Merge pull request #315 from HackSoftware/blog/timestamps-autos-and-defaults

Timestamps: autos, defaults & opinions

Author: RadoRado

config/django/base.py

@@ -41,6 +41,7 @@
     "styleguide_example.integrations.apps.IntegrationsConfig",
     "styleguide_example.files.apps.FilesConfig",
     "styleguide_example.emails.apps.EmailsConfig",
+    "styleguide_example.blog_examples.apps.BlogExamplesConfig",
 ]
 
 THIRD_PARTY_APPS = [

styleguide_example/blog_examples/__init__.py

@@ -0,0 +1,6 @@
+from django.apps import AppConfig
+
+
+class BlogExamplesConfig(AppConfig):
+    default_auto_field = "django.db.models.BigAutoField"
+    name = "styleguide_example.blog_examples"

styleguide_example/blog_examples/apps.py

@@ -0,0 +1,47 @@
+# Generated by Django 4.1.3 on 2023-01-28 14:23
+
+from django.db import migrations, models
+import django.utils.timezone
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='TimestampsOpinionated',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created_at', models.DateTimeField(default=django.utils.timezone.now)),
+                ('updated_at', models.DateTimeField(blank=True, null=True)),
+            ],
+        ),
+        migrations.CreateModel(
+            name='TimestampsWithAuto',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+            ],
+        ),
+        migrations.CreateModel(
+            name='TimestampsWithAutoAndDefault',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created_at', models.DateTimeField(default=django.utils.timezone.now)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+            ],
+        ),
+        migrations.CreateModel(
+            name='TimestampsWithDefault',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('created_at', models.DateTimeField(default=django.utils.timezone.now)),
+                ('updated_at', models.DateTimeField(default=django.utils.timezone.now)),
+            ],
+        ),
+    ]

styleguide_example/blog_examples/migrations/0001_initial.py

@@ -0,0 +1,31 @@
+from django.db import models
+from django.utils import timezone
+
+
+class TimestampsWithAuto(models.Model):
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+
+class TimestampsWithAutoAndDefault(models.Model):
+    created_at = models.DateTimeField(default=timezone.now)
+    updated_at = models.DateTimeField(auto_now=True)
+
+
+class TimestampsWithDefault(models.Model):
+    created_at = models.DateTimeField(default=timezone.now)
+    updated_at = models.DateTimeField(default=timezone.now)
+
+
+class TimestampsOpinionated(models.Model):
+    """
+    We want to have the following behavior:
+
+    1. created_at is set by default, but can be overridden.
+    2. updated_at is not set on initial creation (stays None).
+    3. The service layer (check `model_update`) takes care of providing value to `updated_at`,
+        if there's no value provided by the caller.
+    """
+
+    created_at = models.DateTimeField(default=timezone.now)
+    updated_at = models.DateTimeField(blank=True, null=True)

