DjangoCon US 2022: Day 1

The Django Admin Is Your Oyster: Let’s Extend Its Functionality

• Don’t make it easy for attackers to find your admin page…don’t use /admin.

• Override ModelAdmin.get_search_results to speed up searching.

• Remember to use prefetch_related and select_related to reduce DB queries.

• Add optional checkboxes to change forms to kickoff extra functions when saved.

  • You can also dynamically set help text for better UX.

• You can use multiple databases in a single admin.

  # Migrate
  $ python manage.py --database=sandbox
  
  # settings.py
  DATABASES = {
    'default': {...},
    'sandbox': {...}
  }
  
  # utils.py
  class SandboxAdminModel(admin.ModelAdmin):
    using = 'sandbox'
  
    def save_model(self, request, obj, form, change):
        obj.save(using=self.using)
  
    def delete_model(self, request, obj):
        obj.delete(using=self.using)
  
    def get_queryset(self, request):
        return super().get_queryset(request).using(self.using)
  
  # admin.py
  @admin.register(MySandboxModel)
  class MySandboxModelAdmin(SandboxModelAdmin):
    ...
  

• Extend change_form.html to add help text for the whole model, not just fields.

  # change_form.html
  {% extends "admin/change_form.html" %}
  
  {% block form_top %}
    {{ original.admin_help_text }}
  {% endblock %}
  
  # models.py
  class MyModel(models.Model):
    admin_help_text = "..."
  

• Create custom actions for bulk changes.

  # admin.py
  def increase_msrp_by_8_perc(modeladmin, request, queryset):
    ...
  
  @admin.register(Car)
  class CarAdmin(admin.ModelAdmin):
    actions = [increase_msrp_by_8_perc]
  

Documenting Django Code in 2022

• https://diataxis.fr: A framework for authoring technical documentation.

You Don’t Need Containers to Run Django in Production

• When should you use containers? When you have…
  • Thousands of programmers.
  • Millions of users.
  • Billions in valuation.
• There is a lot of FOMO around containers. For example, reproducibility is a big selling point for containers, but generally, this benefit is rarely taken advantage of.
• Some downsides of using containers are added complexity and cost.
• What do we want in production?
  • Secure environment.
  • Protection against malicious users.
  • Don’t want to wake up in the middle of the night.
  • Seamless code updates.
• Web Server (WSGI vs ASGI):
  • WSGI is 20 years old…and it shows.
    • Limited concurrency.
    • Graphic: Showed that as clients scale with gunicorn, response time gets worse. The graph represented a BEST case scenario.
  • ASGI is 5 years old…and it shows.
    • Unlimited concurrency (ignoring memory).
    • Graphic: Showed that as clients scale with uvicorn, response time gets worse. The graph represented a WORST case scenario.
• Reverse Proxy (nginx):
  • Can help limit concurrency as needed.
  • nginx can handle 20 million RPM on a 8 core VM.
  • Caddy is a new/easier alternative, but nginx is tried and tested.
• Process Monitor (SystemD)
• Deployment (Git Deploy Config)
• Bonus Tip: Use software that offers LTS.

Herding your database queries: diagnosing, improving and guarding performance of DB interactions in your Django apps

• Blog Post

• Tools like django-debug-toolbar and django-silk are great for diagnosing rogue queries, but there can be cases where these tools are not going to help directly (e.g. with a js frontend).

• To solve this, they rolled their own custom middleware to analyze queries per request and output the result to the terminal.

  Received request GET /library/books/, status 200, db_query_count=29, db_query_time_ms=136.421, duration_ms=192.56
  

• After you optimize your queries, you can protect yourself from regression with unit tests by taking advantage of django_assert_max_num_queries.

• You can also use coverage context to check new endpoints that are created and don’t have unit tests.

The Django Jigsaw Puzzle: Aligning All the Pieces

• (other) MVC == MVT (django)
  • Model == Model
  • View == Template
  • Controller == View
• The Django Admin is great, but if your admin.py is growing past 20 lines, you might be relying on it too much.
• django-extensions: One of the things it does is auto import models in the django shell.
• Don’t use /admin!

                                        WSGI Server
                                        ┌────────────────────────────────────────────────┐
                                        │ Middlware                                      │
                                        │ ┌────────────────────────────────────────────┐ │
                                        │ │ Django app                                 │ │
         HTTP request                   │ │ ┌────────────────────────────────────────┐ │ │
        ─────────────► ┌──────────┐ ──► │ │ │ ┌────────┐     ┌─────┐     ┌──────┐    │ │ │   ┌─────────┐
Browser                │Web Server│     │ │ │ │URL conf│ ──► │     │ ─── │Models│ ───┼─┼─┼── │Databases│
        ◄───────────── └──────────┘ ◄── │ │ │ └────────┘     │     │     └──────┘    │ │ │   └─────────┘
         HTTP response      ▲           │ │ │                │Views│                 │ │ │
                            │           │ │ │                │     │     ┌─────────┐ │ │ │
                            ▼           │ │ │                │     │ ─── │Templates│ │ │ │
                         ┌──────┐       │ │ │                └─────┘     └─────────┘ │ │ │
                         │ File │       │ │ └────────────────────────────────────────┘ │ │
                         │System│       │ └────────────────────────────────────────────┘ │
                         └──────┘       └────────────────────────────────────────────────┘

Nurturing a “Legacy” Codebase

• What is a “legacy” codebase?
  • Code with, potentially forgotten, history.
  • Code that follow outdated conventions.
  • Usually still running in production.
• Should you evolve or rebuild? Ask yourself…
  • Does the code meet current requirements?
  • Are there frequent or sever production issues?
  • How healthy are the dependencies?
• Lets say you choose “evolve,” what should you do?
  • Automated tests with good coverage.
  • Upgrade/Replace outdated dependencies.
  • Use a linter and/or black for code formatting.
  • Use pre-commit for cross-team consistency.
  • Make sure current devs understand the story of the code.
  • Help future devs by writing detailed commit messages along with an issue tracker.
  • Document!
  • Build a culture of leaving clues for the future!