I want to switch from Rails to Django, to broaden my mind, and a question has bobbed up in my mind.
My Rails app is quite a mess, since my hobby-based development approach is a patch-and-glue one. I have seen very early that Django divied between a project and an app. According to their site, a project is made of many apps, and one app can be used for many projects.
This intrigued me, since that would made the lines between my site's areas clearer. I tried to find some more examples and information on that, but I couldn't answer my question, which is:
How big/small is such an app? Are they able/supposed to interact closely?
It is, for example smart to have one app to deal with user's profiles, and another app to deal with blog-posts and comments, from those users? (In my site, a user can have several blogs, with different profiles). Or are they meant to be used otherwise?
A django App is a fancy name for a python package. Really, that's it. The only thing that would distinguish a django app from other python packages is that it makes sense for it to appear in the INSTALLED_APPS list in settings.py, because it contains things like templates, models, or other features that can be auto-discovered by other django features.
A good django app will do just one thing, do it well, and not be tightly coupled to any other app that might use it. A wide variety of apps are provided with django in the contrib namespace that follow this convention.
In your example, a good way to devise apps is to have one for user profiles (or use one of the many existing profile apps), one app for blog posts (or one of the many that already do this), one app for comments, separate from blog posts (again, you can use an existing app for this), and finally, a very tiny app that ties the three together, since they don't and shouldn't depend on each other directly.
The purpose of using app's is to make them reusable. Django likes DRY principle DRY stands for DO NOT repeat yourself
An app should be as small as it can, and loosely coupled. So, for an app should not need another app to work properly.
Django recommends writing an app for each table (well, not always, but as soon as you want to grow your app, you will definitely need to divide tables to pair apps. Or else you will have hard time for maintaining your code.)
You can, for example, create an app for users, an app for sales, an app for comments, an app for articles. It will be easier to maintain your code and if you have done it right, you can use the app in other project with a little (if any) modification in the app.
Project's are, compilation of app's. Users app, articles app, comments app can come together an make a project, or in other words, a website.
If you want to learn django, I suggest you to check out:
http://www.djangobook.com/
http://docs.djangoproject.com/
One word of advice, do not, in any case, copy/paste. Not only your code has great chance to fail, but you will not know what the code is doing. If you are going to use someone elses code in your project, at least type them, this will make you understand what the code is doing, or at least, it will give an idea.
Writing your own code is always better for maintance, but this does not mean that you should reinvent the world, you can use libraries, look at their documentation to use it properly.
Documentations, tutorials are you best friend.
Good luck.
A project is basically a place where your project lives...in your project you setup your url's, project settings, etc.
An app defines its own data models and views to be used within a project. You can move these between projects if you like.
I highly recommend running through the tutorials from the Django site as they will show you what a project and app are, how to manage both, how to use the admin panel, how to make the app usable in multiple projects, etc.
A portal = A django project
A ads system, gallery photos, catalog of products = Apps
Related
I have been using django for a while, but there is something im not quite clear on.
How big should a django app be. If for example a django app should only be user authentication or if it should be an entire website in one app.
If I have a project with several apps and each app is a whole website with a lot of code, is that the way it suppose to be or should all apps related to a single site within a project ?
Im thinking of creating one django project for each site, but im now wondering if I should be creating one project where each app is one site. Can anyone please comment on this, what it the preferred way to do it ?
In the django documentation one app is only used for a poll, so it seems to be that, according to the documentation, that each app should be some part of functionality on the site.
An app is a submodule of a project which contains functionality (views, models, urls etc) for a specific part of the larger site and is as decoupled from the other apps as possible. The project as a whole is the website and your apps make up the separate parts of functionality for your site.
If your sites are going to basically contain the same functionality, it might be worth looking into the Sites framework which django provides.
So taking the polls example further.
