When is MVC no longer applicable in large projects? - model-view-controller

Having used some PHP frameworks such as Codeigniter and Kohana for some smaller sites, I'm starting to wonder if MVC is still applicable for larger projects and, if so, what precautions need to be taken to maintain clean clode. What practices do the larger sites use in order to prevent this? Does Amazon's or Flickr's code use MVC or some variant of it? Is there a guide that, given a certain problem, shows you how best to implement MVC for large projects?
-- Tangent --
On a current project using Kohana, I started to question what role my models should have. Often times, a model can only describe a small part of an object that I'm trying to build. I.e., need an object for a User, so I extract my user from the Users table using my Users_Model. But each user also has several items in their inventory, so I need to also use the Users_Inventory_Model. But, each inventory item also has other tables associated with it, and so on, until I find that building up a single User in my controller has required me to access several models. Now, imagine doing this in many different controllers and suddenly I find myself with messy and redundant code and very fat controllers.
This led me to think that maybe I should have libraries which handle most of the grunt work. That way, I could have a Users library and let it load all of my pertinent user data and run most of the logic such as updating, deleting, etc. Is this the way most MVC projects evolve? Letting libraries do most of the interaction with the models, while the controllers call the libraries and prepare the data for the views? Anyway, this is just one of the questions I've had about MVC, which I haven't been able to find an answer to online.

In fact, it's for big projects where all these MVPs and MVCs really shine. All software design patterns are "created" (besides establishing common vocabulary) to deal with complexity of software. Thus, used properly, MVC will be of great help to you in big projects.
Contrast with small apps, which can be hacked together with mouse-only approach, but are a nightmare to support since there's no proper separation nor they're SOLID enough.

Related

Codeigniter seperate front-end and back-end

I'm currently learning myself the Codeigniter framework. I want to create a project that will have a front-end (which will be used by users) and a back-end (which would be used by administrators).
I have looked through different articles, all of them suggest using HMVC to separate the public and admin controllers/views. I have also considered to create two separate projects, one for the public and one for the admin, both using the same database.
I have tried to do research on which one of the methods mentioned above would be the best solution for a potentially large project, but could not come up with any sustainable answer.
Is it possible that two separate CodeIgniter projects can access and use the same database simultaneously?
Edit:
The client project would mostly just query the database for results, whereas the admin project would be full CRUD.
If indeed creating multiple projects would be the recommended way to go, the admin project would be running on a sub-domain i.e admin.example.com whilst the client project would be running on example.com
It is valid to use any of the approaches you mention. It is a matter of personal preference (read: opinion). I have used each singly and in combination with more or less the same outcome. I have settled on using none of the above. Instead, I use a single project, no HMVC, no subdomains, standard CI file structure. I feel keeping it simple ultimately makes it easier to build and maintain. YMMV.
What separates the public-users from admin-users is authentication and authorization (A&A). Nobody gets into an admin controller without the proper login credentials and permissions. You're going to need A&A anyway to keep the public from accidentally discovering the admin area. IMO, a "special" file structure and subdomains actually make implementing A&A harder.
Depending on your deadline for this project you might want to look at using CodeIgniter Version 4. It's a thoroughly modern revamp of the framework. It is still in beta test mode, but I've found it to be quite stable. They are working hard to get to the release version. There is no published release date yet, but all indications are it will be sooner rather than later.
The answer as to how to configure CI is really dependent on your needs and what you feel is best. There is no right answer or "acceptable" way of doing things in this regard.
When I first started with Codeigniter, I had just a sub-folder for backend controllers called admin as well as an Admin base/core controller that all admin classes extended rather than CI_Controller. Models/views can be similarly organized in to sub-folders. This was a perfectly acceptable solution in my opinion for small-scale applications.
I moved in to HMVC and found that it really isn't that much different in terms of keeping them both separate. Although you can easily drag-and-drop modules from different projects so long as they are decoupled, you'll still have to jump through hoops to get front/back ends separate. I believe I used this is a starting point: https://github.com/jmtolibas/HMVC-CI3-with-Separate-Backend-and-Frontend
In terms of what you mentioned, having 2 separate projects wouldn't necessarily be a bad idea. You could even share the same system folder with a modification in index.php regarding the system path. Multiple database connections shouldn't be an issue.
So basically, all 3 approach will work, it is up to you to determine which one you like working with the most.
If you want my opinion, I would use Laravel or Lumen on any new project, and separation of front/back end is rather easy with packages, namespacing, .etc.

