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• Does complex JOINs causes high coupling and maintenance problems ?

  - by ashkan.kh.nazary

  Our project has ~40 tables with complex relations.A colleague believes in using long join queries which enforces me to learn about tables outside of my module but I think I should not concern about tables not directly related to my module and use data access functions (written by those responsible for other modules) when I need data from them. Let me clarify: I am responsible for the ContactVendor module which enables the customers to contact the vendor and start a conversation about some specific product. Products module has it's own complex tables and relations with functions that encapsulate details (for example i18n, activation, product availability etc ...). Now I need to show the product title of some product related to some conversation between the vendor and customers. I may either write a long query that retrieves the product info along with conversation stuff in one shot (which enforces me to learn about Product tables) OR I may pass the relevant product_id to the get_product_info(int) function. First approach is obviously demanding and introduces many bad practices and things I normally consider fault in programming. The problem with the second approach seems to be the countless mini queries these access functions cause and performance loss is a concern when a loop tries to fetch product titles for 100 products using functions that each perform a separate query. So I'm stuck between "don't code to the implementation, code to interface" and performance. What is the right way of doing things ? UPDATE: I'm specially concerned about possible future modifications to those tables outside of my module. What if the Products module decided to change the way they are doing things? or for some reason modify the schema? It means some other modules would break or malfunction until the change is integrated to them. The usual ripple effect problem.

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• Scenario to illustrate how unit testing leads to better design

  - by Cocowalla

  For an internal training session, I'm trying to come up with a simple scenario that illustrates how unit testing leads to better design, by forcing you to think about things like coupling before you start coding. The idea is that I get the participants to code something first, without considering unit testing, then we do it again, but considering unit testing. Hopefully the code produced second time round should be more decoupled and maintainable. I'm struggling to come up with a scenario that can be coded quickly, yet can still demonstrate how unit testing can lead to better overall design.

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• Have I mistakenly assumed that my routines are loosely coupled?

  - by Tarun

  My Selenium test structures goes as - Data Object class - public class RegistrationData { String firstName = "test first name"; String lastName = "test last name"; // Getter Setter Here } Page Object class which carries out operations on a Web Page - public class RegistrationPage { private RegistrationData regData; public void setRegistrationData(RegistrationData regData) { this.regData = regData(); public NewAccountPage fillRegForm() { enterFirstName("FirstNameTextBoxLocator", regData.getFirstName); enterLastName("LastNameTextBoxLocator", regData.getLastName); // Some more fields are filled here return NewAccountPage(); } } And test class uses them as - public class TestRegistration extends SelTestCase { @Test public void testRegNewUser() { RegistrationData regData = new RegistrationData(); RegistrationPage regPage = New RegistrationPage(); regPage.setRegistrationData(regData) regPage.fillRegForm(); // Some assertion here } } Now since fillRegForm method does not take any argument, Can I assume that it is an example of loose coupling despite I need to set RegistrationData in RegistrationPage before being able to use fillRegForm method.

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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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• what is the difference between loose coupling and tight coupling in obect oriented paradigm?

  - by Jim

  Hi, can any one describe the exact difference between loose coupling and tight coupling in Object oriented paradigm?? I am too much confused on this. Thanks, Jim.

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• Which approach is the most maintainable?

  - by 2rs2ts

  When creating a product which will inherently suffer from regression due to OS updates, which of these is the preferable approach when trying to reduce maintenance cost and the likelihood of needing refactoring, when considering the task of interpreting system state and settings for a lay user? Delegate the responsibility of interpreting the results of inspecting the system to the modules which perform these tasks, or, Separate the concerns of interpretation and inspection into two modules? The first obviously creates a blob in which a lot of code would be verbose, redundant, and hard to grok; the second creates a strong coupling in which the interpretation module essentially has to know what it expects from inspection routines and will have to adapt to changes to the OS just as much as the inspection will. I would normally choose the second option for the separation of concerns, foreseeing the possibility that inspection routines could be re-used, but a developer updating the product to deal with a new OS feature or something would have to not only write an inspection routine but also write an interpretation routine and link the two correctly - and it gets worse for a developer who has to change which inspection routines are used to get a certain system setting, or worse yet, has to fix an inspection routine which broke after an OS patch. I wonder, is it better to have to patch one package a lot or two packages, each somewhat less so?

