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• Obtaining FontMetrics before getting a Graphics instance

  - by Tom Castle

  Typically, I'd obtain a graphics instance something like this: BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB); Graphics2D g = img.createGraphics(); However, in the current project I'm working on, the width and height variables above are dependent upon the size of a number of text fragments that will later be drawn onto the graphics instance. But, to obtain the dimensions of the font being used I would usually use the FontMetrics that I get from the graphics object. FontMetrics metrics = g.getFontMetrics(); So, I have a nasty little dependency cycle. I cannot create the graphics object until I know the size of the text, and I cannot know the size of the text until I have a graphics object. One solution is just to create another BufferedImage/Graphics pair first in order to get the FontMetrics instance I need, but this seems unnecessary. So, is there a nicer way? Or is it the case that the width, height etc. properties for a Font are somehow dependent upon what (graphics, component...) the text is to be drawn on?

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• JPA entitylisteners and @embeddable

  - by seanizer

  I have a class hierarchy of JPA entities that all inherit from a BaseEntity class: @MappedSuperclass @EntityListeners( { ValidatorListener.class }) public abstract class BaseEntity implements Serializable { // other stuff } I want all entities that implement a given interface to be validated automatically on persist and/or update. Here's what I've got. My ValidatorListener: public class ValidatorListener { private enum Type { PERSIST, UPDATE } @PrePersist public void checkPersist(final Object entity) { if (entity instanceof Validateable) { this.check((Validateable) entity, Type.PERSIST); } } @PreUpdate public void checkUpdate(final Object entity) { if (entity instanceof Validateable) { this.check((Validateable) entity, Type.UPDATE); } } private void check(final Validateable entity, final Type persist) { switch (persist) { case PERSIST: if (entity instanceof Persist) { ((Persist) entity).persist(); } if (entity instanceof PersistOrUpdate) { ((PersistOrUpdate) entity).persistOrUpdate(); } break; case UPDATE: if (entity instanceof Update) { ((Update) entity).update(); } if (entity instanceof PersistOrUpdate) { ((PersistOrUpdate) entity).persistOrUpdate(); } break; default: break; } } } and here's my Validateable interface that it checks against (the outer interface is just a marker, the inner contain the methods): public interface Validateable { interface Persist extends Validateable { void persist(); } interface PersistOrUpdate extends Validateable { void persistOrUpdate(); } interface Update extends Validateable { void update(); } } All of this works, however I would like to extend this behavior to Embeddable classes. I know two solutions: call the validation method of the embeddable object manually from the entity validation method: public void persistOrUpdate(){ // validate my own properties first // then manually validate the embeddable property: myEmbeddable.persistOrUpdate(); // this works but I'd like something that I don't have to call manually } use reflection, checking all properties to see if their type is of one of their interface types. This would work, but it's not pretty. Is there a more elegant solution?

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• Link Button on asp.net user control not firing

  - by andyriome

  Hi I have a user control, which is added to another user control. The nested user control is built up of a gridview, an image button and a link button. The nested user control is added to the outer control as a collection object based upon the results bound to the gridview. The problem that I have is that my link button doesn't work. I click on it and the event doesn't fire. Even adding a break point was not reached. As the nested user control is added a number of times, I have set image button to have unique ids and also the link button. Whilst image button works correctly with its java script. The link button needs to fire an event in the code behind, but despite all my efforts, I can't make it work. I am adding the link button to the control dynamically. Below is the relevant code that I am using: public partial class ucCustomerDetails : System.Web.UI.UserControl { protected override void CreateChildControls( ) { base.CreateChildControls( ); string strUniqueID = lnkShowAllCust.UniqueID; strUniqueID = strUniqueID.Replace('$','_'); this.lnkShowAllCust.ID = strUniqueID; this.lnkShowAllCust.Click += new EventHandler(this.lnkShowAllCust_Click); this.Controls.Add(lnkShowAllCust); } protected override void OnInit (EventArgs e) { CreateChildControls( ); base.OnInit(e); } protected override void OnLoad(EventArgs e) { base.EnsureChildControls( ); } protected void Page_Load(object sender, EventArgs e) { if (IsPostBack) { CreateChildControls( ); } } protected void lnkShowAllCust_Click(object sender, EventArgs e) { this.OnCustShowAllClicked(new EventArgs ( )); } protected virtual void OnCustShowAllClicked(EventArgs args) { if (this.ViewAllClicked != null) { this.ViewAllClicked(this, args); } } public event EventHandler ViewAllClicked; } I have been stuggling with this problem for the last 3 days and have had no success with it, and I really do need some help. Can anyone please help me?

