fix sketchy model migration to match ORM definition

lemarche/siaes/migrations/0081_fix_improper_migration.py

@@ -0,0 +1,97 @@
+"""
+Fixes 0022_siae_users_m2m_add_through.py
+The problem was that because of obscure SQL script ran into the migration,
+an undeclared unique constraint persisted, without any trace of it on the model.
+This led to mysterious integrity constraints errors.
+"""
+
+import django.db.models.deletion
+import django.utils.timezone
+from django.conf import settings
+from django.db import migrations, models
+
+
+def copy_trough_model_data(apps, schema_editor):
+    """Copy data from SiaeUser to TEMP_SiaeUser"""
+    old_siae_user_model = apps.get_model("siaes", "SiaeUser")
+    new_siae_user_model = apps.get_model("siaes", "TEMP_SiaeUser")
+
+    new_siae_user_list = []
+    for old_siae_user in old_siae_user_model.objects.all():
+        new_siae_user_list.append(
+            new_siae_user_model(
+                siae=old_siae_user.siae,
+                user=old_siae_user.user,
+                created_at=old_siae_user.created_at,
+                updated_at=old_siae_user.updated_at,
+            )
+        )
+    new_siae_user_model.objects.bulk_create(new_siae_user_list)
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("siaes", "0080_remove_historicalsiae_is_cocontracting_and_more"),
+    ]
+
+    operations = [
+        # Create a temporary Through model
+        migrations.CreateModel(
+            name="TEMP_SiaeUser",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name="ID"),
+                ),
+                (
+                    "siae",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE, to="siaes.siae", verbose_name="Structure"
+                    ),
+                ),
+                (
+                    "user",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        to=settings.AUTH_USER_MODEL,
+                        verbose_name="Utilisateur",
+                    ),
+                ),
+                (
+                    "created_at",
+                    models.DateTimeField(default=django.utils.timezone.now, verbose_name="Date de création"),
+                ),
+                (
+                    "updated_at",
+                    models.DateTimeField(auto_now=True, verbose_name="Date de modification"),
+                ),
+            ],
+        ),
+        # Create a temporary model field, linked to the temporary Through model
+        migrations.AddField(
+            model_name="siae",
+            name="temp_users",
+            field=models.ManyToManyField(
+                blank=True,
+                related_name="siaes",
+                through="siaes.TEMP_SiaeUser",
+                to=settings.AUTH_USER_MODEL,
+                verbose_name="Gestionnaires",
+            ),
+        ),
+        # Copy the old through model data to the new one
+        migrations.RunPython(copy_trough_model_data, migrations.RunPython.noop),
+        # Remove old SiaeUser and associated fields
+        migrations.RemoveField(model_name="siae", name="users"),
+        migrations.DeleteModel("SiaeUser"),
+        # Rename new TEMP_SiaeUser to override the old one
+        migrations.RenameField(
+            model_name="siae",
+            old_name="temp_users",
+            new_name="users",
+        ),
+        migrations.RenameModel(
+            old_name="TEMP_SiaeUser",
+            new_name="SiaeUser",
+        ),
+    ]