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SQLAlchemy and Elixir (in a few minutes) Neil Blakey-Milner http://nxsy.org/writings/ctpug-sqlalchemy-elixir/. Installing SQLAlchemy. easy_install SQLAlchemy Oh, and a DBAPI2 provider (pysqlite3 part of Python 2.5). Connect to the database. from sqlalchemy import * - PowerPoint PPT Presentation
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SQLAlchemy and Elixir(in a few minutes)
Neil Blakey-Milner
http://nxsy.org/writings/ctpug-sqlalchemy-elixir/
Installing SQLAlchemy
easy_install SQLAlchemy Oh, and a DBAPI2 provider (pysqlite3 part of Python 2.5)
Connect to the database...
from sqlalchemy import *
db = create_engine('sqlite:///tutorial.db')
metadata = BoundMetaData(db)
Declaring a table
>>> users_table = Table('users', metadata,
... Column('user_id', Integer, primary_key=True),
... Column('user_name', String(40)),
... Column('password', String(10))
... )
Creating a table
>>> metadata.engine.echo = True
>>> users_table.create()
CREATE TABLE users (
user_id INTEGER NOT NULL,
user_name VARCHAR(40),
password VARCHAR(10),
PRIMARY KEY (user_id)
)
Declaring a table from DB
users_table = Table('users', metadata, autoload=True)
Inserting into a table
>>> i = users_table.insert()
>>> i.execute(user_name='Mary', password='secure')
INSERT INTO users (user_name, password) VALUES (?, ?)
['Mary', 'secure']
COMMIT
Inserting multiple lines
>>> i.execute({'user_name':'Tom'}, {'user_name':'Fred'}, {'user_name':'Harry'})
INSERT INTO users (user_name) VALUES (?)
[['Tom'], ['Fred'], ['Harry']]
COMMIT
Selecting
>>> r = users_table.select(users_table.c.user_name == 'Harry').execute()
SELECT users.user_id, users.user_name, users.password
FROM users
WHERE users.user_name = ?
['Harry']
>>> print r.fetchone()
(4, u'Harry', None)
Table relationships
>>> email_addresses_table = Table('email_addresses',
... metadata,
... Column('address_id', Integer, primary_key=True),
... Column('email_address', String(100), nullable=False),
... Column('user_id', Integer,
... ForeignKey('users.user_id')))
Table relationships (2)
>>> email_addresses_table.create()
CREATE TABLE email_addresses (
address_id INTEGER NOT NULL,
email_address VARCHAR(100) NOT NULL,
user_id INTEGER,
PRIMARY KEY (address_id),
FOREIGN KEY(user_id) REFERENCES users (user_id)
)
Selecting across tables (1)
>>> email_addresses_table.insert().execute(
... {'email_address':'[email protected]',
... 'user_id':2},
... {'email_address':'[email protected]',
... 'user_id':1})
INSERT INTO email_addresses (email_address, user_id) VALUES (?, ?)
[['[email protected]', 2], ['[email protected]', 1]]
COMMIT
Selecting across tables (2)
>>> r = users_table.join(
... email_addresses_table
... ).select(
... order_by = users_table.c.user_id
... ).execute()
SELECT users.user_id, users.user_name, users.password, email_addresses.address_id, email_addresses.email_address, email_addresses.user_id
FROM users JOIN email_addresses ON users.user_id = email_addresses.user_id ORDER BY users.user_id
Selecting across tables (3)
>>> print [row for row in r]
[(1, u'Mary', u'secure', 2, u'[email protected]', 1),
(2, u'Tom', None, 1, u'[email protected]', 2)]
Mappers
SQLAlchemy allows you to associate a Table object with a Python class
>>> class User(object):... pass>>> mapper(User, users_table)>>> ed = User()>>> ed.user_name = 'Ed'>>> ed.password = 'edspassword'>>> session.save(ed)
Elixir
Elixir allows you to combine the steps, and use a declarative “domain specific language” to define the table.