Should the regular and mobile site be separate in spring?

I'm about to start developing a site that will have a regular and mobile version using spring. At this point I need to make a decision on how to approach this. I foresee two options:
Independent sites on the same server. Develop an independent set of controllers and views for each of the sites. Trying to reuse the controllers as much as possible.
Intermingled sites. Develop content aware controllers that would send to different views depending on the type of device. Controllers send to different views depending on the device.
Option 1 seems more practical, but I'm afraid I'm going to end up with a lot of controller repetition. Also I would need to separate the site into http://something.com/ and http://something.com/m as the base for the mobile version.
Option 2 seems that it will turn unmanageable very soon, since changes in the regular version will have impact on the mobile one. Nevertheless it will have much more code reuse.
How would you approach this?
Option 2 always seems tempting, but in my experience it turns out to be impractical. Invariably, for anything more than trivial sites the page flow becomes different between full-fat and mobile versions, with data different data being rendered. It becomes more than just a different skin.
My advice to is to make a strong effort to identifying the common business logic, and put those into general code. Keep the controllers as thin as you can, but by having desktop- and mobile-specific controllers you can keep them focussed. Yes, there will be some duplication, but hopefully it can be minimised.
Define the common logic as beans in the webapp-level /WEB-INF/applicationContext.xml beans file. Then define a separate DispatcherServlet for each site, containing the specific controllers, sharing the common beans.
If it is only presentation that differs ie different views but same model and same business logic I would suggest trying to identify the client in an aspect for each controller.
If they should use different underlying calls I would go for extra controllers with different urls but still in the same servlet.

