  I have a user control that wraps a grid. I want to be able to set the underlying grid's data source, but through the user control, like this: <my:CustomGrid DataSource="{Binding Path=CollectionView}" /> I have set this up in the grid like this: private static readonly DependencyProperty DataSourceProperty = DependencyProperty.Register("DataSource", typeof(IEnumerable), typeof(CustomGrid)); public IEnumerable DataSource { get { return (IEnumerable)GetValue(DataSourceProperty); } set { SetValue(DataSourceProperty, value); underlyingGrid.DataSource = value; } } But this doesn't work (it doesn't give me an error either). The data source is never set. What am I missing?

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• Is there a way to make this C# method shorter and more readable with the help of Linq?

  - by Hamish Grubijan

  The following works, but I figured - since it is all based on IEnumerable, Linq can come handy here is well. By the way, is there an equivalent to Directory.GetFiles() which would return an IEnumerable instead of the array? If it exists, then would it make the code run any faster? The last part of the question is inspired by Python language which favors lightweight generators over concrete lists. private IEnumerable<string> getFiles(string strDirectory, bool bCompressedOnly) { foreach (var strFile in Directory.GetFiles(strDirectory)) { // Don't add any existing Zip files since we don't want to delete previously compressed files. if (!bCompressedOnly || Path.GetExtension(strFile).ToLower().Equals(".zip")) { yield return strFile; } } foreach (var strDir in Directory.GetDirectories(strDirectory)) { foreach (var strFile in getFiles(strDir, bCompressedOnly)) { yield return strFile; } } }

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• Container<ImplementerOfIInterface> is not Container<IInterface>. Why not?

  - by Chris Simmons

  Why wouldn't DoesntWork() work below? The error is: Cannot implicitly convert type 'List' to 'IEnumerable'. An explicit conversion exists (are you missing a cast?). I know this is something about generic/templates I'm not getting, but List is IEnumerable and Implementer is an IInterface. I don't see why this needs to be casted (or if it really can be). public interface IInterface { // ... } public class Implementer : IInterface { // ... } IEnumerable<IInterface> DoesntWork() { List<Implementer> result = new List<Implementer>(); return result; }

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• Linq to SQL - How to compare against a collection in the where clause?

  - by Sgraffite

  I'd like to compare against an IEnumerable collection in my where clause. Do I need to manually loop through the collection to pull out the column I want to compare against, or is there a generic way to handle this? I want something like this: public IEnumerable<Cookie> GetCookiesForUsers(IEnumerable<User> Users) { var cookies = from c in db.Cookies join uc in db.UserCookies on c.CookieID equals uc.CookieID join u in db.Users on uc.UserID equals u.UserID where u.UserID.Equals(Users.UserID) select c; return cookies.ToList(); } I'm used to using the lambda Linq to SQL syntax, but I decided to try the SQLesque syntax since I was using joins this time. What is a good way to do this?

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• In C#: How to declare a generic Dictionary whose key and value types have a common constraint type?

  - by Marcel

  Hi all, I want to declare a dictionary that stores typed IEnumerable's of a specific type, with that exact type as key, like so: private IDictionary<T, IEnumerable<T>> _dataOfType where T: BaseClass; //does not compile! The concrete classes I want to store, all derive from BaseClass, therefore the idea to use it as constraint. The compiler complains that it expects a semicolon after the member name. If it would work, I would expect this would make the later retrieval from the dictionary simple like: IEnumerable<ConcreteData> concreteData; _sitesOfType.TryGetValue(typeof(ConcreteType), out concreteData); How to define such a dictionary?

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• Why does this MSDN example for Func<> delegate have a superfluous Select() call?

  - by Dan

  The MSDN gives this code example in the article on the Func Generic Delegate: Func<String, int, bool> predicate = ( str, index) => str.Length == index; String[] words = { "orange", "apple", "Article", "elephant", "star", "and" }; IEnumerable<String> aWords = words.Where(predicate).Select(str => str); foreach (String word in aWords) Console.WriteLine(word); I understand what all this is doing. What I don't understand is the Select(str => str) bit. Surely that's not needed? If you leave it out and just have IEnumerable<String> aWords = words.Where(predicate); then you still get an IEnumerable back that contains the same results, and the code prints the same thing. Am I missing something, or is the example misleading?

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• Workarounds for supporting MVVM in the Silverlight TreeView Control

