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  • Visitor Pattern can be replaced with Callback functions?

    - by getit
    Is there any significant benefit to using either technique? In case there are variations, the Visitor Pattern I mean is this: http://en.wikipedia.org/wiki/Visitor_pattern And below is an example of using a delegate to achieve the same effect (at least I think it is the same) Say there is a collection of nested elements: Schools contain Departments which contain Students Instead of using the Visitor pattern to perform something on each collection item, why not use a simple callback (Action delegate in C#) Say something like this class Department { List Students; } class School { List Departments; VisitStudents(Action<Student> actionDelegate) { foreach(var dep in this.Departments) { foreach(var stu in dep.Students) { actionDelegate(stu); } } } } School A = new School(); ...//populate collections A.Visit((student)=> { ...Do Something with student... }); *EDIT Example with delegate accepting multiple params Say I wanted to pass both the student and department, I could modify the Action definition like so: Action class School { List Departments; VisitStudents(Action<Student, Department> actionDelegate, Action<Department> d2) { foreach(var dep in this.Departments) { d2(dep); //This performs a different process. //Using Visitor pattern would avoid having to keep adding new delegates. //This looks like the main benefit so far foreach(var stu in dep.Students) { actionDelegate(stu, dep); } } } }

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  • Telerik Object reference not set to an instance of an object

    - by Duncan
    Hi, I have a main form which contains multiple worker threads. These threads raise events which update Telerik controls on the main form. The event handlers contain code which check if InvokeRequired and BeginInvoke where required. At random interval I am receiving the following exception, and have no idea on how where to find this? I was wondering if the following is understandable to anyone to point me in the right direction. Thanks in advance System.Reflection.TargetInvocationException was unhandled Message="Exception has been thrown by the target of an invocation." Source="mscorlib" StackTrace: at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Delegate.DynamicInvokeImpl(Object[] args) at System.Windows.Forms.Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme) at System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(Object obj) at System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Windows.Forms.Control.InvokeMarshaledCallback(ThreadMethodEntry tme) at System.Windows.Forms.Control.InvokeMarshaledCallbacks() at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.ScrollableControl.WndProc(Message& m) at Telerik.WinControls.RadControl.WndProc(Message& m) at Telerik.WinControls.UI.RadStatusStrip.WndProc(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg) at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData) at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) at System.Windows.Forms.Application.Run(ApplicationContext context) at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun() at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel() at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine) at MyFX.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81 at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException: System.NullReferenceException Message="Object reference not set to an instance of an object." Source="Telerik.WinControls" StackTrace: at Telerik.WinControls.Layouts.ContextLayoutManager.LayoutQueue.RemoveOrphans(RadElement parent) at Telerik.WinControls.Layouts.ContextLayoutManager.LayoutQueue.Add(RadElement e) at Telerik.WinControls.RadElement.InvalidateArrange(Boolean recursive) at Telerik.WinControls.RadElement.InvalidateArrange() at Telerik.WinControls.RadElement.Measure(SizeF availableSize) at Telerik.WinControls.Layouts.ImageAndTextLayoutPanel.MeasureOverride(SizeF availableSize) at Telerik.WinControls.RadElement.MeasureCore(SizeF availableSize) at Telerik.WinControls.RadElement.Measure(SizeF availableSize) at Telerik.WinControls.Layouts.ContextLayoutManager.UpdateLayout() at Telerik.WinControls.Layouts.ContextLayoutManager.UpdateLayoutCallback(ILayoutManager manager)

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  • Why did object-oriented paradigms take so long to go mainstream?

    - by Earlz
    I read this question and it got me thinking about another fairly recent thing. Object oriented languages. I'm not sure when the first one was created, but why did it take so long before they became mainstream? C became vastly popular, but didn't become the object-oriented C++ for years(decades?) later No mainstream language before the 90s was object oriented Object oriented really seemed to take off with Java and C++ around the same time Now, my question, why did this take so long? Why wasn't C originally conceived as an object-oriented language? Taking a very small subset of C++ wouldn't have affected the core language a whole lot, so why was this idea not popular until the 90s?

