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  • Process a batch of items, return an object to report on status

    - by Naeem Sarfraz
    I'm looking for a pattern (or good practice) for the following scenario: My function List<BatchItemResponse> Process(List<BatchItem> Data) {..} will process a list of data, and return info on where each item in the batch could be processed. struct BatchItemResponse { int BatchItemID; bool Processed; string Description; } Any thoughts? Is what I've proposed as good as it gets?

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  • Messaging strategies to connect different systems

    - by n002213f
    I have a system to handle Applications online and a different system to send SMS/Email notifications to applicants on completion using web services. I can't guarantee the availability of the SMS/Email gateway. Option 1 After an application is complete, place a message on a JMS queue. A Message Driven bean receives the message and make a call for the web service, if it fails leave the message on the queue. I suspect (please correct if incorrect) that if the gate way is offline the continuosly try to send the message which might use up valuable resources. Can the above option be refined are are there any other messaging strategies that can be used?

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  • Should I create subclass NSManagedObject or not?

    - by TP
    Hi, I have spent a few days learning and writing NSCoding and finally got it working. However, it took very long to archive and unarchive the (quite complex) object graph, which is unacceptable. After searching the internet for some time, I think the better way is to use core data. Do you recommend that 1) I should rewrite all my classes as subclasses of NSManagedObject or 2) should I create an instance variable of NSManagedObject in each of my class so that any changes to the class also updates its core data representation? Doing either way will need significant changes to the exiting classes and I think I have to update lots of unit test cases as well if it changes the way the classes are initialized. What do you recommend? I really don't want to head to the wrong approach again... Thanks!

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  • How would you code an efficient Circular Buffer in Java or C#

    - by Cheeso
    I want a simple class that implements a fixed-size circular buffer. It should be efficient, easy on the eyes, generically typed. EDIT: It need not be MT-capable, for now. I can always add a lock later, it won't be high-concurrency in any case. Methods should be: .Add and I guess .List, where I retrieve all the entries. On second thought, Retrieval I think should be done via an indexer. At any moment I will want to be able to retrieve any element in the buffer by index. But keep in mind that from one moment to the next Element[n] may be different, as the Circular buffer fills up and rolls over. This isn't a stack, it's a circular buffer. Regarding "overflow": I would expect internally there would be an array holding the items, and over time the head and tail of the buffer will rotate around that fixed array. But that should be invisible from the user. There should be no externally-detectable "overflow" event or behavior. This is not a school assignment - it is most commonly going to be used for a MRU cache or a fixed-size transaction or event log.

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  • What do you find wrong or strange in this Perl code to simulate objects without bless?

    - by user350571
    I'm new to Perl and its blessing stuff to imitate class like functionality made me feel strange I even had to go to the bathroom. Now, please tell me: what do you don't like, find wrong or strange with this code: sub Person { my $age = shift || 15; return { printAge => sub { print "Age -> $age\n"; }, changeAge => sub { $age = shift } } } my $p = Person(); my $p2 = Person(27); $p->{printAge}->(); $p->{changeAge}->(30); $p->{printAge}->(); $p2->{printAge}->();

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  • Game logic dynamically extendable architecture implementation patterns

    - by Vlad
    When coding games there are a lot of cases when you need to inject your logic into existing class dynamically and without making unnecessary dependencies. For an example I have a Rabbit which can be affected by freeze ability so it can't jump. It could be implemented like this: class Rabbit { public bool CanJump { get; set; } void Jump() { if (!CanJump) return; ... } } But If I have more than one ability that can prevent it from jumping? I can't just set one property because some circumstances can be activated simultanously. Another solution? class Rabbit { public bool Frozen { get; set; } public bool InWater { get; set; } bool CanJump { get { return !Frozen && !InWater; } } } Bad. The Rabbit class can't know all the circumstances it can run into. Who knows what else will game designer want to add: may be an ability that changes gravity on an area? May be make a stack of bool values for CanJump property? No, because abilities can be deactivated not in that order in which they were activated. I need a way to seperate ability logic that prevent the Rabbit from jumping from the Rabbit itself. One possible solution for this is making special checking event: class Rabbit { class CheckJumpEventArgs : EventArgs { public bool Veto { get; set; } } public event EventHandler<CheckJumpEvent> OnCheckJump; void Jump() { var args = new CheckJumpEventArgs(); if (OnCheckJump != null) OnCheckJump(this, args); if (!args.Veto) return; ... } } But it's a lot of code! A real Rabbit class would have a lot of properties like this (health and speed attributes, etc). I'm thinking of borrowing something from MVVM pattern where you have all the properties and methods of an object implemented in a way where they can be easily extended from outside. Then I want to use it like this: class FreezeAbility { void ActivateAbility() { _rabbit.CanJump.Push(ReturnFalse); } void DeactivateAbility() { _rabbit.CanJump.Remove(ReturnFalse); } // should be implemented as instance member // so it can be "unsubscribed" bool ReturnFalse(bool previousValue) { return false; } } Is this approach good? What also should I consider? What are other suitable options and patterns? Any ready to use solutions? UPDATE The question is not about how to add different behaviors to an object dynamically but how its (or its behavior) implementation can be extended with external logic. I don't need to add a different behavior but I need a way to modify an exitsing one and I also need a possibiliity to undo changes.

