Establish relation between provider message and message number

this is so we can access brodcast_provider_message_number from
BroadcastProviderMessage object

app/celery/broadcast_message_tasks.py

@@ -32,10 +32,10 @@ def send_broadcast_event(broadcast_event_id):
 def send_broadcast_provider_message(broadcast_event_id, provider):
     broadcast_event = dao_get_broadcast_event_by_id(broadcast_event_id)
 
-    broadcast_provider_message, message_number = create_broadcast_provider_message(broadcast_event, provider)
+    broadcast_provider_message = create_broadcast_provider_message(broadcast_event, provider)
     formatted_message_number = None
     if provider == BroadcastProvider.VODAFONE:
-        formatted_message_number = format_sequential_number(message_number.broadcast_provider_message_number)
+        formatted_message_number = format_sequential_number(broadcast_provider_message.message_number)
 
     current_app.logger.info(
         f'invoking cbc proxy to send '

app/dao/broadcast_message_dao.py

@@ -60,4 +60,4 @@ def create_broadcast_provider_message(broadcast_event, provider):
             broadcast_provider_message_id=broadcast_provider_message_id)
         db.session.add(provider_message_number)
         db.session.commit()
-    return provider_message, provider_message_number
+    return provider_message

app/models.py

@@ -2483,6 +2483,8 @@ class BroadcastProviderMessage(db.Model):
 
     UniqueConstraint(broadcast_event_id, provider)
 
+    message_number = association_proxy('broadcast_provider_message_number', 'broadcast_provider_message_number')
+
 
 class BroadcastProviderMessageNumber(db.Model):
     """
@@ -2500,6 +2502,9 @@ class BroadcastProviderMessageNumber(db.Model):
     broadcast_provider_message_id = db.Column(
         UUID(as_uuid=True), db.ForeignKey('broadcast_provider_message.id'), nullable=False
     )
+    broadcast_provider_message = db.relationship(
+        'BroadcastProviderMessage', backref=db.backref("broadcast_provider_message_number", uselist=False)
+    )
 
 
 class ServiceBroadcastProviderRestriction(db.Model):

tests/app/dao/test_broadcast_message_dao.py

@@ -53,7 +53,7 @@ def test_create_broadcast_provider_message_creates_in_correct_state(sample_broad
         transmitted_content={'body': 'Initial content'}
     )
 
-    broadcast_provider_message, message_number = create_broadcast_provider_message(broadcast_event, 'fake-provider')
+    broadcast_provider_message = create_broadcast_provider_message(broadcast_event, 'fake-provider')
 
     assert broadcast_provider_message.status == 'sending'
     assert broadcast_provider_message.broadcast_event_id == broadcast_event.id