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• Capturing wildcards in java generics

  - by Rollerball

  From this orcale java tutorial: The WildcardError example produces a capture error when compiled: import java.util.List; public class WildcardError { void foo(List<?> i) { i.set(0, i.get(0)); } } After this error demonstration, they fix the problem by using a helper method: public class WildcardFixed { void foo(List<?> i) { fooHelper(i); } // Helper method created so that the wildcard can be captured // through type inference. private <T> void fooHelper(List<T> l) { l.set(0, l.get(0)); } } First, they say that the list input parameter (i) is seen as an Object: In this example, the compiler processes the i input parameter as being of type Object. Why then i.get(0) does not return an Object? if it was already passed in as such? Furthermore what is the point of using a <?> when then you have to use an helper method using <T>. Would not be better using directly which can be inferred?

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• Unit Testing an Event Firing From a Thread

  - by Dougc

  I'm having a problem unit testing a class which fires events when a thread starts and finishes. A cut down version of the offending source is as follows: public class ThreadRunner { private bool keepRunning; public event EventHandler Started; public event EventHandler Finished; public void StartThreadTest() { this.keepRunning = true; var thread = new Thread(new ThreadStart(this.LongRunningMethod)); thread.Start(); } public void FinishThreadTest() { this.keepRunning = false; } protected void OnStarted() { if (this.Started != null) this.Started(this, new EventArgs()); } protected void OnFinished() { if (this.Finished != null) this.Finished(this, new EventArgs()); } private void LongRunningMethod() { this.OnStarted(); while (this.keepRunning) Thread.Sleep(100); this.OnFinished(); } } I then have a test to check that the Finished event fires after the LongRunningMethod has finished as follows: [TestClass] public class ThreadRunnerTests { [TestMethod] public void CheckFinishedEventFiresTest() { var threadTest = new ThreadRunner(); bool finished = false; object locker = new object(); threadTest.Finished += delegate(object sender, EventArgs e) { lock (locker) { finished = true; Monitor.Pulse(locker); } }; threadTest.StartThreadTest(); threadTest.FinishThreadTest(); lock (locker) { Monitor.Wait(locker, 1000); Assert.IsTrue(finished); } } } So the idea here being that the test will block for a maximum of one second - or until the Finish event is fired - before checking whether the finished flag is set. Clearly I've done something wrong as sometimes the test will pass, sometimes it won't. Debugging seems very difficult as well as the breakpoints I'd expect to be hit (the OnFinished method, for example) don't always seem to be. I'm assuming this is just my misunderstanding of the way threading works, so hopefully someone can enlighten me.

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• Should we point to an NSManagedObject entity with weak instead of strong pointer?

