I'm using MySQL/PHP/Jquery and a custom MVC structure because my app is fairly small. My question is (and this could be in any language): When using a MVC programming structure where do the files you hit via ajax go?
For example I use long polling to show the status (progress bar) of background processing. In my non-MVC version of this tool I just have a php file that is only hit by the ajax call, it makes an object and calls a method to return the percentage done. Ajax returns my number and updates a progress bar.
How does this ajax loading fit into a MVC structure?
Thank you!
MVC is just a pattern. JavaScript code itself can implement this pattern, so I don't think of it as fitting into some other portion of your server side framework's pattern. Check out Backbone for a good example of using MVC in JavaScript code.
You can model your JavaScript code off of similar concepts that you model your server side code with. The JavaScript code itself will get served up through the view of your server side application, but unless you're only adding eye candy with JavaScript code (which you're not) then the JavaScript code is really its own entity and doesn't necessarily fit into your server side MVC paradigm.
Try to separate the JavaScript code from anything server side. Just consider it an 'add on' that, if disabled in the browser, won't break your application from running. I just add some niceties to allow for better interaction, etc. How you actually model the JavaScript code is up to you, (but I do highly recommend Backbone)
One could also do a Rich frontend in javascript backed only by a data source. In this case, once again, javascript will be responsible for maintaining models, views and controllers.
Domain model generally just refers to the business logic of your application. The brains so to speak of what should actually happen in your app. It's kind of an abstract concept encapsulating all the business logic of an app.
im using codeigniter, im using an dedicated controller for ajax and checking $_SERVER['HTTP_X_REQUESTED_WITH'] to determine if its an ajax request.
you can use same approach, and you can keep all of your structure(use your models in ajax controller etc...)
Related
To my understanding, MVC is a way to implement the separation of presentation tier from business and data tier. Am I understanding this correctly? If so, MVC should separate the business logic completely from presentation, right?
So to me it seems like javascript (or jquery) is somehow violating the MVC design since it takes over some of the logic on the client side, isn't it? Is model = data tier, controller = business tier, view = presentation tier? I think I have misunderstood the whole concept.
You seem to have a decent understanding of MVC. The trouble is that you are looking at two different potential MVC structures as one and the same. On the server, you can have data models, controllers, and views. On the client side, you can ALSO have data models, controllers, and views. If you want to look at your client side JavaScript as MVC, then jQuery is simply a utility that the view controllers can use to manipulate the view (the DOM).
Simply put, the client side doesn't always have to be only the view. If you use a web application client-side framework like Backbone, for example, then you can have models, views, and controllers all on the client side, which communicate with another, SEPARATE MVC structure on your server.
What you describe does actually pose a challenge for a lot of implementations. Frameworks such as the ASP.NET MVC Framework have been making attempts to auto-render JavaScript to the UI based on business logic in the middle tier (validation rules for form fields, primarily). But they're a long way off from having a truly compelling JavaScript user experience which doesn't repeat logic.
Personally, I like to think of the JavaScript as purely a UI concern. The application internally handles all of the logic. The JavaScript, as part of the UI, may duplicate some of that logic... but only for strictly UI purposes. Remember that the application should regress gracefully into a still-working state if the user has JavaScript disabled. That is, it should still use server-side (middle-tier) code to get the job done. All the JavaScript did was add a richer user experience to the UI layer.
JavaScript isn't the only culprit for this, either. Suppose you have a lot of validation logic in your middle tier defining what's valid or invalid for your objects. When you persist those objects to a database (which is on the periphery of the application just like the UI is), doesn't that database also contain duplicate validation logic? Non-nullable fields and such.
Congratulations! Your understanding of MVC is completely wrong. It has nothing to do with n-tier architecture (which is what you seem to be confusing it with).
The core idea of MVC is separation of concerns. This is used by dividing the application it two major layers:
model layer: contains all of the domain business logic and rules.
presentation layer: deals it user interface
The presentation then is further split into controllers (for handling the user input) and views (for dealing with response).
When applied to web applications, you either have MVC (or MVC-like) structure only on server-side, or, for larger and more complicated applications, you have separate MVC triads for both frontend and backend.
Also, when working with applications, the user of MVC is not human being, but the browser.
In latter case the backend acts like one data source for frontend application. An the whole frontend part of MVC is written in javascript.
P.S. In case if you are able to read PHP code, you can find a quite simple explanation of model layer in this answer. And, yes. It is the "simple version" because MVC is a pattern for enforcing a structure in large application, not for making a guesbook.
You can go to http://www.asp.net/mvc site and refer tutorials / samples to learn about MVC using Microsoft technologies.
i have to start a new project, a webapp with lots of forms and screens and i really don't know which technology fit best. The application is an ERP like app, with very few animations and lot of forms. The goal is to reduce at minimum reloads and waiting time, it has to be as close as possible to a normal desktop app (a lot of work to look like a marvelous VB6 app :-)
On the one hand we have client side MVC (backbone). It's cool to have all the code running on client but in my mind this implies repetition of lot of code (for example all models definitions) from server (PHP + Fuel). Sure once loaded all the informations task like paginations or grid work without any delay but it also present some problems of synchronization (other users can change data and i have to manually invalidate data on client).
