This document discusses Python object-relational mappers (ORMs) and provides examples of using SQLite3, Django ORM, and Peewee to interact with databases. It introduces ORM concepts like data mapping and ActiveRecord and ActiveRecord patterns. Code samples are given to demonstrate creating models, querying, and retrieving data using Django ORM and Peewee with SQLite databases. Resources for further information on SQLAlchemy, ORM comparisons, and PonyORM are also listed.

1. Python ORMs
Cosmin Poieana
<cmin@ropython.org>
→ baze de date
→ tipuri de ORM (modele)
→ comparații (exemple)
→ peewee
→ resurse

2. Database APIs
NoSQL
● redis
● mongodb
● …
SQL
● pyodbc
● sqlite3
● pymysql
● ...

3. sqlite3
● Nu are nevoie de driver, server
● Static pe disc / memorie
● Interogări simple (+ mici diferențe)
1. conexiune
2. obținere cursor
3. execuție interogare
*. commit
4. închidere

4. sqlite3
>>> import sqlite3
>>> conn = sqlite3.connect("ropy.db")
>>> c = conn.cursor()
>>> c.execute("CREATE TABLE persoana (nume text,
adresa text, varsta real)")
>>> c.execute("INSERT INTO persoana VALUES
('Nume1', 'Adresa1', 20)")
>>> conn.commit()
>>> c.execute("SELECT * FROM persoana")
>>> c.fetchall()
[(u'Nume1', u'Adresa1', 20.0)]

5. ORM
● Object-relational mapping
(convertire date dintr-un sistem incompatibil in
POO)
● Pony, Django ORM, peewee, SQLAlchemy
● Modele
– DataMapper
– ActiveRecord
● SQLite, MySQL, PostgreSQL[, Oracle]

6. Django ORM
$ django-admin.py startproject ropy
$ cd ropy
$ python manage.py syncdb
>>> from django.db import models
>>> class Person(models.Model):
... name = models.TextField()
... class Meta:
... app_label = 'demo'
>>> class Address(models.Model):
... address = models.TextField()
... person = models.ForeignKey(Person)
... class Meta:
... app_label = 'demo'

7. Django ORM
>>> p = Person(name='person')
>>> p.save()
>>> print "%r, %r" % (p.id, p.name)
1, 'person'
>>> a = Address(person=p, address='address')
>>> a.save()
>>> print "%r, %r" % (a.id, a.address)
1, 'address'

8. Django ORM
>>> persons = Person.objects.filter(name='person')
>>> p = persons[0]
>>> print "%r, %r" % (p.id, p.name)
1, u'person'
>>> addresses = Address.objects.filter(person=p)
>>> addresses
[<address>]
>>> a = addresses[0]
>>> print "%r, %r" % (a.id, a.address)
1, u'address'

9. Peewee
>>> from peewee import SqliteDatabase, CharField,
ForeignKeyField, Model
>>> db = SqliteDatabase(':memory:')
>>> class Person(Model):
... name = CharField()
... class Meta:
... database = db
>>> class Address(Model):
... address = CharField()
... person = ForeignKeyField(Person)
... class Meta:
... database = db
>>> Person.create_table()
>>> Address.create_table()

10. Peewee
>>> p = Person(name='person')
>>> p.save()
>>> a = Address(address='address',
person=p)
>>> a.save()

11. Peewee
>>> person = Person.select().where(Person.name ==
'person').get()
>>> print '%r, %r' % (person.id, person.name)
1, u'person'
>>> address = Address.select().where(Address.person ==
person).get()
>>> print '%r, %r' % (address.id, address.address)
1, u'address'

12. Resurse
● http://www.pythoncentral.io/sqlalchemy-vs-orms/
● http://peewee.readthedocs.org/en/latest/
● http://effectivedjango.com/orm.html
● http://www.sqlalchemy.org/
● http://ponyorm.com/