class User(Entity): has_field('user_id', Integer, primary_key = True) has_field('user_name', String(40)) has_field('password', String(10))
Unit of work (1)
>>> mary = User.get_by(user_name = "Mary")
>>> harry = User.get_by(user_name = "Harry")
>>> fred = User.get_by(user_name = “Fred”)
>>> mary.password = “marysnewpassword”
>>> harry.password = “harrysnewpassword”
>>> fred.delete()
>>> ed = User(user_name = “Ed”, password = “ed”)
Unit of Work (2)
>>> objectstore.flush()
BEGINUPDATE user SET password=? WHERE user.user_id = ?['marysnewpassword', 1]UPDATE user SET password=? WHERE user.user_id = ?['harrysnewpassword', 2]INSERT INTO user (user_name, password) VALUES (?, ?)['ed', 'ed']DELETE FROM user WHERE user.user_id = ?[3]COMMIT
Elixir Relationships (1)
class Movie(Entity): has_field('title', Unicode(30)) has_field('year', Integer) has_field('description', Unicode)
belongs_to('genre', of_kind='Genre')
def __repr__(self): return '<Movie "%s" (%d)>' % (self.title, self.year)
class Genre(Entity): has_field('name', Unicode(15))
has_many('movies', of_kind='Movie')
def __repr__(self): return '<Genre "%s">' % self.name
Elixir Relationships (2)
scifi = Genre('Science Fiction')action = Genre('Action')
alien = Movie(title="Alien", year=1979)starwars = Movie(title="Star Wars", year=1977)brunner = Movie(title="Blade Runner", year=1982)frcon = Movie(title="The French Connection", year=1971)prof = Movie(title="The Professional", year=1994)
scifi.movies.append(alien)scifi.movies.append(starwars)scifi.movies.append(brunner)action.movies.append(frcon)action.movies.append(prof)
Elixir Relationships (3)
CREATE TABLE genre ( name VARCHAR(15), id INTEGER NOT NULL, PRIMARY KEY (id))
CREATE TABLE movie ( id INTEGER NOT NULL, year INTEGER, description TEXT, title VARCHAR(30), genre_id INTEGER, PRIMARY KEY (id), CONSTRAINT movie_genre_fk FOREIGN KEY(genre_id) REFERENCES genre (id))
CREATE INDEX ix_movie_genre_id ON movie (genre_id)
Elixir Relationships (4)
BEGININSERT INTO genre (name) VALUES (?)['Science Fiction']INSERT INTO genre (name) VALUES (?)['Action'] INSERT INTO movie (year, description, title, genre_id) VALUES (?, ?, ?, ?)[1979, None, 'Alien', 1]INSERT INTO movie (year, description, title, genre_id) VALUES (?, ?, ?, ?)[1977, None, 'Star Wars', 1] INSERT INTO movie (year, description, title, genre_id) VALUES (?, ?, ?, ?)[1982, None, 'Blade Runner', 1]INSERT INTO movie (year, description, title, genre_id) VALUES (?, ?, ?, ?)[1971, None, 'The French Connection', 2]INSERT INTO movie (year, description, title, genre_id) VALUES (?, ?, ?, ?)[1994, None, 'The Professional', 2]COMMIT
Elixir Relationships (5)
class Movie(Entity): has_field('title', Unicode(30)) has_field('year', Integer) has_field('description', Unicode)
has_and_belongs_to_many('genre', of_kind='Genre')
def __repr__(self): return '<Movie "%s" (%d)>' % (self.title, self.year)
class Genre(Entity): has_field('name', Unicode(15))
has_and_belongs_to_many('movies', of_kind='Movie')
def __repr__(self): return '<Genre "%s">' % self.name
Elixir Relationships (6)
scifi = Genre(name = 'Science Fiction')action = Genre(name = 'Action')thriller = Genre(name = 'Thriller')crime = Genre(name = 'Crime')
alien = Movie(title="Alien", year=1979)starwars = Movie(title="Star Wars", year=1977)brunner = Movie(title="Blade Runner", year=1982)frcon = Movie(title="The French Connection", year=1971)prof = Movie(title="The Professional", year=1994)manch = Movie(title="Manchurian Candidate", year=1962)
Elixir Relationships (7)
