I am new to Django and want to know deeper about the concept of signals.
I know how it works but really don't understand when should one really use it.
From the doc it says 'They’re especially useful when many pieces of code may be interested in the same events.'
What are some real applications that use signals for its advantage?
e.x. I'm trying to make a phone verification after user signup. Because it can be integrated inside the single app and the event that interested for the signal is only this 'verify' function, therefore I don't really need signal. I can just pass the information from one view to the other, rather than using pre_save signal from the registration.
I'm sorry if my question is kind of basic. But I really want to know some insight what is the real application, in which many codes interested in one particular event and what are some trade off in my application.
Thanks!!
Often signals is used when you need to do some database-specific low-level stuff. For example, if you use ElasticSearch for better searching documents on your site, you may want to automatically update search indexes, when new document is created or old one was edited.
Also you may have some complex logic of managing database objects. For example, you may need some specific logic of deleting object. For example, when user is deleted, you may want change all the links to his profile by some placeholder, or when new message is created or other action is performed by user, you want to update "last visited" field in user's profile and there's no direct relation between this action and updating the profile.
But when you're just implementing business-logic as in your example with verification, you don't need to use signals, because you don't need any universal logic related to deleting/creating/editing any object: you have a certain object with which you work and can do stuff directly.
Related
I want to use third party's REST API providing real-time foreign exchange rates in my django app which should continuously show changing exchange rates.
my code works but only on every page reload. but I want my code to be running continuously and showing exchange rate on page even if the page is not reloaded.
def example(request)
RATE__API_URL = 'REST API url'
while True
rate = requests.get(RATE__API_URL).json()
b = rate['rates']['EURUSD']['rate']
context = {'b': b}
return render(request, 'example.html', context)
on my example.html
<h1>
{{b}}
</h1>
code is running and does not show any errors
There are a few ways you can solve your requirement and none of them are the "right way", also much of it depends of what you have in your code, so I'll try to lay them out for you, and given the extent of what needs to be done while providing some links so you can work on it, but I will not give code because you'll require a fair amount of tailored code (sorry for that) and the references are good enough for you to develop your own solution.
The first thing you have to keep in mind is than you'll need to solve two really big and really different requirements:
The first part of your solution is retrieving the data from the source in a timely manner. The second part is to have a way to update the data in the template without the need for the user to reload the page.
To retrieve the data you said you already have an API where you'll get the data, but your code is not an efficient way to approach this, and it also may generate a risk because it is prone to hit too many times the API server; the best way I can think of would be if the API has webhooks or push notifications to which you can subscribe (which I doubt), the second best choice is to implement a Celery task, that way you will be calling the data regularly, and you'll not eat the API service resources.
With the first part out of the way, what you have left to do is to implement a way to call regularly from the UI for the newest data. Perhaps the simplest way to solve it is to implement an asynchronous call with Javascript/JQuery embedded in a script inside your template, but remember:
For this to work you'll need a model to store the data (If you don't
have an use for historic data, then just keep the most recent
one).
You'll need a view that exposes the data to your UI call (one that sends a JSON)
Another solution is to implement websockets, and the best way to achieve this for Django is using django-channels. You'll have to implement two main things:
In the backed you need to define the consumers flow so you can send
the data to the UI.
In the template you need to implement the websocket connection and a way to handle the updating part of the data for the user.
If you choose this way, and given than you don't need historic data, you can obviate the model and go straight from the Celery task to the UI through the consumer.
I have got an architectural question. Where should I check user permissions for certain operations?
For example:
1) In a controller, I get parameters from view and start a process in the intermediate model.
2) Intermediate model decide which parameter should be converted and transformed in any way and modify or create data through Models
3) Model communicate directly with DataBase
Where do You think is the right place in that "architecture" to check privileges to for example save sth to database?
I would actually put the authorization check before the controller is being called, kinda like described here (I really need to update that old post). Preferably as a decorator around the controller instance, which would give you a fine-grained control over what operation user is permitted to do, based on controller+method pair.
Another point where you might think about is "authorization lookup" helper function for use in your templates, because you might need to show or hide some UI elements from users, who should not be able to perform the associated operations. The controller+method check, before execution would still work as the actual safeguard then, but it tends to be a quality-of-life improvement.
You should not put the authorization checks inside the each controller or (even worse) model layer, because that tends to promote an excessive amount of copy-paste, which in turn can cause mistakes and becomes a huge problem, when you want to alter the mechanics of your authorization system.
I'm an advanced beginner at django and python. I'm writing an app to handle registration and abstract submission for a conference, and I'm trying to use class-based views. Users get an emailed link that includes their registration code in the url. Starting at this url, users move through a series of views that collect all the necessary info.
