add constraint to prevent adjacent eventsessions for the same eventtype and location, and add some missing migrations

src/program/migrations/0095_event_duration_not_null_eventuuid_unique_proposal_duration_desc_and_new_eventsession_constraint.py

@@ -0,0 +1,54 @@
+# Generated by Django 3.0.3 on 2020-06-21 23:56
+
+import uuid
+
+import django.contrib.postgres.constraints
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("program", "0094_tags_blank"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="event",
+            name="duration_minutes",
+            field=models.PositiveIntegerField(
+                blank=True,
+                default=None,
+                help_text="The duration of this event in minutes. Leave blank to use the default from the event_type.",
+            ),
+        ),
+        migrations.AlterField(
+            model_name="event",
+            name="uuid",
+            field=models.UUIDField(
+                default=uuid.uuid4,
+                editable=False,
+                help_text="This field is not the PK of the model. It is used to create EventSlot UUID for FRAB and iCal and other calendaring purposes.",
+                unique=True,
+            ),
+        ),
+        migrations.AlterField(
+            model_name="eventproposal",
+            name="duration",
+            field=models.IntegerField(
+                blank=True,
+                help_text="How much time (in minutes) should we set aside for this event?",
+            ),
+        ),
+        migrations.AddConstraint(
+            model_name="eventsession",
+            constraint=django.contrib.postgres.constraints.ExclusionConstraint(
+                expressions=[
+                    ("event_location", "="),
+                    ("event_type", "="),
+                    ("when", "-|-"),
+                ],
+                name="prevent_adjacent_eventsessions",
+            ),
+        ),
+    ]

src/program/models.py

@@ -521,7 +521,7 @@ class EventProposal(UserSubmittedModel):
 
     duration = models.IntegerField(
         blank=True,
-        help_text="How much time (in minutes) should we set aside for this act? Please keep it between 60 and 180 minutes (1-3 hours).",
+        help_text="How much time (in minutes) should we set aside for this event?",
     )
 
     submission_notes = models.TextField(
@@ -842,6 +842,15 @@ class EventSession(CampRelatedModel):
                     ("event_type", RangeOperators.EQUAL),
                 ],
             ),
+            # we do not want adjacent sessions for the same type and location
+            ExclusionConstraint(
+                name="prevent_adjacent_eventsessions",
+                expressions=[
+                    ("event_location", RangeOperators.EQUAL),
+                    ("event_type", RangeOperators.EQUAL),
+                    ("when", RangeOperators.ADJACENT_TO),
+                ],
+            ),
         ]
 
     camp = models.ForeignKey(