Added dao methods needed to add or update multiple sms senders for a service.

Remove the unique constraint for service on the ServiceSmsSender model.

app/dao/service_sms_sender_dao.py

@@ -32,3 +32,80 @@ def insert_service_sms_sender(service, sms_sender):
                                       is_default=True
                                       )
     db.session.add(new_sms_sender)
+
+
+def dao_get_service_sms_senders_by_id(service_id, service_sms_sender_id):
+    return ServiceSmsSender.query.filter_by(
+        id=service_sms_sender_id,
+        service_id=service_id
+    ).one()
+
+
+def dao_get_sms_senders_by_service_id(service_id):
+    return ServiceSmsSender.query.filter_by(service_id=service_id).all()
+
+
+@transactional
+def dao_add_sms_sender_for_service(service_id, sms_sender, is_default, inbound_number_id=None):
+    old_default = _get_existing_default(service_id=service_id)
+    if is_default:
+        _reset_old_default_to_false(old_default)
+    else:
+        _raise_when_no_default(old_default)
+
+    new_sms_sender = ServiceSmsSender(
+        service_id=service_id,
+        sms_sender=sms_sender,
+        is_default=is_default,
+        inbound_number_id=inbound_number_id
+    )
+
+    db.session.add(new_sms_sender)
+    return new_sms_sender
+
+
+@transactional
+def dao_update_service_sms_sender(service_id, service_sms_sender_id, is_default, sms_sender=None):
+    old_default = _get_existing_default(service_id)
+    if is_default:
+        _reset_old_default_to_false(old_default)
+    else:
+        if old_default.id == service_sms_sender_id:
+            raise Exception("You must have at least one SMS sender as the default")
+
+    sms_sender_to_update = ServiceSmsSender.query.get(service_sms_sender_id)
+    sms_sender_to_update.is_default = is_default
+    if not sms_sender_to_update.inbound_number_id and sms_sender:
+        sms_sender_to_update.sms_sender = sms_sender
+    db.session.add(sms_sender_to_update)
+    return sms_sender_to_update
+
+
+def _get_existing_default(service_id):
+    sms_senders = dao_get_sms_senders_by_service_id(service_id=service_id)
+    if sms_senders:
+        old_default = [x for x in sms_senders if x.is_default]
+        if len(old_default) == 1:
+            return old_default[0]
+        else:
+            raise Exception(
+                "There should only be one default sms sender for each service. Service {} has {}".format(
+                    service_id,
+                    len(old_default)
+                )
+            )
+    return None
+
+
+def _reset_old_default_to_false(old_default):
+    if old_default:
+        old_default.is_default = False
+        db.session.add(old_default)
+
+
+def _raise_when_no_default(old_default):
+    # check that the update is not updating the only default to false
+    if not old_default:
+        raise Exception("You must have at least one letter contact as the default.", 400)
+
+