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  • Is there a recommended way to use the Observer pattern in MVP using GWT?

    - by Tomislav Nakic-Alfirevic
    I am thinking about implementing a user interface according to the MVP pattern using GWT, but have doubts about how to proceed. These are (some of) my goals: - the presenter knows nothing about the UI technology (i.e. uses nothing from com.google.*) - the view knows nothing about the model or the presenter - the model knows nothing of the view or the presenter (...obviously) I would place an interface between the view and the presenter and use the Observer pattern to decouple the two: the view generates events and the presenter gets notified. What confuses me is that java.util.Observer and java.util.Observable are not supported in GWT. This suggests that what I'm doing is not the recommended way to do it, as far as GWT is concerned, which leads me to my questions: what is the recommended way to implement MVP using GWT, specifically with the above goals in mind? How would you do it?

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  • How to perform different operations within Observer's update() in Java?

    - by Nazgulled
    I just started playing with Observable, Observer and it's update() method and I can't understand what should I do when different actions call notifyObservers(). I mean, my Observable class has a few different methods that call setChanged() and notifyObservers() in the end. Depending on the called method, some part of the UI (Swing) needs to be updated. However, there is only one update() method implemented in the Observer class. I though of passing something to the notifyObservers() method and then I can check the argument on update() but it doesn't seem feel like a good way to do it. Even if it did, what should I pass? A string with a short description of the action/method? And int, like an action/method code? Something else? What's the best way to handle this situation?

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  • Attempting to extract a pattern within a string

    - by Brian
    I'm attempting to extract a given pattern within a text file, however, the results are not 100% what I want. Here's my code: import java.util.regex.Matcher; import java.util.regex.Pattern; public class ParseText1 { public static void main(String[] args) { String content = "<p>Yada yada yada <code> foo ddd</code>yada yada ...\n" + "more here <2004-08-24> bar<Bob Joe> etc etc\n" + "more here again <2004-09-24> bar<Bob Joe> <Fred Kej> etc etc\n" + "more here again <2004-08-24> bar<Bob Joe><Fred Kej> etc etc\n" + "and still more <2004-08-21><2004-08-21> baz <John Doe> and now <code>the end</code> </p>\n"; Pattern p = Pattern .compile("<[1234567890]{4}-[1234567890]{2}-[1234567890]{2}>.*?<[^%0-9/]*>", Pattern.MULTILINE); Matcher m = p.matcher(content); // print all the matches that we find while (m.find()) { System.out.println(m.group()); } } } The output I'm getting is: <2004-08-24> bar<Bob Joe> <2004-09-24> bar<Bob Joe> <Fred Kej> <2004-08-24> bar<Bob Joe><Fred Kej> <2004-08-21><2004-08-21> baz <John Doe> and now <code> The output I want is: <2004-08-24> bar<Bob Joe> <2004-08-24> bar<Bob Joe> <2004-08-24> bar<Bob Joe> <2004-08-21> baz <John Doe> In short, the sequence of "date", "text (or blank)", and "name" must be extracted. Everything else should be avoided. For example the tag "Fred Kej" did not have any "date" tag before it, therefore, it should be flagged as invalid. Also, as a side question, is there a way to store or track the text snippets that were skipped/rejected as were the valid texts. Thanks, Brian

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  • How to improve the builder pattern?