  - by cibrax

  MVVM (Model-View-ViewModel) is the pattern that you will typically choose for building testable user interfaces either in WPF or Silverlight. This pattern basically relies on the data binding support in those two technologies for mapping an existing model class (the view model) to the different parts of the UI or view. Unfortunately, MVVM was not threated as first citizen for some of controls released out of the box in the Silverlight runtime or the Silverlight toolkit. That means that using data binding for implementing MVVM is not always something trivial and usually requires some customization in the existing controls. In ran into different problems myself trying to fully support data binding in controls like the tree view or the context menu or things like drag & drop.  For that reason, I decided to write this post to show how the tree view control or the tree view items can be customized to support data binding in many of its properties. In first place, you will typically use a tree view for showing hierarchical data so the view model somehow must reflect that hierarchy. An easy way to implement hierarchy in a model is to use a base item element like this one, public abstract class TreeItemModel { public abstract IEnumerable<TreeItemModel> Children; } You can later derive your concrete model classes from that base class. For example, public class CustomerModel { public string FullName { get; set; } public string Address { get; set; } public IEnumerable<OrderModel> Orders { get; set; } }   public class CustomerTreeItemModel : TreeItemModel { public CustomerTreeItemModel(CustomerModel customer) { }   public override IEnumerable<TreeItemModel> Children { get { // Return orders } } } The Children property in the CustomerTreeItem model implementation can return for instance an ObservableCollection<TreeItemModel> with the orders, so the tree view will automatically subscribe to all the changes in the collection. You can bind this model to the tree view control in the UI by using a Hierarchical data template. <e:TreeView x:Name="TreeView" ItemsSource="{Binding Customers}"> <e:TreeView.ItemTemplate> <sdk:HierarchicalDataTemplate ItemsSource="{Binding Children}"> <!-- TEMPLATE --> </sdk:HierarchicalDataTemplate> </e:TreeView.ItemTemplate> </e:TreeView> An interesting behavior with the Children property and the Hierarchical data template is that the Children property is only invoked before the expansion, so you can use lazy load at this point (The tree view control will not expand the whole tree in the first expansion). The problem with using MVVM in this control is that you can not bind properties in model with specific properties of the TreeView item such as IsSelected or IsExpanded. Here is where you need to customize the existing tree view control to support data binding in tree items. public class CustomTreeView : TreeView { public CustomTreeView() { }   protected override DependencyObject GetContainerForItemOverride() { CustomTreeViewItem tvi = new CustomTreeViewItem(); Binding expandedBinding = new Binding("IsExpanded"); expandedBinding.Mode = BindingMode.TwoWay; tvi.SetBinding(CustomTreeViewItem.IsExpandedProperty, expandedBinding); Binding selectedBinding = new Binding("IsSelected"); selectedBinding.Mode = BindingMode.TwoWay; tvi.SetBinding(CustomTreeViewItem.IsSelectedProperty, selectedBinding); return tvi; } }   public class CustomTreeViewItem : TreeViewItem { public CustomTreeViewItem() { }   protected override DependencyObject GetContainerForItemOverride() { CustomTreeViewItem tvi = new CustomTreeViewItem(); Binding expandedBinding = new Binding("IsExpanded"); expandedBinding.Mode = BindingMode.TwoWay; tvi.SetBinding(CustomTreeViewItem.IsExpandedProperty, expandedBinding); Binding selectedBinding = new Binding("IsSelected"); selectedBinding.Mode = BindingMode.TwoWay; tvi.SetBinding(CustomTreeViewItem.IsSelectedProperty, selectedBinding); return tvi; } } You basically need to derive the TreeView and TreeViewItem controls to manually add a binding for the properties you need. In the example above, I am adding a binding for the “IsExpanded” and “IsSelected” properties in the items. The model for the tree items now needs to be extended to support those properties as well, public abstract class TreeItemModel : INotifyPropertyChanged { bool isExpanded = false; bool isSelected = false;   public abstract IEnumerable<TreeItemModel> Children { get; }   public bool IsExpanded { get { return isExpanded; } set { isExpanded = value; if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("IsExpanded")); } }   public bool IsSelected { get { return isSelected; } set { isSelected = value; if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("IsSelected")); } }   public event PropertyChangedEventHandler PropertyChanged; } However, as soon as you use this custom tree view control, you lose all the automatic styles from the built-in toolkit themes because they are tied to the control type (TreeView in this case).  The only ugly workaround I found so far for this problem is to copy the styles from the Toolkit source code and reuse them in the application.

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• ASP.NET Web API - Screencast series Part 4: Paging and Querying

