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  • If I cast an IQueryable as an IEnumerable then call a Linq extension method, which implementation gets called?

    - by James Morcom
    Considering the following code: IQueryable<T> queryable; // something to instantiate queryable var enumerable = (IEnumerable<T>) queryable; var filtered = enumerable.Where(i => i > 3); In the final line, which extension method gets called? Is it IEnumerable<T>.Where(...)? Or will IQueryable<T>.Where(...) be called because the actual implementation is still obviously a queryable? Presumably the ideal would be for the IQueryable version to be called, in the same way that normal polymorphism will always use the more specific override. In Visual Studio though when I right-click on the Where method and "Go to Definition" I'm taken to the IEnumerable version, which kind of makes sense from a visual point-of-view. My main concern is that if somewhere in my app I use Linq to NHibernate to get a Queryable, but I pass it around using an interface that uses the more general IEnumerable signature, I'll lose the wonders of deferred database execution!

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  • fastest way to check to see if a certain index in a linq statement is null

    - by tehdoommarine
    Basic Details I have a linq statement that grabs some records from a database and puts them in a System.Linq.Enumerable: var someRecords = someRepoAttachedToDatabase.Where(p=>true); Suppose this grabs tons (25k+) of records, and i need to perform operations on all of them. to speed things up, I have to decided to use paging and perform the operations needed in blocks of 100 instead of all of the records at the same time. The Question The line in question is the line where I count the number of records in the subset to see if we are on the last page; if the number of records in subset is less than the size of paging - then that means there are no more records left. What I would like to know is what is the fastest way to do this? Code in Question int pageSize = 100; bool moreData = true; int currentPage = 1; while (moreData) { var subsetOfRecords = someRecords.Skip((currentPage - 1) * pageSize).Take(pageSize); //this is also a System.Linq.Enumerable if (subsetOfRecords.Count() < pageSize){ moreData = false;} //line in question //do stuff to records in subset currentPage++; } Things I Have Considered subsetOfRecords.Count() < pageSize subsetOfRecords.ElementAt(pageSize - 1) == null (causes out of bounds exception - can catch exception and set moreData to false there) Converting subsetOfRecords to an array (converting someRecords to an array will not work due to the way subsetOfRecords is declared - but I am open to changing it) I'm sure there are plenty of other ideas that I have missed.

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  • An Array returned by a model association is not an Array?

    - by Warren
    We have a model association that looks something like this: class Example < ActiveRecord::Base has_many :others, :order => 'others.rank' end The rank column is an integer type. The details of these particular models are not really important though as we have found the same problem with other has_many associations between other models. We have also added to the Enumerable module: module Enumerable def method_missing(name) super unless name.to_s[0..7] == 'collect_' method = name.to_s[8..-1] collect{|element| element.send(method)} end end This adds a collect_id method that we can use to get an array of record ids from an array of ActiveRecord objects. So if we use a normal ActiveRecord find :all, we get a nice array which we can then use collect_id on but if we use Example.others.collect_id, we get NoMethodError: undefined method `collect_id' for #<Class:0x2aaaac0060a0> Example.others.class returns "Array" so is it lying or confused? Our solution thus far has been to use it this way: Example.others.to_a.collect_id This works but this seems a bit strange. Why would you have to do that? We are on Ruby 1.8.7 and Rails 2.3.4

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  • Why can't I create a templated sublcass of System::Collections::Generic::IEnumerable<T>?

    - by fiirhok
    I want to create a generic IEnumerable implementation, to make it easier to wrap some native C++ classes. When I try to create the implementation using a template parameter as the parameter to IEnumerable, I get an error. Here's a simple version of what I came up with that demonstrates my problem: ref class A {}; template<class B> ref class Test : public System::Collections::Generic::IEnumerable<B^> // error C3225... {}; void test() { Test<A> ^a = gcnew Test<A>(); } On the indicated line, I get this error: error C3225: generic type argument for 'T' cannot be 'B ^', it must be a value type or a handle to a reference type If I use a different parent class, I don't see the problem: template<class P> ref class Parent {}; ref class A {}; template<class B> ref class Test : public Parent<B^> // no problem here {}; void test() { Test<A> ^a = gcnew Test<A>(); } I can work around it by adding another template parameter to the implementation type: ref class A {}; template<class B, class Enumerable> ref class Test : public Enumerable {}; void test() { using namespace System::Collections::Generic; Test<A, IEnumerable<A^>> ^a = gcnew Test<A, IEnumerable<A^>>(); } But this seems messy to me. Also, I'd just like to understand what's going on here - why doesn't the first way work?