    - by tangens
    Motivation Recently I searched for a way to initialize a complex object without passing a lot of parameter to the constructor. I tried it with the builder pattern, but I don't like the fact, that I'm not able to check at compile time if I really set all needed values. Traditional builder pattern When I use the builder pattern to create my Complex object, the creation is more "typesafe", because it's easier to see what an argument is used for: new ComplexBuilder() .setFirst( "first" ) .setSecond( "second" ) .setThird( "third" ) ... .build(); But now I have the problem, that I can easily miss an important parameter. I can check for it inside the build() method, but that is only at runtime. At compile time there is nothing that warns me, if I missed something. Enhanced builder pattern Now my idea was to create a builder, that "reminds" me if I missed a needed parameter. My first try looks like this: public class Complex { private String m_first; private String m_second; private String m_third; private Complex() {} public static class ComplexBuilder { private Complex m_complex; public ComplexBuilder() { m_complex = new Complex(); } public Builder2 setFirst( String first ) { m_complex.m_first = first; return new Builder2(); } public class Builder2 { private Builder2() {} Builder3 setSecond( String second ) { m_complex.m_second = second; return new Builder3(); } } public class Builder3 { private Builder3() {} Builder4 setThird( String third ) { m_complex.m_third = third; return new Builder4(); } } public class Builder4 { private Builder4() {} Complex build() { return m_complex; } } } } As you can see, each setter of the builder class returns a different internal builder class. Each internal builder class provides exactly one setter method and the last one provides only a build() method. Now the construction of an object again looks like this: new ComplexBuilder() .setFirst( "first" ) .setSecond( "second" ) .setThird( "third" ) .build(); ...but there is no way to forget a needed parameter. The compiler wouldn't accept it. Optional parameters If I had optional parameters, I would use the last internal builder class Builder4 to set them like a "traditional" builder does, returning itself. Questions Is this a well known pattern? Does it have a special name? Do you see any pitfalls? Do you have any ideas to improve the implementation - in the sense of fewer lines of code?

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  • Tab Sweep: Java EE 6 Scopes, Observer, SSL, Workshop, Virtual Server, JDBC Connection Validation

    - by arungupta
    Recent Tips and News on Java, Java EE 6, GlassFish & more : • How Java EE 6 Scopes Affect User Interactions (DevX.com) • Why is Java EE 6 better than Spring ? (Arun Gupta) • JavaEE Revisits Design Patterns: Observer (Murat Yener) • Getting started with Glassfish V3 and SSL (JavaDude) • Software stacks market share within Jelastic: March 2012 (Jelastic) • All aboard the Java EE 6 Love Boat! (Bert Ertman) • Full stack Java EE workshop (Kito Mann) • Create a virtual server from console in glassfish (Hector Guzman) • Glassfish – JDBC Connection Validation explained (Alexandru Ersenie) • Automatically setting the label of a component in JSF 2 (Arjan Tijms) • JSF2 + Primefaces3 + Spring3 & Hibernate4 Integration Project (Eren Avsarogullari) • THE EXECUTABLE FEEL OF JAX-RS 2.0 CLIENT (Adam Bien) Here are some tweets from this week ... web-app dtd(s) on http://t.co/4AN0057b R.I.P. using http://t.co/OTZrOEEr instead. Thank you Oracle! finally got GlassFish and Cassandra running embedded so I can unit test my app #jarhell #JavaEE6 + #NetBeans is really a pleasure to work with! Reading latest chapter in #Spring vs #JavaEE wars https://t.co/RqlGmBG9 (and yes, #JavaEE6 is better :P) @javarebel very easy install and very easy to use in combination with @netbeans and @glassfish. Save your time.

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  • BizTalk host throttling &ndash; Singleton pattern and High database size