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  • Explain "Leader/Follower" Pattern

    - by Alex B
    I can't seem to find a good explanation of "Leader/Follower" pattern. All explanations either simply refer to it in the context of some problem, or are completely meaningless. Can anyone explain to the the mechanics of how this pattern works, and why and how it improves performance over more traditional asynchronous IO models? Examples and links to diagrams are appreciated too.

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  • Delivering activity feed items in a moderately scalable way

    - by sotangochips
    The application I'm working on has an activity feed where each user can see their friends' activity (much like Facebook). I'm looking for a moderately scalable way to show a given users' activity stream on the fly. I say 'moderately' because I'm looking to do this with just a database (Postgresql) and maybe memcached. For instance, I want this solution to scale to 200k users each with 100 friends. Currently, there is a master activity table that stores the rendered html for the given activity (Jim added a friend, George installed an application, etc.). This master activity table keeps the source user, the html, and a timestamp. Then, there's a separate ('join') table that simply keeps a pointer to the person who should see this activity in their friend feed, and a pointer to the object in the main activity table. So, if I have 100 friends, and I do 3 activities, then the join table will then grow to 300 items. Clearly this table will grow very quickly. It has the nice property, though, that fetching activity to show to a user takes a single (relatively) inexpensive query. The other option is to just keep the main activity table and query it by saying something like: select * from activity where source_user in (1, 2, 44, 2423, ... my friend list) This has the disadvantage that you're querying for users who may never be active, and as your friend list grows, this query can get slower and slower. I see the pros and the cons of both sides, but I'm wondering if some SO folks might help me weigh the options and suggest one way or they other. I'm also open to other solutions, though I'd like to keep it simple and not install something like CouchDB, etc. Many thanks!

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  • Need a good way to store data in a DB from a table on a webpage that can have N columns.

    - by Abe Miessler
    Users need to be able to add a specific type of column to an otherwise static table on my web page and then save the information they enter in there to the database. I've been told that in reality they will almost never go over 5 columns but I would rather support N. The columns will all be of the same datatype. My first thought was to have an XML column with the values from all added columns in there but I was curious if anyone else had come up with a better solution. Suggestions?

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  • What is so bad about Singletons

    - by Ewan Makepeace
    The Singleton pattern is a fully paid up member of the GoF Patterns Book but lately seems rather orphaned by the developer world. I still use quite a lot of singletons, especially for Factory classes, and while you have to be a bit careful about multithreading issues (like any class actually) fail to see why they are so awful. This site especially seems to assume that everyone agrees that Singletons are evil. Why?

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  • What technologies/tools do people use to implement live websites ?

    - by MadSeb
    Hi, I have the following situation: -I have a server A hooked up to a piece of hardware that sends values and information out of every second. Programs on the server machine can read these values. This server A is in a very remote location so Internet connection is very slow and not reliable but the connection does exist. Let's say it's a weather station in the Arctic. -Users from the home location want to monitorize the weather values somehow. Well, the users can use a remote desktop connection the server A but that would be too too slow. My idea is somehow to have a website on a web server (let's call the webserver - B and B is in a home location ) and make the server A connect to the server B and somehow send values and the web application reads the values and displays them....... but how to do such a system ?? I know I can use MySQL and have the server A connect to a SQL server on server B and send INSERT queries and have the web application running on server B constantly read from the SQL server but I think that would be way way too slow and I think there has to be a better solution. Any ideas ? BTW. The users should be able to send information to the weather station from the website as well ( so an ADMIN user should be allowed to shut down the weather station from the website or whatever) Best regards, MadSeb

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  • .Net - Whats the difference between a Session Facade and Business Delegate?