  - by Jon Galloway

  We're continuing a six part series on ASP.NET Web API that accompanies the getting started screencast series. This is an introductory screencast series that walks through from File / New Project to some more advanced scenarios like Custom Validation and Authorization. The screencast videos are all short (3-5 minutes) and the sample code for the series is both available for download and browsable online. I did the screencasts, but the samples were written by the ASP.NET Web API team. In Part 1 we looked at what ASP.NET Web API is, why you'd care, did the File / New Project thing, and did some basic HTTP testing using browser F12 developer tools. In Part 2 we started to build up a sample that returns data from a repository in JSON format via GET methods. In Part 3, we modified data on the server using DELETE and POST methods. In Part 4, we'll extend on our simple querying methods form Part 2, adding in support for paging and querying. This part shows two approaches to querying data (paging really just being a specific querying case) - you can do it yourself using parameters passed in via querystring (as well as headers, other route parameters, cookies, etc.). You're welcome to do that if you'd like. What I think is more interesting here is that Web API actions that return IQueryable automatically support OData query syntax, making it really easy to support some common query use cases like paging and filtering. A few important things to note: This is just support for OData query syntax - you're not getting back data in OData format. The screencast demonstrates this by showing the GET methods are continuing to return the same JSON they did previously. So you don't have to "buy in" to the whole OData thing, you're just able to use the query syntax if you'd like. This isn't full OData query support - full OData query syntax includes a lot of operations and features - but it is a pretty good subset: filter, orderby, skip, and top. All you have to do to enable this OData query syntax is return an IQueryable rather than an IEnumerable. Often, that could be as simple as using the AsQueryable() extension method on your IEnumerable. Query composition support lets you layer queries intelligently. If, for instance, you had an action that showed products by category using a query in your repository, you could also support paging on top of that. The result is an expression tree that's evaluated on-demand and includes both the Web API query and the underlying query. So with all those bullet points and big words, you'd think this would be hard to hook up. Nope, all I did was change the return type from IEnumerable<Comment> to IQueryable<Comment> and convert the Get() method's IEnumerable result using the .AsQueryable() extension method. public IQueryable<Comment> GetComments() { return repository.Get().AsQueryable(); } You still need to build up the query to provide the $top and $skip on the client, but you'd need to do that regardless. Here's how that looks: $(function () { //--------------------------------------------------------- // Using Queryable to page //--------------------------------------------------------- $("#getCommentsQueryable").click(function () { viewModel.comments([]); var pageSize = $('#pageSize').val(); var pageIndex = $('#pageIndex').val(); var url = "/api/comments?$top=" + pageSize + '&$skip=' + (pageIndex * pageSize); $.getJSON(url, function (data) { // Update the Knockout model (and thus the UI) with the comments received back // from the Web API call. viewModel.comments(data); }); return false; }); }); And the neat thing is that - without any modification to our server-side code - we can modify the above jQuery call to request the comments be sorted by author: $(function () { //--------------------------------------------------------- // Using Queryable to page //--------------------------------------------------------- $("#getCommentsQueryable").click(function () { viewModel.comments([]); var pageSize = $('#pageSize').val(); var pageIndex = $('#pageIndex').val(); var url = "/api/comments?$top=" + pageSize + '&$skip=' + (pageIndex * pageSize) + '&$orderby=Author'; $.getJSON(url, function (data) { // Update the Knockout model (and thus the UI) with the comments received back // from the Web API call. viewModel.comments(data); }); return false; }); }); So if you want to make use of OData query syntax, you can. If you don't like it, you're free to hook up your filtering and paging however you think is best. Neat. In Part 5, we'll add on support for Data Annotation based validation using an Action Filter.

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• A DirectoryCatalog class for Silverlight MEF (Managed Extensibility Framework)

