refactor(people): Move relationship answers to answer set

Answers to the relationship questions have been moved from the relationship
to another model RelationshipAnswerSet.  A new answer set is created each
time a user answers the relationship questions.

Resolves #16
Resolves #17
Resolves #18

people/migrations/0016_add_answer_set.py

@@ -0,0 +1,78 @@
+# Generated by Django 2.2.10 on 2020-03-04 12:09
+import logging
+
+from django.db import migrations, models
+import django.db.models.deletion
+import django.utils.timezone
+
+logger = logging.getLogger(__name__)
+
+
+def forward_migration(apps, schema_editor):
+    """
+    Move existing data forward into answer sets from the relationship.
+    """
+    Relationship = apps.get_model('people', 'Relationship')
+
+    for relationship in Relationship.objects.all():
+        answer_set = relationship.answer_sets.first()
+        if answer_set is None:
+            answer_set = relationship.answer_sets.create()
+
+        for answer in relationship.question_answers.all():
+            answer_set.question_answers.add(answer)
+
+            
+def backward_migration(apps, schema_editor):
+    """
+    Move data backward from answer sets onto the relationship.
+    """
+    Relationship = apps.get_model('people', 'Relationship')
+
+    for relationship in Relationship.objects.all():
+        answer_set = relationship.answer_sets.last()
+
+        try:
+            for answer in answer_set.question_answers.all():
+                relationship.question_answers.add(answer)
+
+        except AttributeError:
+            pass
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('people', '0015_shrink_name_fields_to_255'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='relationship',
+            name='created',
+            field=models.DateTimeField(auto_now_add=True, default=django.utils.timezone.now),
+            preserve_default=False,
+        ),
+        migrations.AddField(
+            model_name='relationship',
+            name='expired',
+            field=models.DateTimeField(blank=True, null=True),
+        ),
+        migrations.CreateModel(
+            name='RelationshipAnswerSet',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('timestamp', models.DateTimeField(auto_now_add=True)),
+                ('question_answers', models.ManyToManyField(to='people.RelationshipQuestionChoice')),
+                ('relationship', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='answer_sets', to='people.Relationship')),
+            ],
+            options={
+                'ordering': ['timestamp'],
+            },
+        ),
+        migrations.RunPython(forward_migration, backward_migration),
+        migrations.RemoveField(
+            model_name='relationship',
+            name='question_answers',
+        ),
+    ]