This is more of a best-practices question, and given that I'm quite tired it mightn't make much sense.
I've been putting together a blog app as a learning experience and as an actual part of a website I am developing.
I've designed it like most apps so that you can list blog posts by multiple criteria i.e.
/blog/categories/
/blog/authors/
/blog/tags/
/blog/popular/
etc.
On each page above I also want to list how many entries are a part of that criteria
i.e. for "categories", I want /blog/categories/ to list all the different categories, but also mention how many blog posts are in that category, and possibly list those entries.
Django seems to give you lots of ways of doing this, but not much indication on what's best in terms of flexibility, reusability and security.
I've noticed that you can either
A: Use generic/very light views, pass a queryset to the template, and gather any remaining necessary information using custom template tags.
i.e. pass the queryset containing the categories, and for each category use a template tag to fetch the entries for that category
or B: Use custom/heavy views, pass one or more querysets + extra necessary information through the view, and use less template tags to fetch information.
i.e. pass a list of dictionaries that contains the categories + their entries.
The way I see it is that the view is there to take in HTTP requests, gather the required information (specific to what's been requested) and pass the HTTP request and Context to be rendered. Template tags should be used to fetch superflous information that isn't particularly related to the current template, (i.e. get the latest entries in a blog, or the most popular entries, but they can really do whatever you like.)
This lack of definition (or ignorance on my part) is starting to get to me, and I'd like to be consistent in my design and implementation, so any input is welcome!
I'd say that your understanding is quite right. The main method of gathering information and rendering it via a template is always the view. Template tags are there for any extra information and processing you might need to do, perhaps across multiple views, that is not directly related to the view you're rendering.
You shouldn't worry about making your views generic. That's what the built-in generic views are for, after all. Once you need to start stepping outside what they provide, then you should definitely make them specific to your use cases. You might of course find some common functionality that is used in multiple views, in which case you can factor that out into a separate function or even a context processor, but on the whole a view is a standalone bit of code for a particular specific use.
Related
I'm developing a website in Django where many of the sites' models' instances are presented to the user in a standardized format on many different pages. I'd like to avoid redundancy in the template coding by creating standard model instance template code then just inserting it each page where a model instance needs to be displayed.
What is the best practice for creating standardized instance display code, then adding it into many different pages?
There are several ways of accomplishing this...
One is to use an include tag and pass your object to the template. Another, similar approach is to create a template tag to render the object, which is useful if you need to do some extra processing in Python before doing the rendering.
Yet another way is to add an instance method to your model to render itself to HTML (or some other format), much the same way a form instance has .as_ul or .as_p that you can call in your template where needed.
Neither way is right or wrong, it just depends on what you're most comfortable with stylistically and what's most efficient for your needs.
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).
Lets say I have a website with a small application that lists the 10 newest members, or something dynamic like that. I want this to view on every page, perhaps in a sidebar. How would i go about doing this.
My thoughts on the matter. I might not get the whole django thing just yet, but when I have a url like /foo/ calling a view bar - but what info do I have to send to the template from this view. Does every view have to send the info to the template (just so I can view my app) or is there someway to call this from the template instead.
I have tried to read through the documentation, but its seems I just can't understand this.
The usual way to provide '10 newest members' type of information from other apps is via a template tag. See this article by James Bennett on best practices (although note it's a bit out of date, as it was written before the inclusion_tag and simple_tag shortcuts were available).
Create a template tag that you can call on the page
Create a context processor and inject extra context variables onto each pageload
I'm sure there are other ways of doing this but those are probably the most logical two. The first gives you more power and will waste less processing time (for pages where you don't want to display the data) but a context processor is much more simple to write (you don't have to bend over backwards to please the template_tag gods).
Both are valuable things to know so there you go. Go and learn!
"Does every view have to send the info to the template (just so I can view my app)"
Yes.
"Is there someway to call this from the template instead."
No.
Your views are just functions. Functions can call other functions. That's ordinary good design. You can still do ordinary good design in Django.