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• Where should you put constants and why?

  - by Tim Meyer

  In our mostly large applications, we usually have a only few locations for constants: One class for GUI and internal contstants (Tab Page titles, Group Box titles, calculation factors, enumerations) One class for database tables and columns (this part is generated code) plus readable names for them (manually assigned) One class for application messages (logging, message boxes etc) The constants are usually separated into different structs in those classes. In our C++ applications, the constants are only defined in the .h file and the values are assigned in the .cpp file. One of the advantages is that all strings etc are in one central place and everybody knows where to find them when something must be changed. This is especially something project managers seem to like as people come and go and this way everybody can change such trivial things without having to dig into the application's structure. Also, you can easily change the title of similar Group Boxes / Tab Pages etc at once. Another aspect is that you can just print that class and give it to a non-programmer who can check if the captions are intuitive, and if messages to the user are too detailed or too confusing etc. However, I see certain disadvantages: Every single class is tightly coupled to the constants classes Adding/Removing/Renaming/Moving a constant requires recompilation of at least 90% of the application (Note: Changing the value doesn't, at least for C++). In one of our C++ projects with 1500 classes, this means around 7 minutes of compilation time (using precompiled headers; without them it's around 50 minutes) plus around 10 minutes of linking against certain static libraries. Building a speed optimized release through the Visual Studio Compiler takes up to 3 hours. I don't know if the huge amount of class relations is the source but it might as well be. You get driven into temporarily hard-coding strings straight into code because you want to test something very quickly and don't want to wait 15 minutes just for that test (and probably every subsequent one). Everybody knows what happens to the "I will fix that later"-thoughts. Reusing a class in another project isn't always that easy (mainly due to other tight couplings, but the constants handling doesn't make it easier.) Where would you store constants like that? Also what arguments would you bring in order to convince your project manager that there are better concepts which also comply with the advantages listed above? Feel free to give a C++-specific or independent answer. PS: I know this question is kind of subjective but I honestly don't know of any better place than this site for this kind of question. Update on this project I have news on the compile time thing: Following Caleb's and gbjbaanb's posts, I split my constants file into several other files when I had time. I also eventually split my project into several libraries which was now possible much easier. Compiling this in release mode showed that the auto-generated file which contains the database definitions (table, column names and more - more than 8000 symbols) and builds up certain hashes caused the huge compile times in release mode. Deactivating MSVC's optimizer for the library which contains the DB constants now allowed us to reduce the total compile time of your Project (several applications) in release mode from up to 8 hours to less than one hour! We have yet to find out why MSVC has such a hard time optimizing these files, but for now this change relieves a lot of pressure as we no longer have to rely on nightly builds only. That fact - and other benefits, such as less tight coupling, better reuseability etc - also showed that spending time splitting up the "constants" wasn't such a bad idea after all ;-)

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• Good patterns for loose coupling in Java?

  - by Eye of Hell

  Hello. I'm new to java, and while reading documentation so far i can't find any good ways for programming with loose coupling between objects. For majority of languages i know (C++, C#, python, javascript) i can manage objects as having 'signals' (notification about something happens/something needed) and 'slots' (method that can be connected to signal and process notification/do some work). In all mentioned languages i can write something like this: Object1 = new Object1Class(); Object2 = new Object2Class(); Connect( Object1.ItemAdded, Object2.OnItemAdded ); Now if object1 calls/emits ItemAdded, the OnItemAdded method of Object2 will be called. Such loose coupling technique is often referred as 'delegates', 'signal-slot' or 'inversion of control'. Compared to interface pattern, technique mentioned don't need to group signals into some interfaces. Any object's methods can be connected to any delegate as long as signatures match ( C++Qt even extends this by allowing only partial signature match ). So i don't need to write additional interface code for each methods / groups of methods, provide default implementation for interface methods not used etc. And i can't see anything like this in Java :(. Maybe i'm looking a wrong way?