  - by Jim Thio

  I think because NSManagedObject is managed by the managedObject context the pointer should be weak. Yet it often goes back to 0 in my cases. for (CategoryNearby * CN in sorted) { //[arrayOfItems addObject:[NSString stringWithFormat:@"%@ - %d",CN.name,[CN.order intValue]]]; NearbyShortcutTVC * tvc=[[NearbyShortcutTVC alloc]init]; tvc.categoryNearby =CN; // tvc.titleString=[NSString stringWithFormat:@"%@",CN.name]; // tvc.displayed=CN.displayed; [arrayOfItemsLocal addObject:tvc]; //CN PO(tvc); PO(tvc.categoryNearby); while (false); } self.arrayOfItems = arrayOfItemsLocal; PO(self.categoriesNearbyInArrayOfItems); [self.tableViewa reloadData]; ... Yet somewhere down the line: tvc.categoryNearby becomes nil. I do not know how or when or where it become nil. How do I debug this? Or should the reference be strong instead? This is the interface of NearbyShortcutTVC by the way @interface NearbyShortcutTVC : BGBaseTableViewCell{ } @property (weak, nonatomic) CategoryNearby * categoryNearby; @end To make sure that we're talking about the same object I print all the memory addresses of the NSArray They're both the exact same object. But somehow the categoryNearby property of the object is magically set to null somewhere. self.categoriesNearbyInArrayOfItems: ( 0x883bfe0, 0x8b6d420, 0x8b6f9f0, 0x8b71de0, 0xb073f90, 0xb061a10, 0xb06a880, 0x8b74940, 0x8b77110, 0x8b794e0, 0x8b7bf40, 0x8b7cef0, 0x8b7f4b0, 0x8b81a30, 0x88622d0, 0x8864e60, 0xb05c9a0 ) self.categoriesNearbyInArrayOfItems: ( 0x883bfe0, 0x8b6d420, 0x8b6f9f0, 0x8b71de0, 0xb073f90, 0xb061a10, 0xb06a880, 0x8b74940, 0x8b77110, 0x8b794e0, 0x8b7bf40, 0x8b7cef0, 0x8b7f4b0, 0x8b81a30, 0x88622d0, 0x8864e60, 0xb05c9a0 )

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• how to bind a list to a dropdown list in gridview

  - by user3721173

  I have a GridView that it contain a Drop-down list.I have a list that wanna to bind this list to drop-down in gridview. <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"OnSelectedIndexChanged="GridView1_SelectedIndexChanged" OnRowDataBound="GridView1_RowDataBound"> <Columns> <ItemTemplate> <asp:Label ID="Label2" runat="server"></asp:Label> <asp:DropDownList ID="DropDownList3" runat="server" AppendDataBoundItems="True" OnSelectedIndexChanged="DropDownList3_SelectedIndexChanged1" > </asp:DropDownList> </ItemTemplate> </asp:TemplateField> </Columns> and protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e) { DropDownList dropdown = (DropDownList)e.Row.FindControl("DropDownList3"); ClassDal obj = new ClassDal(); List<phone> list = obj.GetAll(); dropdown.DataTextField = "phone"; dropdown.DataValueField = "id"; dropdown.DataSource = list.ToList(); dropdown.DataBind(); } and namespace sample_table { public class ClassDal { public List<phone> GetAll() { using (PracticeDBEntities1 context = new PracticeDBEntities1()) { return context.phone.ToList(); } } } } but i received this exception :Object reference not set to an instance of an object on the row: dropdown.DataTextField = "phone";

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• Can somebody explain this remark in the MSDN CreateMutex() documentation about the bInitialOwner fla

  - by Tom Williams

  The MSDN CreatMutex() documentation (http://msdn.microsoft.com/en-us/library/ms682411%28VS.85%29.aspx) contains the following remark near the end: Two or more processes can call CreateMutex to create the same named mutex. The first process actually creates the mutex, and subsequent processes with sufficient access rights simply open a handle to the existing mutex. This enables multiple processes to get handles of the same mutex, while relieving the user of the responsibility of ensuring that the creating process is started first. When using this technique, you should set the bInitialOwner flag to FALSE; otherwise, it can be difficult to be certain which process has initial ownership. Can somebody explain the problem with using bInitialOwner = TRUE? Earlier in the same documentation it suggests a call to GetLastError() will allow you to determine whether a call to CreateMutext() created the mutex or just returned a new handle to an existing mutex: Return Value If the function succeeds, the return value is a handle to the newly created mutex object. If the function fails, the return value is NULL. To get extended error information, call GetLastError. If the mutex is a named mutex and the object existed before this function call, the return value is a handle to the existing object, GetLastError returns ERROR_ALREADY_EXISTS, bInitialOwner is ignored, and the calling thread is not granted ownership. However, if the caller has limited access rights, the function will fail with ERROR_ACCESS_DENIED and the caller should use the OpenMutex function.

