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• abstract method signature, inheritance, and "Do" naming convention

  - by T. Webster

  I'm learning about design patterns and in examples of code I've seen a convention where the abstract class declares a method, for example: public abstract class ServiceBase { ... public virtual object GetSomething(); and then protected abstract object DoGetSomething(); My question is on why these two methods exist, since they appear to serve the same purpose. Is this so that the base class GetSomething() method logic cannot be overridden by inherited classes? But then again, the method is marked virtual, so it can be overridden anyway. What is the usefulness here in requiring derived class implementers to implement the abstract method when the virtual method can be called anyway?

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• How does one pre-populate a Python Formish form?

  - by Jace

  How does one pre-populate a Formish form? The obvious method as per the documentation doesn't seem right. Using one of the provided examples: import formish, schemaish structure = schemaish.Structure() structure.add( 'a', schemaish.String() ) structure.add( 'b', schemaish.Integer() ) schema = schemaish.Structure() schema.add( 'myStruct', structure ) form = formish.Form(schema, 'form') If we pass this a valid request object: form.validate(request) The output is a structure like this: {'myStruct': {'a': 'value', 'b': 0 }} However, pre-populating the form using defaults requires this: form.defaults = {'myStruct.a': 'value', 'myStruct.b': 0} The dottedish package has a DottedDict object that can convert a nested dict to a dotted dict, but this asymmetry doesn't seem right. Is there a better way to do this?

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• How to invoke a delegate with a null parameter?

  - by Rodney Burton

  I get a null exception if I try to pass a null parameter to a delegate during an invoke. Here's what the code looks like: public void RequestPhoto() { WCF.Service.BeginGetUserPhoto(Contact.UserID, new AsyncCallback(RequestPhotoCB), null); } public void RequestPhotoCB(IAsyncResult result) { var photo = WCF.Service.EndGetUserPhoto(result); UpdatePhoto(photo); } public delegate void UpdatePhotoDelegate(Binary photo); public void UpdatePhoto(Binary photo) { if (InvokeRequired) { var d = new UpdatePhotoDelegate(UpdatePhoto); Invoke(d, new object[] { photo }); } else { var ms = new MemoryStream(photo.ToArray()); var bmp = new Bitmap(ms); pbPhoto.BackgroundImage = bmp; } } The problem is with the line: Invoke(d, new object[] { photo }); If the variable "photo" is null. What is the correct way to pass a null parameter during an invoke? Thanks!

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• About Network Address Translation (NAT)?

  - by Rudi

  Just curious about a particular scenario of NAT. Let's suppose we have 4 computers sharing a global IP address under the NAT. I understand that the NAT box keeps an internal record to know which computer to forward requests to. But let's say on computer #2 I'm trying to download a file. And let's say on computer #1, #3, and #4, I'm just browsing the web normally. When the browser initiates a TCP connection to get that file, how does it know which computer to give it to? I mean like, each of the four computers is using port 80 to browse the web right? How does the NAT's record distinguish which "port 80" belongs to which computer?

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• New programming jargon you coined?

  - by jdk

  What programming terms have you coined that have taken off in your own circles? (i.e. have heard others repeating it?) It might be within your own team, workplace or garnered greater popularity on the Internet. Define your programming term, word or phrase in bold followed by an explanation, citation and/or usage example so we can use it in appropriate context. This question serves in the spirit of communication among programmers through sharing of terminology with each other, to benefit us by its propagation within our own teams and environments. Please no repeats of common jargon already ingrained in the programming culture like: "kludge", "automagically", "cruft", etc. (unless you coined it). Stealing from the comments: A shared vocabulary is the basis of communication, not just among programmers, Note: This Programming question has been reworded/reorganized to phrase a real question and remove ambiguity, vagueness and rhetorical device. It is not difficult to know what is being asked & question can be reasonably answered (see answers below).