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  • Q1 2010 New Feature: Paging with RadGridView for Silverlight and WPF

    We are glad to announce that the Q1 2010 Release has added another weapon to RadGridViews growing arsenal of features. This is the brand new RadDataPager control which provides the user interface for paging through a collection of data. The good news is that RadDataPager can be used to page any collection. It does not depend on RadGridView in any way, so you will be free to use it with the rest of your ItemsControls if you chose to do so. Before you read on, you might want to download the samples solution that I have attached. It contains a sample project for every scenario that I will discuss later on. Looking at the code while reading will make things much easier for you. There is something for everyone among the 10 Visual Studio projects that are included in the solution. So go and grab it. I. Paging essentials The single most important piece of software concerning paging in Silverlight is the System.ComponentModel.IPagedCollectionView interface. Those of you who are on the WPF front need not worry though. As you might already know, Teleriks Silverlight and WPF controls is share the same code-base. Since WPF does not contain a similar interface, Telerik has provided its own Telerik.Windows.Data.IPagedCollectionView. The IPagedCollectionView interface contains several important members which are used by RadGridView to perform the actual paging. Silverlight provides a default implementation of this interface which, naturally, is called PagedCollectionView. You should definitely take a look at its source code in case you are interested in what is going on under the hood. But this is not a prerequisite for our discussion. The WPF default implementation of the interface is Teleriks QueryableCollectionView which, among many other interfaces, implements IPagedCollectionView. II. No Paging In order to gradually build up my case, I will start with a very simple example that lacks paging whatsoever. It might sound stupid, but this will help us build on top of this paging-devoid example. Let us imagine that we have the simplest possible scenario. That is a simple IEnumerable and an ItemsControl that shows its contents. This will look like this: No Paging IEnumerable itemsSource = Enumerable.Range(0, 1000); this.itemsControl.ItemsSource = itemsSource; XAML <Border Grid.Row="0" BorderBrush="Black" BorderThickness="1" Margin="5">     <ListBox Name="itemsControl"/> </Border> <Border Grid.Row="1" BorderBrush="Black" BorderThickness="1" Margin="5">     <TextBlock Text="No Paging"/> </Border> Nothing special for now. Just some data displayed in a ListBox. The two sample projects in the solution that I have attached are: NoPaging_WPF NoPaging_SL3 With every next sample those two project will evolve in some way or another. III. Paging simple collections The single most important property of RadDataPager is its Source property. This is where you pass in your collection of data for paging. More often than not your collection will not be an IPagedCollectionView. It will either be a simple List<T>, or an ObservableCollection<T>, or anything that is simply IEnumerable. Unless you had paging in mind when you designed your project, it is almost certain that your data source will not be pageable out of the box. So what are the options? III. 1. Wrapping the simple collection in an IPagedCollectionView If you look at the constructors of PagedCollectionView and QueryableCollectionView you will notice that you can pass in a simple IEnumerable as a parameter. Those two classes will wrap it and provide paging capabilities over your original data. In fact, this is what RadGridView does internally. It wraps your original collection in an QueryableCollectionView in order to easily perform many useful tasks such as filtering, sorting, and others, but in our case the most important one is paging. So let us start our series of examples with the most simplistic one. Imagine that you have a simple IEnumerable which is the source for an ItemsControl. Here is how to wrap it in order to enable paging: Silverlight IEnumerable itemsSource = Enumerable.Range(0, 1000); var pagedSource = new PagedCollectionView(itemsSource); this.radDataPager.Source = pagedSource; this.itemsControl.ItemsSource = pagedSource; WPF IEnumerable itemsSource = Enumerable.Range(0, 1000); var pagedSource = new QueryableCollectionView(itemsSource); this.radDataPager.Source = pagedSource; this.itemsControl.ItemsSource = pagedSource; XAML <Border Grid.Row="0"         BorderBrush="Black"         BorderThickness="1"         Margin="5">     <ListBox Name="itemsControl"/> </Border> <Border Grid.Row="1"         BorderBrush="Black"         BorderThickness="1"         Margin="5">     <telerikGrid:RadDataPager Name="radDataPager"                               PageSize="10"                              IsTotalItemCountFixed="True"                              DisplayMode="All"/> This will do the trick. It is quite simple, isnt it? The two sample projects in the solution that I have attached are: PagingSimpleCollectionWithWrapping_WPF PagingSimpleCollectionWithWrapping_SL3 III. 2. Binding to RadDataPager.PagedSource In case you do not like this approach there is a better one. When you assign an IEnumerable as the Source