Incompleted transactions with PostgreSQL

How to deal with incompleted transactions in PostgreSQL? It seems we can’t make queries after single transaction fail. Instead we get: psycopg2.InternalError: current transaction is aborted, commands ignored until end of transaction block

Here’s minimal code sample to reproduce the issue:

import peewee
db = peewee.PostgresqlDatabase(
            database='test',
            host='localhost',
            port=None,
            user='test',
            password=None)

class User(peewee.Model):
   username = peewee.CharField(max_length=50, unique=True)

   class Meta:
       database = db

User.create_table()
User.create(username='test')

So, I get single user with username “test”. If I try to create another one, I’ll get an error:

>>> User.create(username='test')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 2193, in create
    inst.save(force_insert=True)
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 2278, in save
    new_pk = insert.execute()
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 1623, in execute
    return self.database.last_insert_id(self._execute(), self.model_class)
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 1314, in _execute
    return self.database.execute_sql(sql, params, self.require_commit)
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 1721, in execute_sql
    res = cursor.execute(sql, params or ())
psycopg2.IntegrityError: duplicate key value violates unique constraint "user_username"
DETAIL:  Key (username)=(test) already exists.

And that’s predictable and fine! (By the way, how should we catch this kind of exception?)

But when I try to make another request, it fails:

>>> User.get(username='test')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 2203, in get
    return sq.get()
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 1521, in get
    return clone.execute().next()
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 1556, in execute
    self._qr = ResultWrapper(self.model_class, self._execute(), query_meta)
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 1314, in _execute
    return self.database.execute_sql(sql, params, self.require_commit)
  File "/Users/test/.virtualenvs/test/lib/python3.3/site-packages/peewee.py", line 1721, in execute_sql
    res = cursor.execute(sql, params or ())
psycopg2.InternalError: current transaction is aborted, commands ignored until end of transaction block

And I need to drop database connection and create a new one to make it work again.

[coleifer]

Added fbd6c20aa3fa75b1a92b74030f201d0e43304e28 which adds a new parameter to the Database class autorollback:

db = PostgresqlDatabase('my_db', autocommit=True, autorollback=True)

[tconkling]

As a new user of peewee (which is great - thanks for creating & maintaining it!), I’m very much in favor of changing the default; the current behavior was confusing to me when I switched my underlying database from sqlite to postgres and started getting errors about open transactions that had not existed with sqlite. Of course, I don’t have tons of code to maintain that uses peewee that would be negatively affected by this change.

Regardless, I’d argue that - semantically speaking - autocommit’s current behavior is broken.