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• Postback problem downloading zip file

  - by Chris Conway

  I've got a problem on a webforms application where a user selects some criteria from dropdowns on the page and hits a button on the page which calls this method: protected void btnSearch_Click(object sender, EventArgs e) They then click on button to download a zip file based on the criteria which calls this method: protected void btnDownload_Click(object sender, EventArgs e) In IE, they are prompted with the bar at the top of the browser that tells them "To help protect your security, Internet Explorer blocked this site from downloading files to your computer". When they click on that bar to download the file, it fires the btnSearch_Click event again. Response.ContentType and Response.AddHeader has been set up correctly. The problem is, that btnSearch appends criteria so basically it is being appended twice and causing problems. Is there something I can do to prevent this? This is a vs2008 web app using c# 3.5 for what it's worth. Thanks!

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• Can anyone telme whats wrong in this part of code

  - by Mobin

  string name = ((DateTimePicker)sender).Name.ToString(); name = name.Substring(0, name.Length - 1); name = name + "4"; TimeSpan duration = new TimeSpan(); duration = ((DateTimePicker)sender).Value - ((DateTimePicker)panel2.Controls[name]).Value; name = name.Substring(0, name.Length - 1); name = name + "6"; ((MaskedTextBox)panel2.Controls[name]).Text = duration.ToString(); on execution it gives me Object reference not set to instance of an object similar functionality is used on other places but can't find out what i have to reinitialize here :$

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• Where would you document standardized complex data that is passed between many objects and methods?

  - by Eli

  Hi All, I often find myself with fairly complex data that represents something that my objects will be working on. For example, in a task-list app, several objects might work with an array of tasks, each of which has attributes, temporal expressions, sub tasks and sub sub tasks, etc. One object will collect data from web forms, standardize it into a format consumable by the class that will save them to the database, another object will pull them from the database, put them in the standard format and pass them to the display object, or the update object, etc. The data itself can become a fairly complex series of arrays and sub arrays, representing a 'task' or list of tasks. For example, the below might be one entry in a task list, in the format that is consumable by the various objects that will work on it. Normally, I just document this in a file somewhere with an example. However, I am thinking about the best way to add it to something like PHPDoc, or another standard doc system. Where would you document your consumable data formats that are for many or all of the objects / methods in your app? Array ( [Meta] => Array ( //etc. ) [Sched] => Array ( [SchedID] => 32 [OwnerID] => 2 [StatusID] => 1 [DateFirstTask] => 2011-02-28 [DateLastTask] => [MarginMonths] => 3 ) [TemporalExpressions] => Array ( [0] => Array ( [type] => dw [TemporalExpID] => 3 [ord] => 2 [day] => 6 [month] => 4 ) [1] => Array ( [type] => dm [TemporalExpID] => 32 [day] => 28 [month] => 2 ) ) [Task] => Array ( [SchedTaskID] => 32 [SchedID] => 32 [OwnerID] => 2 [UserID] => 5 [ClientID] => 9 [Title] => Close Prior Year [Body] => [DueTime] => ) [SubTasks] => Array ( [101] => Array ( [SchedSubTaskID] => 101 [ParentST] => [RootT] => 32 [UserID] => 2 [Title] => Review Profit and Loss by Class [Body] => [DueDiff] => 0 ) [102] => Array ( [SchedSubTaskID] => 102 [ParentST] => [RootT] => 32 [UserID] => 2 [Title] => Review Balance Sheet [Body] => [DueDiff] => 0 ) [103] => Array ( [SchedSubTaskID] => 103 [ParentST] => [RootT] => 32 [UserID] => 2 [Title] => Review Current Year for Prior Year Expenses to Accrue [Body] => Look at Journal Entries that are templates as well. [DueDiff] => 0 ) [104] => Array ( [SchedSubTaskID] => 104 [ParentST] => [RootT] => 32 [UserID] => 2 [Title] => Review Prior Year Membership from 11/1 - 12/31 to Accrue to Current Year [Body] => [DueDiff] => 0 ) [105] => Array ( [SchedSubTaskID] => 105 [ParentST] => [RootT] => 32 [UserID] => 2 [Title] => Enter Vacation Accrual [Body] => [DueDiff] => 0 ) [106] => Array ( [SchedSubTaskID] => 106 [ParentST] => 105 [RootT] => 32 [UserID] => 2 [Title] => Email Peter requesting Vacation Status of Employees at Year End [Body] => We need Employee Name, Rate and Days of Vacation left to use. We also need to know if the employee used any of the prior year's vacation. [DueDiff] => 43 ) [107] => Array ( [SchedSubTaskID] => 107 [ParentST] => [RootT] => 32 [UserID] => 2 [Title] => Grants Receivable at Year End [Body] => [DueDiff] => 0 ) [108] => Array ( [SchedSubTaskID] => 108 [ParentST] => 107 [RootT] => 32 [UserID] => 2 [Title] => Email Peter Requesting if there were and Grants Receivable at year end [Body] => [DueDiff] => 43 ) ) )