scifi.movies.append(alien)scifi.movies.append(starwars)scifi.movies.append(brunner)thriller.movies.append(alien)
frcon.genres.append(action)frcon.genres.append(crime)frcon.genres.append(thriller)
prof.genres.extend([action, crime])manch.genres.extend([action, thriller])
Elixir Relationship (8)
CREATE TABLE genre ( name VARCHAR(15), id INTEGER NOT NULL, PRIMARY KEY (id))
CREATE TABLE movie ( id INTEGER NOT NULL, year INTEGER, description TEXT, title VARCHAR(30), PRIMARY KEY (id))
CREATE TABLE movie_genres__genre_movies ( genre_id INTEGER, movie_id INTEGER, CONSTRAINT genre_movies_fk FOREIGN KEY(genre_id) REFERENCES genre (id), CONSTRAINT movie_genres_fk FOREIGN KEY(movie_id) REFERENCES movie (id))
Elixir Relationship (9)
BEGININSERT INTO movie (year, description, title) VALUES (?, ?, ?)[1979, None, 'Alien']...INSERT INTO movie (year, description, title) VALUES (?, ?, ?)[1994, None, 'Manchurian Candidate']INSERT INTO genre (name) VALUES (?)['Science Fiction']...INSERT INTO genre (name) VALUES (?)['Crime']INSERT INTO movie_genres__genre_movies (genre_id, movie_id) VALUES (?, ?)[[2, 4], [4, 4], [3, 4], [2, 5], [4, 5], [2, 6], [3, 6]]INSERT INTO movie_genres__genre_movies (genre_id, movie_id) VALUES (?, ?)[[3, 1], [1, 1], [1, 2], [1, 3]]COMMIT
More queries (1)
>>> Movie.select(Movie.join_to('genres') & (Genre.c.name == "Science Fiction"))
SELECT movie.title AS movie_title, movie.description AS movie_description, movie.id AS movie_id, movie.year AS movie_year
FROM movie, movie_genres__genre_movies, genre
WHERE (movie.id = movie_genres__genre_movies.movie_id AND genre.id = movie_genres__genre_movies.genre_id) AND genre.name = ? ORDER BY movie.oid
['Science Fiction']
[<Movie "Alien" (1979)>,
<Movie "Star Wars" (1977)>,
<Movie "Blade Runner" (1982)>]
More queries (2)
>>> Movie.select(Movie.join_to('genres') & (Genre.c.name == "Science Fiction") & (Movie.c.year < 1980))
SELECT movie.title AS movie_title, movie.description AS movie_description, movie.id AS movie_id, movie.year AS movie_year
FROM movie, movie_genres__genre_movies, genre
WHERE ((movie.id = movie_genres__genre_movies.movie_id AND genre.id = movie_genres__genre_movies.genre_id) AND genre.name = ?) AND movie.year < ? ORDER BY movie.oid
['Science Fiction', 1980]
[<Movie "Alien" (1979)>, <Movie "Star Wars" (1977)>]
More queries (3)
>>> from sqlalchemy import and_
>>> Movie.select(and_(Movie.join_to('genres'), Genre.c.name == "Science Fiction", Movie.c.year.between(1978, 1982)))
SELECT movie.title AS movie_title, movie.description AS movie_description, movie.id AS movie_id, movie.year AS movie_year
FROM movie, movie_genres__genre_movies, genre
WHERE (movie.id = movie_genres__genre_movies.movie_id AND genre.id = movie_genres__genre_movies.genre_id) AND genre.name = ? AND movie.year BETWEEN ? AND ? ORDER BY movie.oid
['Science Fiction', 1978, 1982]
[<Movie "Alien" (1979)>, <Movie "Blade Runner" (1982)>]
More queries (4)
def getTags(limit = None, min = None): s = select([Tag.c.tag_id, func.count(Post.c.post_id)], Tag.join_to('posts'), group_by=[Tag.c.tag_id], order_by=[desc(func.count(Post.c.post_id))]) if limit: s.limit = limit if min: s.having = func.count(Post.c.post_id) > min r = s.execute() for tag_id, num in r: yield Tag.get(tag_id), num
Other features
Deferred loading of class attributes (ie, columns in the table)
Inheritance – single and multiple, polymorphic or not
Mapping a class against an arbitrary select clause Multiple column primary keys Ordered lists of associated items Extensible association relations
