broadcast migrations: replace older ones & add final removal

migrations/versions/0336_broadcast_msg_content_2.py

@@ -11,14 +11,28 @@ from notifications_utils.template import BroadcastMessageTemplate
 from sqlalchemy.dialects import postgresql
 from sqlalchemy.orm.session import Session
 
-
 revision = '0336_broadcast_msg_content_2'
 down_revision = '0335_broadcast_msg_content'
 
 
 def upgrade():
-    pass
+
+    conn = op.get_bind()
+
+    results = conn.execute(sa.text("""
+        UPDATE
+            broadcast_message
+        SET
+            content = templates_history.content
+        FROM
+            templates_history
+        WHERE
+            broadcast_message.content is NULL and
+            broadcast_message.template_id = templates_history.id and
+            broadcast_message.template_version = templates_history.version
+        ;
+    """))
 
 
 def downgrade():
-    pass
+    op.alter_column('broadcast_message', 'content', nullable=True)