Rework upsert to use a transaction; #406

This avoids creating and then deleting participants.

gittip/elsewhere/__init__.py

@@ -34,30 +34,36 @@ def upsert(platform, user_id, username, user_info):
  user_id = unicode(user_id)
 
 
- # Create a new participant.
- # =========================
-
- participant_id = reserve_a_random_participant_id()
-
-
- # Upsert the account elsewhere.
+ # Insert the account if needed.
  # =============================
+ # Do this with a transaction so that if the insert fails, the
+ # participant we reserved for them is rolled back as well.
 
- INSERT = """\
+ try:
+ with db.get_transaction() as txn:
+ participant_id = reserve_a_random_participant_id(txn)
+ INSERT = """\
 
- INSERT INTO elsewhere
- (platform, user_id, participant_id)
- VALUES (%s, %s, %s)
+  INSERT INTO elsewhere
+  (platform, user_id, participant_id)
+  VALUES (%s, %s, %s)
 
- """
- try:
- db.execute(INSERT, (platform, user_id, participant_id))
+ """
+ txn.execute(INSERT, (platform, user_id, participant_id))
  except IntegrityError:
+ pass
 
- # That account elsewhere is already in our db. Back out the stub
- # participant we just created.
 
- db.execute("DELETE FROM participants WHERE id=%s", (participant_id,))
+ # Update their user_info.
+ # =======================
+ # Cast everything to unicode, because (I believe) hstore can take any type
+ # of value, but psycopg2 can't.
+ #
+ # https://postgres.heroku.com/blog/past/2012/3/14/introducing_keyvalue_data_storage_in_heroku_postgres/
+ # http://initd.org/psycopg/docs/extras.html#hstore-data-type
+
+ for k, v in user_info.items():
+ user_info[k] = unicode(v)
 
  UPDATE = """\
 
@@ -67,12 +73,7 @@ def upsert(platform, user_id, username, user_info):
  RETURNING participant_id
 
  """
- for k, v in user_info.items():
- # Cast everything to unicode. I believe hstore can take any type of
- # value, but psycopg2 can't.
- # https://postgres.heroku.com/blog/past/2012/3/14/introducing_keyvalue_data_storage_in_heroku_postgres/
- # http://initd.org/psycopg/docs/extras.html#hstore-data-type
- user_info[k] = unicode(v)
+
  rec = db.fetchone(UPDATE, (user_info, platform, user_id))
  participant_id = rec['participant_id']