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• What are the benefits and risks of moving to a Model Driven Architecture approach?

  - by Tone

  I work for a company with about 350 employees and we are in the process of growing. Our current codebase is not structured very well and we are looking both at how to improve it immediately (by organizing objects into namespaces, separating concerns, etc.) and moving to a model driven architecture approach, where we model and design everything first with uml, then generate code from that model. We have been looking heavily at Sparx Systems Enterprise Architect (EA) (which is UML 2.0 capable) and we are also considering the tools in VS 2010. I know there are other tools out there (Rational XDE being one) but I really do not think we can spend $1500+ per license at this point. I'm not looking for answers on which tool is better than another but more for experiences moving from a cowboy coding environment (that is, little planning and design, just jump in and start coding) to a model driven architecture. Looking back was it helpful to your organization? What are the pain points? What are the risks? What are the benefits?

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• Mysterious HttpSession and session-config dependency

  - by OneMoreVladimir

  Good day. I'm developing a Java web app with Servlets\JSP using Tomcat 7.0. During request from client I put and object into the session and use forward. After the forward processing the same request the object can be retreived if the secure parameter is false otherwise it is not stored in session. <session-config> <session-timeout>15</session-timeout> <cookie-config> <http-only>true</http-only> <secure>true</secure> </cookie-config> <tracking-mode>COOKIE</tracking-mode> </session-config> I've figured out that "...cookies can be created with the 'secure' flag, which ensures that the browser will never transmit the specified cookie over non-SSL...". I've configured Tomcat to use SSL, but that haven't helped. Changing the tracking mode to SSL haven't helped as well. How do session-config and HttpSession object correlate in this case? What could be the problem?

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• Issue with dynamically loading a user control on button click

  - by Kumar

  I have a page in which I am loading a user control dynamically as follows: Default.aspx: <cc1:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"> </cc1:ToolkitScriptManager> <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder> Default.aspx.cs: protected void Page_Load(object sender, EventArgs e) { var ctrl = LoadControl("~/UserCtrl1.ascx"); ctrl.ID = "ucUserCtrl1"; PlaceHolder1.Controls.Add(ctrl); } Below is the code for UserCtrl1.ascx <asp:Label ID="Label1" runat="server"></asp:Label> <asp:Button ID="Button1" runat="server" Text="Button1" OnClick="Button1_Click" /> <br /> <asp:PlaceHolder ID="PlaceHolder2" runat="server"></asp:PlaceHolder> I am dynamically loading another user control when the Button1 is clicked UserCtrl1.ascx.cs protected void Button1_Click(object sender, EventArgs e) { Label1.Text = "UserControl - 1 button clicked!"; var ctrl = LoadControl("~/UserCtrl2.ascx"); ctrl.ID = "ucUserCtrl2"; PlaceHolder2.Controls.Add(ctrl); } Below is the markup for UserCtrl2.ascx <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional"> <ContentTemplate> <asp:Label ID="Label2" runat="server"></asp:Label> <asp:Button ID="Button2" runat="server" Text="Button2" OnClick="Button2_Click" /> </ContentTemplate> </asp:UpdatePanel> UserCtrl2.ascx.cs protected void Button2_Click(object sender, EventArgs e) { Label2.Text = "UserControl - 2 button clicked!"; } After the page loads when I click the Button1 in UserCtrl1 the click event fires and I am able to see the Label1 text. It also properly loads the UserCtrl2, but when I click the Button2 in UserCtrl2 the click event dosent fire and even worse when I click the Button2 twice the UserCtrl2 control dissappears from the page. How can I fix this?