    - by S.E.R.
    Originally posted on: http://geekswithblogs.net/SERivas/archive/2013/06/30/biztalk-host-throttling-ndash-singleton-pattern-and-high-database-size.aspxI have worked for some days around the singleton pattern (for those unfamiliar with it, read this post by Victor Fehlberg) and have come across a few very interesting posts, among which one dealt with performance issues (here, also by Victor Fehlberg). Simply put: if you have an orchestration which implements the singleton pattern, then performances will continuously decrease as the orchestration receives and consumes messages, and that behavior is more obvious when the orchestration never ends (ie : it keeps looping and never terminates or completes). As I experienced the same kind of problem (actually I was alerted by SCOM, which told me that the host was being throttled because of High database size), I thought it would be a good idea to dig a little bit a see what happens deep inside BizTalk and thus understand the reasons for this behavior. NOTE: in this article, I will focus on this High database size throttling condition. I will try and work on the other conditions in some not too distant future… Test conditions The singleton orchestration For the purpose of this study, I have created the following orchestration, which is a very basic implementation of a singleton that piles up incoming messages, then does something else when a certain timeout has been reached without receiving another message: Throttling settings I have two distinct hosts : one that hosts the receive port (basic FILE port) : Ports_ReceiveHostone that hosts the orchestration : ProcessingHost In order to emphasize the throttling mechanism, I have modified the throttling settings for each of these hosts are as follows (all other parameters are set to the default value): [Throttling thresholds] Message count in database: 500 (default value : 50000) Evolution of performance counters when submitting messages Since we are investigating the High database size throttling condition, here are the performance counter that we should take a look at (all of them are in the BizTalk:Message Agent performance object): Database sizeHigh database sizeMessage delivery throttling stateMessage publishing throttling stateMessage delivery delay (ms)Message publishing delay (ms)Message delivery throttling state durationMessage publishing throttling state duration (If you are not used to Perfmon, I strongly recommend that you start using it right now: it is a wonderful tool that allows you to open the hood and see what is going on inside BizTalk – and other systems) Database size It is quite obvious that we will start by watching the database size and high database size counters, just to see when the first reaches the configured threshold (500) and when the second rings the alarm. NOTE : During this test I submitted 600 messages, one message at a time every 10ms to see the evolution of the counters we have previously selected. It might not show very well on this screenshot, but here is what happened: From 15:46:50 to 15:47:50, the database size for the Ports_ReceiveHost host (blue line) kept growing until it reached a maximum of 504.At 15:47:50, the high database size alert fires At first I was surprised by this result: why is it the database size of the receiving host that keeps growing since it is the processing host that piles up messages? Actually, it makes total sense. This counter measures the size of the database queue that is being filled by the host, not consumed. Therefore, the high database size alert is raised on the host that fills the queue: Ports_ReceiveHost. More information is available on the Public MPWiki page. Now, looking at the Message publishing throttling state for the receiving host (green line), we can see that a throttling condition has been reached at 15:47:50: We can also see that the Message publishing delay(ms) (blue line) has begun growing slowly from this point. All of this explains why performances keep decreasing when a singleton keeps processing new messages: the database size grows and when it has exceeded the Message count in database threshold, the host is throttled and the publishing delay keeps increasing. Digging further So, what happens to the database queue then? Is it flushed some day or does it keep growing and growing indefinitely? The real question being: will the host be throttled forever because of this singleton? To answer this question, I set the Message count in database threshold to 20 (this value is very low in order not to wait for too long, otherwise I certainly would have fallen asleep in front of my screen) and I submitted 30 messages. The test was started at 18:26. At 18:56 (ie : exactly 30min later) the throttling was stopped and the database size was divided by 2. 30 min later again, the database size had dropped to almost zero: I guess I’ll have to find some documentation and do some more testing before I sort this out! My guess is that some maintenance job is at work here, though I cannot tell which one Digging even further If we take a look at the Message delivery throttling state counter for the processing host, we can see that this host was also throttled during the submission of the 600 documents: The value for the counter was 1, meaning that Message delivery incoming rate for the host instance exceeds the Message delivery outgoing rate * the specified Rate overdrive factor (percent) value. We will see this another day… :) A last word Let’s end this article with a warning: DO NOT CHANGE THE THROTTLING SETTINGS LIGHTLY! The temptation can be great to just bypass throttling by setting very high values for each parameter (or zero in some cases, which simply disables throttling). Nevertheless, always keep in mind that this mechanism is here for a very good reason: prevent your BizTalk infrastructure from exploding!! So whatever you do with those settings, do a lot of testing and benchmarking!

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  • Repository pattern - Switch out the database and switch in XML files

    - by glasto red
    Repository pattern - Switch out the database and switch in XML files. Hello I have an asp.net MVC 2.0 project and I have followed the Repository pattern. Periodically, I am losing access to the database server so I want to have another mechanism in place (XML files) to continue developing. It is not possible to have a local version of the db unfortunately! I thought this would be relatively easy using the Repository pattern, to switch out the db repositories and switch in XML versions. However, I am having real trouble coming up with a solution. I have tried LinqToXML but then ran into problems trying to return a List of News items as the LinqToXML ToList returns Generic.List Should I be mapping the XElement list over to the News list by hand? It just seems a bit clunky compared to LinqToSQL attributes on the News class and then simply doing a Table.....ToList(); Any direction would be appreciated. Thanks

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  • Scala wont pattern match with java.lang.String and Case Class

    - by Stefan
    Hello fellow Scala Programmers I have been working with Scala for some month now, however I have a problem with some properly basic stuff, I am hoping you will help my out with it. case class PersonClass(name: String, age: Int) object CaseTester { def main(args:Array[String]) { val string = "hej" string match { case e:String => println(string) case PersonClass => println(string) } } } When I am doing like this I get error: pattern type is incompatible with expected type; found : object PersonClass required: java.lang.String case PersonClass = println(string) And if I then change the second line in the pattern matching to the following: case e:PersonClass => println(string) I then get the error: error: scrutinee is incompatible with pattern type; found : PersonClass required: java.lang.String case e:PersonClass = println(string) However if I change the string definition to the following it compiles fine in both cases. val string:AnyRef = "hej"