On the other hand we have pjax. The idea is to make all the templating and so on on server, just implement a logic to return the page without the frame for pjax request or full page on new requests. No code duplication, very simple client side.
I've read the the story from basecamp and from twitter and both the point make sense to me. You can't relay on visitor computer (features, performance ...)
The more i think about it the mode i like pjax over MVC, but maybe i'm missing something. Which are the MVC advantages over pjax or pjax disadvantages over Client side MVC ?
Thanks a lot
Backbone.js is good for heavy, single page web apps that never truly post back, but have lots of ajaxian things going on, interdependent cascading dropdowns, etc. It has a very good API for events and collections. If you have plentiful client side javascript, it can be a helpful way to organize it. It is opinionated in the sense that it expects your server-side architecture to be RESTful by default, and you have to make some effort to use it for non RESTful APIs.
The project I'm working on is an ERP web app as well, with asp.net MVC on the server-side. I've learned that Backbone (with handlebars as the templating system), and .net mvc really don't play together that well. If you go Backbone, you really have to go full-hog (controller methods serve up json, that's it). On pages in this app that are more or less 'normal' web pages with some forms, Backbone is the wrong choice.
I just googled pjax for the first time, so I've basically just read the short description at the top of the page, but I suspect that might be the way to go for your scenario, in keeping with Keep It Simple Silly principles.
I used to utilize MVC 3 Razor engine to render pages. Sometimes I had to use AJAX calls to transfer Razor-rendered HTML and inserting it into the page using JQuery. As new project is starting, we do consider to utilize MVC 4 Single Page Application framework which is new to us. I took the first glance at it which left me with mixed feelings:
On the one hand it implies all your data are transferred by JSON and client does all the job to render them and encode some UI-related logic which is great for server and network performance. On the other hand the client (HTML+JavaScript) becomes much more heavy with a bunch of magic strings and hidden relations inside it which seems to be hard to maintain. We got used to VS intellisense, type-safed .NET server code to render pages which we have to exchange for client scripts and Knockout binding statements in case of SPA.
I wonder are any prons and cons of using SPA comparing to Razor, other that this obvious one I've mentioned here? Thanks
Razor is a server based technology where SPA (Single Page Application) is an architecture approach used on the client (web browser). Both can be used together.
From a high level, SPA moves the rendering and data retrieval to the client. The web server becomes a services tier sitting in front of the database. An MVC pattern works best when using SPA. Frameworks like Knockout.js and Backbone.js can be used for this. The net results is a rich responsive desktop like experience.
To achieve this you'll need to be a descent javascript programmer or be willing to learn javascript.
Yes it's moving business requirements from C# into javascript. In Visual Studio there is limited intelli-sense for javascript. To have confidence in your javascript you'll need to lean on unit testing. The up side is the rich user experience (think gmail or google maps).
I think it sounds like you are already fairly well apprised of most of the trade-offs here; you'll have reduced network load with SPA, and will shift a measure of the processing to the client. You will, however, increase the complexity of your code, and make it slightly harder to easily maintain the system (simply because of the increased complexity - not due to any architectural problems inherent in SPA).
Another thing to keep in mind is compatibility. The reason I mentioned a "false choice" in my comment to your question is that to keep the site usable for folks with Javascript disabled, you will still need to provide regular, whole-page views. This is also a good idea to do for the sake of SEO; a crawler will browse your site as a user with JS disabled, and can then index your site. The site should then handle such incoming URLs properly so that those with JS enabled will find themselves in your SPA looking at the same content (as opposed to being dumped in the "no JS" view unnecessarily).
There's something else I'll mention as a possibility that might help with the above, but it breaks the ideals of an SPA; that is, using Ajax-loaded partials in some places, rather than JSON data. For example, say you have a typical "Contact EMail" form on the site; you want that to load within the context of the SPA, but it's probably easier to do so by loading the partial via AJAX. (Though certainly, yes; you could do it with a JSON object describing the fields to display in the e-mail form).
There will also likely be content that is more "content" than "data", which you may still wish to load via partials and Ajax.
An SPA is definitely an interesting project, and I'm about to deploy one myself. I've used a mix of JSON and partials in it, but that may not be your own choice.
I am trying to find the optimal architecture for an ajax-heavy Django application I'm currently building. I'd like to keep a consistent way of doing forms, validation, fetching data, JSON message format but find it exceedingly hard to find a solution that can be used consistently.
Can someone point me in the right direction or share their view on best practice?
I make everything as normal views which display normally in the browser. That includes all the replies to AJAX requests (sub pages).
When I want to make bits of the site more dynamic I then use jQuery to do the AJAX, or in this case AJAH and just load the contents of one of the divs in the sub page into the requesting page.
This technique works really well - it is very easy to debug the sub pages as they are just normal pages, and jQuery makes your life very easy using these as part of an AJA[XH]ed page.
For all the answers to this, I can't believe no one's mentioned django-piston yet. It's mainly promoted for use in building REST APIs, but it can output JSON (which jQuery, among others, can consume) and works just like views in that you can do anything with a request, making it a great option for implementing AJAX interactions (or AJAJ [JSON], AJAH, etc whatever). It also supports form validation.
