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Object Data Mapper for pulsar asynchronous framework

Project Description

Pulsar-odm is build on top of pulsar, sqlalchemy and greenlet libraries to provide an implicit asynchronous object data mapper to use with code written with asyncio. Currently only one dialect is implemented and tested:

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
Release History

Release History

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0.6.2

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0.1.0

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File Name & Checksum SHA256 Checksum Help Version File Type Upload Date
pulsar_odm-0.6.2-py3-none-any.whl (20.2 kB) Copy SHA256 Checksum SHA256 3.6 Wheel Nov 20, 2016
pulsar-odm-0.6.2.tar.gz (14.9 kB) Copy SHA256 Checksum SHA256 Source Nov 20, 2016

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