    - by KP65
    What I understand so far: Business Delegate - In the presentation tier, as an ASP component, provides an interface for ASP views to access business components without exposing their API, therefore reducing coupling between the two. Session Facade - In the business tier, as a com+ component, encapsulates business objects, provides a course grain interface for views to access business components. Reduces coupling, hides complex business component interaction from views. So what is the actual difference? They seem pretty similar to me..

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  • anti-if campaign

    - by Andrew Siemer
    I recently ran against a very interesting site that expresses a very interesting idea - the anti-if campaign. You can see this here at www.antiifcampaign.com. I have to agree that complex nested IF statements are an absolute pain in the rear. I am currently on a project that up until very recently had some crazy nested IFs that scrolled to the right for quite a ways. We cured our issues in two ways - we used Windows Workflow Foundation to address routing (or workflow) concerns. And we are in the process of implementing all of our business rules utilizing ILOG Rules for .NET (recently purchased by IBM!!). This for the most part has cured our nested IF pains...but I find myself wondering how many people cure their pains in the manner that the good folks at the AntiIfCampaign suggest (see an example here) by creating numerous amounts of abstract classes to represent a given scenario that was originally covered by the nested IF. I wonder if another way to address the removal of this complexity might also be in using an IoC container such as StructureMap to move in and out of different bits of functionality. Either way... Question: Given a scenario where I have a nested complex IF or SWITCH statement that is used to evaluate a given type of thing (say evaluating an Enum) to determine how I want to handle the processing of that thing by enum type - what are some ways to do the same form of processing without using the IF or SWITCH hierarchical structure? public enum WidgetTypes { Type1, Type2, Type3, Type4 } ... WidgetTypes _myType = WidgetTypes.Type1; ... switch(_myType) { case WidgetTypes.Type1: //do something break; case WidgetTypes.Type2: //do something break; //etc... }

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  • Events in Classes (VB.NET)

    - by Otaku
    I find that I write a lot of code within my classes to keep properties in sync with each other. I've read about Events in Classes, but have not been able to wrap my head around how to make them work for what I'm looking for. I could use some advice here. For example, in this one I always want to keep myColor up to date with any change whatsoever in any or all of the Red, Green or Blue properties. Class myColors Private Property Red As Byte Private Property Green As Byte Private Property Blue As Byte Private Property myColor As Color Sub New() myColor = Color.FromArgb(0, 0, 0) End Sub Sub ChangeRed(ByVal r As Byte) Red = r myColor = Color.FromArgb(Red, Green, Blue) End Sub Sub ChangeBlue(ByVal b As Byte) Blue = b myColor = Color.FromArgb(Red, Green, Blue) End Sub End Class If one or more of those changes, I want myColor to be updated. Easy enough as above, but is there a way to work with events that would automatically do this so I don't have to put myColor = Color.FromArgb(Red, Green, Blue) in every sub routine?

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  • Performance improvement of client server system

    - by Tanuj
    I have a legacy client server system where the server maintains a record of some data stored in a sqlite database. The data is related to monitoring access patterns of files stored on the server. The client application is basically a remote viewer of the data. When the client is launched, it connects to the server and gets the data from the server to display in a grid view. The data gets updated in real time on the server and the view in the client automatically gets refreshed. There are two problems with the current implementation: When the database gets too big, it takes a lot of time to load the client. What are the best ways to deal with this. One option is to maintain a cache at the client side. How to best implement a cache ? How can the server maintain a diff so that it only sends the diff during the refresh cycle. There can be multiple clients and each client needs to display the latest data available on the server. The server is a windows service daemon. Both the client and the server are implemented in C#

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  • Implementing the procducer-consumer pattern with .NET 4.0

    - by bitbonk
    With alle the new paralell programming features in .NET 4.0, what would be a a simple and fast way to implement the producer-consumer pattern (where at least one thread is producing/enqueuing task items and another thread executes/dequeues these tasks). Can we benfit from all these new APIs? What is your preferred implementation of this pattern?