I can't think of any standard way to insert ajax into a Django application, but you can have a look to this tutorial.
You will also find more details on django's page about Ajax
Two weeks ago I made a write up how I implement sub-templates to use them in "normal" and "ajax" request (for Django it is the same). Maybe it is helpful for you.
+1 to Nick for pages displaying normally in the browser. That seems to be the best starting point.
The problem with the simplest AJAX approaches, such as Nick and vikingosegundo propose, is that you'll have to rely on the innerHTML property in your Javascript. This is the only way to dump the new HTML sent in the JSON. Some would consider this a Bad Thing.
Unfortunately I'm not aware of a standard way to replicate the display of forms using Javascript that matches the Django rendering. My approach (that I'm still working on) is to subclass the Django Form class so it outputs bits of Javascript along with the HTML from as_p() etc. These then replicate the form my manipulating the DOM.
From experience I know that managing an application where you generate the HTML on the server side and just "insert" it into your pages, becomes a nightmare. It is also impossible to test using the Django test framework. If you're using Selenium or a similar tool, it's ok, but you need to wait for the ajax request to go return so you need tons of sleeps in your test script, which may slow down your test suite.
If the purpose of using the Ajax technique is to create a good user interface, I would recommend going all in, like the GMail interface, and doing everything in the browser with JavaScript. I have written several apps like this using nothing but jQuery, state machines for managing UI state and JSON with ReST on the backend. Django, IMHO, is a perfect match for the backend in this case. There are even third party software for generating a ReST-interface to your models, which I've never used myself, but as far as I know they are great at the simple things, but you of course still need to do your own business logic.
With this approach, you do run into the problem of duplicating code in the JS and in your backend, such as form handling, validation, etc. I have been thinking about solving this with generating structured information about the forms and validation logic which I can use in JS. This could be compiled at deploy-time and be loaded as any other JS file.
Also, avoid XML. The browsers are slow at parsing it, it is a pain to generate and a pain to work with in the browser. Use JSON.
Im currently testing:
jQuery & backbone.js client-side
django-piston (intermediate layer)
Will write later my findings on my blog http://blog.sserrano.com
I'm currently diving into web development after ten years of desktop development and I'm trying to get a high level grasp on the many concepts I'm learning. The two most recent concepts I've been reading up on are MVC (specifically ASP.NET MVC) and AJAX. I understand MVC is a pattern used to separate logic and data and AJAX is a combination of various web technologies for creating asynchronous and dynamic web pages.
How are the two related?
Can or should the two be used together?
If so, can you give some simple examples?
I apologize if these are strange questions and I'm comparing apples to oranges, forgive me as I'm still a huge gigantic noob.
Ajax is just of way of requesting data : generally, with Ajax, instead of requesting a full HTML webpage, you just request :
either a part of the page (say, the HTML code of one part of the screen you want to refresh without reloading the whole page)
or some data ; using JSON or XML as data-exchange format, for instance
MVC describes the stacks used to :
Access the data and do actions / calculations / whatever on it (M)
Present it (V)
Going through the Controller, which determine which Model and View should be used to serve the data you requested.
When you use an Ajax request, you do exactly as you'd do serving a full page :
get a request
determine which Model and method should be called
call them (maybe they'll do something with a Database, or whatever they have to)
pass the data to the View, which will render it
The two differences are :
The "View", in one case, renders a full HTML page : in the other case, only a part of it, or some JSON / XML format
In one case, the request is generally done in asynchronous mode
Ajax or not, you are free to use MVC... or not !
If you are using MVC for non-Ajax request, then, why not do so for Ajax requests too ?
Sorry, I won't give any example of code - I'm not a .NET developer, so won't be able to help with that (but the concept is the same in other languages ;-) )
I'll bite...
They're not related in any way other than they're both web concepts. Ajax is a method of performing an HTTP request and handling the result. MVC is an architectural pattern for building your web application.
Yes. No matter what architecture you use for your web apps, you should use Ajax where it makes sense. Ajax can increase the performance of your app, and improve the user experience and UI by eliminating bloated data transfer and screen flickering/refresh.
You can use Ajax easily through a number of javascript frameworks such as JQuery. Simply download and include the framework .js files in your application, reference it from your html, and read the documentation on how to make Ajax requests.
How are they related?
I'm assuming you're taking this from the POV of an ASP.NET dev.
It's really just because plain Ajax (+JSON) works much better with ASP.NET MVC than ASP.NET Webforms. Because of the way ASP.NET Webforms muddled together the view and the controller (and not to mention having Postback & Viewstate -- its crutch to allow pre-Ajax pages to overcome web statelessness), this was initially very difficult.
The way ASP.NET server controls cannot be directly (or at least easily) accessed from Javascript practically made it impossible to use conventional Ajax until ASP.NET Ajax UpdatePanels came along (which was, IMHO, another crutch).
With the advent of ASP.NET MVC it's now much easier to use straight Ajax libraries and JSON for ASP.NET web applications.