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• Architecture Best Practice (MVC): Repository Returns Object & Object Member Accessed Directly or Repository Returns Object Member

  - by coderabbi

  Architecturally speaking, which is the preferable approach (and why)? $validation_date = $users_repository->getUser($user_id)->validation_date; Seems to violate Law of Demeter by accessing member of object returned by method call Seems to violate Encapsulation by accessing object member directly $validation_date = $users_repository->getUserValidationDate($user_id); Seems to violate Single Responsibility Principle as $users_repository no longer just returns User objects

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• Using packages (gems, eggs, etc.) to create decoupled architectures

  - by Juan Carlos Coto

  The main issue Seeing the good support most modern programming platforms have for package management (think gem, npm, pip, etc), does it make sense to design an application or system be composed of internally developed packages, so as to promote and create a loosely coupled architecture? Example An example of this would be to create packages for database access, as well as for authentication and other components of the system. These, of course, use external packages as well. Then, your system imports and uses these packages - instead of including their code within its own code base. Considerations To me, it seems that this would promote code decoupling and help maintainability, almost in a Web-based-vs.-desktop-application kind of way (updates are applied almost automatically, single code base for single functionality, etc.). Does this seem like a rational and sane design concept? Is this actually used as a standard way of structuring applications today? Thanks very much!

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• Sequential coupling in code

  - by dotnetdev

  Hi, Is sequential coupling (http://en.wikipedia.org/wiki/Sequential_coupling) really a bad thing in code? Although it's an anti-pattern, the only risk I see is calling methods in the wrong order but documentation of an API/class library with this anti-pattern should take care of that. What other problems are there from code which is sequential? Also, this pattern could easily be fixed by using a facade it seems. Thanks

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• Loose Coupling of Components

  - by David

  I have created a class library (assembly) that provides messaging, email and sms. This class library defines an interface IMessenger which the classes EmailMessage and SmsMessage both implement. I see this is a general library that would be part of my infrastructure layer and would / can be used across any development. Now, in my application layer I have a class that requires to use a messaging component, I obviously want to use the messaging library that I have created. Additionally, I will be using an IoC container (Spring.net) to allow me to inject my implementation i.e. either email or sms. Therefore, I want to program against an interface in my application layer class, do I then need to reference my message class library from my application layer class? Is this tightly coupling my application layer class to my message class library? Should I be defining the interface - IMessenger in a seperate library? Or should I be doing something else?

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• How exactly does dependency injection reduce coupling?

  - by dotnetdev

  Hi, I've done plenty of reading on Dependency Injection, but I have no idea, how does it actually reduce coupling? The analogy I have of DI is that all components are registered with a container, so theyre are like in a treasure chest. To get a component, you obviously register it first, but then you would have to interrogate the treasure chest (which is like a layer of indirection). Is this the right analogy? It doesn't make obvious how the "injection" happens, though (how would that fit in with this analogy?). Thanks

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• Calling services from the Orchestrating layer in SOA?

  - by Martin Lee

  The Service Oriented Architecture Principles site says that Service Composition is an important thing in SOA. But Service Loose Coupling is important as well. Does that mean that the "Orchestrating layer" should be the only one that is allowed to make calls to services in the system? As I understand SOA, the "Orchestrating layer" 'glues' all the services together into one software application. I tried to depict that on Fig.A and Fig.B. The difference between the two is that on Fig.A the application is composed of services and all the logic is done in the "Orchestrating layer" (all calls to services are done from the "Orchestrating layer" only). On Fig.B the application is composed from services, but one service calls another service. Does the architecture on Fig.B violate the "Service Loose Coupling" principle of SOA? Can a service call another service in SOA? And more generally, can the architecture on Fig.A be considered superior to the one on Fig.B in terms of service loose coupling, abstraction, reusability, autonomy, etc.? My guess is that the A architecture is much more universal, but it can add some unnecessary data transfers between the "Orchestrating layer" and all the called services.

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• Loose coupling of COM in C# or How to avoid COMException 0x80040154

  - by user283318

  I have a .Net 2 C# application I am developing which uses a VB 6 generated COM DLL. The VB DLL is updated frequently any my application crashes with a System.Runtime.InteropServices.COMException (0x80040154). The part of the COM DLL I use does not change but the version (and CLSID) will. The "Specific Version" option for the reference is false. The WrapperTool is tlbimp. How do I tell my application not to worry about changes in the DLL? Is there any way of checking just the functions I am using?

