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  • Should universities put more emphasis on teaching their students about design patterns?

    - by gablin
    While I've heard about design patterns being mentioned in a few courses at uni, I know of only a single course which actually teaches design patterns. In almost all other areas (algorithms, parallelism, architecture, dynamic languages, paradigms, etc), there are several, often a basic course and an advanced course. Should universities put more emphasis about teaching their students about design patterns and provide more courses in design patters? Are lack of knowledge about design patterns common in just-graduated junior developers?

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  • Which design pattern to use when using ORM?

    - by RPK
    I am writing a small ASP.NET Web Forms application. In my solution explorer, I added various class library projects to define layers, viz: Model Repository Presentation WebUI Someone suggested me that this layered approach is not of much sense if I am using ORM tool like PetaPoco, which itself takes care of separation of data access layer. I want to use PetaPoco micro-ORM and want to know which design pattern is suitable with ORM tools. Do I still need several class library projects to separate the concerns?

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  • DDD: Service or Repository

    - by tikhop
    I am developing an app in DDD manner. And I have a little problem with it. I have a Fare (airline fare) and FareRepository objects. And at some point I should load additional fare information and set this information to existing Fare. I guess that I need to create an Application Service (FareAdditionalInformationService) that will deal with obtaining data from the server and than update existing Fare. However, some people said me that it is necessary to use FareRepository for this problem. I don't know wich place is better for my problem Service or Repository.

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  • Good Video Game User Interface Design Books/Websites?

    - by Tucker Morgan
    I having been programming games for some time, but while my teachers say that my code is good and advanced, my friends say that the interface is hard to understand and not the easiest to navigate. I want to learn how to design good user interfaces so that I can program better games, and people will have a easier time getting around. Does anyone know of any good books or websites about designing video game interfaces?

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  • Manager/Container class vs static class methods

    - by Ben
    Suppose I a have a Widget class that is part of a framework used independently by many applications. I create Widget instances in many situations and their lifetimes vary. In addition to Widget's instance specified methods, I would like to be able to perform the follow class wide operations: Find a single Widget instance based on a unique id Iterate over the list of all Widgets Remove a widget from the set of all widgets In order support these operations, I have been considering two approaches: Container class - Create some container or manager class, WidgetContainer, which holds a list of all Widget instances, support iteration and provides methods for Widget addition, removal and lookup. For example in C#: public class WidgetContainer : IEnumerable<Widget { public void AddWidget(Widget); public Widget GetWidget(WidgetId id); public void RemoveWidget(WidgetId id); } Static class methods - Add static class methods to Widget. For example: public class Widget { public Widget(WidgetId id); public static Widget GetWidget(WidgetId id); public static void RemoveWidget(WidgetId id); public static IEnumerable<Widget AllWidgets(); } Using a container class has the added problem of how to access the container class. Make it a singleton?..yuck! Create some World object that provides access to all such container classes? I have seen many frameworks that use the container class approach, so what is the general consensus?

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  • DDD and filtering

    - by tikhop
    I am developing an app in ddd maner. So I have a complex domain model. Suppose I have a Fare object and Airline. Each Airline should contain several or much more Fares. My UI should represent Model (only small part of complex model) as a list of Airline, when the user select the Airline, I must show the list of Fares. User can filtering the Fares (by travel time, cost, etc.). What is the appropriate place for filtering Fares and Airlines? I am assuming that I should do it in ViewModel. Like: My domain model has wrapped with Service Layer - UI works with ViewModel - ViewModel obtain data from Service Layer filtering it and create DTO objects for UI. Or I'm wrong?

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  • Why should ViewModel route actions to Controller when using the MVCVM pattern?

    - by Lea Hayes
    When reading examples across the Internet (including the MSDN reference) I have found that code examples are all doing the following type of thing: public class FooViewModel : BaseViewModel { public FooViewModel(FooController controller) { Controller = controller; } protected FooController Controller { get; private set; } public void PerformSuperAction() { // This just routes action to controller... Controller.SuperAction(); } ... } and then for the view: public class FooView : BaseView { ... private void OnSuperButtonClicked() { ViewModel.PerformSuperAction(); } } Why do we not just do the following? public class FooView : BaseView { ... private void OnSuperButtonClicked() { ViewModel.Controller.SuperAction(); // or, even just use a shortcut property: Controller.SuperAction(); } }

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  • Is loose coupling w/o use cases an anti-pattern?