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  • Explanation of the definition of interface inheritance as described in GoF book

    - by Geek
    I am reading the first chapter of the Gof book. Section 1.6 discusses about class vs interface inheritance: Class versus Interface Inheritance It's important to understand the difference between an object's class and its type. An object's class defines how the object is implemented.The class defines the object's internal state and the implementation of its operations.In contrast,an object's type only refers to its interface--the set of requests on which it can respond. An object can have many types, and objects of different classes can have the same type. Of course, there's a close relationship between class and type. Because a class defines the operations an object can perform, it also defines the object's type . When we say that an object is an instance of a class, we imply that the object supports the interface defined by the class. Languages like c++ and Eiffel use classes to specify both an object's type and its implementation. Smalltalk programs do not declare the types of variables; consequently,the compiler does not check that the types of objects assigned to a variable are subtypes of the variable's type. Sending a message requires checking that the class of the receiver implements the message, but it doesn't require checking that the receiver is an instance of a particular class. It's also important to understand the difference between class inheritance and interface inheritance (or subtyping). Class inheritance defines an object's implementation in terms of another object's implementation. In short, it's a mechanism for code and representation sharing. In contrast,interface inheritance(or subtyping) describes when an object can be used in place of another. I am familiar with the Java and JavaScript programming language and not really familiar with either C++ or Smalltalk or Eiffel as mentioned here. So I am trying to map the concepts discussed here to Java's way of doing classes, inheritance and interfaces. This is how I think of of these concepts in Java: In Java a class is always a blueprint for the objects it produces and what interface(as in "set of all possible requests that the object can respond to") an object of that class possess is defined during compilation stage only because the class of the object would have implemented those interfaces. The requests that an object of that class can respond to is the set of all the methods that are in the class(including those implemented for the interfaces that this class implements). My specific questions are: Am I right in saying that Java's way is more similar to C++ as described in the third paragraph. I do not understand what is meant by interface inheritance in the last paragraph. In Java interface inheritance is one interface extending from another interface. But I think the word interface has some other overloaded meaning here. Can some one provide an example in Java of what is meant by interface inheritance here so that I understand it better?

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  • Silverlight 4 HttpWebRequest user agent string is null

    - by Dan B
    The problem I have a page with a silverlight object. It attempts to retrieve XML from the page. But I am struggling with a security exception. I have this code working brilliantly in WPF. When using a website hosting a silverlight application with the same code, the user agent string of the HttpRequest object is null (and seemingly cannot be set). In fact there is no header information at all - this causes a security exception when attempting to make my asynchronous call. The question Why is the user-agent string (and header information) null in my silverlight 4 application when making an asynchronous call using HttpWebRequest? Thanks in advance!

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  • MVC null model problem

    - by femi
    hello, i have created two create actions..one to call the create view and the other to process the create view using httppost. when i call the create view, it gets published correctly , dropdowns and all. the problem is that when i fill out the create form and click on the submit button, i get an error; Object reference not set to an instance of an object. My first thoughts are that i am passing a null model to the httppost create action.. How can i check to see if i am passing in a null model to the httppost create action? thanks

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  • NULL value when using NSDateFormatter

    - by David A Gibson
    Hello, I am using the following code to try and display in a time in a table cell. TimeSlot *timeSlot = [timeSlots objectAtIndex:indexPath.row]; NSDateFormatter *timeFormat = [[NSDateFormatter alloc] init]; [timeFormat setDateFormat:@"%1m/%1d/%Y"]; NSLog(@"Time: %@", timeSlot.time); NSDate *mydate = timeSlot.time; NSLog(@"Time: %@", mydate); NSString *theTime = [timeFormat stringFromDate:mydate]; NSLog(@"Time: %@", theTime); The log output is this: 2010-04-14 10:23:54.626 MyApp[1080:207] Time: 2010-04-14T10:23:54 2010-04-14 10:23:54.627 MyApp[1080:207] Time: 2010-04-14T10:23:54 2010-04-14 10:23:54.627 MyApp[1080:207] Time: (null) I am new to developing for the iPhone and as it all compiles with no errors or warnings I am at a loss as to why I am getting NULL in the log. Is there anything wrong with this code? Thanks

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  • Order by null/not null with ICriteria

    - by Kristoffer
    I'd like to sort my result like this: First I want all rows/objects where a column/property is not null, then all where the colmn/property is null. Then I want to sort by another column/property. How can I do this with ICriteria? Do I have to create my own Order class, or can it be done with existing code? ICriteria criteria = Session.CreateCriteria<MyClass>() .AddOrder(Order.Desc("NullableProperty")) // What do I do here? IProjection? Custom Order class? .AddOrder(Order.Asc("OtherProperty"));