The complication comes from the fact that users often stop half way through, and then want to complete the process several days or weeks later. This means that they might continue from the current page, or they might just click that original link. In addition, after several weeks they might have missed certain deadlines, so, e.g., they can no longer submit an abstract (but they can still register). Along the way, they have checked or unchecked various options that also influence the path they should take through the app.
My question is: where is the best place to put the logic that determines if the user is currently allowed to view that page, and if not, the best url to redirect them too? I thought I would create a custom view class that, e.g., overrides the dispatch method to include global checks (e.g., is conference registration open?), and then subclasses could add additional checks (e.g., has the user entered all the necessary info for her abstract?). The problem I ran into was that the checks were run in the wrong order (I want base class checks run first). I then started investigating custom view decorators or custom middleware. At this point I realized I could use some expert advice about which approach to take. (If it matters, I am not using the django authentication system.) Thanks in advance.
Maybe the form wizard could help you managing the viewing sequence.
In general django greybeards advocate keeping row-wise logic in Models, and table-wise logic in Managers, so it seems appropriate to keep complex view logic in a master view class.
The wizard class can help maintain the order of the views, but to resume an out-dated session you may need to do some model saves (which could get too complex very quickly) or some cookie handling.
In the past, when presented with a similar situation, I took the simplest route and separated user registration and the task that the user wants to perform (event registration). The user registers once but if they fluff up the event registration, they just have to log back in at a later date and do it again (their hassle - not yours!).
Should I be writing application logic in my view code? For example, on submission of a form element, I need to create a user and send him an activation email. Is this something to do from a view function, or should I create a separate function to make it easier to test down the road? What does Django recommend here?
I found it very hard to figure out where everything goes when I started using django. It really depends on the type of logic you are writing.
First start with the models: model-methods and managers are a good place to perform row-level logic and table level logic i.e. a model manager would be a good place to write code to get a list of categories that are associated with all blogposts. A model method is a good place to count the characters in a particular blogpost.
View level logic should deal with bringing it all together - taking the request, performing the necessary steps to get to the result you need (maybe using the model managers) and then getting it ready for the template.
If there is code that doesn't fit in else where, but has a logical structure you can simply write a module to perform that. Similarly if there are scraps of code that you don't think belong, keep a utils.py to hold them.
You shouldn't perform any logic really in your templates - instead use template tags if you have to. These are good for using reusable pieces of code that you you neither want in every request cycle nor one single request cycle - you might want them in a subset (i.e. displaying a list of categories while in the blog section of your website)
If you do want some logic to be performed in every request cycle, use either context processors or middleware. If you want some logic to be performed only in one single request cycle, the view is probably the place.
TLDR: Writing logic in your view is fine, but there are plenty of places that might be more appropriate
Separating the registration code into it's own function to make testing easier is a good reason. If you allowed admins to register users in a separate, private view, then a registration function would be more DRY. Personally, I don't think a little application logic in the code will do to much harm.
You might find it instructive to have a look at the registration view in the django-registration app -- just to see how it's written, I'm not saying you should or have to use it. It has encapsulated the user registration into it's own function (there's a level of indirection as well, because the registration backends are pluggable).
I need to attach a significant number of additional properties to every user in my Django project. Some of these properties are simple CharFields, others are more complex ManyToManyFields. The trouble for me, is that in my digging around of ways to do this, I've found two options: The user profile method explained in the documentation, and the user subclassing method I see floating around the internet.
They both look complicated, and I'd rather not choose one only to find out that I need to go back and switch everything to the other method after months of development, so I ask here. Which way is the right way?
I have always done it traditional way, which means user profile, because it was suggested in the docs, but this is not the very clearest and elegant solution. You must always handle the possibility of user not having a profile, which I don't like very much. In the next project I would like to use the subclassing and if only it is in stable version of Django, I will press co-workers in my company to try this. This seems much more natural.
If you want to stay safe, use proile. If you prefer to take a little risk and benefit from a much better solution, use subclassing. It was introduced for a reason - there were several talks about weaknesses of profile solution.
The recommended, and, it seems, easiest, is the user profile method.
I've chosen a different path: I had a Clients model, witch should be authenticated. Instead of extending the user model to adjust to my Clients model, I left them separated. And then, when I save a new Client, in the Client save() method I create a user for that client. Then I do the same for updating and deleting to keep them in sync. I tried the other two options, but each had a lot of cons, that's why I gave up on them. And this has been working for me very well.
Regards. Aldo.
Like aldux, I prefer to create a separated Model and let User model untouched.