of a RadDataPager it will automatically wrap it in a QueryableCollectionView and expose it through its PagedSource property. From then on, you can attach any number of ItemsControls to the PagedSource and they will be automatically paged. Here is how to do this entirely in XAML: Using RadDataPager.PagedSource <Border Grid.Row="0"         BorderBrush="Black"         BorderThickness="1" Margin="5">     <ListBox Name="itemsControl"              ItemsSource="{Binding PagedSource, ElementName=radDataPager}"/> </Border> <Border Grid.Row="1"         BorderBrush="Black"         BorderThickness="1"         Margin="5">     <telerikGrid:RadDataPager Name="radDataPager"                               Source="{Binding ItemsSource}"                              PageSize="10"                              IsTotalItemCountFixed="True"                              DisplayMode="All"/> The two sample projects in the solution that I have attached are: PagingSimpleCollectionWithPagedSource_WPF PagingSimpleCollectionWithPagedSource_SL3 IV. Paging collections implementing IPagedCollectionView Those of you who are using WCF RIA Services should feel very lucky. After a quick look with Reflector or the debugger we can see that the DomainDataSource.Data property is in fact an instance of the DomainDataSourceView class. This class implements a handful of useful interfaces: ICollectionView IEnumerable INotifyCollectionChanged IEditableCollectionView IPagedCollectionView INotifyPropertyChanged Luckily, IPagedCollectionView is among them which lets you do the whole paging in the server. So lets do this. We will add a DomainDataSource control to our page/window and connect the items control and the pager to it. Here is how to do this: MainPage <riaControls:DomainDataSource x:Name="invoicesDataSource"                               AutoLoad="True"                               QueryName="GetInvoicesQuery">     <riaControls:DomainDataSource.DomainContext>         <services:ChinookDomainContext/>     </riaControls:DomainDataSource.DomainContext> </riaControls:DomainDataSource> <Border Grid.Row="0"         BorderBrush="Black"         BorderThickness="1"         Margin="5">     <ListBox Name="itemsControl"              ItemsSource="{Binding Data, ElementName=invoicesDataSource}"/> </Border> <Border Grid.Row="1"         BorderBrush="Black"         BorderThickness="1"         Margin="5">     <telerikGrid:RadDataPager Name="radDataPager"                               Source="{Binding Data, ElementName=invoicesDataSource}"                              PageSize="10"                              IsTotalItemCountFixed="True"                              DisplayMode="All"/> By the way, you can replace the ListBox from the above code snippet with any other ItemsControl. It can be RadGridView, it can be the MS DataGrid, you name it. Essentially, RadDataPager is sending paging commands to the the DomainDataSource.Data. It does not care who, what, or how many different controls are bound to this same Data property of the DomainDataSource control. So if you would like to experiment with this, you can throw in any number of other ItemsControls next to the ListBox, bind them in the same manner, and all of them will be paged by our single RadDataPager. Furthermore, you can throw in any number of RadDataPagers and bind them to the same property. Then when you page with any one of them will automatically update all of the rest. The whole picture is simply beautiful and we can do all of this thanks to WCF RIA Services. The two sample projects (Silverlight only) in the solution that I have attached are: PagingIPagedCollectionView PagingIPagedCollectionView.Web IV. Paging RadGridView While you can replace the ListBox in any of the above examples with a RadGridView, RadGridView offers something extra. Similar to the DomainDataSource.Data property, the RadGridView.Items collection implements the IPagedCollectionView interface. So you are already thinking: Then why not bind the Source property of RadDataPager to RadGridView.Items? Well thats exactly what you can do and you will start paging RadGridView out-of-the-box. It is as simple as that, no code-behind is involved: MainPage <Border Grid.Row="0"         BorderBrush="Black"         BorderThickness="1" Margin="5">     <telerikGrid:RadGridView Name="radGridView"                              ItemsSource="{Binding ItemsSource}"/> </Border> <Border Grid.Row="1"         BorderBrush="Black"         BorderThickness="1"         Margin="5">     <telerikGrid:RadDataPager Name="radDataPager"                               Source="{Binding Items, ElementName=radGridView}"                              PageSize="10"                              IsTotalItemCountFixed="True"                              DisplayMode="All"/> The two sample projects in the solution that I have attached are: PagingRadGridView_SL3 PagingRadGridView_WPF With this last example I think I have covered every possible paging combination. In case you would like to see an example of something that I have not covered, please let me know. Also, make sure you check out those great online examples: WCF RIA Services with DomainDataSource Paging Configurator Endless Paging Paging Any Collection Paging RadGridView Happy Paging! Download Full Source Code Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Visual Tree Enumeration

