Usage

To be able to use the object data mapper within standard blocking code, one needs to use pulsar GreenPool as the following snippet highlights:

from datetime import datetime

from sqlalchemy import Integer, Column, String, DateTime, Boolean

from pulsar.apps.greenio import GreenPool

import odm


class Task(odm.Model):
    id = Column(Integer, primary_key=True)
    subject = Column(String(250))
    done = Column(Boolean, default=False)
    created = Column(DateTime, default=datetime.utcnow)

    def __str__(self):
        return '%d: %s' % (self.id, self.subject)


def example(mp):
    # Make sure table is available
    mp.table_create()
    # Insert a new Task in the table
    with mp.begin() as session:
        task = mp.task(subject='my task')
        session.add(task)
    return task


if __name__ == '__main__':
    pool = GreenPool()
    mp = odm.Mapper('postgresql+green://odm:odmtest@127.0.0.1:5432/odmtests')
    mp.register(Task)
    task = pool._loop.run_until_complete(pool.submit(example, mp))
    print(task)

The example function is executed in a greenlet other than the main one. This is important otherwise the call fails:

>> example(mp)
>> Traceback (most recent call last):
...
RuntimeError: acquire in main greenlet

Running the function on the greenlet pool guarantees the correct asynchronous execution. When psycopg2 executes a command against the database on a child greenlet, it switches control to the parent (main) greenlet, which is controlled by the asyncio eventloop so that other asynchronous operations can be carried out. Once the result of the execution is ready, the execution switches back to the original child greenlet so that the example function can continue.

Testing

To run tests, create a new role and database, for postgresql:

psql -a -f tests/db.sql

Changelog

• Version 0.6

• Version 0.5

• Version 0.4

• Versions pre 0.4