  - by Dixin

  In the MEF (Managed Extension Framework) for .NET, there are useful ComposablePartCatalog implementations in System.ComponentModel.Composition.dll, like: System.ComponentModel.Composition.Hosting.AggregateCatalog System.ComponentModel.Composition.Hosting.AssemblyCatalog System.ComponentModel.Composition.Hosting.DirectoryCatalog System.ComponentModel.Composition.Hosting.TypeCatalog While in Silverlight, there is a extra System.ComponentModel.Composition.Hosting.DeploymentCatalog. As a wrapper of AssemblyCatalog, it can load all assemblies in a XAP file in the web server side. Unfortunately, in silverlight there is no DirectoryCatalog to load a folder. Background There are scenarios that Silverlight application may need to load all XAP files in a folder in the web server side, for example: If the Silverlight application is extensible and supports plug-ins, there would be a /ClinetBin/Plugins/ folder in the web server, and each pluin would be an individual XAP file in the folder. In this scenario, after the application is loaded and started up, it would like to load all XAP files in /ClinetBin/Plugins/ folder. If the aplication supports themes, there would be a /ClinetBin/Themes/ folder, and each theme would be an individual XAP file too. The application would qalso need to load all XAP files in /ClinetBin/Themes/. It is useful if we have a DirectoryCatalog: DirectoryCatalog catalog = new DirectoryCatalog("/Plugins"); catalog.DownloadCompleted += (sender, e) => { }; catalog.DownloadAsync(); Obviously, the implementation of DirectoryCatalog is easy. It is just a collection of DeploymentCatalog class. Retrieve file list from a directory Of course, to retrieve file list from a web folder, the folder’s “Directory Browsing” feature must be enabled: So when the folder is requested, it responses a list of its files and folders: This is nothing but a simple HTML page: <html> <head> <title>localhost - /Folder/</title> </head> <body> <h1>localhost - /Folder/</h1> <hr> <pre> <a href="/">[To Parent Directory]</a><br> <br> 1/3/2011 7:22 PM 185 <a href="/Folder/File.txt">File.txt</a><br> 1/3/2011 7:22 PM &lt;dir&gt; <a href="/Folder/Folder/">Folder</a><br> </pre> <hr> </body> </html> For the ASP.NET Deployment Server of Visual Studio, directory browsing is enabled by default: The HTML <Body> is almost the same: <body bgcolor="white"> <h2><i>Directory Listing -- /ClientBin/</i></h2> <hr width="100%" size="1" color="silver"> <pre> <a href="/">[To Parent Directory]</a> Thursday, January 27, 2011 11:51 PM 282,538 <a href="Test.xap">Test.xap</a> Tuesday, January 04, 2011 02:06 AM &lt;dir&gt; <a href="TestFolder/">TestFolder</a> </pre> <hr width="100%" size="1" color="silver"> <b>Version Information:</b>&nbsp;ASP.NET Development Server 10.0.0.0 </body> The only difference is, IIS’s links start with slash, but here the links do not. Here one way to get the file list is read the href attributes of the links: [Pure] private IEnumerable<Uri> GetFilesFromDirectory(string html) { Contract.Requires(html != null); Contract.Ensures(Contract.Result<IEnumerable<Uri>>() != null); return new Regex( "<a href=\"(?<uriRelative>[^\"]*)\">[^<]*</a>", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant) .Matches(html) .OfType<Match>() .Where(match => match.Success) .Select(match => match.Groups["uriRelative"].Value) .Where(uriRelative => uriRelative.EndsWith(".xap", StringComparison.Ordinal)) .Select(uriRelative => { Uri baseUri = this.Uri.IsAbsoluteUri ? this.Uri : new Uri(Application.Current.Host.Source, this.Uri); uriRelative = uriRelative.StartsWith("/", StringComparison.Ordinal) ? uriRelative : (baseUri.LocalPath.EndsWith("/", StringComparison.Ordinal) ? baseUri.LocalPath + uriRelative : baseUri.LocalPath + "/" + uriRelative); return new Uri(baseUri, uriRelative); }); } Please notice the folders’ links end with a slash. They are filtered by the second Where() query. The above method can find files’ URIs from the specified IIS folder, or ASP.NET Deployment Server folder while debugging. To support other formats of file list, a constructor is needed to pass into a customized method: /// <summary> /// Initializes a new instance of the <see cref="T:System.ComponentModel.Composition.Hosting.DirectoryCatalog" /> class with <see cref="T:System.ComponentModel.Composition.Primitives.ComposablePartDefinition" /> objects based on all the XAP files in the specified directory URI. /// </summary> /// <param name="uri"> /// URI to the directory to scan for XAPs to add to the catalog. /// The URI must be absolute, or relative to <see cref="P:System.Windows.Interop.SilverlightHost.Source" />. /// </param> /// <param name="getFilesFromDirectory"> /// The method to find files' URIs in the specified directory. /// </param> public DirectoryCatalog(Uri uri, Func<string, IEnumerable<Uri>> getFilesFromDirectory) { Contract.Requires(uri != null); this._uri = uri; this._getFilesFromDirectory = getFilesFromDirectory ?? this.GetFilesFromDirectory; this._webClient = new Lazy<WebClient>(() => new WebClient()); // Initializes other members. } When the getFilesFromDirectory parameter is null, the above GetFilesFromDirectory() method will be used as default. Download the directory’s XAP file list Now a public method can be created to start the downloading: /// <summary> /// Begins downloading the XAP files in the directory. /// </summary> public void DownloadAsync() { this.ThrowIfDisposed(); if (Interlocked.CompareExchange(ref this._state, State.DownloadStarted, State.Created) == 0) { this._webClient.Value.OpenReadCompleted += this.HandleOpenReadCompleted; this._webClient.Value.OpenReadAsync(this.Uri, this); } else { this.MutateStateOrThrow(State.DownloadCompleted, State.Initialized); this.OnDownloadCompleted(new AsyncCompletedEventArgs(null, false, this)); } } Here the HandleOpenReadCompleted() method is invoked when the file list HTML is downloaded. Download all XAP files After retrieving all files’ URIs, the next thing becomes even easier. HandleOpenReadCompleted() just uses built in DeploymentCatalog to download the XAPs, and aggregate them into one AggregateCatalog: private void HandleOpenReadCompleted(object sender, OpenReadCompletedEventArgs e) { Exception error = e.Error; bool cancelled = e.Cancelled; if (Interlocked.CompareExchange(ref this._state, State.DownloadCompleted, State.DownloadStarted) != State.DownloadStarted) { cancelled = true; } if (error == null && !cancelled) { try { using (StreamReader reader = new StreamReader(e.Result)) { string html = reader.ReadToEnd(); IEnumerable<Uri> uris = this._getFilesFromDirectory(html); Contract.Assume(uris != null); IEnumerable<DeploymentCatalog> deploymentCatalogs = uris.Select(uri => new DeploymentCatalog(uri)); deploymentCatalogs.ForEach( deploymentCatalog => { this._aggregateCatalog.Catalogs.Add(deploymentCatalog); deploymentCatalog.DownloadCompleted += this.HandleDownloadCompleted; }); deploymentCatalogs.ForEach(deploymentCatalog => deploymentCatalog.DownloadAsync()); } } catch (Exception exception) { error = new InvalidOperationException(Resources.InvalidOperationException_ErrorReadingDirectory, exception); } } // Exception handling. } In HandleDownloadCompleted(), if all XAPs are downloaded without exception, OnDownloadCompleted() callback method will be invoked. private void HandleDownloadCompleted(object sender, AsyncCompletedEventArgs e) { if (Interlocked.Increment(ref this._downloaded) == this._aggregateCatalog.Catalogs.Count) { this.OnDownloadCompleted(e); } } Exception handling Whether this DirectoryCatelog can work only if the directory browsing feature is enabled. It is important to inform caller when directory cannot be browsed for XAP downloading. private void HandleOpenReadCompleted(object sender, OpenReadCompletedEventArgs e) { Exception error = e.Error; bool cancelled = e.Cancelled; if (Interlocked.CompareExchange(ref this._state, State.DownloadCompleted, State.DownloadStarted) != State.DownloadStarted) { cancelled = true; } if (error == null && !cancelled) { try { // No exception thrown when browsing directory. Downloads the listed XAPs. } catch (Exception exception) { error = new InvalidOperationException(Resources.InvalidOperationException_ErrorReadingDirectory, exception); } } WebException webException = error as WebException; if (webException != null) { HttpWebResponse webResponse = webException.Response as HttpWebResponse; if (webResponse != null) { // Internally, WebClient uses WebRequest.Create() to create the WebRequest object. Here does the same thing. WebRequest request = WebRequest.Create(Application.Current.Host.Source); Contract.Assume(request != null); if (request.CreatorInstance == WebRequestCreator.ClientHttp && // Silverlight is in client HTTP handling, all HTTP status codes are supported. webResponse.StatusCode == HttpStatusCode.Forbidden) { // When directory browsing is disabled, the HTTP status code is 403 (forbidden). error = new InvalidOperationException( Resources.InvalidOperationException_ErrorListingDirectory_ClientHttp, webException); } else if (request.CreatorInstance == WebRequestCreator.BrowserHttp && // Silverlight is in browser HTTP handling, only 200 and 404 are supported. webResponse.StatusCode == HttpStatusCode.NotFound) { // When directory browsing is disabled, the HTTP status code is 404 (not found). error = new InvalidOperationException( Resources.InvalidOperationException_ErrorListingDirectory_BrowserHttp, webException); } } } this.OnDownloadCompleted(new AsyncCompletedEventArgs(error, cancelled, this)); } Please notice Silverlight 3+ application can work either in client HTTP handling, or browser HTTP handling. One difference is: In browser HTTP handling, only HTTP status code 200 (OK) and 404 (not OK, including 500, 403, etc.) are supported In client HTTP handling, all HTTP status code are supported So in above code, exceptions in 2 modes are handled differently. Conclusion Here is the whole DirectoryCatelog’s looking: Please click here to download the source code, a simple unit test is included. This is a rough implementation. And, for convenience, some design and coding are just following the built in AggregateCatalog class and Deployment class. Please feel free to modify the code, and please kindly tell me if any issue is found.