styleguide_example/blog_examples/migrations/__init__.py

@@ -0,0 +1,185 @@
+from datetime import timedelta
+
+from django.test import TestCase
+from django.utils import timezone
+
+from styleguide_example.blog_examples.models import (
+    TimestampsOpinionated,
+    TimestampsWithAuto,
+    TimestampsWithAutoAndDefault,
+    TimestampsWithDefault,
+)
+
+
+class TimestampsTests(TestCase):
+    def test_timestamps_with_auto_behavior(self):
+        """
+        Timestamps are set automatically
+        """
+        obj = TimestampsWithAuto()
+        obj.full_clean()
+        obj.save()
+
+        self.assertIsNotNone(obj.created_at)
+        self.assertIsNotNone(obj.updated_at)
+
+        self.assertNotEqual(obj.created_at, obj.updated_at)
+
+        """
+        Timestamps cannot be overridden
+        """
+        timestamp = timezone.now() - timedelta(days=1)
+
+        obj = TimestampsWithAuto(created_at=timestamp, updated_at=timestamp)
+        obj.full_clean()
+        obj.save()
+
+        self.assertNotEqual(timestamp, obj.created_at)
+        self.assertNotEqual(timestamp, obj.updated_at)
+
+        """
+        updated_at gets auto updated, while created_at stays the same
+        """
+        obj = TimestampsWithAuto()
+        obj.full_clean()
+        obj.save()
+
+        original_created_at = obj.created_at
+        original_updated_at = obj.updated_at
+
+        obj.save()
+        # Get a fresh object
+        obj = TimestampsWithAuto.objects.get(id=obj.id)
+
+        self.assertEqual(original_created_at, obj.created_at)
+        self.assertNotEqual(original_updated_at, obj.updated_at)
+
+    def test_timestamps_with_mixed_behavior(self):
+        """
+        Timestamps are set automatically / by default
+        """
+        obj = TimestampsWithAutoAndDefault()
+        obj.full_clean()
+        obj.save()
+
+        self.assertIsNotNone(obj.created_at)
+        self.assertIsNotNone(obj.updated_at)
+
+        self.assertNotEqual(obj.created_at, obj.updated_at)
+
+        """
+        Some timestamps can be overridden
+        """
+        timestamp = timezone.now() - timedelta(days=1)
+
+        obj = TimestampsWithAutoAndDefault(created_at=timestamp, updated_at=timestamp)
+        obj.full_clean()
+        obj.save()
+
+        # This is default
+        self.assertEqual(timestamp, obj.created_at)
+        # This is auto_now
+        self.assertNotEqual(timestamp, obj.updated_at)
+
+        """
+        updated_at gets auto updated, while created_at stays the same
+        """
+        obj = TimestampsWithAutoAndDefault()
+        obj.full_clean()
+        obj.save()
+
+        original_created_at = obj.created_at
+        original_updated_at = obj.updated_at
+
+        obj.save()
+        # Get a fresh object
+        obj = TimestampsWithAutoAndDefault.objects.get(id=obj.id)
+
+        self.assertEqual(original_created_at, obj.created_at)
+        self.assertNotEqual(original_updated_at, obj.updated_at)
+
+    def test_timestamps_with_default_behavior(self):
+        """
+        Timestamps are set by default
+        """
+        obj = TimestampsWithDefault()
+        obj.full_clean()
+        obj.save()
+
+        self.assertIsNotNone(obj.created_at)
+        self.assertIsNotNone(obj.updated_at)
+
+        self.assertNotEqual(obj.created_at, obj.updated_at)
+
+        """
+        Both timestamps can be overridden
+        """
+        timestamp = timezone.now() - timedelta(days=1)
+
+        obj = TimestampsWithDefault(created_at=timestamp, updated_at=timestamp)
+        obj.full_clean()
+        obj.save()
+
+        self.assertEqual(timestamp, obj.created_at)
+        self.assertEqual(timestamp, obj.updated_at)
+        # And by transitivity
+        self.assertEqual(obj.created_at, obj.updated_at)
+
+        """
+        created_at / updated_at are not auto updated
+        """
+        obj = TimestampsWithDefault()
+        obj.full_clean()
+        obj.save()
+
+        original_created_at = obj.created_at
+        original_updated_at = obj.updated_at
+
+        obj.save()
+        # Get a fresh object
+        obj = TimestampsWithDefault.objects.get(id=obj.id)
+
+        self.assertEqual(original_created_at, obj.created_at)
+        self.assertEqual(original_updated_at, obj.updated_at)
+
+    def test_timestamps_with_opinionated_behavior(self):
+        """
+        created_at is only set by default
+        """
+        obj = TimestampsOpinionated()
+        obj.full_clean()
+        obj.save()
+
+        self.assertIsNotNone(obj.created_at)
+        self.assertIsNone(obj.updated_at)
+
+        """
+        Both timestamps can be overridden
+        """
+        timestamp = timezone.now() - timedelta(days=1)
+
+        obj = TimestampsOpinionated(created_at=timestamp, updated_at=timestamp)
+        obj.full_clean()
+        obj.save()
+
+        self.assertEqual(timestamp, obj.created_at)
+        self.assertEqual(timestamp, obj.updated_at)
+        # And by transitivity
+        self.assertEqual(obj.created_at, obj.updated_at)
+
+        """
+        updated_at is not auto updated, created_at stays the same
+        """
+        obj = TimestampsOpinionated()
+        obj.full_clean()
+        obj.save()
+
+        original_created_at = obj.created_at
+        original_updated_at = obj.updated_at
+
+        obj.save()
+        # Get a fresh object
+        obj = TimestampsOpinionated.objects.get(id=obj.id)
+
+        self.assertEqual(original_created_at, obj.created_at)
+        self.assertEqual(original_updated_at, obj.updated_at)

styleguide_example/blog_examples/models.py

@@ -0,0 +1,21 @@
+# Generated by Django 4.1.3 on 2023-01-28 14:33
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('common', '0005_simplemodel_randommodel_simple_objects'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='simplemodel',
+            name='created_at',
+        ),
+        migrations.RemoveField(
+            model_name='simplemodel',
+            name='updated_at',
+        ),
+    ]