The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
Object-relational mapping in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language...
Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...
The MIT License is a free software license originating at the Massachusetts Institute of Technology . It is a permissive license, meaning that it permits reuse within proprietary software provided all copies of the licensed software include a copy of the MIT License terms...
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SQLAlchemy provides "a full suite of well known enterprise-level persistence patterns, designed for efficient and high-performing database access, adapted into a simple and Pythonic domain language". SQLAlchemy's philosophy is that SQL databases behave less and less like object collections the more size and performance start to matter, while object collections behave less and less like tables and rows the more abstraction starts to matter. For this reason it has adopted the Data Mapper pattern (like Hibernate
Hibernate (Java)
Hibernate is an object-relational mapping library for the Java language, providing a framework for mapping an object-oriented domain model to a traditional relational database...
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
In software engineering, the active record pattern is an architectural pattern found in software that stores its data in relational databases. It was named by Martin Fowler in his 2003 book Patterns of Enterprise Application Architecture...
used by a number of other object-relational mappers. However, optional plugins such as Elixir and declarative allow users to develop using declarative syntax.
SQLAlchemy was first released in February, 2006 and has quickly become one of the most widely used object-relational mapping tools in the Python community.
Example
The following example represents an n-to-1 relationship between movies and their directors. It is shown how user-defined Python classes create according database tables, how instances with relationships are created from either side of the relationship, and finally how the data can be queried -- illustrating automatically-generated SQL queries for both lazy and eager loading.
Schema definition
Creating two Python classes and according database tables in the DBMS:
from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relation, sessionmaker
Base = declarative_base
class Movie(Base):
__tablename__ = 'movies'
id = Column(Integer, primary_key=True)
title = Column(String(255), nullable=False)
year = Column(Integer)
directed_by = Column(Integer, ForeignKey('directors.id'))
director = relation("Director", backref='movies', lazy=False)
def __init__(self, title=None, year=None):
self.title = title
self.year = year
def __repr__(self):
return "Movie(%r, %r, %r)" % (self.title, self.year, self.director)
class Director(Base):
__tablename__ = 'directors'
id = Column(Integer, primary_key=True)
name = Column(String(50), nullable=False, unique=True)
alldata = session.query(Movie).all
for somedata in alldata:
print somedata
SQLAlchemy issues the following query to the DBMS (omitting aliases):
SELECT movies.id, movies.title, movies.year, movies.directed_by, directors.id, directors.name
FROM movies LEFT OUTER JOIN directors ON directors.id = movies.directed_by
Setting lazy=True (default) instead, SQLAlchemy would first issue a query to get the list of movies and only when needed (lazy) for each director a query to get the name of the according director:
SELECT movies.id, movies.title, movies.year, movies.directed_by
FROM movies
SELECT directors.id, directors.name
FROM directors
WHERE directors.id = %s
SQLObject is a Python object-relational mapper between a SQL database and Python objects. It is currently experiencing community popularity, and forms a part of many applications...
TurboGears is a Python web application framework consisting of several WSGI components such as Pylons, SQLAlchemy, Genshi and Repoze.TurboGears is designed around the model-view-controller architecture, much like Struts or Ruby on Rails, designed to make rapid web application development in Python...
Django
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