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  • Mapping to a JSON method with url-pattern

    - by Brian
    I'm creating a Spring MVC application that will have a controller with 'RequestMapping'-annotated methods, including a JSON method. It currently has static content that resides in webapps/static, and the app itself resides in webapps/myapp. I assume that Catalina's default servlet is handling the static content, and my *.htm url-pattern in web.xml is returning the request for my JSP page, but I haven't been able to get the JSON method to be called. How do I write the url-pattern in the servlet mapping to do so? Using /* has not worked; it prevents the app from being accessed at all. Is there anything else to be aware of? EDIT: The url-pattern '/' appears to allow the JSON request through, because a 406 error is returned. What then would need to be modified to allow JSON to be returned?

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  • Using the Module Pattern for larger projects

    - by Rob
    I'm interested in using the Module Pattern to better organize my future projects. Unfortunately, there are only a few brief tutorials and proof-of-concept examples of the Module Pattern. Using the module pattern, I would like to organize projects into this sort of structure: project.arm.object.method(); Where "project" is my global project name, "arm" is a sub-section or branch of the project, "object" is an individual object, and so on to the methods and properties. However, I'm not sure how I should be declaring and organizing multiple "arms" and "objects" under "project". var project = window.project || {}; project.arm = project.arm || {}; project.arm.object = (function() { var privateVar = "Private contents."; function privateMethod() { alert(privateVar); } return { method: privateMethod }; }()); Are there any best practices or conventions when defining a complex module structure? Should I just declare a new arm/object underneath the last?

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  • Javascript: Using the Module Pattern for larger projects

    - by Rob
    I'm interested in using the Module Pattern to better organize my future projects. Unfortunately, there are only a few brief tutorials and proof-of-concept examples of the Module Pattern. Using the module pattern, I would like to organize projects into this sort of structure: project.arm.object.method(); Where "project" is my global project name, "arm" is a sub-section or branch of the project, "object" is an individual object, and so on to the methods and properties. However, I'm not sure how I should be declaring and organizing multiple "arms" and "objects" under "project". var project = window.project || {}; project.arm = project.arm || {}; project.arm.object = (function() { var privateVar = "Private contents."; function privateMethod() { alert(privateVar); } return { method: privateMethod }; }()); Are there any best practices or conventions when defining a complex module structure? Should I just declare a new arm/object underneath the last?

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  • Is it possible, with simple F# pattern matching transformations, to ignore unmatched values without

    - by Phobis
    So, I previously asked this question: http://stackoverflow.com/questions/2820234/can-someone-help-me-compare-using-f-over-c-in-this-specific-example-ip-address I was looking at the posted code and I was wondering if this code could be written without it producing a warning: let [|a;b;c;d|] = s.Split [|'.'|] IP(parseOrParts a, parseOrParts b, parseOrParts c, parseOrParts d) Is it possible to do something for the match _ pattern ot ignore? Without adding in something like Active Patterns? i want to keep the code as simple as possible... can I do this without drastically changing this code? NOTE: Warning is as follows Warning Incomplete pattern matches on this expression. For example, the value '[|_; _; _; _; _|]' may indicate a case not covered by the pattern(s).

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  • What is this Design Pattern?

    - by Can't Tell
    I read the Wikipedia articles on FactoryMethod and AbstractFactory but the following code doesn't seem to fit anywhere. Can someone explain to me what the following pattern is or if it is an anti-pattern? interace PaymentGateway{ void makePayment(); } class PaypalPaymentGateway implements PaymentGateway { public void makePayment() { //some implementation } } class AuthorizeNetPaymentGateway implements PaymentGateway { public void makePayment() { //some implementation } } class PaymentGatewayFacotry{ PaymentGateway createPaymentGateway(int gatewayId) { if(gatewayId == 1) return PaypalPaymentGateway(); else if(gatewayId == 2) return AuthorizeNetPaymentGateway(); } } Let's say the user selects the payment method using a radio button on an html page and the gatewayId is derived from the radio button value. I have seen code like this and thought it was the AbstractFactory pattern but after reading the Wikipedia article, I'm having doubts.