    - by dsimcha
    Loose coupling is, to some developers, the holy grail of well-engineered software. It's certainly a good thing when it makes code more flexible in the face of changes that are likely to occur in the foreseeable future, or avoids code duplication. On the other hand, efforts to loosely couple components increase the amount of indirection in a program, thus increasing its complexity, often making it more difficult to understand and often making it less efficient. Do you consider a focus on loose coupling without any use cases for the loose coupling (such as avoiding code duplication or planning for changes that are likely to occur in the foreseeable future) to be an anti-pattern? Can loose coupling fall under the umbrella of YAGNI?

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  • Rails: Law of Demeter Confusion

    - by user2158382
    I am reading a book called Rails AntiPatterns and they talk about using delegation to to avoid breaking the Law of Demeter. Here is their prime example: They believe that calling something like this in the controller is bad (and I agree) @street = @invoice.customer.address.street Their proposed solution is to do the following: class Customer has_one :address belongs_to :invoice def street address.street end end class Invoice has_one :customer def customer_street customer.street end end @street = @invoice.customer_street They are stating that since you only use one dot, you are not breaking the Law of Demeter here. I think this is incorrect, because you are still going through customer to go through address to get the invoice's street. I primarily got this idea from a blog post I read: http://www.dan-manges.com/blog/37 In the blog post the prime example is class Wallet attr_accessor :cash end class Customer has_one :wallet # attribute delegation def cash @wallet.cash end end class Paperboy def collect_money(customer, due_amount) if customer.cash < due_ammount raise InsufficientFundsError else customer.cash -= due_amount @collected_amount += due_amount end end end The blog post states that although there is only one dot customer.cash instead of customer.wallet.cash, this code still violates the Law of Demeter. Now in the Paperboy collect_money method, we don't have two dots, we just have one in "customer.cash". Has this delegation solved our problem? Not at all. If we look at the behavior, a paperboy is still reaching directly into a customer's wallet to get cash out. EDIT I completely understand and agree that this is still a violation and I need to create a method in Wallet called withdraw that handles the payment for me and that I should call that method inside the Customer class. What I don't get is that according to this process, my first example still violates the Law of Demeter because Invoice is still reaching directly into Customer to get the street. Can somebody help me clear the confusion. I have been searching for the past 2 days trying to let this topic sink in, but it is still confusing.

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  • Defining formula through user interface in user form

    - by BriskLabs Pakistan
    I am a student and developing a simple assignment - windows form application in visual studio 2010. The application is suppose to construct formulas as per user requirement. The process: It has to pick data from columns of Microsoft Access database and the user should be able to pick the data by column name like we do in a drop down menu. and create reusable formulas in it ( configure it once and can change it again). followings are column titles from database that can be picked for example. e.g Col -1 : Marks in Maths Col -2 : Total Marks in Maths Col -3 : Marks in science Col -4 : Total marks in science Finally we should be able to construct any formula in the UI like (Col 1 + Col 3 ) / ( col 2 + col 4) = Formula 1 once this is formula is set saved and a name is assigned to it by user. he/she can use the formula and results shall appear in a window below. i.e He would be able to calculate his desired figures (formula) by only manipulating underlying data on the UI layer....choose the data for a period and apply the formula and get the answer Problem: It looks like I have to create an app where rules are set through UI....... this means no stored procedures are required in SQL.... please suggest the right approach.

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  • Do you leverage the benefits of the open-closed principle?

    - by Kaleb Pederson
    The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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  • How to model an address type in DDD?

    - by Songo
    I have an User entity that has a Set of Address where Address is a value object: class User{ ... private Set<Address> addresses; ... public setAddresses(Set<Address> addresses){ //set all addresses as a batch } ... } A User can have a home address and a work address, so I should have something that acts as a look up in the database: tbl_address_type ------------------------------------------------ | address_type_id | address_type | ------------------------------------------------ | 1 | work | ------------------------------------------------ | 2 | home | ------------------------------------------------ and correspondingly tbl_address ------------------------------------------------------------------------------------- | address_id | address_description |address_type_id| user_id | ------------------------------------------------------------------------------------- | 1 | 123 main street | 1 | 100 | ------------------------------------------------------------------------------------- | 2 | 456 another street | 1 | 100 | ------------------------------------------------------------------------------------- | 3 | 789 long street | 2 | 200 | ------------------------------------------------------------------------------------- | 4 | 023 short street | 2 | 200 | ------------------------------------------------------------------------------------- Should the address type be modeled as an Entity or Value type? and Why? Is it OK for the Address Value object to hold a reference to the Entity AdressType (in case it was modeled as an entity)? Is this something feasible using Hibernate/NHibernate? If a user can change his home address, should I expose a User.updateHomeAddress(Address homeAddress) function on the User entity itself? How can I enforce that the client passes a Home address and not a work address in this case? (a sample implementation is most welcomed) If I want to get the User's home address via User.getHomeAddress() function, must I load the whole addresses array then loop it and check each for its type till I found the correct type then return it? Is there a more efficient way than this?

