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  • Some basic UML questions

    - by devoured elysium
    What does it mean when you have something as the following picture? Each Customer has none, one or more Orders while each Order has only one Customer? And in relationship to the following one: What does the black diamond mean in this context? How is that black diamond called? Thanks

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  • Grasp Controller, Does it really need a UI to exist?

    - by dbones
    I have a Domain model which can be in multiple states, and if these states go out of a given range it the domain should automatically react. For example I have a Car which is made of multiple things which have measurements the Engine - Rev counter and Temperature the Fuel Tank - capacity Is is plaseable to have a CarStateController, which observses the engine and the tank, and if these states go out of range IE the engine temperature goes above range, turn the engine fan on?? There is no UI, (you could argue it would show a light on the dash board, but for this case it does not) is this a valid use of a GRASP controller pattern? if not what is this CarStateController Called? Or have I completely missed the point and this should be the State Pattern?

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  • Designing different Factory classes (and what to use as argument to the factories!)

    - by devoured elysium
    Let's say we have the following piece of code: public class Event { } public class SportEvent1 : Event { } public class SportEvent2 : Event { } public class MedicalEvent1 : Event { } public class MedicalEvent2 : Event { } public interface IEventFactory { bool AcceptsInputString(string inputString); Event CreateEvent(string inputString); } public class EventFactory { private List<IEventFactory> factories = new List<IEventFactory>(); public void AddFactory(IEventFactory factory) { factories.Add(factory); } //I don't see a point in defining a RemoveFactory() so I won't. public Event CreateEvent(string inputString) { try { //iterate through all factories. If one and only one of them accepts //the string, generate the event. Otherwise, throw an exception. return factories.Single(factory => factory.AcceptsInputString(inputString)).CreateEvent(inputString); } catch (InvalidOperationException e) { throw new InvalidOperationException("No valid factory found to generate this kind of Event!", e); } } } public class SportEvent1Factory : IEventFactory { public bool AcceptsInputString(string inputString) { return inputString.StartsWith("SportEvent1"); } public Event CreateEvent(string inputString) { return new SportEvent1(); } } public class MedicalEvent1Factory : IEventFactory { public bool AcceptsInputString(string inputString) { return inputString.StartsWith("MedicalEvent1"); } public Event CreateEvent(string inputString) { return new MedicalEvent1(); } } And here is the code that runs it: static void Main(string[] args) { EventFactory medicalEventFactory = new EventFactory(); medicalEventFactory.AddFactory(new MedicalEvent1Factory()); medicalEventFactory.AddFactory(new MedicalEvent2Factory()); EventFactory sportsEventFactory = new EventFactory(); sportsEventFactory.AddFactory(new SportEvent1Factory()); sportsEventFactory.AddFactory(new SportEvent2Factory()); } I have a couple of questions: Instead of having to add factories here in the main method of my application, should I try to redesign my EventFactory class so it is an abstract factory? It'd be better if I had a way of not having to manually add EventFactories every time I want to use them. So I could just instantiate MedicalFactory and SportsFactory. Should I make a Factory of factories? Maybe that'd be over-engineering? As you have probably noticed, I am using a inputString string as argument to feed the factories. I have an application that lets the user create his own events but also to load/save them from text files. Later, I might want to add other kinds of files, XML, sql connections, whatever. The only way I can think of that would allow me to make this work is having an internal format (I choose a string, as it's easy to understand). How would you make this? I assume this is a recurrent situation, probably most of you know of any other more intelligent approach to this. I am then only looping in the EventFactory for all the factories in its list to check if any of them accepts the input string. If one does, then it asks it to generate the Event. If you find there is something wrong or awkward with the method I'm using to make this happen, I'd be happy to hear about different implementations. Thanks! PS: Although I don't show it in here, all the different kind of events have different properties, so I have to generate them with different arguments (SportEvent1 might have SportName and Duration properties, that have to be put in the inputString as argument).