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• Are there any nasty side affects if i lock the HttpContext.Current.Cache.Insert method

  - by Ekk

  Apart from blocking other threads reading from the cache what other problems should I be thinking about when locking the cache insert method for a public facing website. The actual data retrieval and insert into the cache should take no more than 1 second, which we can live with. More importantly i don't want multiple thread potentially all hitting the Insert method at the same time. The sample code looks something like: public static readonly object _syncRoot = new object(); if (HttpContext.Current.Cache["key"] == null) { lock (_syncRoot) { HttpContext.Current.Cache.Insert("key", "DATA", null, DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration, CacheItemPriority.Normal, null); } } Response.Write(HttpContext.Current.Cache["key"]);

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• Differences between WPF Custom Control Library and plain Class Library?

  - by David Veeneman

  I posted a question a few months ago about sharing resource dictionaries across assemblies. It turns out you can do that using the Component Resource Key markup extension. At the time, I could only get it working with a WPF Custom Control project, not with a plain Class Library project. Now I need to use an existing plain Class Library project to host a shared resource dictionary. That means I need to retrofit the Class Library project to support the Component Resource Key markup extension. I have added a Themes folder and a Generic.xaml resource dictionary document to the Class Library project, as well as references to PresentationCore, PresentationFramework, and WindowsBase. Unfortunately, that doesn't seem to do the trick. So, here is my question: Other than the above, what does a WPF Custom Control Library project have that a plain Class Library project doesn't? Or, to put it another way, what else could I add to my class library project to get this feature working? Thanks.

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• How to pass an event to a method and then subscribe to it?

  - by Ryan Peschel

  Event Handler public void DeliverEvent(object sender, EventArgs e) { } #1: This Works public void StartListening(Button source) { source.Click += DeliverEvent; } #2: And so does this.. public void StartListening(EventHandler eventHandler) { eventHandler += DeliverEvent; } But in #2, you cannot call the method because if you try something like this: StartListening(button.Click); You get this error: The event 'System.Windows.Forms.Control.Click' can only appear on the left hand side of += or -= Is there any way around that error? I want to be able to pass the event and not the object housing the event to the StartListening method.

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• Is it illegal to statically link LGPL

  - by Pirate for Profit

  IF you also provide an identical .dll based version, BUT not the object files?

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• Form based authentication - Login get fails

  - by Sachin

  Hi All, I am using form based suthentication in my site. I have used one custom user control in my site which read items in sharepoint list and display it in a grid. Everything works fine with windows authentication but when I change the authentication to form based the login process get fails. I see the Error log it is giving me an error saying that "An SPRequest object was not disposed before the end of this thread" Then I have dispose all my spweb and spsite object that I have used in user control but still login process is not wotking. Thanks in advance

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• Composite Views and View Controllers