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• Flattening a Jagged Array with LINQ

  - by PSteele

  Today I had to flatten a jagged array.  In my case, it was a string[][] and I needed to make sure every single string contained in that jagged array was set to something (non-null and non-empty).  LINQ made the flattening very easy.  In fact, I ended up making a generic version that I could use to flatten any type of jagged array (assuming it's a T[][]): private static IEnumerable<T> Flatten<T>(IEnumerable<T[]> data) { return from r in data from c in r select c; } Then, checking to make sure the data was valid, was easy: var flattened = Flatten(data); bool isValid = !flattened.Any(s => String.IsNullOrEmpty(s)); You could even use method grouping and reduce the validation to: bool isValid = !flattened.Any(String.IsNullOrEmpty); Technorati Tags: .NET,LINQ,Jagged Array

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• Local Entities with NHibernate

  - by Ricardo Peres

  You may know that Entity Framework Code First has a nice property called Local which lets you iterate through all the entities loaded by the current context (first level cache). This comes handy at times, so I decided to check if it would be difficult to have it on NHibernate. It turned out it is not, so here it is! Another nice addition to an NHibernate toolbox! public static class SessionExtensions { public static IEnumerable<T> Local<T>(this ISession session) { ISessionImplementor impl = session.GetSessionImplementation(); IPersistenceContext pc = impl.PersistenceContext; foreach (Object key in pc.EntityEntries.Keys) { if (key is T) { yield return ((T) key); } } } } //simple usage IEnumerable<Post> localPosts = session.Local<Post>(); SyntaxHighlighter.config.clipboardSwf = 'http://alexgorbatchev.com/pub/sh/2.0.320/scripts/clipboard.swf'; SyntaxHighlighter.brushes.CSharp.aliases = ['c#', 'c-sharp', 'csharp']; SyntaxHighlighter.all();

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• Does my GetEnumerator cause a deadlock?