You do have the ability to provide a "context". This is still done in the views to provide additional "context" for the templates. See http://docs.djangoproject.com/en/dev/ref/templates/api/#writing-your-own-context-processors for writing your own context processor.
Nothing (well almost nothing) is done in the template except render the objects provided by the view into HTML (or XML).
If you have a page that is an amalgamation of stuff from many small apps, then you have two tiers of apps.
Independent Apps.
Composite Apps that depend on Composite or Independent Apps.
Your composite app can call other app view functions to gather data.
Your composite app template can include other app template elements to present that data.
You have all the power of Python to decompose the independent apps into "data production" functions, view functions, template components and final page templates.
An independent app Page will use a view function and a template. The view function will use the data production functions. The template will use template components.
Decomposition still works, even in Django.
The whole point of an MVC framework is to separate design (templates) from logic (controllers). However, template languages often afford a limited degree of "design logic" to occur. This includes basic if statements, loops, filtering, etc.
I've created a Django template tag that can take any list or QuerySet and "pagify" it. It splits the list up into pages based on a specified page size then adds the pages into the Context. The usage is as follows:
{% pagify articles by 20 as pages %}
I can then call a separate include to iterate over the pages and produce a nice list of pages wherever I needed it.
This seemed like an optimal way to do it because it allowed me to page any list in the context; I didn't have to rely on the controller to return paged results. But a colleague argued that this seemed like too much logic for the template. I thought this still fell within the realm of design-based logic since the page would still function even without paging, and determining page size feels like a template responsibility.
My question, is this too much logic for the template? or is this a clean way to be handling this?
It's always been my understanding that the view isn't supposed to be devoid of logic. It's just supposed to be devoid of any controller logic. Paging just has to do with how the data is displayed which is exactly what the view logic is supposed to contain.
Put it this way; what if you were using your data model in another medium, say, not on the web but via some kind of console-based application or background task? Wouldn't it be nice to be able to get "pages" of data through a controller (or manager) rather than having to somehow rely on a template to do this work for you?
While I'd certainly agree that the "look" of the paged data should be handled by your template, the "act" of paging should be left up to a controller (Django view) or even through some kind of custom manager (models.Manager) method.
The view should not contain business logic or navigation logic. What you are describing is presentation functionality (carefully avoiding the l-word here), which can be placed in the view layer.
You may want to check out django-pagination, which provides a similar template tag.
I agree with your colleague; the template should be fed paginated data rather than performing the pagination. The key question, I think, is whether determining page size is a template duty, and I don't think so; I'd say it should be handled at a higher level.
I'm working on a blog application, and I want to have a sidebar that includes a list of all the months the blog has been in existence, to provide links to archives pages. Moreover, I'd like to make this automatically update when the month changes, rather than hardcoding it in the template. Of course, as far as I can tell, this means that I'll have to calculate the list of months in every view, and pass it into every template from every view.
I'd like to avoid this, if possible. Is there a way to calculate the list once and automatically apply it to every template, without having to explicitly pass it into the template from every view?
There are a few possible solutions to your problem.
If you really want to have this on every page on your site a context processor is probably your best choice. Context processors are basic way to inject data into all template contexts. Be aware however that the context processor will be called on every request.
An alternative solution would be to create a custom template tag and use it on a shared base template for all of the pages you wish to have your sidebar. Template tags are a bit more complex to create but they are more flexible.
With either solution you should also look at Django's cache framework. The cache framework makes it pretty easy to temporarily store your calculated values for a while to save some work on each request.
You want a template context processor
Django - having middleware communicate with views/templates
http://docs.djangoproject.com/en/dev/ref/templates/api/?from=olddocs#id1
Django's template inheritance should cover this. You could create a base template that handles your sidebar functionality. Your other views extend this template.
Template Inheritance:
http://www.djangobook.com/en/1.0/chapter04/#s-template-inheritance
A combination of custom template tags as mentioned previously and template fragment caching should do the trick.