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  • why Observable snapshot observer vector

    - by han14466
    In Observable's notifyObservers method, why does the coder use arrLocal = obs.toArray();? Why does not coder iterate vector directly? Thanks public void notifyObservers(Object arg) { Object[] arrLocal; synchronized (this) { /* We don't want the Observer doing callbacks into * arbitrary code while holding its own Monitor. * The code where we extract each Observable from * the Vector and store the state of the Observer * needs synchronization, but notifying observers * does not (should not). The worst result of any * potential race-condition here is that: * 1) a newly-added Observer will miss a * notification in progress * 2) a recently unregistered Observer will be * wrongly notified when it doesn't care */ if (!changed) return; arrLocal = obs.toArray(); clearChanged(); } for (int i = arrLocal.length-1; i>=0; i--) ((Observer)arrLocal[i]).update(this, arg); }

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  • OOW content for Pattern Matching....

    - by KLaker
    If you missed my sessions at OpenWorld then don't worry - all the content we used for pattern matching (presentation and hands-on lab) is now available for download. My presentation "SQL: The Best Development Language for Big Data?" is available for download from the OOW Content Catalog, see here: https://oracleus.activeevents.com/2013/connect/sessionDetail.ww?SESSION_ID=9101 For the hands-on lab ("Pattern Matching at the Speed of Thought with Oracle Database 12c") we used the Oracle-By-Example content. The OOW hands-on lab uses Oracle Database 12c Release 1 (12.1) and uses the MATCH_RECOGNIZE clause to perform some basic pattern matching examples in SQL. This lab is broken down into four main steps: Logically partition and order the data that is used in the MATCH_RECOGNIZE clause with its PARTITION BY and ORDER BY clauses. Define patterns of rows to seek using the PATTERN clause of the MATCH_RECOGNIZE clause. These patterns use regular expressions syntax, a powerful and expressive feature, applied to the pattern variables you define. Specify the logical conditions required to map a row to a row pattern variable in the DEFINE clause. Define measures, which are expressions usable in the MEASURES clause of the SQL query. You can download the setup files to build the ticker schema and the student notes from the Oracle Learning Library. The direct link to the example on using pattern matching is here: http://apex.oracle.com/pls/apex/f?p=44785:24:0::NO:24:P24_CONTENT_ID,P24_PREV_PAGE:6781,2.

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  • EF Query Object Pattern over Repository Example

    - by Dale Burrell
    I have built a repository which only exposes IEnumerable based mostly on the examples in "Professional ASP.NET Design Patterns" by Scott Millett. However because he mostly uses NHibernate his example of how to implement the Query Object Pattern, or rather how to best translate the query into something useful in EF, is a bit lacking. I am looking for a good example of an implementation of the Query Object Pattern using EF4.

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  • Count number of occurrences of a pattern in a file (even on same line)

    - by jrdioko
    When searching for number of occurrences of a string in a file, I generally use: grep pattern file | wc -l However, this only finds one occurrence per line, because of the way grep works. How can I search for the number of times a string appears in a file, regardless of whether they are on the same or different lines? Also, what if I'm searching for a regex pattern, not a simple string? How can I count those, or, even better, print each match on a new line?

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  • Aggregate Pattern and Performance Issues

    - by Mosh
    Hello, I have read about the Aggregate Pattern but I'm confused about something here. The pattern states that all the objects belonging to the aggregate should be accessed via the Aggregate Root, and not directly. And I'm assuming that is the reason why they say you should have a single Repository per Aggregate. But I think this adds a noticeable overhead to the application. For example, in a typical Web-based application, what if I want to get an object belonging to an aggregate (which is NOT the aggregate root)? I'll have to call Repository.GetAggregateRootObject(), which loads the aggregate root and all its child objects, and then iterate through the child objects to find the one I'm looking for. In other words, I'm loading lots of data and throwing them out except the particular object I'm looking for. Is there something I'm missing here? PS: I know some of you may suggest that we can improve performance with Lazy Loading. But that's not what I'm asking here... The aggregate pattern requires that all objects belonging to the aggregate be loaded together, so we can enforce business rules.

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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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  • 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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