ruff: Two flake8-django issues to be fixed

[cclauss]

Good First Issue

% pipx install ruff % ruff --select=DJ --show-source .

test_app/models.py:12:7: DJ008 Model does not define `__str__` method
   |
12 | class Company(models.Model):
   |       ^^^^^^^ DJ008
13 |     name = models.CharField(
14 |         max_length=100,
   |

waffle/models.py:107:5: DJ012 Order of model's inner classes, methods, and fields does not follow
    the Django Style Guide: `save` method should come before custom method
    |
105 |           cache.delete_many(keys)
106 |
107 |       def save(self, *args: Any, **kwargs: Any) -> None:
    |  _____^
108 | |         self.modified = timezone.now()
109 | |         ret = super().save(*args, **kwargs)
110 | |         if hasattr(transaction, 'on_commit'):
111 | |             transaction.on_commit(self.flush)
112 | |         else:
113 | |             self.flush()
114 | |         return ret
    | |__________________^ DJ012
115 |
116 |       def delete(self, *args: Any, **kwargs: Any) -> tuple[int, dict[str, int]]:
    |

Found 2 errors.

---

% ruff rule DJ008

django-model-without-dunder-str (DJ008)

Derived from the flake8-django linter.

What it does

Checks that __str__ method is defined in Django models.

Why is this bad?

Django models should define __str__ method to return a string representation of the model instance, as Django calls this method to display the object in the Django Admin and elsewhere.

Models without __str__ method will display a non-meaningful representation of the object in the Django Admin.

Example

from django.db import models

class MyModel(models.Model):
    field = models.CharField(max_length=255)

Use instead:

from django.db import models

class MyModel(models.Model):
    field = models.CharField(max_length=255)

    def __str__(self):
        return f"{self.field}"

---

% ruff rule DJ012

Derived from the flake8-django linter.

What it does

Checks for the order of Model's inner classes, methods, and fields as per the [Django Style Guide].

Why is this bad?

The [Django Style Guide] specifies that the order of Model inner classes, attributes and methods should be as follows:

1. All database fields
2. Custom manager attributes
3. class Meta
4. def __str__()
5. def save()
6. def get_absolute_url()
7. Any custom methods

Examples

from django.db import models

class StrBeforeFieldModel(models.Model):
    class Meta:
        verbose_name = "test"
        verbose_name_plural = "tests"

    def __str__(self):
        return "foobar"

    first_name = models.CharField(max_length=32)
    last_name = models.CharField(max_length=40)

Use instead:

from django.db import models

class StrBeforeFieldModel(models.Model):
    first_name = models.CharField(max_length=32)
    last_name = models.CharField(max_length=40)

    class Meta:
        verbose_name = "test"
        verbose_name_plural = "tests"

    def __str__(self):
        return "foobar"