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• Nhibernate + Gridview + TargetInvocationException

  - by Scott

  For our grid views, we're setting the data sources as a list of results from an Nhibernate query. We're using lazy loading, so the objects are actually proxied... most of the time. In some instances the list will consist of types of Student and Composition_Aop_Proxy_jklasjdkl31231, which implements the same members as the Student class. We've still got the session open, so the lazy loading would resolve fine, if GridView didn't throw an error about the different types in the gridview. Our current workaround is to clone the object, which results in fetching all of the data that can be lazily loaded, even though most of it won't be accessed.. ever. This, however, converts the proxy into an actual object and the grid view is happy. The performance implications kind of scare me as we're getting closer to rolling the code out as is. I've tried evicting the object after a save, which should ensure that everything is a proxy, but this doesn't seem like a good idea either. Does anyone have any suggestions/workarounds?

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• Java, Massive message processing with queue manager (trading)

  - by Ronny

  Hello, I would like to design a simple application (without j2ee and jms) that can process massive amount of messages (like in trading systems) I have created a service that can receive messages and place them in a queue to so that the system won't stuck when overloaded. Then I created a service (QueueService) that wraps the queue and has a pop method that pops out a message from the queue and if there is no messages returns null, this method is marked as "synchronized" for the next step. I have created a class that knows how process the message (MessageHandler) and another class that can "listen" for messages in a new thread (MessageListener). The thread has a "while(true)" and all the time tries to pop a message. If a message was returned, the thread calls the MessageHandler class and when it's done, he will ask for another message. Now, I have configured the application to open 10 MessageListener to allow multi message processing. I have now 10 threads that all time are in a loop. Is that a good design?? Can anyone reference me to some books or sites how to handle such scenario?? Thanks, Ronny

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• Dynamcally resising an open Accordion

  - by alavers

  I have an Accordion and the height of its content can be dynamically resized. I would like to see the Accordion dynamically respond to the child item's height, but I'm having trouble doing this. <lt:Accordion Name="MyAccordion" SelectionMode="ZeroOrOne" HorizontalAlignment="Stretch"> <lt:AccordionItem Name="MyAccordionItem" Header="MyAccordion" IsSelected="True" HorizontalContentAlignment="Stretch" VerticalAlignment="Stretch"> <StackPanel> <Button Content="Grow" Click="Grow"/> <Button Content="Shrink" Click="Shrink"/> <TextBox Name="GrowTextBox" Text="GrowTextBox" Height="400" Background="Green" SizeChanged="GrowTextBox_SizeChanged"/> </StackPanel> </lt:AccordionItem> </lt:Accordion> private void Grow(object sender, System.Windows.RoutedEventArgs e) { GrowTextBox.Height += 100; } private void Shrink(object sender, System.Windows.RoutedEventArgs e) { GrowTextBox.Height -= 100; } private void GrowTextBox_SizeChanged(object sender, System.Windows.SizeChangedEventArgs e) { MyAccordion.UpdateLayout(); MyAccordionItem.UpdateLayout(); } Mind you, if I collapse and then re-open the accordion, it takes shape just the way I want, but I'd like this resizing to occur immediately when the child resizes. I feebly attempted to fix this by adding a SizeChanged event handler that calls UpdateLayout() on the Accordion and AccordionItem, but this doesn't have any visual effect. I can't figure out where proper resizing takes place inside the Accordion control. Does anyone have an idea?

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• Is this reference or code in mistake or bug?

  - by mikezang

  I copied some text from NSDate Reference as below, please check Return Value, it is said the format will be in YYYY-MM-DD HH:MM:SS ±HHMM, but I got as below in my app, so the reference is mistake? or code in mistake? Saturday, January 1, 2011 12:00:00 AM Japan Standard Time or 2011?1?1????0?00?00? ????? descriptionWithLocale: Returns a string representation of the receiver using the given locale. - (NSString *)descriptionWithLocale:(id)locale Parameters locale An NSLocale object. If you pass nil, NSDate formats the date in the same way as the description method. On Mac OS X v10.4 and earlier, this parameter was an NSDictionary object. If you pass in an NSDictionary object on Mac OS X v10.5, NSDate uses the default user locale—the same as if you passed in [NSLocale currentLocale]. Return Value A string representation of the receiver, using the given locale, or if the locale argument is nil, in the international format YYYY-MM-DD HH:MM:SS ±HHMM, where ±HHMM represents the time zone offset in hours and minutes from GMT (for example, “2001-03-24 10:45:32 +0600”)