  - by BillyK

  Hi, I'm somewhat new to Android and am in the process of designing an application with a couple fairly complex views. One of the views is intended to involve a complex view displaying information associated with model objects and segregated into several different views; the navigation of which is meant to be achieved using sliding effects (i.e. sliding one's finger across the screen to traverse from one screen to the next, etc). The view itself will be used to host multiple sets of views for varying types of model objects, but with a general structure that is reused between them all. As a rough example, the view might come up to display information about a person (the model object), displaying several details views: a view for general information, a view displaying a list of hobbies, and a view displaying a list of other individuals associated with their social network. The same general view, when given a model object representing a particular car would give several different views: A general view with details, A view containing photo images for that vehicle, a view representing locations which it could be purchased from, and a view providing a list of related cars. (NOTE: This is not the real data involved, but is representative of the general intent for the view). The subviews will NOT cover the entire screen real-estate and other features within the view should be both visible and able to be interacted with by the user. The idea here is that there is a general view structure that is reusable and which will manage a set of subviews dynamically generated based upon the type of model object handed to the view. I'm trying to determine the appropriate way to leverage the Android framework in order to best achieve this without violating the integrity of the framework. Basically, I'm trying to determine how to componentize this larger view into reusable units (i.e. general view, model-specific sub-view controllers, and individual detail views). To be more specific, I'm trying to determine if this view is best designed as a composite of several custom View classes or a composite of several Activity classes. I've seen several examples of custom composite views, but they typically are used to compose simple views without complex controllers and without attention to the general Activity lifecycle (i.e. storing and retrieving data related to the model objects, as appropriate). On the other hand, the only real example I've seen regarding a view comprised of a composite of Activities is the TabActivity itself, and that isn't customizable in the fashion that would be necessary for this. Does anyone have any suggestions as to the appropriate way to structure my view to achieve the application framework I'm looking for? Views? Activities? Something else? Any guidance would be appreciated. Thanks in advance.

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• F# Interactive bug?

  - by John Reynolds

  I've tried the following code in VS2010: open System.Security.Cryptography let rsaTest1 = let ecKey = [|0uy..143uy|] // junk data for testing let ecKeyMod = ecKey.[8..8+128-1] let ecKeyExp = ecKey.[136..136+8-1] let rsa = RSAParameters(Modulus = ecKeyMod, Exponent = ecKeyExp) rsa let rsaTest2 = let ecKey = [|0uy..143uy|] // junk data for testing let rsa = RSAParameters(Modulus = ecKey.[8..8+128-1], Exponent = ecKey.[136..136+8-1]) rsa If I highlight all code and send it to F# Interactive (Alt+Enter), then rsaTest1 works, but rsaTest2 gives an error message, System.NullReferenceException: Object reference not set to an instance of an object. at <StartupCode$FSI_0004>.$FSI_0004.main@() in P:\proj\Tachograph\Project\CompuTachTest\CompuTachTest\rsaTest.fsx:line 16 However, if I change rsaTest2 from a value into a function and call it, let rsaTest2 () = let ecKey = [|0uy..143uy|] // junk data for testing let rsa = RSAParameters(Modulus = ecKey.[8..8+128-1], Exponent = ecKey.[136..136+8-1]) rsa let x = rsaTest2 () then there is no error. F# bug or my mistake?

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• Castle ActiveRecord: session error search and access to lazy loading property in different threads

  - by sc911

  Hi *, I've got a problem with an multi-threaded desktop application using Castle ActiveRecord in C#: To keep the GUI alive while searching for the objects based on userinput I'm using the BackgroundWorker for the search-function. Some of the properties of the objects, especially some HasMany-Relations, are marked as Lazy. Now, when the search is finished and the user selects an resulting object, some of the properties of this object should be displayed. But as the search was done by the BackgroundWorker in a different thread, accessing the properties fails as the session for the lazy-access is no longer available. What will be the best way to do the search in an extra thread to keep the GUI alive and to access all properties correctly including those marked as lazy? Thanks for any advise! Regards sc911

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• What is your favourite Windbg tip/trick?

  - by user15071

  I have come to realize that Windbg is a very powerful debugger for the Windows platform & I learn something new about it once in a while. Can fellow Windbg users share some of their mad skills? ps: I am not looking for a nifty command, those can be found in the documentation. How about sharing tips on doing something that one couldn't otherwise imagine could be done with windbg? e.g. Some way to generate statistics about memory allocations when a process is run under windbg.

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• does close() imply flush() in Python?