Lets say the website is a survey site. There would be the polls app, which would contain the relevant models and views for creating and recording poll results. Then you might need to view the data, so you could create an analysis app, which would store the views for displaying dashboards and contain functions for data processing. Then we could take things a bit further, and have users be able to log in and see their own results (and give us the chance to link users to poll results), so you would make an accounts app, which would hold views for logging in/out, maybe a profile page etc.
So each of these different parts of functionality would be separated out into distinct apps, which would make up the project (site) as a whole.
If the apps have been decoupled properly, you could reuse the different apps in other projects (e.g. the accounts app could be dropped into a new project do provide logging in/out functionality)
In my experience so far, an app should be a reusable entity. There many guiding principles for choosing what to go and what not in an app. Separating authentication is one example. A projcet is one big collection of may apps and a reusable app can be in many projects.
Nowadays, there is a trend to move to micro service architecture, which is next level of separation of functionality with each service doing best one thing.
Each project is a unit in itself, not an individual app. So you host the project, not the app. I recommend using different project for each site and using micro-service architecture. A lot depends on your existing codebase too.
i'm a bit of a newcomer to Django/Python but trying to figure something out--hope you can help.
I'm trying to create a personal website with a page dedicated to some of the Python and Django projects that I've completed through several different online courses.
I'm just having a tough time figuring out the best way to link through and assemble the project directories on my server.
My first project is just the files for my blog itself. I've created a new directory in the same home root as the blog project housing another of my django projects. Just looking for a bit of assistance on how i link out to the second project from my blog.
I thought i could use the urls.py file for my blog to redirect link to the second project (ie projects/project2) utilizing a views definition from the views.py file for one of the apps in the blog. But then--i'm getting tripped up on how to render that link to the second project.
Any forward guidance is greatly appreciated.
In general, anything that makes sense to be served under different domain (not necessarily subdomain) would better be a separate project for sure. Exceptional case would be a project with almost same functionality but different branding within same organization. In such case, Django's built-in sites framework can be considered.
For different projects, you need different project roots along with different wsgi/port bindings and processes. They can still be listed within a single nginx configuration as a deployment example. Another popular way is using Docker but deployment methods vary.
For different apps in a single project, there is only one binding and one root already. Create apps and list them in your settings.py and urls.py. If you need subdomains with single deployment, tkaemming/django-subdomains might be helpful.
For different policies (rarely) in a single app under different domains, learn about sites framework. You need to hand code the difference in views.
and so on...
This question has been troubling me for some days now and I've tried asking in many places for advice, but it seems that nobody can answer it clearly or even provide a reference to an answer.
I've also tried searching for tutorials, but I just cannot find any type of tutorial that explains how you would use a reusable third-party django app (most tutorials explain how to write them, none explain how to use them).
Also, I've taken a look here:
How to re-use a reusable app in Django - it doesn't explain how to actually use it IN a project itself
and here:
How to bind multiple reusable Django apps together? - the answer by aquaplanet kind of makes sense, but I thought I would ask this question to solve the mental block I am facing in trying to understand this.
In order to best explain this, let me do so by example (note, it is not something I am actually building).
I am creating a project that acts like Reddit. I will have users, links and voting/points. Based on this crude example, I will want to reuse 3 (arbitrary) third-party apps: user, voting/points and links.
I decide to use each of them as any other python package (meaning that they will be treated as a package and none of their code should be touched) [would this method actually work? Or do you have to be able to edit third-party apps to build a project??)
With these apps now within my project, I will use a main app to handle all the template stuff (meaning everything I see on the frontend will be in a single app).
I will then either use that same main app for custom logic (in views.py) or I will break up that logic among different apps (but will still use a single frontend-only app).
From the 3 paragraphs above, is this structure applicable (or can it work) ?
Now lets say that this structure is applicable and I am using a single main app for the frontend and custom logic.
What would I write in models.py? How would I integrate things from the 3 reusable apps into the main models.py file?
How would I reference the reusable apps in views.py? Lets take the example of contrib.auth
With this built-in app, for logging out I would write:
from django.contrib.auth import logout
from django.contrib.auth.decorators import login_required
from django.shortcuts import redirect
#login_required
def user_logout(request):
logout(request)
return redirect('/home/')
Although the above code is simple, is that basically how things would be done with any reusable app?