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  • PHP fopen returning null on files that work fine with include and get_file_contents

    - by brad allred
    Hi, I have XAMPP installed on a windows 2000 server. everything is working great except the PHP fopen function. I can neither create nor open files with it. the strange thing is that i can include/require/file_get_contents/other file related functions; also fopen does not generate any errors or notices it just returns NULL. I have gone as far as to grant full control of the file and all enclosing folders to everybody but i still get NULL instead of a file pointer. I have tried this on php 5.2.9, 5.2.13, and 5.3.1 with the same effect. i have gone through the php.ini file looking for something that is breaking it; i have even tried deleting and using the basic ini file from a linux box where fopen is working and still nothing. I know i have to restart apache after changing my ini and all that and have been (I have even restarted the server) so thats not it. I am at this poing assuming it is an apache configuration issue somehow, tomorrow im going to run a test through php-cli to make sure. I really don't want to bruise my head anymore over this can some apache/php wizard come to my aid? Hi guys, thanks for the responses. you are right is is not any config problem. the problem has to be with one of my dlls or one of my included files. I just tried the same code that isn't working in a new file without any include and i disabled my custom libraries and it worked. for the record here is what I was doing that wasn't working: $test_file = 'c:\\test.csv';//everybody has full control. is very large. if(file_exists($test_file) && is_readable($test_file)){ $fp = fopen($test_file, 'r'); echo var_export($fp, true);//outputs NULL. on my linux box this is a number. if($fp !== false){ //do the work fread($fp, 10);//throws the error that $fp is not a valid file handle } } something that i am including must be breaking fopen somehow. works as expected in new file with no includes.

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  • JPA Cascading Delete: Setting child FK to NULL on a NOT NULL column

    - by JBristow
    I have two tables: t_promo_program and t_promo_program_param. They are represented by the following JPA entities: @Entity @Table(name = "t_promo_program") public class PromoProgram { @Id @Column(name = "promo_program_id") private Long id; @OneToMany(cascade = {CascadeType.REMOVE}) @JoinColumn(name = "promo_program_id") private List<PromoProgramParam> params; } @Entity @Table(name = "t_promo_program_param") public class PromoProgramParam { @Id @Column(name = "promo_program_param_id") private Long id; //@NotNull // This is a Hibernate annotation so that my test db gets created with the NOT NULL attribute, I'm not married to this annotation. @ManyToOne @JoinColumn(name = "PROMO_PROGRAM_ID", referencedColumnName = "promo_program_id") private PromoProgram promoProgram; } When I delete a PromoProgram, Hibernate hits my database with: update T_PROMO_PROGRAM_PARAM set promo_program_id=null where promo_program_id=? delete from t_promo_program where promo_program_id=? and last_change=? I'm at a loss for where to start looking for the source of the problem.

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  • I've got a ComboBox that's giving me grief in WPF using the MVVM pattern

    - by Mike
    Here's my code: <ComboBox Grid.Column="1" Grid.Row="9" ItemsSource="{Binding Path=PriorityEntries}" SelectedItem="{Binding Path=Priority,Mode=TwoWay}"/> The comboBox is bound properly with PriorityEntries, and when i change the value of the comboBox the "set" of the bound property(Priority) is called setting it to what it needs to be. However, when i close the UserControl that this combobox resides, it calls the set property again with a value of null and then sets what the selectedItem was to null. Why is the comboBox being bound again when I close the usercontrol. I tried setting the mode to OneTime, but that won't reflect any changes...

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  • C# ProgressBar design pattern

    - by MadSeb
    Hi, I'm working on a database upgrader application. The upgrader updates the schema of a database ( adds new columns, renames columns , adds new tables, new views to an existing database by executing SQL statements ). When a user wants to upgrade from version 1.0 to 2.0 , "Upgrader" objects are taken from an object factory and the "Execute" method of each "Upgrader" is called. The GUI of the application has a progress bar and each time an upgrader object performs a SQL statement the progress bar gets incremented. while (!version.Equal(CurrentVersion)) { IUpgrader myUpgrader = UpgraderFactory.GetUpgrader(version); myUpgrader.Execute(UpgradedFile,progressbar); version.Increment(); } My question is very simple : how should the upgrader object communicate with the progressbar. In the code above, the upgrader object is given direct access to the progressbar but I'm wondering if some better way of doing this or better design pattern exists. Regards, Seb

