created nickname model object

uses a genericforeignkey so it can be "to" events or superevents.
name of the nickname is unique, and can only be applied to one event
or superevent at a time.

next up, add some logic for creating GWs and populating nicknames.

gracedb/events/migrations/0056_nickname.py

+# Generated by Django 2.2.10 on 2020-09-28 20:15
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('contenttypes', '0002_remove_content_type_name'),
+        ('events', '0055_add_catalog_search'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Nickname',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=50, unique=True)),
+                ('description', models.TextField()),
+                ('object_id', models.PositiveIntegerField()),
+                ('content_type', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='contenttypes.ContentType')),
+            ],
+        ),
+    ]

gracedb/events/models.py

@@ -13,6 +13,8 @@ from model_utils.managers import InheritanceManager
 
 from django.contrib.auth import get_user_model
 from django.contrib.contenttypes.models import ContentType
+from django.contrib.contenttypes.fields import GenericForeignKey
+from django.contrib.contenttypes.fields import GenericRelation
 
 from guardian.models import GroupObjectPermission
 import logging; log = logging.getLogger(__name__)
@@ -158,6 +160,23 @@ class Label(models.Model):
         # applied, but a user tries to apply 'ADVREQ')
         pass
 
+# Creating "Nickname" object class. Set up a generic foreign key so that a
+# nickname object can be linked to either an event or a superevent. 
+#
+# https://medium.com/@bhrigu/django-how-to-add-foreignkey-to-multiple-models-394596f06e84
+
+@python_2_unicode_compatible
+class Nickname(models.Model):
+    name = models.CharField(max_length=50,  unique=True)
+    description = models.TextField(blank=False)
+
+    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
+    object_id = models.PositiveIntegerField()
+    content_object = GenericForeignKey('content_type', 'object_id')
+
+    def __str__(self):
+        return self.name
+
 
 @python_2_unicode_compatible
 class Event(models.Model):
@@ -234,6 +253,14 @@ class Event(models.Model):
 
     gw_id = models.CharField(max_length=25, blank=True, null=True, unique=True)
 
+    # Update: new development. many-to-one relationship between nickname(s) and 
+    # events and superevents. Some GWs were "confirmed" before the advent of 
+    # superevents and so the nickname object should be applied to either events or 
+    # superevents. That's why there's all this genericforeignkey business instead of
+    # just a foreignkey.
+
+    gw_ids = GenericRelation(Nickname)
+
 
     class Meta:
         ordering = ["-id"]

gracedb/superevents/models.py

@@ -14,6 +14,7 @@ from django.conf import settings
 from django.contrib.auth import get_user_model
 from django.contrib.auth.models import Group as AuthGroup
 from django.contrib.contenttypes.models import ContentType
+from django.contrib.contenttypes.fields import GenericRelation
 from django.core.exceptions import ValidationError
 from django.db import models, IntegrityError
 from django.urls import reverse
@@ -28,7 +29,7 @@ from core.models import CleanSaveModel, AutoIncrementModel, LogBase, \
 from core.time_utils import posixToGpsTime, gpsToUtc
 from core.utils import int_to_letters, letters_to_int
 from events.models import Event, SignoffBase, VOEventBase, EMObservationBase, \
-    EMFootprintBase
+    EMFootprintBase, Nickname
 
 # AEP experimental: try computedfields stuff:
 # https://django-computedfields.readthedocs.io/en/
@@ -119,6 +120,9 @@ class Superevent(CleanSaveModel, AutoIncrementModel, ComputedFieldsModel):
     # Cannibalizing gw_id field, putting into DB as a user-defined parameter. 
     gw_id = models.CharField(max_length=25, blank=True, null=True, unique=True)
 
+    # Adding gw_ids generic relation.
+    gw_ids = GenericRelation(Nickname)
+
     # Booleans
     is_gw = models.BooleanField(default=False)
     # Because there are multiple actions/permissions involved with exposing a