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• Preventing ActiveRecord save() on an instance

  - by Craig Walker

  I have an ActiveRecord model object Foo; it represents a standard database row. I want to be able to display modified versions of instances of this object. I'd like to reuse the class itself, as it already has all the hooks & aspects I'll need. (For example: I already have a view that displays the appropriate attributes). Basically I want to clone the model instance, modify some of its properties, and feed it back to the caller (view, test, etc). I do not want these attribute modifications getting back into the database. However, I do want to include the id attribute in the cloned version, as it makes dealing with the route-helpers much easier. Thus, I plan on calling ActiveRecord::Base.clone(), manually setting the ID of the cloned instance, and then making the appropriate attribute changes to the new instance. This has me worried though; one save() on the modified instance and my original data will get clobbered. So, I'm looking to lock down the new instance so that it won't hurt anything else. I'm already planning on calling freeze() (on the understanding that this prevents further modification to the object, though the documentation isn't terribly clear). However, I don't see any obvious way to prevent a save(). What would be the best approach to achieving this?

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• Unit Testing the Use of TransactionScope

  - by Randolpho

  The preamble: I have designed a strongly interfaced and fully mockable data layer class that expects the business layer to create a TransactionScope when multiple calls should be included in a single transaction. The problem: I would like to unit test that my business layer makes use of a TransactionScope object when I expect it to. Unfortunately, the standard pattern for using TransactionScope is a follows: using(var scope = new TransactionScope()) { // transactional methods datalayer.InsertFoo(); datalayer.InsertBar(); scope.Complete(); } While this is a really great pattern in terms of usability for the programmer, testing that it's done seems... unpossible to me. I cannot detect that a transient object has been instantiated, let alone mock it to determine that a method was called on it. Yet my goal for coverage implies that I must. The Question: How can I go about building unit tests that ensure TransactionScope is used appropriately according to the standard pattern? Final Thoughts: I've considered a solution that would certainly provide the coverage I need, but have rejected it as overly complex and not conforming to the standard TransactionScope pattern. It involves adding a CreateTransactionScope method on my data layer object that returns an instance of TransactionScope. But because TransactionScope contains constructor logic and non-virtual methods and is therefore difficult if not impossible to mock, CreateTransactionScope would return an instance of DataLayerTransactionScope which would be a mockable facade into TransactionScope. While this might do the job it's complex and I would prefer to use the standard pattern. Is there a better way?

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• JQuery modal box form validation

  - by vikitor

  Hi, I was using a view to create an object for my specific project, but now I have to adapt this to another requirements, such as the creation of this object must be integrated in the creation of another one. The thing is, that this object must be created before starting to create the other one, and the way of doing it will be poping up a modal dialog box with JQuery with the form to create it. I've got to adapt the creation and it works fine, except for the validation messages. It is made in the controller like : if (not.NotName.Trim().Length == 0) { ModelState.AddModelError("NotName", "Name is required"); } if (_notification.checkIfExists(not.NotName, not.NotRecID)) { ModelState.AddModelError("NotName", "Notification already exists"); } And before with a normal view it worked fine, but now I'm not able to get the validation messages as I did. How can you get this validation messages thrown by the controller in the Modal Box? Because now when I made a mistake on purpose in the form in order to get the error it doesn't appear. I've seen the error is displayed in the site, because I've seen it on firebug, but it doesn't appear in my model box. How can I retrieve this errors? Do you know any tutorial that could help me with this? Thank you

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• In perl, how can I call a method whose name I have in a string?

