fix eventinstance uuid migration with this abomination https://docs.djangoproject.com/en/dev/howto/writing-migrations/#migrations-that-add-unique-fields

src/program/migrations/0079_eventinstance_uuid.py

@@ -19,7 +19,7 @@ class Migration(migrations.Migration):
                 default=uuid.uuid4,
                 editable=False,
                 help_text="This field is mostly here to keep Frab happy, it is not the PK of the model",
-                unique=True,
+                null=True,
             ),
         ),
     ]

src/program/migrations/0081_populate_eventinstance_uuids.py

@@ -0,0 +1,23 @@
+# Generated by Django 3.0.3 on 2020-02-22 15:13
+
+import uuid
+
+from django.db import migrations
+
+
+def gen_uuid(apps, schema_editor):
+    MyModel = apps.get_model("program", "EventInstance")
+    for row in MyModel.objects.all():
+        row.uuid = uuid.uuid4()
+        row.save(update_fields=["uuid"])
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("program", "0080_auto_20200222_1547"),
+    ]
+
+    operations = [
+        migrations.RunPython(gen_uuid),
+    ]

src/program/migrations/0082_eventinstance_uuid_not_null.py

@@ -0,0 +1,25 @@
+# Generated by Django 3.0.3 on 2020-02-22 15:13
+
+import uuid
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("program", "0081_populate_eventinstance_uuids"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="eventinstance",
+            name="uuid",
+            field=models.UUIDField(
+                default=uuid.uuid4,
+                editable=False,
+                help_text="This field is mostly here to keep Frab happy, it is not the PK of the model",
+                unique=True,
+            ),
+        ),
+    ]