    - by codingbloke
    I feel compelled to post this blog because I find I’m repeatedly posting this same code in silverlight and windows-phone-7 answers in Stackoverflow. One common task that we feel we need to do is burrow into the visual tree in a Silverlight or Windows Phone 7 application (actually more recently I found myself doing this in WPF as well).  This allows access to details that aren’t exposed directly by some controls.  A good example of this sort of requirement is found in the “Restoring exact scroll position of a listbox in Windows Phone 7”  question on stackoverflow.  This required that the scroll position of the scroll viewer internal to a listbox be accessed. A caveat One caveat here is that we should seriously challenge the need for this burrowing since it may indicate that there is a design problem.  Burrowing into the visual tree or indeed burrowing out to containing ancestors could represent significant coupling between module boundaries and that generally isn’t a good idea. Why isn’t this idea just not cast aside as a no-no?  Well the whole concept of a “Templated Control”, which are in extensive use in these applications, opens the coupling between the content of the visual tree and the internal code of a control.   For example, I can completely change the appearance and positioning of elements that make up a ComboBox.  The ComboBox control relies on specific template parts having set names of a specified type being present in my template.  Rightly or wrongly this does kind of give license to writing code that has similar coupling. Hasn’t this been done already? Yes it has.  There are number of blogs already out there with similar solutions.  In fact if you are using Silverlight toolkit the VisualTreeExtensions class already provides this feature.  However I prefer my specific code because of the simplicity principle I hold to.  Only write the minimum code necessary to give all the features needed.  In this case I add just two extension methods Ancestors and Descendents, note I don’t bother with “Get” or “Visual” prefixes.  Also I haven’t added Parent or Children methods nor additional “AndSelf” methods because all but Children is achievable with the addition of some other Linq methods.  I decided to give Descendents an additional overload for depth hence a depth of 1 is equivalent to Children but this overload is a little more flexible than simply Children. So here is the code:- VisualTreeEnumeration public static class VisualTreeEnumeration {     public static IEnumerable<DependencyObject> Descendents(this DependencyObject root, int depth)     {         int count = VisualTreeHelper.GetChildrenCount(root);         for (int i = 0; i < count; i++)         {             var child = VisualTreeHelper.GetChild(root, i);             yield return child;             if (depth > 0)             {                 foreach (var descendent in Descendents(child, --depth))                     yield return descendent;             }         }     }     public static IEnumerable<DependencyObject> Descendents(this DependencyObject root)     {         return Descendents(root, Int32.MaxValue);     }     public static IEnumerable<DependencyObject> Ancestors(this DependencyObject root)     {         DependencyObject current = VisualTreeHelper.GetParent(root);         while (current != null)         {             yield return current;             current = VisualTreeHelper.GetParent(current);         }     } }   Usage examples The following are some examples of how to combine the above extension methods with Linq to generate the other axis scenarios that tree traversal code might require. Missing Axis Scenarios var parent = control.Ancestors().Take(1).FirstOrDefault(); var children = control.Descendents(1); var previousSiblings = control.Ancestors().Take(1)     .SelectMany(p => p.Descendents(1).TakeWhile(c => c != control)); var followingSiblings = control.Ancestors().Take(1)     .SelectMany(p => p.Descendents(1).SkipWhile(c => c != control).Skip(1)); var ancestorsAndSelf = Enumerable.Repeat((DependencyObject)control, 1)     .Concat(control.Ancestors()); var descendentsAndSelf = Enumerable.Repeat((DependencyObject)control, 1)     .Concat(control.Descendents()); You might ask why I don’t just include these in the VisualTreeEnumerator.  I don’t on the principle of only including code that is actually needed.  If you find that one or more of the above  is needed in your code then go ahead and create additional methods.  One of the downsides to Extension methods is that they can make finding the method you actually want in intellisense harder. Here are some real world usage scenarios for these methods:- Real World Scenarios //Gets the internal scrollviewer of a ListBox ScrollViewer sv = someListBox.Descendents().OfType<ScrollViewer>().FirstOrDefault(); // Get all text boxes in current UserControl:- var textBoxes = this.Descendents().OfType<TextBox>(); // All UIElement direct children of the layout root grid:- var topLevelElements = LayoutRoot.Descendents(0).OfType<UIElement>(); // Find the containing `ListBoxItem` for a UIElement:- var container = elem.Ancestors().OfType<ListBoxItem>().FirstOrDefault(); // Seek a button with the name "PinkElephants" even if outside of the current Namescope:- var pinkElephantsButton = this.Descendents()     .OfType<Button>()     .FirstOrDefault(b => b.Name == "PinkElephants"); //Clear all checkboxes with the name "Selector" in a Treeview foreach (CheckBox checkBox in elem.Descendents()     .OfType<CheckBox>().Where(c => c.Name == "Selector")) {     checkBox.IsChecked = false; }   The last couple of examples above demonstrate a common requirement of finding controls that have a specific name.  FindName will often not find these controls because they exist in a different namescope. Hope you find this useful, if not I’m just glad to be able to link to this blog in future stackoverflow answers.

