Django - Requiring Prefetching

06 May 2020 https://github.com/pawl/django_require_prefetch_select_related_example

I made a repository to try to figure out the best way to require prefech_related/select_related when fetching a model's related objects. I also want to figure out a good pattern for avoiding duplicated prefetch_related/select_related for multiple places in a codebase that need the related objects eager loaded in the same way.

Nginx - WebDAV

29 Apr 2020 Just learned Nginx has WebDAV support: https://nginx.org/en/docs/http/ngx_http_dav_module.html

It's a lot faster than the Python package I was using: https://github.com/mar10/wsgidav

Wsgidav is great though. It's super customizable and the documentation is great too.

Django - ModelChoiceField queryset caching

23 Apr 2020

It would be nice to know a better way to cache the ModelChoiceField’s queryset when it’s used in a form that runs “is_valid()” in a loop (like Formsets do). The best way I know how at the moment is by not using a ModelChoiceField at all. The solution requires using a ChoiceField, running the query for choices outside of the loop, then passing the choices into the form to override the ChoiceField choices.

Here’s an example:

# See full example: https://github.com/pawl/django_modelchoicefield_caching/blob/master/myapp/views.py#L31-L51 for song in playlist: form_data = {'title': song["title"], 'artist': song["artist"]} song_form = forms.SongFormWithModelChoiceField(data=form_data) song_form.is_valid() # runs a query to get the ModelChoiceField queryset each time print('ModelChoiceField - query count AFTER validating all songs:', len(connection.queries)) # 5 queries # query for choices outside of the loop to prevent unnecessary queries artist_choices = [(artist.pk, artist.name) for artist in models.Artist.objects.all()] for song in playlist: form_data = {'title': song["title"], 'artist': song["artist"]} # pass choices into the Form song_form = forms.SongFormWithChoiceField( artist_choices=artist_choices, data=form_data) song_form.is_valid() print('ChoiceField w/ choices passed in - query count AFTER validating all songs:', len(connection.queries)) # 6 queries (only 1 more query!)

Django API Forms

23 Apr 2020 Just found a really cool library for using Django's built-in forms to validate JSON: https://github.com/Sibyx/django_api_forms

I made a small example with it to show how it works with ModelChoiceFields: https://github.com/pawl/django_api_forms_modelchoicefield_example

Seems like a more lightweight version of DRF's serializers (but only for deserializing and validating) and with a similar API to Django's built-in forms.

Learning Vue Through Terrible Pull Requests

18 Apr 2020 I made a pull request asking to "remove the unused public/index.html" file from django-vue-template: https://github.com/gtalarico/django-vue-template/pull/53

Well, the author responded and it turns out it's definitely used (by vue magic): https://cli.vuejs.org/guide/html-and-static-assets.html

Oops, definitely should have googled "vue public/index.html" before making that pull request. I made another pull request to add a link about it to the django-vue-template docs: https://github.com/gtalarico/django-vue-template/pull/54

Server Side Templates Vs Front End Framework

12 Apr 2020 These Reddit comments have some of the best descriptions I've seen for the type of scenario where you'd use a front end framework over server side templates:

"Server side templating can work really well when the website is static. The problem is that as you add more and more dynamic elements, you either have to go to the server and re-render everything with every change (which can be slow), or you can make the changes on the client side with something like jQuery. But the latter option presents a challenge because you'll eventually find yourself duplicating functionality.

For example, imagine a to-do list website that you render on the server with a templating language. It fetches the user's to-do items from the database and then renders the list. Now let's say you want to let a user add a new item without re-rendering the entire page. You could use AJAX to tell the server to add the new item, but now you need to update your UI list accordingly. You could use jQuery to construct a new DOM element and append it, but now that list element exists in two different places: in your jQuery code and in your template on the server. If your website becomes very dynamic, this situation can get really unwieldy from a programming perspective.

Both Angular (from what I've read) and React (from personal experience) are highly suitable for creating single page apps, with the goal of creating a dynamic, fast, and maintainable website. There are other benefits, as well as downsides, to using Angular and React, but I hope this clears it up a little bit. Both of them make server side templating unnecessary by moving UI logic/rendering from your server to the client's browser. So a user who visits your React powered to-list website would get the React code as a JS bundle, it would make an AJAX call to your server to get just the data, and then it would render the UI based on the data." -/u/VertiGuo (https://www.reddit.com/r/node/comments/6t22cr/back_end_templating_engine_or_front_end_framework/dlhukkf/)

"for example putting together a form, and handle the response is easy, but if you have to manage a list of items where the user can add/remove items, or change the schema of items based on a selector (e.g. phone type or address) you have to split the logic, and put some on client side scripts, which can become very messy. not to mention live updates like chat, comments etc.

creating a separate backend and frontend solves this problem, as the backend's responsibility will be only manipulating the database, retrieve data and run jobs providing an api and the frontend's will be the only the representation of these data, providing the user interface. this separation lets developers use different technologies and languages on the two side, as well as specializing in these. for the beginning this approach is a bit hard to learn, but it will worth it on the long run." -/u/bdvx (https://www.reddit.com/r/webdev/comments/cbrdte/html_templating_vs_spa/etifiar/)

Integrating Django and Vue.js

08 Apr 2020 This is a great guide for including vue bundles in server side templates: https://medium.com/@rodrigosmaniotto/integrating-django-and-vuejs-with-vue-cli-3-and-webpack-loader-145c3b98501a

Otherwise, if you're starting a fresh project with a separate front-end, this is a good template: https://github.com/gtalarico/django-vue-template/

The deepest reason why modern JavaScript frameworks exist

04 Apr 2020 Another really good article about why using a front-end framework is a good idea:
https://medium.com/dailyjs/the-deepest-reason-why-modern-javascript-frameworks-exist-933b86ebc445

Make your life easier with Vue.js

02 Apr 2020 This is a really great article that shows how vue can make dynamic forms so much better: https://dev.to/tsanak/make-your-life-easier-with-vuejs-4mj5

Django - RelatedManager.set not removing models

14 Feb 2020

In my opinion, one of django's biggest gotchas is using `RelatedManager.set` with models that have non-nullable ForeignKey fields. ### Example Models.py (with a one-to-many relationship and a non-nullable ForeignKey): ``` class Reporter(models.Model): name = models.CharField(max_length=255) class Article(models.Model): title = models.CharField(max_length=255) reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE) ``` Guess how many articles are on the reporter after you do this?: ``` reporter = Reporter.objects.create(name="paul") # add 2 articles to the reporter article_1 = reporter.article_set.create(title="blah") reporter.article_set.create(title="blah2") # set only 1 article on the reporter reporter.article_set.set([article_1]) ``` I expected just one article to be on the reporter. Nope: ``` reporter.article_set.count() 2 ``` How do the docs say it should work? >This method accepts a clear argument to control how to perform the operation. If False (the default), the elements missing from the new set are removed using remove() and only the new ones are added. Well, crap, what's going on? It turns out you need to read the docs for `RelatedManager.remove` for a hint: >For ForeignKey objects, this method only exists if null=True. So, it turns out that `set()` is using `remove()` and `remove()` is only available on models with ForeignKeys that are `null=True`. What does `set()` do with things it needs to `remove()` when `remove()` isn't available? Nothing...

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