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  • Avoiding bloated Domain Objects

    - by djcredo
    We're trying to move data from our bloated Service layer into our Domain layer using a DDD approach. We currently have a lot of business logic in our services, which is spread out all over the place and doesn't benefit from inheritance. We have a central Domain class which is the focus of most of our work - a Trade. The Trade object will know how to price itself, how to estimate risk, validate itself, etc. We can then replace conditionals with polymorphism. Eg: SimpleTrade will price itself one way, but ComplexTrade will price itself another. However, we are worried that this will bloat the Trade class(s). It really should be in charge of its own processing but the class size is going to increase exponentially as more features are added. So we have choices: Put processing logic in Trade class. Processing logic is now polymorphic based on the type of the trade, but Trade class is now has multiple responsibilites (pricing, risk, etc) and is large Put processing logic into other class such as TradePricingService. No longer polymorphic with the Trade inheritance tree, but classes are smaller and easier to test. What would be the suggested approach?

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  • Design pattern for isomorphic trees

    - by Peregring-lk
    I want to create a data structure to work with isomorphic tree. I don't search for a "algorithms" or methods to check if two or more trees are isomorphic each other. Just to create various trees with the same structure. Example: 2 - - - - - - - 'a' - - - - - - - 3.5 / \ / \ / \ 3 3 'f' 'y' 1.0 3.1 / \ / \ / \ 4 7 'e' 'f' 2.3 7.7 The first "layer" or tree is the "natural tree" (a tree with natural numbers), the second layer is the "character tree" and the third one is the "float tree". The data structure has a method or iterator to traverse the tree and to make diferent operations with its values. These operations could change the value of nodes, but never its structure (first I create the structure and then I configure the tree with its diferent layers). In case of that I add a new node, this would be applied to each layer. Which known design pattern fits with this description or is related with it?

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  • Email Content creation | Proper design

    - by Umesh Awasthi
    Working on an E commerce application where we need to send so many email to customer like Registration email Forget Password Order placed There are many other emails that can be sent, I already have emailService in place which is responsible for sending email and It needs an Email object, Everything is working find, but I am struck at one point and not sure how best this can be done. We need to create content so as it can be passed to emailService and not sure how to design this. For example, in Customer registration, I have a customerFacade which is working between Controller and ServiceLayer, I just want to delegate this Email Content creation work away from Facade layer and to make it more flexible. Currently I am creating Registration email content inside customerFacade and some how I am not liking this way, since that means for each email, I need to create content in respective Facade. What is best way to go or current approach is fine enough?

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  • How to design application for scaling the application?

    - by Muhammad
    I have one application which handles hardware events connected on the same computer's PCIe slots. The maximum number of PCIe slots on motherboard are two. I have utilized both slots. Now for scaling the application I need either more PCIe slots in same computer or I use another computer. So consider I am using another computer with same application and hardware connected on the PCIe Slots. Now my problem is that I want to design application over it which can access both computers hardware devices and does the process on it. The processed data should be send back to the respective PC's hardware. Please refer the attached diagram for expansion.

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  • Object-Oriented Operating System

    - by nmagerko
    As I thought about writing an operating system, I came across a point that I really couldn't figure out on my own: Can an operating system truly be written in an Object-Oriented Programming (OOP) Language? Being that these types of languages do not allow for direct accessing of memory, wouldn't this make it impossible for a developer to write an entire operating system using only an OOP Language? Take, for example, the Android Operating System that runs many phones and some tablets in use around the world. I believe that this operating system uses only Java, an Object-Oriented language. In Java, I have been unsuccessful in trying to point at and manipulate a specific memory address that the run-time environment (JRE) has not assigned to my program implicitly. In C, C++, and other non-OOP languages, I can do this in a few lines. So this makes me question whether or not an operating system can be written in an OOP, especially Java. Any counterexamples or other information is appreciated.

