Fix CompensationAction unit None

* adds correct declaration of unit (qm -> m2) for template rendering
* adds migration to transform existing qm units to m2

compensation/migrations/0013_auto_20221117_0819.py

@@ -0,0 +1,35 @@
+# Generated by Django 3.1.3 on 2022-11-17 07:19
+
+from django.db import migrations
+
+from compensation.models import UnitChoices
+
+
+def harmonize_action_units(apps, schema_editor):
+    """
+    CompensationAction units (based on UnitChoices) can be mixed up at this point where
+        * qm represents m²  and
+        * m2 represents m²
+
+    We drop qm in support of m2
+
+    """
+    CompensationAction = apps.get_model("compensation", "CompensationAction")
+    actions = CompensationAction.objects.filter(
+        unit="qm"
+    )
+
+    for action in actions:
+        action.unit = UnitChoices.m2
+        action.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('compensation', '0012_auto_20221116_1322'),
+    ]
+
+    operations = [
+        migrations.RunPython(harmonize_action_units),
+    ]

compensation/models/action.py

@@ -19,8 +19,9 @@ class UnitChoices(models.TextChoices):
     """
     cm = "cm", _("cm")
     m = "m", _("m")
+    m2 = "m2", _("m²")
+    m3 = "m3", _("m³")
     km = "km", _("km")
-    qm = "qm", _("m²")
     ha = "ha", _("ha")
     st = "pcs", _("Pieces")  # pieces