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• ASP.NET MVC and NHibernate coupling

  - by Ben

  I have just started learning NHibernate. Over the past few months I have been using IoC / DI (structuremap) and the repository pattern and it has made my applications much more loosely coupled and easier to test. When switching my persistence layer to NHibernate I decided to stick with my repositories. Currently I am creating a new session on each method call but of course this means that I can not benefit from lazy loading. Therefore I wish to implement session-per-request but in doing so this will make my web project dependent on NHibernate (perhaps this is not such a bad thing?). I was planning to inject ISession into my repositories and create and dispose sessions on beginrequest/endrequest events (see http://ayende.com/Blog/archive/2009/08/05/do-you-need-a-framework.aspx) Is this a good approach? Presumably I cannot use session-per-request without having a reference to NHibernate in my web project? Having the web project dependent on NHibernate prompts my next (few) questions - why even bother with the repository? Since my web app is calling services that talk to the repositories, why not ditch the repositories and just add my NHibernate persistance code inside the services? And finally, is there really any need to split out into so many projects. Is a web project and an infrastructure project sufficient? I realise that I have veered off a bit from my original question but it seems that everyone seems to have their own opinion on these topics. Some people use the repository pattern with NHibernate, some don't. Some people stick their mapping files with the related classes, others have a separate project for this. Many thanks, Ben

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• I know of three ways in which SRP helps reduce coupling. Are there even more? [closed]

  - by user1483278

  I'd like to figure all the possible ways SRP helps us reduce coupling. Thus far I can think of three: 1) If class A has more than one responsibility, these responsibilities become coupled and as such changes to one of these responsibilities may require changes to other of A's responsibilities. 2) Related functionality usually needs to be changed for the same reason and by grouping it togerther in a single class, the changes can be made in as few places as possible ( at best changes only need be made to the class which groups together these functionalities) 3) Assuming class A performs two tasks ( thus may change for two reasons ), then number of classes utilising A will be greater than if A performed just a single task ( reason being that some classes will need A to perform first task, other will need A for second task, and still others will utilise it for both tasks ).This also means that when A breaks, the number of classes ( utilising A ) being impaired will be greater than if A performed just a single task. Can SRP also help reduce coupling in any other way, not described above? Thank you

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• Why should a web architecture be loosely coupled?

  - by Rookian

  When I look at ASP.NET MVC projects I everytime see loose coupled architecture. For what do I need a loose coupling in a web architecture (if I do not make unit tests)? What are advantages and disadvantages of this?

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• Cohesion and Decoupling.

  - by dbtek

  Can anyone tell me what are Cohesion and Decoupling? I found coupling but there is no Decoupling anywhere. I need to learn their meanings. Any help will be appreciated. Thanks for replying.

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• Are self-described / auto-descriptive services loosely or tightly coupled in a SOA architecture ?

  - by snowflake

  I consider a self-described / auto-descriptive service as a good thing in a SOA architecture, since (almost) everything you know to call the service is present in the service contract (such a WSDL). Sample of a non self-described service for me is Facebook Query Language (FQL http://wiki.developers.facebook.com/index.php/FQL), or any web service exchanging XML flow in a one String parameter for then parsing XML and performing treatments. Last ones seem further more technically decoupled, since technically you can switch implementations without technical impact on the caller, handling compatibility between implementations/versions at a business level. On the other side, having no strong interface (diluted into the service and its version), make the service tightly coupled to the existing implementation (more difficulty to interchange the service and to ensure perfect compatibility). This question is related to http://stackoverflow.com/questions/2503071/how-to-implement-loose-coupling-with-a-soa-architecture So, are self-described / auto-descriptive services loosely or tightly coupled in a SOA architecture ? What are the impacts regarding ESBs ? Any pointer will be appreciated.