  - by Ryan Thompson

  I'm trying to write some abstract code for searching through a list of similar objects for the first one whose attributes match specific values. In order to do this, I need to call a bunch of accessor methods and check all their values one by one. I'd like to use an abstraction like this: sub verify_attribute { my ($object, $attribute_method, $wanted_value) = @_; if ( call_method($object, $attribute_method) ~~ $wanted_value ) { return 1; } else { return; } } Then I can loop through a hash whose keys are accessor method names and whose values are the values I'm looking for for those attributes. For example, if that hash is called %wanted, I might use code like this to find the object I want: my $found_object; FINDOBJ: foreach my $obj (@list_of_objects) { foreach my $accessor (keys %wanted) { next FINDOBJ unless verify_attribute($obj, $accessor, $wanted{$accessor}); } # All attrs verified $found_object = $obj; last FINDOBJ; } Of course, the only problem is that call_method does not exsit. Or does it? How can I call a method if I have a string containing its name? Or is there a better solution to this whole problem?

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• WCF data services - Limiting related objects returned based on critera

  - by Mike Morley

  I have an object graph consisting of a base employee object, and a set of related message objects. I am able to return the employee objects based on search criteria on the employee properties (eg team) etc. However, if I expand on the messages, I get the full collection of messages back. I would like to be able to either take the top n messages (i.e. restrict to 10 most recent) or ideally use a date range on the message objects to limit how many are brought back. So far I have not been able to figure out a way of doing this: I get an error if I attempt to filter on properties on the message (&$filter=employee/message/StartDate gives an error "No property 'StartDate' exists in type 'System.Data.Objects.DataClasses.EntityCollection`1). Attempting to use Top on the message related object doesn't work either. I have also tried using a WebGet extension that takes a string list of employee IDs. That works until the list gets too long, and then fails due to the URL getting too long (it might be possible to setup a paging mechanism on this approach)... Unfortunately the UI control I am using requires the data to be in a fairly specific hierarchical shape, so I can't easily come at this from starting on the message side and working backwards. Outside of making multiple calls does anyone know of a method to accomplish this with wcf data services? Thanks! M.

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• Can Haskell's monads be thought of as using and returning a hidden state parameter?

  - by AJM

  I don't understand the exact algebra and theory behind Haskell's monads. However, when I think about functional programming in general I get the impression that state would be modelled by taking an initial state and generating a copy of it to represent the next state. This is like when one list is appended to another; neither list gets modified, but a third list is created and returned. Is it therefore valid to think of monadic operations as implicitly taking an initial state object as a parameter and implicitly returning a final state object? These state objects would be hidden so that the programmer doesn't have to worry about them and to control how they gets accessed. So, the programmer would not try to copy the object representing the IO stream as it was ten minutes ago. In other words, if we have this code: main = do putStrLn "Enter your name:" name <- getLine putStrLn ( "Hello " ++ name ) ...is it OK to think of the IO monad and the "do" syntax as representing this style of code? putStrLn :: IOState -> String -> IOState getLine :: IOState -> (IOState, String) main :: IOState -> IOState -- main returns an IOState we can call "state3" main state0 = putStrLn state2 ("Hello " ++ name) where (state2, name) = getLine state1 state1 = putStrLn state0 "Enter your name:"

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• friend declaration in C++

  - by Happy Mittal

  In Thinking in C++ by Bruce eckel, there is an example given regarding friend functions as // Declaration (incomplete type specification): struct X; struct Y { void f(X*); }; struct X { // Definition private: int i; public: friend void Y::f(X*); // Struct member friend }; void Y::f(X* x) { x->i = 47; } Now he explained this: Notice that Y::f(X*) takes the address of an X object. This is critical because the compiler always knows how to pass an address, which is of a fixed size regardless of the object being passed, even if it doesn’t have full information about the size of the type. If you try to pass the whole object, however, the compiler must see the entire structure definition of X, to know the size and how to pass it, before it allows you to declare a function such as Y::g(X). But when I tried void f(X); as declaration in struct Y, it shows no error. Please explain why?

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• How can manage a FIFO-queue in an database with SQL?