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  • overflow-x AND Middle Mouse Button Moving

    - by Rad The Mad
    My Page is 980px in Width, but I have a few design elements (which belong with the background). I positioned them with position: absolute;. This creates a horizontal scrollbar for those who have a =< 1024 resolution. I disabled that scrollbar with overflow-x:hidden on (and for IE7 and etc). However, when I hold my middle mouse button,(i think this applies to laptop touchpads as well) it let's me move around to the right, is it possible to fix this with anything? (javascript, css)? Tested this issues in Chrome, IE, Firefox.

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  • Doctrine: Relating a model to itself using a link table, like "This event is related to to the following other events"

    - by mattalexx
    So in English, the relationship would sound like "This event is related to to the following other events". My first instinct is to create an EventEvent model, with a first_event_id field and a second_event_id field. Then I would define the following two relationships in the Event model: $this->hasMany('Event as FirstRelatedEvents', array('local' => 'first_event_id', 'foreign' => 'second_event_id', 'refClass' => 'EventEvent')); $this->hasMany('Event as SecondRelatedEvents', array('local' => 'second_event_id', 'foreign' => 'first_event_id', 'refClass' => 'EventEvent')); But I would rather not have to use two relationships on the Event model. Is there a better way to do this?

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  • How to apply Abstract Factory Pattern ???

    - by Amit
    I am new to Design Pattern and I have a scenario here... and not sure as how to implement the pattern ... We have multiple vendors Philips, Onida... Each vendor (philips, onida...) may have different type of product i.e. Plasma or Normal TV I want specific product of each vendor using Abstract Factory Pattern... Thanks in advance for any help... My implementation so far... public enum TvType { Samsung = 0,LG = 1,Philips = 2, Sony = 3 } public enum Product { Plasma = 0,NormalTV = 1 } concrete class of each vendor.... that returns each product and also the interface that contains ProductInfo i.e. if Vendor is ... then it must have this product....

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  • How to implement "drag n drop" user interface on website?

    - by Nikkeloodeni
    Hello, I was wondering what would be the best way to implement some kind of "drag n drop" user interface? What i mean is that there would be one main page and every link click (eg. other sections like about, gallery, contact form) would open a new drag n drop element on top of that main page. Something like windows desktop where you can move your application windows around the screen. Would it be best to call different functions with AJAX when a link is clicked? Like "gallery" link would call gallery-function and retrieve dynamically generated contents of that "window" with AJAX call and then just load that stuff on some div? Or would some other type of approach suit better for this? I hope I was able to explain this clearly enough. I'm looking for a proper "design pattern" to implement this. All suggestions are wellcome! :)

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  • Inheritence and usage of dynamic_cast

    - by Mewzer
    Hello, Suppose I have 3 classes as follows (as this is an example, it will not compile!): class Base { public: Base(){} virtual ~Base(){} virtual void DoSomething() = 0; virtual void DoSomethingElse() = 0; }; class Derived1 { public: Derived1(){} virtual ~Derived1(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD1DoSomething{ ... } }; class Derived2 { public: Derived2(){} virtual ~Derived2(){} virtual void DoSomething(){ ... } virtual void DoSomethingElse(){ ... } virtual void SpecialD2DoSomething{ ... } }; I want to create an instance of Derived1 or Derived2 depending on some setting that is not available until run-time. As I cannot determine the derived type until run-time, then do you think the following is bad practice?... class X { public: .... void GetConfigurationValue() { .... // Get configuration setting, I need a "Derived1" b = new Derived1(); // Now I want to call the special DoSomething for Derived1 (dynamic_cast<Derived1*>(b))->SpecialD1DoSomething(); } private: Base* b; }; I have generally read that usage of dynamic_cast is bad, but as I said, I don't know which type to create until run-time. Please help!

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  • When should I use a struct instead of a class?

    - by Esteban Araya
    MSDN says that you should use structs when you need lightweight objects. Are there any other scenarios when a struct is preferable over a class? Edit: Some people have forgotten that: 1. structs can have methods! 2. structs have no inheritance capabilites. Another Edit: I understand the technical differences, I just don't have a good feel for WHEN to use a struct.

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  • PHP Access property of a class from within a class instantiated in the original class.