  - by Scott Chamberlain

  I am starting to write my first parallel applications. This partitioner will enumerate over a IDataReader pulling chunkSize records at a time from the data-source. TLDR; version private object _Lock = new object(); public IEnumerator GetEnumerator() { var infoSource = myInforSource.GetEnumerator(); //Will this cause a deadlock if two threads lock (_Lock) //use the enumator at the same time? { while (infoSource.MoveNext()) { yield return infoSource.Current; } } } full code protected class DataSourcePartitioner<object[]> : System.Collections.Concurrent.Partitioner<object[]> { private readonly System.Data.IDataReader _Input; private readonly int _ChunkSize; public DataSourcePartitioner(System.Data.IDataReader input, int chunkSize = 10000) : base() { if (chunkSize < 1) throw new ArgumentOutOfRangeException("chunkSize"); _Input = input; _ChunkSize = chunkSize; } public override bool SupportsDynamicPartitions { get { return true; } } public override IList<IEnumerator<object[]>> GetPartitions(int partitionCount) { var dynamicPartitions = GetDynamicPartitions(); var partitions = new IEnumerator<object[]>[partitionCount]; for (int i = 0; i < partitionCount; i++) { partitions[i] = dynamicPartitions.GetEnumerator(); } return partitions; } public override IEnumerable<object[]> GetDynamicPartitions() { return new ListDynamicPartitions(_Input, _ChunkSize); } private class ListDynamicPartitions : IEnumerable<object[]> { private System.Data.IDataReader _Input; int _ChunkSize; private object _ChunkLock = new object(); public ListDynamicPartitions(System.Data.IDataReader input, int chunkSize) { _Input = input; _ChunkSize = chunkSize; } public IEnumerator<object[]> GetEnumerator() { while (true) { List<object[]> chunk = new List<object[]>(_ChunkSize); lock(_Input) { for (int i = 0; i < _ChunkSize; ++i) { if (!_Input.Read()) break; var values = new object[_Input.FieldCount]; _Input.GetValues(values); chunk.Add(values); } if (chunk.Count == 0) yield break; } var chunkEnumerator = chunk.GetEnumerator(); lock(_ChunkLock) //Will this cause a deadlock? { while (chunkEnumerator.MoveNext()) { yield return chunkEnumerator.Current; } } } } IEnumerator IEnumerable.GetEnumerator() { return ((IEnumerable<object[]>)this).GetEnumerator(); } } } I wanted IEnumerable object it passed back to be thread safe (the MSDN example was so I am assuming PLINQ and TPL could need it) will the lock on _ChunkLock near the bottom help provide thread safety or will it cause a deadlock? From the documentation I could not tell if the lock would be released on the yeld return. Also if there is built in functionality to .net that will do what I am trying to do I would much rather use that. And if you find any other problems with the code I would appreciate it.

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• Why is ListBoxFor not selecting items, but ListBox is?

  - by Roger Rogers

  I have the following code in my view: <%= Html.ListBoxFor(c => c.Project.Categories, new MultiSelectList(Model.Categories, "Id", "Name", new List<int> { 1, 2 }))%> <%= Html.ListBox("MultiSelectList", new MultiSelectList(Model.Categories, "Id", "Name", new List<int> { 1, 2 }))%> The only difference is that the first helper is strongly typed (ListBoxFor), and it fails to show the selected items (1,2), even though the items appear in the list, etc. The simpler ListBox is working as expected. I'm obviously missing something here. I can use the second approach, but this is really bugging me and I'd like to figure it out. For reference, my model is: public class ProjectEditModel { public Project Project { get; set; } public IEnumerable<Project> Projects { get; set; } public IEnumerable<Client> Clients { get; set; } public IEnumerable<Category> Categories { get; set; } public IEnumerable<Tag> Tags { get; set; } public ProjectSlide SelectedSlide { get; set; } } Update I just changed the ListBox name to Project.Categories (matching my model) and it now FAILS to select the item. <%= Html.ListBox("Project.Categories", new MultiSelectList(Model.Categories, "Id", "Name", new List<int> { 1, 2 }))%> I'm obviously not understanding the magic that is happening here. Update 2 Ok, this is purely naming, for example, this works... <%= Html.ListBox("Project_Tags", new MultiSelectList(Model.Tags, "Id", "Name", Model.Project.Tags.Select(t => t.Id)))%> ...because the field name is Project_Tags, not Project.Tags, in fact, anything other than Tags or Project.Tags will work. I don't get why this would cause a problem (other than that it matches the entity name), and I'm not good enough at this to be able to dig in and find out.

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• Please help with 'System.Data.DataRowView' does not contain a property with the name...