  - by Jonas

  I have two tables in my database, one for In and one for Out. They have two columns, Quantity and Price. How can I write a SQL-query that selects the correct price? In example: If I have 3 items in for 75 and then 3 items in for 80. Then I have two out for 75, and the third out should be for 75 (X) and the fourth out should be for 80 (Y). How can I write the price query for X and Y? They should use the price from the third and forth row. In example, is there any way to SELECT the third row in the In-table? I can not use auto_increment as identifier for i.e. "third" row, because the tables will contain post for other items too. The rows will not be deleted, they will be saved for accountability reasons. SELECT Price FROM In WHERE ...? NEW database design: +----+ | In | +----+------+-------+ | Supply_ID | Price | +-----------+-------+ | 1 | 75 | | 1 | 75 | | 1 | 75 | | 2 | 80 | | 2 | 80 | +-----------+-------+ +-----+ | Out | +-----+-------+-------+ | Delivery_ID | Price | +-------------+-------+ | 1 | 75 | | 1 | 75 | | 2 | X | <- ? | 3 | Y | <- ? +-------------+-------+ OLD database design: +----+ | In | +----+------+----------+-------+ | Supply_ID | Quantity | Price | +-----------+----------+-------+ | 1 | 3 | 75 | | 2 | 3 | 80 | +-----------+----------+-------+ +-----+ | Out | +-----+-------+----------+-------+ | Delivery_ID | Quantity | Price | +-------------+----------+-------+ | 1 | 2 | 75 | | 2 | 1 | X | <- ? | 3 | 1 | Y | <- ? +-------------+----------+-------+

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• Strange behaviour of DataTable with DataGridView

  - by Paul

  Please explain me what is happening. I have created a WinForms .NET application which has DataGridView on a form and should update database when DataGridView inline editing is used. Form has SqlDataAdapter _da with four SqlCommands bound to it. DataGridView is bound directly to DataTable _names. Such a CellValueChanged handler: private void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e) { _da.Update(_names); } does not update database state although _names DataTable is updated. All the rows of _names have RowState == DataRowState.Unchanged Ok, I modified the handler: private void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e) { DataRow row = _names.Rows[e.RowIndex]; row.BeginEdit(); row.EndEdit(); _da.Update(_names); } this variant really writes modified cell to database, but when I attempt to insert new row into grid, I get an error about an absence of row with index e.RowIndex So, I decided to improve the handler further: private void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e) { if (_names.Rows.Count<e.RowIndex) { DataRow row = _names.Rows[e.RowIndex]; row.BeginEdit(); row.EndEdit(); } else { DataRow row = _names.NewRow(); row["NameText"] = dataGridView1["NameText", e.RowIndex].Value; _names.Rows.Add(row); } _da.Update(_names); } Now the really strange things happen when I insert new row to grid: the grid remains what it was until _names.Rows.Add(row); After this line THREE rows are inserted into table - two rows with the same value and one with Null value. The slightly modified code: DataRow row = _names.NewRow(); row["NameText"] = "--------------" _names.Rows.Add(row); inserts three rows with three different values: one as entered into the grid, the second with "--------------" value and third - with Null value. I really got stuck in guessing what is happening.

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• Python: why can't descriptors be instance variables?

  - by Continuation

  Say I define this descriptor: class MyDescriptor(object): def __get__(self, instance, owner): return self._value def __set__(self, instance, value): self._value = value def __delete__(self, instance): del(self._value) And I use it in this: class MyClass1(object): value = MyDescriptor() >>> m1 = MyClass1() >>> m1.value = 1 >>> m2 = MyClass1() >>> m2.value = 2 >>> m1.value 2 So value is a class attribute and is shared by all instances. Now if I define this: class MyClass2(object) value = 1 >>> y1 = MyClass2() >>> y1.value=1 >>> y2 = MyClass2() >>> y2.value=2 >>> y1.value 1 In this case value is an instance attribute and is not shared by the instances. Why is it that when value is a descriptor it can only be a class attribute, but when value is a simple integer it becomes an instance attribute?

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