    - by Iain
    I'm not certain how to explain this with the correct terms so maybe an example is the best method... $master = new MasterClass(); $master->doStuff(); class MasterClass { var $a; var $b; var $c; var $eventProccer; function MasterClass() { $this->a = 1; $this->eventProccer = new EventProcess(); } function printCurrent() { echo '<br>'.$this->a.'<br>'; } function doStuff() { $this->printCurrent(); $this->eventProccer->DoSomething(); $this->printCurrent(); } } class EventProcess { function EventProcess() {} function DoSomething() { // trying to access and change the parent class' a,b,c properties } } My problem is i'm not certain how to access the properties of the MasterClass from within the EventProcess-DoSomething() method? I would need to access, perform operations on and update the properties. The a,b,c properties will be quite large arrays and the DoSomething() method would be called many times during the execuction of the script. Any help or pointers would be much appreciated :)

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  • Passing arguments between classes - use public properties or pass a properties class as argument?

    - by devoured elysium
    So let's assume I have a class named ABC that will have a list of Point objects. I need to make some drawing logic with them. Each one of those Point objects will have a Draw() method that will be called by the ABC class. The Draw() method code will need info from ABC class. I can only see two ways to make them have this info: Having Abc class make public some properties that would allow draw() to make its decisions. Having Abc class pass to draw() a class full of properties. The properties in both cases would be the same, my question is what is preferred in this case. Maybe the second approach is more flexible? Maybe not? I don't see here a clear winner, but that sure has more to do with my inexperience than any other thing. If there are other good approaches, feel free to share them. Here are both cases: class Abc1 { public property a; public property b; public property c; ... public property z; public void method1(); ... public void methodn(); } and here is approach 2: class Abc2 { //here we make take down all properties public void method1(); ... public void methodn(); } class Abc2MethodArgs { //and we put them here. this class will be passed as argument to //Point's draw() method! public property a; public property b; public property c; ... public property z; } Also, if there are any "formal" names for these two approaches, I'd like to know them so I can better choose the tags/thread name, so it's more useful for searching purposes. That or feel free to edit them.

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  • How to program a connection pool?

    - by the_drow
    Is there a known algorithm for implementing a connection pool? If not what are the known algorithms and what are their trade-offs? What design patterns are common when designing and programming a connection pool? Are there any code examples implement a connection pool using boost.asio? Is it a good idea to use a connection pool for presisting connections (not http)? How is threading related to connection pooling? When do you need a new thread?

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  • Persistance Queue Implementation

    - by Winter
    I was reading an article on Batch Processing in java over at JDJ http://java.sys-con.com/node/415321 . The article mentioned using a persistence queue as a Batch Updater instead of immediately sending an individual insert or update to the database. The author doesn't give a concrete example of this concept so I googled Persistence Queue but that didn't come up with much. Does anyone know of a good example of this?

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  • What would be a good starting point for development of a 3D application for representation of struct

    - by Lela Dax
    I was thinking QT on OpenGL. Multiplatform ability and being able to be closed (at no cost) at a later point would be important points. But I'm very interested in finding a way that is not only viable but also has the least amount of reinvention of the wheel. e.g. "Why not Ogre? A ready powerful 3D engine without reinventing that part". But I'm very uncertain in what is the optimal collection of tools for that job.

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  • Guidelines for solution source code organisation(OO/DDD)

    - by fearofawhackplanet
    I'm starting on my first business project (.NET) and am trying to follow DDD principles. Are there any guidelines or common patterns for orgaining source code and namespaces? For example, do your domain objects go in a namespace MyProject.Domain or whatever? Would you separate the concrete implementations and the interfaces? In different namespaces? Different folders? Different solutions? I know a lot of this is subjective and dependent on project size, but a few pointers or suggestions to get started on a relatively small but extensible n-tier project would be useful.

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  • Patterns and Libraries for working with raw UI values.