  - by Catalin

  My application works just fine until, in some unidentified conditions, it begins throwing this errors: When these errors start appearing, they appear in all over the application, no matter the code is built using ObjectDataSource or SqlDataSource. However, apparently, if the code uses some "classic", code-behind data-binding, that code does not throw errors (they do not show in the application event log), the page is displayed but it does not contain any data.... Please HELP tracking these very strange errors !!!!!! Here is the error log from the Event Viewer Exception information: Exception type: HttpUnhandledException Exception message: Exception of type 'System.Web.HttpUnhandledException' was thrown. Request information: Request URL: http://SITE/agsis/Default.aspx?tabid=1281&error=DataBinding5/7/2009 10:23:03 AMa+'System.Data.DataRowView'+does+not+contain+a+property+with+the+name+'DenumireMaterie'. Request path: /agsis/Default.aspx User host address: 299.299.299.299 ;) User: georgeta Is authenticated: True Authentication Type: Forms Thread account name: NT AUTHORITY\NETWORK SERVICE Thread information: Thread ID: 1 Thread account name: NT AUTHORITY\NETWORK SERVICE Is impersonating: False Stack trace: at System.Web.UI.Page.HandleError(Exception e) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) at System.Web.UI.Page.ProcessRequest() at System.Web.UI.Page.ProcessRequest(HttpContext context) at ASP.errorpage_aspx.ProcessRequest(HttpContext context) at System.Web.HttpServerUtility.ExecuteInternal(IHttpHandler handler, TextWriter writer, Boolean preserveForm, Boolean setPreviousPage, VirtualPath path, VirtualPath filePath, String physPath, Exception error, String queryStringOverride) Here is the error log from my application: AssemblyVersion: 04.05.01 PortalID: 18 PortalName: Stiinte Economice UserID: 85 UserName: georgeta ActiveTabID: 1281 ActiveTabName: Plan Invatamant RawURL: /agsis/Default.aspx?tabid=1281&error=DataBinding%3a+'System.Data.DataRowView'+does+not+contain+a+property+with+the+name+'DenumireMaterie'. AbsoluteURL: /agsis/Default.aspx AbsoluteURLReferrer: http://SITE/agsis/Default.aspx?tabid=1281&ctl=Login&returnurl=%2fagsis%2fDefault.aspx%3ftabid%3d1281%26ctl%3dNotePlanSemestru%26mid%3d2801%26ID_PlanSemestru%3d518%26ID_PlanInvatamant%3d304%26ID_FC%3d206%26ID_FCForma%3d85%26ID_Domeniu%3d418%26ID_AnStudiu%3d7%26ID_Specializare%3d6522%26ID_AnUniv%3d27 UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; SIMBAR={8C326639-C677-4045-B6D9-F59C330790E7}) DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider ExceptionGUID: c56dc33e-973f-467a-a90d-2a8fc7193aec InnerException: DataBinding: 'System.Data.DataRowView' does not contain a property with the name 'ID_PlanInvatamant'. FileName: FileLineNumber: 0 FileColumnNumber: 0 Method: System.Web.UI.DataBinder.GetPropertyValue StackTrace: Message: DotNetNuke.Services.Exceptions.PageLoadException: DataBinding: 'System.Data.DataRowView' does not contain a property with the name 'ID_PlanInvatamant'. --- System.Web.HttpException: DataBinding: 'System.Data.DataRowView' does not contain a property with the name 'ID_PlanInvatamant'. at System.Web.UI.DataBinder.GetPropertyValue(Object container, String propName) at System.Web.UI.WebControls.GridView.CreateChildControls(IEnumerable dataSource, Boolean dataBinding) at System.Web.UI.WebControls.CompositeDataBoundControl.PerformDataBinding(IEnumerable data) at System.Web.UI.WebControls.GridView.PerformDataBinding(IEnumerable data) at System.Web.UI.WebControls.DataBoundControl.OnDataSourceViewSelectCallback(IEnumerable data) at System.Web.UI.WebControls.DataBoundControl.PerformSelect() at System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound() at System.Web.UI.WebControls.CompositeDataBoundControl.CreateChildControls() at System.Web.UI.Control.EnsureChildControls() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Control.PreRenderRecursiveInternal() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace --- Source: Server Name: SERVER2 Thank you, Catalin

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• How to load entities into private collections using the entity framework

  - by Anton P

  I have a POCO domain model which is wired up to the entity framework using the new ObjectContext class. public class Product { private ICollection<Photo> _photos; public Product() { _photos = new Collection<Photo>(); } public int Id { get; set; } public string Name { get; set; } public virtual IEnumerable<Photo> Photos { get { return _photos; } } public void AddPhoto(Photo photo) { //Some biz logic //... _photos.Add(photo); } } In the above example i have set the Photos collection type to IEnumerable as this will make it read only. The only way to add/remove photos is through the public methods. The problem with this is that the Entity Framework cannot load the Photo entities into the IEnumerable collection as it's not of type ICollection. By changing the type to ICollection will allow callers to call the Add mentod on the collection itself which is not good. What are my options? Edit: I could refactor the code so it does not expose a public property for Photos: public class Product { public Product() { Photos = new Collection<Photo>(); } public int Id { get; set; } public string Name { get; set; } private Collection<Photo> Photos {get; set; } public IEnumerable<Photo> GetPhotos() { return Photos; } public void AddPhoto(Photo photo) { //Some biz logic //... Photos.Add(photo); } } And use the GetPhotos() to return the collection. The other problem with the approach is that I will loose the change tracking abilities as I cannot mark the collection as Virtual - It is not possible to mark a property as private virtual. In NHibernate I believe it's possible to map the proxy class to the private collection via configuration. I hope that this will become a feature of EF4. Currently i don't like the inability to have any control over the collection!

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• ASP.NET MVC2: Can you get ModelMetadata.ContainerType from within a collection?