  - by Adam Matan

  Hi, In Python, and in general - does a close() operation on a file object imply a flush() operation? Adam

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• Iterate through a VB6 Dictionary

  - by Dinah

  I'm a non-VB6 person who had the misfortune of inheriting a buggy legacy VB6/Classic ASP project. There's a section where a lot of entries are put into a Dictionary and I want to see all it contains. I tried this (oParams is a Dictionary): Dim o As Object Dim sDicTempAggr As String sDicTempAggr = "" For Each o In oParams sDicTempAggr = sDicTempAggr & ", " & o Next Which returned: Object doesn't support this property or method : 438 Using Option Explicit, how do I iterate through a VB6 Dictionary to find out everything it contains?

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• Should I use the ref or out keyword here?

  - by Blankman

  I have an object that may be null, which I will pass to a method that will set its properties. So my code looks like: User user = null; // may or may not be null at this point. SetUserProperties(user); UpdateUser(user); public void SetUserProperties(User user) { if(user == null) user = new User(); user.Firstname = "blah"; .... } So I am updating the same object I pass into SetUserProperties. Should I use the 'ref' keyword in my method SetUserProperties?

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• Does Ruby on Rails "has_many" array provide data on a "need to know" basis?

  - by Jian Lin

  On Ruby on Rails, say, if the Actor model object is Tom Hanks, and the "has_many" fans is 20,000 Fan objects, then actor.fans gives an Array with 20,000 elements. Probably, the elements are not pre-populated with values? Otherwise, getting each Actor object from the DB can be extremely time consuming. So it is on a "need to know" basis? So does it pull data when I access actor.fans[500], and pull data when I access actor.fans[0]? If it jumps from each record to record, then it won't be able to optimize performance by doing sequential read, which can be faster on the hard disk because those records could be in the nearby sector / platter layer -- for example, if the program touches 2 random elements, then it will be faster just to read those 2 records, but what if it touches all elements in random order, then it may be faster just to read all records in a sequential way, and then process the random elements. But how will RoR know whether I am doing only a few random elements or all elements in random?

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• View bound to paged collection view not updating all of the time.