Organizing application in layers

I’m developing a part of an application, named A. The application I want to plug my DLL into, called application B is in vb 6, and my code is in vb.net. (Application B will in time be converted to vb.net) My main question i, how is the best way for me to organize my code (application A)?
I want to split application A into layers (Service, Business, Data access), so it will be easy to integrate application A into B when B is converted to vb.net. I also want to learn about all the topics like layered architecture, patterns, inversion of dependency, entity framework and so on. Although my application (A) is small I want to organize my code in the best way.
The application I’m working with (A) is using web services for authenticating users and for sending schema to an organization. The user of application B is selecting a menu point in application B and then some functions in my application A is called.
In application A I have an auto generated schema class from an xsd schema. I fill this schema object with data and serialize the object to a memory string (is it a good solution to use memory string, I don’t have to save the data yet), wrap the xml inside a CDATA block and return the CDATA block as a string and assign the CDATA block to a string property of a web service.
I am also using Entity framework for database communication (to learn how this is done for the future work with application B). I have two entities in my .edmx, User and Payer.
I also want to use the repository pattern (is this a good choice?) to make a façade between the DAL and the BLL.
My application has functions for GeneratingSchema (filling the schema object with data), GetSchemaContent, GetSchemaInformation, GenerateCDATABlock, WriteToTextFile, MemoryStreamToString, EncryptData and some functions that uses web services, like SendShema, AuthenticateUser, GetAvalibelServises and so on.
I’m not sure where I should put it all?
I think I have to have some Interfaces like IRepository, ISchema (contract for the auto generated schema class, how can I do this?) ICryptoManager, IFileManager and so on, and classes that implements the interfaces.
My DAL will be the Entity framework. And I want a repository façade in my BLL (IRepository, UserRepository, PayerRepository) and classes for management (like the classes I have mention above) holding functions like WriteToFile, EncryptData …..
Is this a good solution (do I need a service layer, all my GUI is in application B) and how can I organize my layers, interfaces, classes an functions in Visual Studio?
Thanks in advance.
This is one heck of a question, thought I might try to chip away at a few parts for you so there's less for the next guy to answer...
For application B (VB6) to call application/assemblies A, I'm going to assume you're exposing the relevant parts of App A as COM Components, using ComVisibleAttributes and similar, much like described in this artcle. I only know of one other way (WCF over COM) but I've never tried it myself.
Splitting your solution(s) into various tiers and layers is a very subjective/debatable topic, and will always come down to a combination of personal preference, business requirements, time available, etc. However, regardless of the depth of your tiers and layers, it is good to understand the how and the why.
To get you started, here's a couple articles:
Wikipedia's general overview on "Multitier Architectures"
MSDN's very own "Building an N-Tier Application in .Net"
Inversion of Control is also a very good pattern to get into right now, with ever increasing (and brilliant!) resources becoming available to the .Net platform, it's definitely worth infesting some time to learn.
Although I haven't explored the full extent of IoC, I do love dependency injection(a type of IoC if I understand correctly though people seem to muddle the IoC/DI terms quite a lot). My personal preference for DI right now is the open source Ninject project, which has plenty of resources online and a reasonable wiki section talking you through the various aspects.
There are many more takes on DI and IoC, so I don't want to even attempt to provide you a comprehensive list for fear of being flamed for missing out somebody's favourite. Just have a search, see which you like the look of and have a play with it. Make sure to try a couple if you have the time.
Again, the Repository Pattern - often complemented well by the Unit of Work Pattern are also great topics to mull over for hours. I've seen a lot of good examples out on the inter-webs, and as many bad examples. My only advice here is to try it for yourself... see what works for you, develop a version of the patterns that suits you best and try to keep things consistent for maintainability.
For organising all these tiers and layers in VS, I recommend trying to keep all your independent tiers/layers in their own Solution Folders (r-click the Solution, Add New Solution Folder), or in some cases (larger projects) there own solutions and preferably an automated build service to update dependent projects with up to date assemblies as required. Again, a broad subject and totally down to personal preference. Just keep an eye out when designing your application for potential upcoming Circular References.
So, I'm afraid that doesn't even slightly answer your question, but hopefully provides you with some resources to check out and a few hours of reading.
Good luck!

web development - MVC and it's limitations

MVC sets up clear distinction between Model, View and Controller.
For the model, now adays, web frameworks provides ability to map the model directly to database entities (ORM), which, IMHO, end up causing performance issues at runtime due to direct database I/O.
The thing is, if that's really the case, why model ORM is so pupular and every web frameworks want to support it either organically or not.
To a web site has huge amount of traffic, it definitely won't work. But what's the work around? Connect directly to database is definitely not a wise solution here.
What's your question?
Is it a good idea to use direct db access from webpages?
A: No.
Is it a good idea to use ORM's?
A: Debatable : See How can I design a Java web application without an ORM and without embedded SQL
Is it a good idea to use MVC model?
A: Yes - it has nothing to do with "Direct" database access - it's about separating your application logic from your model and your display. (Put simply).
And the rationale for not putting database logic inside webpages has nothing to do with performance - it's about security/maintainability etc etc. Calling a usp from a webpage is likely to be MORE performant than using an ORM, but it's bad because the performance gain is negligible, and the cons are significant.
As to workaround: if you mean how do you hook up a database to a web application...?
The simplest way is to use something like Entity Frameworks or Linq-Sql with your Model - there are plenty of examples of this in tutorials on the web.
A better method IMO, is to have a separate Services layer (which may be WCF based), and have all the database access inside that, with DTO's transferring the data to your Web Application which has it's own ViewModel.
Mvc is not about orm but about separation of display logics and business logics. There is no reason your exposed model needs to be identical to you database model and many reasons to ensure that the exposed model closely matches what is to be displayed.
The other part of the solution to scale well would be to implement caching in the control and be able to distribute load on sevaral instances.
I think #BonyT has given a good answer, (and I've voted for it :) ), I'd just add that:
"web frameworks provide the ability to map the model directly to database entities (ORM), which, IMHO, ends up causing performance issues at runtime due to direct database I/O"
Even if this is true, using an ORM can solve a lot of problems with a model being easy to update and translate back and forth between a database. Solving a performance hit by buying extra web servers or cloud instances is much cheaper than having to buy extra developers or extra hours in development to solve things other people have already written ORMs to do for you.