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  • Zend database query result converts column values to null

    - by David Zapata
    Hi again. I am using the next instructions to get some registers from my Database. Create the needed models (from the params module): $obj_paramtype_model = new Params_Model_DbTable_Paramtype(); $obj_param_model = new Params_Model_DbTable_Param(); Getting the available locales from the database // This returns a Zend_Db_Table_Row_Abstract class object $obj_paramtype = $obj_paramtype_model->getParamtypeByValue('available_locales'); // This is a query used to add conditions to the next sentence. This is executed from the Params_Model_DbTable_Param instance class, that depends from Params_Model_DbTable_Paramtype class (reference map and dependentTables arrays are fine in both classes) $obj_select = $this->select()->where('deleted_at IS NULL')->order('name'); // Execute the next query, applying the select restrictions. This returns a Zend_Db_Table_Rowset_Abstract class object. This means "Find Params by Paramtype" $obj_params_rowset = $obj_paramtype->findDependentRowset('Params_Model_DbTable_Param', 'Paramtype', $obj_paramtype); // Here the firebug log displays the queries.... Zend_Registry::get('log')->debug($obj_params_rowset); I have a profiler for all my DB executions from Zend. At this point the log and profiler objects (that includes Firebug writers), shows the executed SQL Queries, and the last line displays the resulting Zend_Db_Table_Rowset_Abstract class object. If I execute the SQL Queries in some MySQL Client, the results are as expected. But the Zend Firebug log writer displays as NULL the column values with latin characters (ñ). In other words, the external SQL client shows es_CO | Español de Colombia and en_US | English of United States but the Query results from Zend displays (and returns) es_CO | null and en_US | English of United States. I've deleted the ñ character from Español de Colombia and the query results are just fine in my Zend Log Firebug screen, and in the final Zend Form element. The MySQL database, tables and columns are in UTF-8 - utf8_unicode_ci collation. All my zend framework pages are in UTF-8 charset. I'm using XAMPP 1.7.1 (PHP 5.2.9, Apache at port 90 and MySQL 5.1.33-community) running on Windows 7 Ultimate; Zend Framework 1.10.1. I'm sorry if there is so much information, but I don't really know why could that happen, so I tryed to provide as much related information as I could to help to find some answer.

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  • SQL count NULL cells

    - by Giuseppe
    Dear All, I have the following problem. I have a table in a db, with many columns. I can do different kind of select queries, to show, for example, for each record that satisfies a condition: all cells from columns with names ending in _t0 all cells from columns with names ending in _t1 ... To get the column lists to form the queries I use the information schema. Now, the problem: each query returns a record with a subset of the columns of the big table. This means that I can get a row of (all!) NULLs. How can I ask my query to reject such rows without having to type in explicitely the column names (i.e. by saying where col_1 is not null, col_2 is not null...)? Is it possible? Thanks in advance!!! Sep

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  • Binding UserControl to a NULL DataContext

    - by user634981
    I have a UserControl and am binding its DataContext to an object. I also bind the IsEnabled property of the UserControl to a boolean property of that object eg: <my:MyUserControl DataContext="{Binding Items.SelectedItem}" IsEnabled="{Binding Path=IsEditable}"/> This works fine provided Items.SelectedItem is not null. However, if it is null (which can happen sometimes if the Items collection is empty), the IsEnabled binding does not get evaluated and is set to true, which is not the desired behaviour. I've tried using a MultiBinding but without success because I don't know if it's possible to bind to the DataContext. I've also tried using a DataTrigger, but again without success. Would somebody kindly point me in the right direction as to the correct way I should be doing this. Thanks!