  - by CodeSponge

  I'm trying to call DisplayFor and DisplayForModel to iterate an IEnumerable< with various element types from within a view. I have Templates defined for each element/Model type. What I would like to do is check the ViewData.ModelMetadata.ContainerType from within the Template so that Template can determine if it was called as part of a collection. A simple example: Index1.aspx: To render a collection of Foos. <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<IEnumerable<Foo>>" %> <asp:Content ContentPlaceHolderID="MainPlaceHolder" runat="server"> <ul><%:Html.DisplayForModel()%></ul> </asp:Content> Index2.aspx: To render a Foo. <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<Foo>" %> <asp:Content ContentPlaceHolderID="MainPlaceHolder" runat="server"> <%:Html.DisplayForModel()%> </asp:Content> Shared\DisplayTemplates\Foo.ascx: A context aware Template for Foo. <%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<Foo>" %> <% var tag = typeof(IEnumerable).IsAssignableFrom(ViewData.ModelMetaData.ContainerType) ? "li" : "div"; %> <<%:tag%>><%:Model.Name%></<%:tag%>> The problem with this example is that ViewData.ModelMetaData.ContainerType is null in the Template when resolved though Index1.aspx. From what I've read on Brad Wilson post and others it has to do with the use of IEnumerable and its being an interface. Is there a way to insure that the ContainerType is set? Perhaps by creating a ModelMetadataProviders? I looked into that breifly but it appears the ContainerType value is determined before and then passed to the Provider. Any suggestions would be appreciated.

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• How to Access a decendant object's internal method in C#

  - by Giovanni Galbo

  I'm trying to access a method that is marked as internal in the parent class (in its own assembly) in an object that inherits from the same parent. Let me explain what I'm trying to do... I want to create Service classes that return IEnumberable with an underlying List to non-Service classes (e.g. the UI) and optionally return an IEnumerable with an underlying IQueryable to other services. I wrote some sample code to demonstrate what I'm trying to accomplish, shown below. The example is not real life, so please remember that when commenting. All services would inherit from something like this (only relevant code shown): public class ServiceBase<T> { protected readonly ObjectContext _context; protected string _setName = String.Empty; public ServiceBase(ObjectContext context) { _context = context; } public IEnumerable<T> GetAll() { return GetAll(false); } //These are not the correct access modifiers.. I want something //that is accessible to children classes AND between descendant classes internal protected IEnumerable<T> GetAll(bool returnQueryable) { var query = _context.CreateQuery<T>(GetSetName()); if(returnQueryable) { return query; } else { return query.ToList(); } } private string GetSetName() { //Some code... return _setName; } } Inherited services would look like this: public class EmployeeService : ServiceBase<Employees> { public EmployeeService(ObjectContext context) : base(context) { } } public class DepartmentService : ServiceBase<Departments> { private readonly EmployeeService _employeeService; public DepartmentService(ObjectContext context, EmployeeService employeeService) : base(context) { _employeeService = employeeService; } public IList<Departments> DoSomethingWithEmployees(string lastName) { //won't work because method with this signature is not visible to this class var emps = _employeeService.GetAll(true); //more code... } } Because the parent class lives is reusable, it would live in a different assembly than the child services. With GetAll(bool returnQueryable) being marked internal, the children would not be able to see each other's GetAll(bool) method, just the public GetAll() method. I know that I can add a new internal GetAll method to each service (or perhaps an intermediary parent class within the same assembly) so that each child service within the assembly can see each other's method; but it seems unnecessary since the functionality is already available in the parent class. For example: internal IEnumerable<Employees> GetAll(bool returnIQueryable) { return base.GetAll(returnIQueryable); } Essentially what I want is for services to be able to access other service methods as IQueryable so that they can further refine the uncommitted results, while everyone else gets plain old lists. Any ideas?

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• Challenge: Neater way of currying or partially applying C#4's string.Join

  - by Damian Powell

  Background I recently read that .NET 4's System.String class has a new overload of the Join method. This new overload takes a separator, and an IEnumerable<T> which allows arbitrary collections to be joined into a single string without the need to convert to an intermediate string array. Cool! That means I can now do this: var evenNums = Enumerable.Range(1, 100) .Where(i => i%2 == 0); var list = string.Join(",",evenNums); ...instead of this: var evenNums = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .Select(i => i.ToString()) .ToArray(); var list = string.Join(",", evenNums); ...thus saving on a conversion of every item to a string, and then the allocation of an array. The Problem However, being a fan of the functional style of programming in general, and method chaining in C# in particular, I would prefer to be able to write something like this: var list = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .string.Join(","); This is not legal C# though. The closest I've managed to get is this: var list = Enumerable.Range(1, 100) .Where(i => i%2 == 0) .ApplyTo( Functional.Curry<string, IEnumerable<object>, string> (string.Join)(",") ); ...using the following extension methods: public static class Functional { public static TRslt ApplyTo<TArg, TRslt>(this TArg arg, Func<TArg, TRslt> func) { return func(arg); } public static Func<T1, Func<T2, TResult>> Curry<T1, T2, TResult>(this Func<T1, T2, TResult> func) { Func<Func<T1, T2, TResult>, Func<T1, Func<T2, TResult>>> curried = f => x => y => f(x, y); return curried(func); } } This is quite verbose, requires explicit definition of the parameters and return type of the string.Join overload I want to use, and relies upon C#4's variance features because we are defining one of the arguments as IEnumerable rather than IEnumerable. The Challenge Can you find a neater way of achieving this using the method-chaining style of programming?

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