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  • Why can we delete some built-in properties of global object?

    - by demix
    I'm reading es5 these days and find that [[configurable]] attribute in some built-in properties of global object is set to true which means we can delete these properties. For example: the join method of Array.prototype object have attributes {[[Writable]]:true, [[Enumerable]]: false, [[Configurable]]: true} So we can easily delete the join method for Array like: delete Array.prototype.join; alert([1,2,3].join); The alert will display undefined in my chromium 17,firefox 9 ,ie 10,even ie6; In Chrome 15 & safari 5.1.1 the [[configurable]] attribute is set to true and delete result is also true but the final result is still function(){[native code]}. Seems like this is a bug and chromium fix it. I haven't notice that before. In my opinion, delete built-in functions in user's code is dangerous, and will bring out so many bugs when working with others.So why ECMAScript make this decision?

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  • Domain Model and Querying

    - by Tyrsius
    I am new to DDD, having worked only in Transaction-Script apps with an anemic model, or just Big Balls of Mud, so please forgive any terminology I abuse. I am trying to understand the proper separation between the domain model and the repository. What is the proper way to construct a domain object that is coming from a database, assuming the (incredibly simplified) need to query for objects by status (returns enumerable), or by ID. Should a factory be building the objects, exposing methods for GetByStatus() and GetByID(), using a DIed repository? Should a repository be called directly, knowing how to build a domain model from the DTO? Should the domain model have a constructor for get by ID, using a DIed repoistory to load the initial state, using some other (?) method for the list? I am not really sure what the best way would be, and this question has an answer advocating each one (these are certainly mutuallu exclusive).

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  • Left Join in Subsonic3

    - by muek
    Hi there, I'm new in subsonic3, and I'm getting some errors when I try to use LeftJoin var q = from c in categories join p in products on c equals p.Category into ps from p in ps.DefaultIfEmpty() select new { Category = c, ProductName = p == null ? "(No products)" : p.ProductName }; The error is "System.Collections.Generic.Enumerable '...' cannot be used for parameter of type System.Linq.IQueryable Does anyone had this error before? Did you fix it? Thanks

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  • asp.net MVC binding specific model results in error for post request