  - by Thomas

  I new to silverlight and trying to make a business application using the mvvm pattern and ria services. I have a view model class that contains a PagedCollectoinView and it is set to the item source of a datagrid. When I update the PagedCollectionView the datagrid is only updated the first time then after that subsequent changes to the data to not reflect in the view until after another edit. Things seem to be delayed one edit. Below is a summarized example of my xaml and code behind. This is the code for my view model public class CustomerContactLinks : INotifyPropertyChanged { private ObservableCollection<CustomerContactLink> _CustomerContact; public ObservableCollection<CustomerContactLink> CustomerContact { get { if (_CustomerContact == null) _CustomerContact = new ObservableCollection<CustomerContactLink>(); return _CustomerContact; } set { _CustomerContact = value; } } private PagedCollectionView _CustomerContactPaged; public PagedCollectionView CustomerContactPaged { get { if (_CustomerContactPaged == null) _CustomerContactPaged = new PagedCollectionView(CustomerContact); return _CustomerContactPaged; } } private TicketSystemDataContext _ctx; public TicketSystemDataContext ctx { get { if (_ctx == null) _ctx = new TicketSystemDataContext(); return _ctx; } } public void GetAll() { ctx.Load(ctx.GetCustomerContactInfoQuery(), LoadCustomerContactsComplete, null); } private void LoadCustomerContactsComplete(LoadOperation<CustomerContactLink> lo) { foreach (var entity in lo.Entities) { CustomerContact.Add(entity as CustomerContactLink); } } #region INotifyPropertyChanged Members public event PropertyChangedEventHandler PropertyChanged; private void RaisePropertyChanged(string propertyName) { if (PropertyChanged != null) { this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName)); } } #endregion } Here is the basics of my XAML <Data:DataGrid x:Name="GridCustomers" MinHeight="100" MaxWidth="1000" IsReadOnly="True" AutoGenerateColumns="False"> <Data:DataGrid.Columns> <Data:DataGridTextColumn Header="First Name" Binding="{Binding Customer.FirstName}" Width="105" /> <Data:DataGridTextColumn Header="MI" Binding="{Binding Customer.MiddleName}" Width="35" /> <Data:DataGridTextColumn Header="Last Name" Binding="{Binding Customer.LastName}" Width="105"/> <Data:DataGridTextColumn Header="Address1" Binding="{Binding Contact.Address1}" Width="130"/> <Data:DataGridTextColumn Header="Address2" Binding="{Binding Contact.Address2}" Width="130"/> <Data:DataGridTextColumn Header="City" Binding="{Binding Contact.City}" Width="110"/> <Data:DataGridTextColumn Header="State" Binding="{Binding Contact.State}" Width="50"/> <Data:DataGridTextColumn Header="Zip" Binding="{Binding Contact.Zip}" Width="45"/> <Data:DataGridTextColumn Header="Home" Binding="{Binding Contact.PhoneHome}" Width="85"/> <Data:DataGridTextColumn Header="Cell" Binding="{Binding Contact.PhoneCell}" Width="85"/> <Data:DataGridTextColumn Header="Email" Binding="{Binding Contact.Email}" Width="118"/> </Data:DataGrid.Columns> </Data:DataGrid> <DataForm:DataForm x:Name="CustomerDetails" Header="Customer Details" AutoGenerateFields="False" AutoEdit="False" AutoCommit="False" CommandButtonsVisibility="Edit" Width="1000" Margin="0,5,0,0"> <DataForm:DataForm.EditTemplate> </DataForm:DataForm.EditTemplate> </DataForm:DataForm> And here is my code behind public Customers() { InitializeComponent(); BusyDialogIndicator.IsBusy = true; Loaded += new RoutedEventHandler(Customers_Loaded); CustomerDetails.BeginningEdit += new EventHandler(CustomerDetails_BeginningEdit); } void CustomerDetails_BeginningEdit(object sender, System.ComponentModel.CancelEventArgs e) { CustomerContacts.CustomerContactPaged.EditItem(CustomerDetails.CurrentItem); } private void Customers_Loaded(object sender, RoutedEventArgs e) { CustomerContacts = new CustomerContactLinks(); CustomerContacts.GetAll(); GridCustomers.ItemsSource = CustomerContacts.CustomerContactPaged; GridCustomerPager.Source = CustomerContacts.CustomerContactPaged; GridCustomers.SelectionChanged += new SelectionChangedEventHandler(GridCustomers_SelectionChanged); BusyDialogIndicator.IsBusy = false; } void GridCustomers_SelectionChanged(object sender, SelectionChangedEventArgs e) { CustomerDetails.CurrentItem = GridCustomers.SelectedItem as CustomerContactLink; } private void SaveChanges_Click(object sender, RoutedEventArgs e) { if (WebContext.Current.User.IsAuthenticated) { bool commited = CustomerDetails.CommitEdit(); if (commited && (!CustomerDetails.IsItemChanged && CustomerDetails.IsItemValid)) { CustomerContacts.Update(CustomerDetails.CurrentItem as CustomerContactLink); CustomerContacts.ctx.SubmitChanges(); CustomerContacts.CustomerContactPaged.CommitEdit(); CustomerContacts.CustomerContactPaged.Refresh(); (GridCustomers.ItemsSource as PagedCollectionView).Refresh(); } } }

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• many-to-many performance concerns with fluent nhibernate.

  - by Ciel

  I have a situation where I have several many-to-many associations. In the upwards of 12 to 15. Reading around I've seen that it's generally believed that many-to-many associations are not 'typical', yet they are the only way I have been able to create the associations appropriate for my case, so I'm not sure how to optimize any further. Here is my basic scenario. class Page { IList<Tag> Tags { get; set; } IList<Modification> Modifications { get; set; } IList<Aspect> Aspects { get; set; } } This is one of my 'core' classes, and coincidentally one of my core tables. Virtually half of the objects in my code can have an IList<Page>, and some of them have IList<T> where T has its own IList<Page>. As you can see, from an object oriented standpoint, this is not really a problem. But from a database standpoint this begins to introduce a lot of junction tables. So far it has worked fine for me, but I am wondering if anyone has any ideas on how I could improve on this structure. I've spent a long time thinking and in order to achieve the appropriate level of association required, I cannot think of any way to improve it. The only thing I have come up with is to make intermediate classes for each object that has an IList<Page>, but that doesn't really do anything that the HasManyToMany does not already do except introduce another class. It does not extend the functionality and, from what I can tell, it does not improve performance. Any thoughts? I am also concerned about Primary Key limits in this scenario. Most everything needs to be able to have these properties, but the Pages cannot be unique to each object, because they are going to be frequently shared and joined between multiple objects. All relationships are one-sided. (That is, a Page has no knowledge of what owns it). Because of this, I also have no Inverse() mapped HasManyToMany collections. Also, I have read the similar question : Usage of ORMs like NHibernate when there are many associations - performance concerns But it really did not answer my concerns.