My question is very long, but I think that this reusable app issue is something a lot of developers aren't quite clear about themselves and maybe this answer will help a lot of others who have heard about the promises of reusable apps, but fail to understand how to actually use them.
TL;DR:
Nope & it depends...
Some (Very) Common Reusable Apps
django.contrib.admin
django.contrib.auth
django.contrib.staticfiles
... those are all reusable Django apps, that happen to be shipped with Django (most of them were not, at some point in time)
Ok, some other reusable apps that don't ship with Django:
django-rest-framework
django-registration
South
Those are all truly reusable apps, and nothing less. There are very many more apps like that.
How do they do it?
To me your question looks more like "how do I build reusable apps", then "how to use them". Actually using them is very different from app to app, because they do very different things. There is only one rule: RTFM No way around that either.
Often, they rely on one or more of the following:
additional value(s) in settings.py
addition (usually one include statement) to urls.py
subclassing and/or mixins for Models, Forms, Fields, Views etc.
template tags and/or filters
management commands
...
Those are all powerful ways though which your app can provide functionality to other apps. There is no recipe (AFAIK) to make a reusable app, because there are so many different scenarios to consider. It all depends on what exactly your app should do.
Reusable apps provide functionalities
I'd argue that it's important to not think of reusable apps as "working together" with other app, but instead recognize that that they "provide functionality." The details of the functionality provided should dictate the way the target developer is supposed to use your library.
Not everything should be reusable
Obviously enough, even though many apps can "in principle" be reusable, it often makes little sense to do so, because it is way faster to clump things together (and make them just "work together").
I'm not sure why you think you need a main app for the "frontend" stuff. The point of a reusable app is that it takes care of everything, you just add (usually) a single URL to include the urls.py of the app, plus your own templates and styling as required.
And you certainly don't need to wrap the app's views in your own views, unless you specifically want to override some functionality.
I don't understand at all your question about models. There's no such thing as a "main" models file, and using a reusable app's models is just the same as using models from any of your own apps.
Normally you would not edit a third-party app, that would make it very hard to integrate updates. Just install the app in your virtualenv (you are using virtualenv, of course!) with pip, which will put it in the lib directory, and you can reference it just like any other app. Make sure you add it to INSTALLED_APPS.
I'm very new to django and python as well. I want to try out a project written in django.
Let say the project have 3 modules
User
CRUD
Forgot password
login
Booking
CRUD
Search
Default (basically is for web users to view)
Home page
about us
All these have different business logic for the same entity.
Should I create 3 apps for this? If 3 different apps, then the table name is all different as it will automatic add a prefix for table name.
Any suggestion?
There's really no correct answer to this. In general, the way in which you break down any programming task into 'modules' is very much a matter of personal taste.
My own view on the subject is to start with a single module, and only break it into smaller modules when it becomes 'necessary', e.g. when a single module becomes excessively large.
With respect to the apps, if all the apps share the same database tables, you'll probably find it easier to do everything in a single app. I think using multiple Django apps is only really necessary when you want to share the same app between multiple projects.
I agree in #aya answer and I also supported your structure for multiple modules. In my project, I created 18 apps. Each app perform different rules:
1. accounts
- login
- forgot password
- register
- profile
2. common
//in here all the common function use by different apps
3. front
- home
- testimonial
4. guides
//tutorials
And lots more apps...
I arrange this way so that it will be easy to trace, debug, and find the codes. If your problem is the name of table you can set the class Meta of db_table.
I am relatively new to Django and Python myself too. In practice, try to have your Django apps do one thing and do it well. If you find that an app is becoming more and more complex, it may be worth splitting this out into multiple apps.
I would not worry about the DB tablename as Django handles the DB interaction for you. If you name your apps and models well, your code should be fairly self documenting.