    - by Tomh
    Hi I'm having the following two actions defined in my controller [Authorize] [HttpGet] public ActionResult Edit() { ViewData.Model = HttpContext.User.Identity; return View(); } [Authorize] [HttpPost] public ActionResult Edit(User model) { return View(); } However if I post my editted data to the second action I get the following error: Server Error in '/' Application. An item with the same key has already been added. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ArgumentException: An item with the same key has already been added. Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. I tried several things like renaming parameters and removing editable fields, but it seems the model type is the problem, what could be wrong? Stack Trace: [ArgumentException: An item with the same key has already been added.] System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) +51 System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) +7464444 System.Linq.Enumerable.ToDictionary(IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer) +270 System.Linq.Enumerable.ToDictionary(IEnumerable`1 source, Func`2 keySelector, IEqualityComparer`1 comparer) +102 System.Web.Mvc.ModelBindingContext.get_PropertyMetadata() +157 System.Web.Mvc.DefaultModelBinder.BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor) +158 System.Web.Mvc.DefaultModelBinder.BindProperties(ControllerContext controllerContext, ModelBindingContext bindingContext) +90 System.Web.Mvc.DefaultModelBinder.BindComplexElementalModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Object model) +50 System.Web.Mvc.DefaultModelBinder.BindComplexModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +1048 System.Web.Mvc.DefaultModelBinder.BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +280 System.Web.Mvc.ControllerActionInvoker.GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor) +257 System.Web.Mvc.ControllerActionInvoker.GetParameterValues(ControllerContext controllerContext, ActionDescriptor actionDescriptor) +109 System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +314 System.Web.Mvc.Controller.ExecuteCore() +105 System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +39 System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +7 System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__4() +34 System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +21 System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +12 System.Web.Mvc.Async.WrappedAsyncResult`1.End() +59 System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +44 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +7 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8679150 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155

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  • Recursive languages vs context-sensitive languages

    - by teehoo
    In Chomsky's hierarchy, the set of recursive languages is not defined. I know that recursive languages are a subset of recursively enumerable languages and that all recursive languages are decidable. What I'm curious about is how recursive languages compare to context-sensitive languages. Can I assume that context-sensitive languages are a strict subset of recursive languages, and therefore all context-sensitive languages are decidable?

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  • How to use Linq in Mono?

    - by Jader Dias
    I can't make System.Linq (aka. Linq-to-objects) work. I am running MonoDevelop 2.2.1 in Ubuntu 10 Lucid Lynx with Mono 2.4.4. They advertise in their site that they implemented Linq, but I can't even find Enumerable.Range or .ToArray(). What's wrong?

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  • Algorithm to retrieve every possible combination of sublists of a two lists

    - by sgmoore
    Suppose I have two lists, how do I iterate through every possible combination of every sublist, such that each item appears once and only once. I guess an example could be if you have employees and jobs and you want split them into teams, where each employee can only be in one team and each job can only be in one team. Eg List<string> employees = new List<string>() { "Adam", "Bob"} ; List<string> jobs = new List<string>() { "1", "2", "3"}; I want Adam : 1 Bob : 2 , 3 Adam : 1 , 2 Bob : 3 Adam : 1 , 3 Bob : 2 Adam : 2 Bob : 1 , 3 Adam : 2 , 3 Bob : 1 Adam : 3 Bob : 1 , 2 Adam, Bob : 1, 2, 3 I tried using the answer to this stackoverflow question to generate a list of every possible combination of employees and every possible combination of jobs and then select one item from each from each list, but that's about as far as I got. I don't know the maximum size of the lists, but it would be certainly be less than 100 and there may be other limiting factors (such as each team can have no more than 5 employees) Update Not sure whether this can be tidied up more and/or simplified, but this is what I have ended up with so far. It uses the Group algorithm supplied by Yorye (see his answer below), but I removed the orderby which I don't need and caused problems if the keys are not comparable. var employees = new List<string>() { "Adam", "Bob" } ; var jobs = new List<string>() { "1", "2", "3" }; int c= 0; foreach (int noOfTeams in Enumerable.Range(1, employees.Count)) { var hs = new HashSet<string>(); foreach( var grouping in Group(Enumerable.Range(1, noOfTeams).ToList(), employees)) { // Generate a unique key for each group to detect duplicates. var key = string.Join(":" , grouping.Select(sub => string.Join(",", sub))); if (!hs.Add(key)) continue; List<List<string>> teams = (from r in grouping select r.ToList()).ToList(); foreach (var group in Group(teams, jobs)) { foreach (var sub in group) { Console.WriteLine(String.Join(", " , sub.Key ) + " : " + string.Join(", ", sub)); } Console.WriteLine(); c++; } } } Console.WriteLine(String.Format("{0:n0} combinations for {1} employees and {2} jobs" , c , employees.Count, jobs.Count)); Since I'm not worried about the order of the results, this seems to give me what I need.