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• Shutting down a WPF application from App.xaml.cs

  - by Johannes Rössel

  I am currently writing a WPF application which does command-line argument handling in App.xaml.cs (which is necessary because the Startup event seems to be the recommended way of getting at those arguments). Based on the arguments I want to exit the program at that point already which, as far as I know, should be done in WPF with Application.Current.Shutdown() or in this case (as I am in the current application object) probably also just this.Shutdown(). The only problem is that this doesn't seem to work right. I've stepped through with the debugger and code after the Shutdown() line still gets executed which leads to errors afterwards in the method, since I expected the application not to live that long. Also the main window (declared in the StartupUri attribute in XAML) still gets loaded. I've checked the documentation of that method and found nothing in the remarks that tell me that I shouldn't use it during Application.Startup or Application at all. So, what is the right way to exit the program at that point, i. e. the Startup event handler in an Application object?

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• Mysterious constraints problem with SQL Server 2000

  - by Ramon

  Hi all I'm getting the following error from a VB NET web application written in VS 2003, on framework 1.1. The web app is running on Windows Server 2000, IIS 5, and is reading from a SQL server 2000 database running on the same machine. System.Data.ConstraintException: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints. at System.Data.DataSet.FailedEnableConstraints() at System.Data.DataSet.EnableConstraints() at System.Data.DataSet.set_EnforceConstraints(Boolean value) at System.Data.DataTable.EndLoadData() at System.Data.Common.DbDataAdapter.FillFromReader(Object data, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords, DataColumn parentChapterColumn, Object parentChapterValue) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, String srcTable, IDataReader dataReader, Int32 startRecord, Int32 maxRecords) at System.Data.Common.DbDataAdapter.FillFromCommand(Object data, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior) at System.Data.Common.DbDataAdapter.Fill(DataSet dataSet) The problem appears when the web app is under a high load. The system runs fine when volume is low, but when the number of requests becomes high, the system starts rejecting incoming requests with the above exception message. Once the problem appears, very few requests actually make it through and get processed normally, about 2 in every 30. The vast majority of requests fail, until a SQL Server restart or IIS reset is performed. The system then start processing requests normally, and after some time it starts throwing the same error. The error occurs when a data adapter runs the Fill() method against a SELECT statement, to populate a strongly-typed dataset. It appears that the dataset does not like the data it is given and throws this exception. This error occurs on various SELECT statements, acting on different tables. I have regenerated the dataset and checked the relevant constraints, as well as the table from which the data is read. Both the dataset definition and the data in the table are fine. Admittedly, the hardware running both the web app and SQL Server 2000 is seriously outdated, considering the numbers of incoming requests it currently receives. The amount of RAM consumed by SQL Server is dynamically allocated, and at peak times SQL Server can consume up to 2.8 GB out of a total of 3.5 GB on the server. At first I suspected some sort of index or database corruption, but after running DBCC CHECKDB, no errors were found in the database. So now I'm wondering whether this error is a result of the hardware limitations of the system. Is it possible for SQL Server to somehow mess up the data it's supposed to pass to the dataset, resulting in constraint violation due to, say, data type/length mismatch? I tried accessing the RowError messages of the data rows in the retrieved dataset tables but I kept getting empty strings. I know that HasErrors = true for the datatables in question. I have not set the EnableConstraints = false, and I don't want to do that. Thanks in advance. Ray

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