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  • What is Object Oriented Programming ill-suited for?

    - by Richard JP Le Guen
    In Martin Fowler's book Refactoring, Fowler speaks of how when developers learn something new, they don't consider when it's inappropriate for the job: Ten years ago it was like that with objects. If someone asked me when not to use objects, it was hard to answer. [...] It was just that I didn't know what those limitations were, although I knew what the benefits were. Reading this, it occurred to me I don't know what the limitations or potential disadvantages of Object-Oriented Programming are. What are the limitations of Object Oriented Programming? When should one look at a project and think "OOP is not best suited for this"?

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  • Design: How to model / where to store relational data between classes

    - by Walker
    I'm trying to figure out the best design here, and I can see multiple approaches, but none that seems "right." There are three relevant classes here: Base, TradingPost, and Resource. Each Base has a TradingPost which can offer various Resources depending on the Base's tech level. Where is the right place to store the minimum tech level a base must possess to offer any given resource? A database seems like overkill. Putting it in each subclass of Resource seems wrong--that's not an intrinsic property of the Resource. Do I have a mediating class, and if so, how does it work? It's important that I not be duplicating code; that I have one place where I set the required tech level for a given item. Essentially, where does this data belong? P.S. Feel free to change the title; I struggled to come up with one that fits.

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  • How to design console application with good seperation of UI from Logic

    - by JavaSa
    Is it considered an overkill for console application to be design like MVC , MVP or N tier architecture? If not which is more common and if you can link me to simple example of it. I want to implement a tic tac toe game in console application. I have a solution which hold two projects: TicTacToeBusinessLogic (Class library project) and TicTacToeConsoleApplication (Console application project) to represent the view logic. In the TicTacToeConsoleApplication I've Program.cs class which holds the main entry point (public static void Main). Now I face a problem. I want the game to handle its own game flow so I can: Create new GameManager class (from BL) but this causing the view to directly know the BL part. So I'm a little confused how to write it in an acceptable way. Should I use delegates? Please show me a simple example.

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  • My proposed design is usually worse than my colleague's - how do I get better?

    - by user151193
    I have been programming for couple of years and am generally good when it comes to fixing problems and creating small-to-medium scripts, however, I'm generally not good at designing large scale programs in object oriented way. Few questions Recently, a colleague who has same number of years of experience as me and I were working on a problem. I was working on a problem longer than him, however, he came up with a better solution and in the end we're going to use his design. This really affected me. I admit his design is better, but I wanted to come up with a design as good as his. I'm even contemplating quitting the job. Not sure why but suddenly I feel under some pressure e.g. what would juniors think of me and etc? Is it normal? Or I'm thinking a little too much into this? My job involves programming in Python. I try to read source code but how do you think I can improve me design skills? Are there any good books or software that I should study? Please enlighten me. I will really appreciate your help.

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  • How to design a scriptable communication emulator?

    - by Hawk
    Requirement: We need a tool that simulates a hardware device that communicates via RS232 or TCP/IP to allow us to test our main application which will communicate with the device. Current flow: User loads script Parse script into commands User runs script Execute commands Script / commands (simplified for discussion): Connect RS232 = RS232ConnectCommand Connect TCP/IP = TcpIpConnectCommand Send data = SendCommand Receive data = ReceiveCommand Disconnect = DisconnectCommand All commands implement the ICommand interface. The command runner simply executes a sequence of ICommand implementations sequentially thus ICommand must have an Execute exposure, pseudo code: void Execute(ICommunicator context) The Execute method takes a context argument which allows the command implementations to execute what they need to do. For instance SendCommand will call context.Send, etc. The problem RS232ConnectCommand and TcpIpConnectCommand needs to instantiate the context to be used by subsequent commands. How do you handle this elegantly? Solution 1: Change ICommand Execute method to: ICommunicator Execute(ICommunicator context) While it will work it seems like a code smell. All commands now need to return the context which for all commands except the connection ones will be the same context that is passed in. Solution 2: Create an ICommunicatorWrapper (ICommunicationBroker?) which follows the decorator pattern and decorates ICommunicator. It introduces a new exposure: void SetCommunicator(ICommunicator communicator) And ICommand is changed to use the wrapper: void Execute(ICommunicationWrapper context) Seems like a cleaner solution. Question Is this a good design? Am I on the right track?