Where is MVC a bad thing?

I've been reading through a couple of questions on here and various articles on MVC and can see how it can even be applied to GUI event intensive applications like a paint app.
Can anyone cite a situation where MVC might be a bad thing and its use ill-advised?
EDIT: I'm specifically talking about GUI applications here!
I tried MVC in my network kernel driver. The patch was rejected.
I think you're looking at it kind of backwards. The point is not to see where you can apply a pattern like MVC, the point is to learn the patterns and recognize when the problem you are trying to solve can naturally be solved by applying the pattern. So if your problem space can be naturally divided into model, view and controller then it is a good candidate for MVC. If you can't easily see which parts of your design fall into the three categories, it may not be the appropriate pattern.
MVC makes sense for web applications.
In web applications, you process some data (on SA: writing questions, adding comments, changing user info), you have state (logged in user), you don't have many different pages, but a lot of different content to fit into those pages. One Question page vs. a million questions.
For making CMS, for example, MVC is useless. You don't have any models, no controllers, just a pages of text with decorations and menus. The problem is no longer processing data - the problem now is serving that text content properly.
Tho, CMS Admin would build on top of MVC just fine, it's just user part that wouldn't.
For web services, you'd better use REST which, I believe, is a distinct paradigm.
WebDAV application wouldn't benefit greatly from MVC, either.
The caveat on Ruby for Web programming is that Rails is better suited for building Web applications. I’ve seen many projects attempt to create a WebDAV server or a content management system CMS with Rails and fail miserably. While you can do a CMS in Rails, there are much more efficient technologies for the task, such as Drupal and Django. In fact, I’d say if you’re looking at a Java Portal development effort, you should evaluate Drupal and Django for the task instead.
Anything where you want to drop in 3rd party components will make it tough to work in the MVC pattern. A good example of this is a CMS.
Each component you get will have their "own" controller objects and you won't be able to share "control" of model -> ui passing.
I don't necessarily know that MVC is ever really a bad idea for a GUI app. But there are alternatives that are arguably better (and also arguably worse depending on whose opinion you're asking). The most common is MVP. See here for an explanation: Everything You Wanted To Know About MVC and MVP But Were Afraid To Ask.
Although I suppose it might be a bad idea to use MVC if you're using a framework or otherwise interacting with software that wasn't designed with MVC in mind.
In other words, it's a lot like comparing programming languages. There's usually not many tasks that one can say that one is better than the other for. It usually boils down to programmer preference, availability of libraries, and the team's experience.
MVC shouldn't be used in applications where performance is critical. I don't know if this still applys with the increase of computing power but one example is a call center application. If you can save .5 seconds per call entering and updating information those savings add up over time. To get the last bit of performance out of your app you should use a desktop app instead of a web app and have it talk directly to the database.
When is it a bad thing? Where ever there is another code-structure that would better fit your project.
There's countless projects where MVC wouldn't "fit", but I don't see how a list of them would be of any benefit..
If MVC fits, use it, if not, use something else..
MVC and ORM are a joke....they are only appropriate when your app is not a database app, or when you want to keep the app database agnostic. If you're using an RDBMS that supports stored procedures, then that's the only way to go. Stored procs are the preferred approach for experienced application developers. MVC and ORM are only promoted by companies trying to sell products or services related to those technologies (e.g. Microsoft trying to sell VS). Stop wasting your time learning Java and C#, focus instead on what really matters, Javascript and SQL.

Resources