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  • nhibernate fluent repository pattern insert problem

    - by voam
    I am trying to use Fluent NHibernate and the repository pattern. I would like my business layer to not be knowledgeable of the data persistence layer. Ideally I would pass in an initialized domain object to the insert method of the repository and all would be well. Where I run into problems is if the object being passed in has a child object. For example say I want to insert an a new order for a customer, and the customer is a property of the order object. I would like to do something like this: Customer c = new Customer; c.CustomerId = 1; Order o = new Order; o.Customer = c; repository.InsertOrder(o); The problem is that using NHiberate the CustomerId field is only privately settable so I can not set it directly like this. so what I have ended up doing is have my repository have an interface of Order InsertOrder(int customerId) where all the foreign keys get passed in as parameters. Somehow this just doesn't seem right. The other approach was to use the NHibernate session variable to load a customer object in my business model and then have the order passed in to the repository but this defeats my persistence ignorance ideal. Should I throw this persistence ignorance out the window or am I missing something here? Thanks

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  • Copying non null-terminated unsigned char array to std::string

    - by karlphillip
    If the array was null-terminated this would be pretty straight forward: unsigned char u_array[4] = { 'a', 's', 'd', '\0' }; std::string str = reinterpret_cast<char*>(u_array); std::cout << "-> " << str << std::endl; However, I wonder what is the most appropriate way to copy a non null-terminated unsigned char array, like the following: unsigned char u_array[4] = { 'a', 's', 'd', 'f' }; into a std::string. Is there any way to do it without iterating over the unsigned char array? Thank you all.

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  • Javascript / jQuery Exec turns up Null

    - by Matrym
    How do I skip over this next line if it turns out to be null? Currently, it (sometimes) "breaks" and prevents the script from continuing. var title = (/(.*?)<\/title/m).exec(response)[1]; $.get(url, function(response){ var title = (/<title>(.*?)<\/title>/m).exec(response)[1]; if (title == null || title == undefined){ return false; } var words = title.split(' '); $.each(words, function(index, value){ $link.highlight(value + " "); $link.highlight(" " + value); }); });

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  • Repository, Service or Domain object - where does logic belong?

    - by betitall
    Take this simple, contrived example: UserRepository.GetAllUsers(); UserRepository.GetUserById(); Inevitably, I will have more complex "queries", such as: //returns users where active=true, deleted=false, and confirmed = true GetActiveUsers(); I'm having trouble determining where the responsibility of the repository ends. GetActiveUsers() represents a simple "query". Does it belong in the repository? How about something that involves a bit of logic, such as: //activate the user, set the activationCode to "used", etc. ActivateUser(string activationCode);

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  • NULL In a Class Destructor

    - by Hyper-DarkStar
    Simple question; Is it pointless to set a pointer( which allocates heap memory ) to NULL in the destructor? class SampleClass { public: SampleClass( int Init = 0 ) { Value = new int( Init ); } ~SampleClass( void ) { delete Value; Value = NULL; // Is this pointless? } int *Value; }; While on the subject of classes, when should I use the explicit keyword? Thanks.

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  • pattern matching and returning new object based on pattern

    - by Rune FS
    Say I'v got some code like this match exp with | Addition(lhs,rhs,_) -> Addition(fix lhs,fix rhs) | Subtraction(lhs,rhs,_) -> Subtraction(fix lhs,fix rhs) is there any way that would allow me to do something like match exp with | Addition(lhs,rhs,_) | Subtraction(lhs,rhs,_) -> X(fix lhs,fix rhs) where X be based on the actual pattern being matched

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  • IoC containers and service locator pattern

    - by TheSilverBullet
    I am trying to get an understanding of Inversion of Control and the dos and donts of this. Of all the articles I read, there is one by Mark Seemann (which is widely linked to in SO) which strongly asks folks not to use the service locator pattern. Then somewhere along the way, I came across this article by Ken where he helps us build our own IoC. I noticed that is is nothing but an implementation of service locator pattern. Questions: Is my observation correct that this implementation is the service locator pattern? If the answer to 1. is yes, then Do all IoC containers (like Autofac) use the service locator pattern? If the answer to 1. is no, then why is this differen? Is there any other pattern (other than DI) for inversion of control?

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  • Repository Pattern with Entity Framework 3.5 and MVVM

    - by Ravi
    I am developing a Database File System. I am using - .Net framework 3.5 Entity Framework 3.5 WPF with MVVM pattern The project spans across multiple assemblies each using same model. One assembly,let's call it a "server", only adds data to the database using EF i.e. same model.Other assemblies (including the UI) both reads and writes the data.The changes made by server should immediately reflect in other assemblies. The database contains self referencing tables where each entity can have single OR no parent and (may be) some children. I want to use repository pattern which can also provide some mechanism to handle this hierarchical nature. I have already done reading on this on Code Project. It shares the same context(entities) everywhere. My question is - Should I share the same context everywhere? What are the advantages and disadvantages of doing that?

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