I have recently learnt a lot of "best practices" in how to setup and layout Django projects from the ebook 2 Scoops of Django. I am not affiliated with them in any way, but have just learnt a lot from it.
Also, definitely run through the Django tutorial if you haven't already.
Hope this has helped!
Focus on making your apps reusable. This way you will save significant number of time in your next project. Good article about it is available at the Django's website.
If you have closely integrated modules or depending on each other, then there's no real benefit of having them in separate apps, because you won't ever use them separately. Organizing in separate Python modules will be just fine.
Also do not think about "how will my tables be named" when you consider project organization. Tables can be easily renamed while bad design will make you trouble as the project will grow.
I just wanted to try to build a project with django. Therefore I have a (basic) question on how to manage such a project. Since I cannot find any guidelines or so on how to split a project into applications.
Let's take a kind of SO as an example. Which applications would you use?
I'd say there should be the applications "users" and "questions". But what if there was a topic system with static articles, too. Maybe they also could receive votes.
How to build the apps structure then? One app for "questions", "votes" and "topics" or just one app "content"?
I have no idea what to do. Maybe it's because I know not very much about Django yet, but I'm interested either...
There aren't hard-and-fast rules, but I would say it's better to err on the side of more specialized applications. Ideally an application should handle just one functional concern: i.e. "tagging" or "commenting" or "auth/auth" or "posts." This type of design will also help you reuse available open source applications instead of reinventing the wheel (i.e. Django comes with auth and comments apps, django-tagging or django-taggable can almost certainly do what you need, etc).
Generic foreign keys can help you decouple applications such as tagging or commenting that might be applied to models from several other applications.
You should try and separate the project in as much applications as possible. For most projects an application will not contain more than 5 models. For example a project like SO would have separate applications for UsersProfiles, Questions, Tags (there's a ready one in django for this), etc. If there was a system with static pages that'd be a separate application too (there are ready ones for this purpose). You should also try and make your applications as generic as possible, so you may reuse them in other projects. There's a good presentation on reusable apps.
Just like any set of dependencies... try to find the most useful stand-alone aspects of the project and make those stand-alone apps. Other Django Apps will have higher level functionality, and reuse the parts of the lowest level apps that you have set up.
In my project, I have a calendar app with its own Event object in its models. I also have a carpool database set up, and for the departure time and the duration I use the calendar's Event object right in my RideShare tables. The carpooling database is calendar-aware, and gets all the nice .ics export and calendar views from the calendar app for 'free.'
There are some tricks to getting the Apps reusable, like naming the templates directory: project/app2/templates/app2/index.html. This lets you refer to app2/index.html from any other app, and get the right template. I picked that one up looking at the built-in reusable apps in Django itself. Pinax is a bit of a monster size-wise but it also demonstrates a nice reusable App structure.
If in doubt, forget about reusable apps for now. Put all your messages and polls in one app and get through one rev. You'll discover during the process what steps feel unnecessary, and could be broken out as something stand-alone in the future.
A good question to ask yourself when deciding whether or not to write an app is "could I use this in another project?". If you think you could, then consider what it would take to make the application as independent as possible; How can you reduce the dependancies so that the app doesn't rely on anything specific to a particular project.
Some of the ways you can do this are:
Giving each app its own urls.py
Allowing model types to be passed in as parameters rather than explicitly declaring what models are used in your views. Generic views use this principle.
Make your templates easily overridden by having some sort of template_name parameter passed in your urls.py
Make sure you can do reverse url lookups with your objects and views. This means naming your views in the urls.py and creating get_absolute_url methods on your models.
In some cases like Tagging, GenericForeignKeys can be used to associate a model in your app to any other model, regardless of whether it has ForeignKeys "looking back" at it.
I'll tell you how I am approaching such question: I usually sit with a sheet of paper and draw the boxes (functionalities) and arrows (interdependencies between functionalities). I am sure there are methodologies or other things that could help you, but my approach usually works for me (YMMV, of course).
Knowing what a site is supposed to be is basic, though. ;)