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  • How best can I extract a logical model from a physical DB model

    - by Dean
    We have made substantial changes to our physical DB, now as it is the ne dof the project I would like to abstract a logical model from this, to allow me to generate schemas for both Oracle and SQL Server. Can anyone guide me as to the best way to achieve this. I was hoping TOAD data modeller would help but I can't seem to see any options to do what I require?

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  • Looking for Programming Language that allows you to change true and false.

    - by Maushu
    For my curiosity sake I'm looking for a dynamic object oriented language that allows you to change true to false and vice versa. Something like this: true = false, false = true; This should also affect any conditional statements, therefore 42 == 42 should return False. Basically, with this premise, nothing in the language would be safe from the programmer. Is there any language like this?

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  • Regarding the ViewModel

    - by mizipzor
    Im struggling to understand the ViewModel part of the MVVM pattern. My current approach is to have a class, with no logic whatsoever (important), except that it implements INotifyPropertyChanged. The class is just a collection of properties, a struct if you like, describing an as small part of the data as possible. I consider this my Model. Most of the WPF code I write are settings dialogs that configure said Model. The code-behind of the dialog exposes a property which returns an instance of the Model. In the XAML code I bind to subproperties of that property, thereby binding directly to the Model's properties. Which works quite well since it implements the INotifyPropertyChanged. I consider this settings dialog the View. However, I havent really been able to figure out what in all this is the ViewModel. The articles Ive read suggests that the ViewModel should tie the View and the Model together, providing the logic the Model lacks but is still to complex to go directly into the View. Is this correct? Would, in my example, the code-behind of the settings dialog be considered the ViewModel? I just feel a bit lost and would like my peers to debunk some of my assumptions. Am I completely off track here?

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  • Managing libraries and imports in a programming language

    - by sub
    I've created an interpreter for a stupid programming language in C++ and the whole core structure is finished (Tokenizer, Parser, Interpreter including Symbol tables, core functions, etc.). Now I have a problem with creating and managing the function libraries for this interpreter (I'll explain what I mean with that later) So currently my core function handler is horrible: // Simplified version myLangResult SystemFunction( name, argc, argv ) { if ( name == "print" ) { if( argc < 1 ) { Error('blah'); } cout << argv[ 0 ]; } else if ( name == "input" ) { if( argc < 1 ) { Error('blah'); } string res; getline( cin, res ); SetVariable( argv[ 0 ], res ); } else if ( name == "exit ) { exit( 0 ); } And now think of each else if being 10 times more complicated and there being 25 more system functions. Unmaintainable, feels horrible, is horrible. So I thought: How to create some sort of libraries that contain all the functions and if they are imported initialize themselves and add their functions to the symbol table of the running interpreter. However this is the point where I don't really know how to go on. What I wanted to achieve is that there is e.g.: an (extern?) string library for my language, e.g.: string, and it is imported from within a program in that language, example: import string myString = "abcde" print string.at( myString, 2 ) # output: c My problems: How to separate the function libs from the core interpreter and load them? How to get all their functions into a list and add it to the symbol table when needed? What I was thinking to do: At the start of the interpreter, as all libraries are compiled with it, every single function calls something like RegisterFunction( string namespace, myLangResult (*functionPtr) ); which adds itself to a list. When import X is then called from within the language, the list built with RegisterFunction is then added to the symbol table. Disadvantages that spring to mind: All libraries are directly in the interpreter core, size grows and it will definitely slow it down.

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  • What's the proper way of importing option lists into an Android app?

    - by Scott
    I have been storing option lists for my Android app in a cloud table. For example, categories like "historical fiction","biography","science fiction", etc. I see the following pros and cons: Pro: I can make changes to the list without sending an app update to Google Play Not normalized - I can use the text in my other data tables instead of a reference ID Con: App needs to take time to download from the web each time (or at least check for changes) English only I believe the "proper" way to do this is the use the XML resource files. But I need to make sure the selection references correctly with my data. That is, my app needs to understand that "Poetry" and "Poesía" are the same thing. Is the correct thing to do: Forget about it since I'll never get to the point where I'm translating my app anyway Use a string-array and use the index (0...x) to know what the selection is Use a 2-dimensional string-array with a reference ID in the first column and the text in the second?

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