    - by ProfK
    By raw values, I mean the application level values provided by UI controls, such as the Text property on a TextBox. Too often I find myself writing code to check and parse such values before they get used as a business level value, e.g. PaymentTermsNumDays. I've mitigated a lot of the spade work with rough and ready extension methods like String.ToNullableInt, but we all know that just isn't right. We can't put the whole world on String's shoulders. Do I look at tasking my UI to provide business values, using a ruleset pushed out from the server app, or open my business objects up a bit to do the required sanitising etc. as they required? Neither of these approaches sits quite right with me; the first seems closer to ideal, but quite a bit of work, while the latter doesn't show much respect to the business objects' single responsibility. The responsibilities of the UI are a closer match. Between these extremes, I could also just implement another DTO layer, an IoC container with sanitising and parsing services, derive enhanced UI controls, or stick to copy and paste inline drudgery.

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  • Avoiding sub-type selection in view code

    - by John Donoghue
    Hi, I have some code where the model contains some classes like (vb.net pseudocode, but could be any OO language): Enum AttributeType Boolean Date String End Enum MustInherit Class Attibute Must Override Function Type As AttributeType End Class Class BooleanAttribute: Attribute Function Type As AttributeType Return AttributeType.Boolean End Function End Class And the view contains some code like: Select Case AttributeType Case Boolean //Display checkbox control Case Date //Display date picker control Case String //Display textbox control End Select I don't really like the code in the view, for the hopefully obvious reasons (what happens when I get a new attribute type etc). My question is, how should I replace it? I could easily add a method to the concrete classes, but that pollutes the model with UI stuff so that's a horrible idea. I could move the select into a factory, but that seems to be just hiding the problem. Can anybody advise a better approach?

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  • Separating code logic from the actual data structures. Best practices?

    - by Patrick
    I have an application that loads lots of data into memory (this is because it needs to perform some mathematical simulation on big data sets). This data comes from several database tables, that all refer to each other. The consistency rules on the data are rather complex, and looking up all the relevant data requires quite some hashes and other additional data structures on the data. Problem is that this data may also be changed interactively by the user in a dialog. When the user presses the OK button, I want to perform all the checks to see that he didn't introduce inconsistencies in the data. In practice all the data needs to be checked at once, so I cannot update my data set incrementally and perform the checks one by one. However, all the checking code work on the actual data set loaded in memory, and use the hashing and other data structures. This means I have to do the following: Take the user's changes from the dialog Apply them to the big data set Perform the checks on the big data set Undo all the changes if the checks fail I don't like this solution since other threads are also continuously using the data set, and I don't want to halt them while performing the checks. Also, the undo means that the old situation needs to be put aside, which is also not possible. An alternative is to separate the checking code from the data set (and let it work on explicitly given data, e.g. coming from the dialog) but this means that the checking code cannot use hashing and other additional data structures, because they only work on the big data set, making the checks much slower. What is a good practice to check user's changes on complex data before applying them to the 'application's' data set?

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  • Enums and inheritance

    - by devoured elysium
    I will use (again) the following class hierarchy: Event and all the following classes inherit from Event: SportEventType1 SportEventType2 SportEventType3 SportEventType4 I have originally designed the Event class like this: public abstract class Event { public abstract EventType EventType { get; } public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } with EventType being defined as: public enum EventType { Sport1, Sport2, Sport3, Sport4 } The original idea would be that each SportEventTypeX class would set its correct EventType. Now that I think of it, I think this approach is totally incorrect for two reasons: If I want to later add a new SportEventType class I will have to modify the enum If I later decide to remove one SportEventType that I feel I won't use I'm also in big trouble with the enum. I have a class variable in the Event class that makes, afterall, assumptions about the kind of classes that will inherit from it, which kinda defeats the purpose of inheritance. How would you solve this kind of situation? Define in the Event class an abstract "Description" property, having each child class implement it? Having an Attribute(Annotation in Java!) set its Description variable instead? What would be the pros/cons of having a class variable instead of attribute/annotation in this case? Is there any other more elegant solution out there? Thanks

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  • How does Undo work?

    - by dontWatchMyProfile
    How does undo work? Does it copy all the managed objects every time any of the values change? Or does it only copy the actual changes together with an information which objects were affected? Is that heavy or lightweight?

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