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  • Injecting all registered instances of a type

    - by James L
    I can successfully perform container.ResolveAll<IMyInterface>(), and I get back an Enumerable containing every registered IMyInterface. However, I can't find a way to have these injected into the constructor of my class. I have tried using ResolvedArrayParameter(), but this gives me an empty enumerator. Am I doing something wrong, or could this be a bug in Unity?

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  • Unable to connect to OpenId Provider

    - by Ramesh V
    When I run in visual studio I am able to connect to openid provider, But if I host app in IIS ,I am not able to connect to openid provider. (I am getting error at CreateRequest) Please let me know what settings has to be done in IIS so that I can connect to the Openid Provider. Below is the error I am getting [InvalidOperationException: Sequence contains no elements] System.Linq.Enumerable.First(IEnumerable`1 source) +336 DotNetOpenAuth.OpenId.RelyingParty.OpenIdRelyingParty.CreateRequest(Identifier userSuppliedIdentifier) [ProtocolException: No OpenID endpoint found.] DotNetOpenAuth.OpenId.RelyingParty.OpenIdRelyingParty.CreateRequest(Identifier userSuppliedIdentifier)

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  • Linq to SQL - Returning two values with one query

    - by Sir Psycho
    Hi, Is it possible to return a single value and an enumerable collection using LINQ to SQL? The problem is, I'm trying to do paging across a large recordset. I only want to return 10 rows at a time so I'm using .Skip(20).Take(10) approach. However I need to know the total number of records so I can show an appropriate page x of y. Trying to avoid two separate queries. Thanks

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  • Ignore collection properties in PropertyInfo

    - by LukePet
    I have a function with this code: foreach (PropertyInfo propertyInfo in typeof(T).GetProperties()){ //SOME CODE if (propertyInfo.CanWrite) propertyInfo.SetValue(myCopy, propertyInfo.GetValue(obj, null), null); } I would avoid to check "collection" properties; to do this now I have insert this control: if (propertyInfo.PropertyType.Name.Contains("List") || propertyInfo.PropertyType.Name.Contains("Enumerable") || propertyInfo.PropertyType.Name.Contains("Collection")) continue; but, It don't like me! Which is a better way to do it?

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  • About extension methods

    - by Srinivas Reddy Thatiparthy
    Shall i always need to throw ArgumentNullException(well,extension methods in Enumerable throw ArgumentNullException) when an extension method is called on null?I would like to have a clarification on this?If the answer is an Yes and No please present both the cases.

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  • How can I use linq to initialize an array of repeated elements?

    - by Eric
    At present, I'm using something like this to build a list of 10 objects: myList = (from _ in Enumerable.Range(0, 9) select new MyObject {...}).toList() This is based off my python background, where I'd write: myList = [MyObject(...) for _ in range(10)] Note that I want my list to contain 10 instances of my object, not the same instance 10 times. Is this still a sensible way to do things in C#? Is there a cost to doing it this way over a simple for loop?

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  • Javascript Iterator Class

    - by Alsciende
    Do you know a js library that implements a generic Iterator class for collections (be it Arrays or some abstract Enumerable) with a full set of features, like the Google Common or the Apache Commons?

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  • Why is there no Sum() extension for IEnumerable<uint>

    - by dss539
    It seems that Sum not defined for IEnumerable<uint> (and other unsigned integers, for that matter) var s = new int[] { 1, 2, 3 }; s.Sum(); //works fine var us = new uint[] { 1, 2, 3 }; us.Sum(); //missing method I would like to know: Have I done something fundamentally wrong/misunderstood the situation? What design decisions might cause the omission of IEnumerable<uint>.Sum()? MSDN: Enumerable.Sum

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