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  • Best Design Pattern for Coupling User Interface Components and Data Structures

    - by szahn
    I have a windows desktop application with a tree view. Due to lack of a sound data-binding solution for a tree view, I've implemented my own layer of abstraction on it to bind nodes to my own data structure. The requirements are as follows: Populate a tree view with nodes that resemble fields in a data structure. When a node is clicked, display the appropriate control to modify the value of that property in the instance of the data structure. The tree view is populated with instances of custom TreeNode classes that inherit from TreeNode. The responsibility of each custom TreeNode class is to (1) format the node text to represent the name and value of the associated field in my data structure, (2) return the control used to modify the property value, (3) get the value of the field in the control (3) set the field's value from the control. My custom TreeNode implementation has a property called "Control" which retrieves the proper custom control in the form of the base control. The control instance is stored in the custom node and instantiated upon first retrieval. So each, custom node has an associated custom control which extends a base abstract control class. Example TreeNode implementation: //The Tree Node Base Class public abstract class TreeViewNodeBase : TreeNode { public abstract CustomControlBase Control { get; } public TreeViewNodeBase(ExtractionField field) { UpdateControl(field); } public virtual void UpdateControl(ExtractionField field) { Control.UpdateControl(field); UpdateCaption(FormatValueForCaption()); } public virtual void SaveChanges(ExtractionField field) { Control.SaveChanges(field); UpdateCaption(FormatValueForCaption()); } public virtual string FormatValueForCaption() { return Control.FormatValueForCaption(); } public virtual void UpdateCaption(string newValue) { this.Text = Caption; this.LongText = newValue; } } //The tree node implementation class public class ExtractionTypeNode : TreeViewNodeBase { private CustomDropDownControl control; public override CustomControlBase Control { get { if (control == null) { control = new CustomDropDownControl(); control.label1.Text = Caption; control.comboBox1.Items.Clear(); control.comboBox1.Items.AddRange( Enum.GetNames( typeof(ExtractionField.ExtractionType))); } return control; } } public ExtractionTypeNode(ExtractionField field) : base(field) { } } //The custom control base class public abstract class CustomControlBase : UserControl { public abstract void UpdateControl(ExtractionField field); public abstract void SaveChanges(ExtractionField field); public abstract string FormatValueForCaption(); } //The custom control generic implementation (view) public partial class CustomDropDownControl : CustomControlBase { public CustomDropDownControl() { InitializeComponent(); } public override void UpdateControl(ExtractionField field) { //Nothing to do here } public override void SaveChanges(ExtractionField field) { //Nothing to do here } public override string FormatValueForCaption() { //Nothing to do here return string.Empty; } } //The custom control specific implementation public class FieldExtractionTypeControl : CustomDropDownControl { public override void UpdateControl(ExtractionField field) { comboBox1.SelectedIndex = comboBox1.FindStringExact(field.Extraction.ToString()); } public override void SaveChanges(ExtractionField field) { field.Extraction = (ExtractionField.ExtractionType) Enum.Parse(typeof(ExtractionField.ExtractionType), comboBox1.SelectedItem.ToString()); } public override string FormatValueForCaption() { return string.Empty; } The problem is that I have "generic" controls which inherit from CustomControlBase. These are just "views" with no logic. Then I have specific controls that inherit from the generic controls. I don't have any functions or business logic in the generic controls because the specific controls should govern how data is associated with the data structure. What is the best design pattern for this?

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  • Object Oriented Database - why most of the companies do not use them

    - by GigaPr
    Hi, I am pretty new to programming(just finished University). I have been thought in the last 4 years about Object Oriented development and the numerous advantages of this approach. My question is Isn't it easier to use a pure Object Oriented database in development applications? Why Object Oriented database are not as much diffuse as relational? From my point of view makes sense to use OO database, the latter will avoid the numerous construction necessary for the mapping of complex objects on the tables.

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  • How to avoid having very large objects with Domain Driven Design

    - by Pablojim
    We are following Domain Driven Design for the implementation of a large website. However by putting the behaviour on the domain objects we are ending up with some very large classes. For example on our WebsiteUser object, we have many many methods - e.g. dealing with passwords, order history, refunds, customer segmentation. All of these methods are directly related to the user. Many of these methods delegate internally to other child object but this still results in some very large classes. I'm keen to avoid exposing lots of child objects e.g. user.getOrderHistory().getLatestOrder(). What other strategies can be used to avoid this problems?

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