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• wrapping aspx user controls commands in a transaction

  - by Hans Gruber

  I'm working on heavily dynamic and configurable CMS system. Therefore, many pages are composed of a dynamically loaded set of user controls. To enable loose coupling between containers (pages) and children (user controls), all user controls are responsible for their own persistence. Each User Control is wired up to its data/service layer dependencies via IoC. They also implement an IPersistable interface, which allows the container .aspx page to issue a Save command to its children without knowledge of the number or exact nature of these user controls. Note: what follows is only pseudo-code: public class MyUserControl : IPersistable, IValidatable { public void Save() { throw new NotImplementedException(); } public bool IsValid() { throw new NotImplementedException(); } } public partial class MyPage { public void btnSave_Click(object sender, EventArgs e) { foreach (IValidatable control in Controls) { if (!control.IsValid) { throw new Exception("error"); } } foreach (IPersistable control in Controls) { if (!control.Save) { throw new Exception("error"); } } } } I'm thinking of using declarative transactions from the System.EnterpriseService namespace to wrap the btnSave_Click in a transaction in case of an exception, but I'm not sure how this might be achieved or any pitfalls to such an approach.

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• Seperation of game- and rendering logic

  - by Qua

  What is the best way to seperate rendering code from the actually game engine/logic code? And is it even a good idea to seperate those? Let's assume we have a game object called Knight. The Knight has to be rendered on the screen for the user to see. We're now left with two choices. Either we give the Knight a Render/Draw method that we can call, or we create a renderer class that takes care of rendering all knights. In the scenario where the two is seperated the Knight should the knight still contain all the information needed to render him, or should this be seperated as well? In the last project we created we decided to let all the information required to render an object be stored inside the object itself, but we had a seperate component to actually read those informations and render the objects. The object would contain information such as size, rotation, scale, and which animation was currently playing and based on this the renderer object would compose the screen. Frameworks such as XNA seem to think joining the object and rendering is a good idea, but we're afraid to get tied up to a specific rendering framework, whereas building a seperate rendering component gives us more freedom to change framework at any given time.

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• creating a wrapper around a 3rd party assembly - swap out and decouple

  - by mrblah

  I have an email component that I am integrating into my application, looking for some tips on how should build a wrapper around it so I can swap it out with another 3rd party component if needed. My approach right now is it: build an interface will the functionality I need. create a class that implements the interface, using my 3rd party component inside this class. any usage of this component will be via the interface so like: IPop3 pop3 = new AcmeIncePop3Wrapper(); pop3.connect(); and inside AcmeIncePop3Wrapper will be: public void connect() { AcmeIncePop3 pop = new AcmeIncePop3(); pop.connect(); } Is that a good approach? I could probably add another abstraction by using ninject so I could swap out implementations, but really this seems to be all I need as i don't expect to be changing 3rd party assemblies every day, just don't want to make things so tightly coupled.

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• Making OR/M loosely coupled and abstracted away from other layers.

  - by Genuine

  Hi all. In an n-tier architecture, the best place to put an object-relational mapping (OR/M) code is in the data access layer. For example, database queries and updates can be delegated to a tool like NHibernate. Yet, I'd like to keep all references to NHibernate within the data access layer and abstract dependencies away from the layers below or above it. That way, I can swap or plug in another OR/M tool (e.g. Entity Framework) or some approach (e.g. plain vanilla stored procedure calls, mock objects) without causing compile-time errors or a major overhaul of the entire application. Testability is an added bonus. Could someone please suggest a wrapper (i.e. an interface or base class) or approach that would keep OR/M loosely coupled and contained in 1 layer? Or point me to resources that would help? Thanks.

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• ASP.Net layered communication

  - by Chris Klepeis

  Hi, We're developing a layered web application. The specs: 3 layers, data layer, business layer, ui layer. Programmed in C# Data Layer uses the entity framework Currently we plan on having the data layer return IEnumerable<T> to the business layer via linq 2 entities, and the business layer will return data to the ui layer. Since the ui layer has no knowledge of the existance of the data layer, how would it handle a result of IEnumerable passed to it from the BLL, where T is defined in the data layer? Are there any GOOD example out there on how to do this. Please note that I'm extremely new to factories / interfaces / abstraction to loosely couple layers. I saw the question here http://stackoverflow.com/questions/917457/passing-data-in-an-ntier-application and it was recommended to have the entity layer shared amongst all layers... however I do not want the other layers to be able to query the database.

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