SQLAlchemy令人费解？

Question

这看起来似乎很有争议,但我刚刚通过了SQLAlchemy的ORM教程,最后得到了以下代码:

from sqlalchemy import create_engine
from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

engine = create_engine('sqlite:///:memory:', echo=True)

metadata = MetaData()
users_table = Table('users', metadata,
    Column('id', Integer, primary_key=True),
    Column('name', String),
    Column('fullname', String),
    Column('password', String)
)

metadata.create_all(engine)

Base = declarative_base()
class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    password = Column(String)

    def __init__(self, name, fullname, password):
        self.name = name
        self.fullname = fullname
        self.password = password

    def __repr__(self):
       return "<User('%s','%s', '%s')>" % (self.name, self.fullname, self.password)

users_table = User.__table__
metadata = Base.metadata

Session = sessionmaker(bind=engine)
Session = sessionmaker()
Session.configure(bind=engine)  # once engine is available
session = Session()

# actually using the ORM isn't too bad..
ed_user = User('ed', 'Ed Jones', 'edspassword')
session.add(ed_user)

our_user = session.query(User).filter_by(name='ed').first() 
print our_user

session.add_all([
    User('wendy', 'Wendy Williams', 'foobar'),
    User('mary', 'Mary Contrary', 'xxg527'),
    User('fred', 'Fred Flinstone', 'blah')])

ed_user.password = 'f8s7ccs'

print session.dirty
print session.new
session.commit()

for instance in session.query(User).order_by(User.id): 
    print instance.name, instance.fullname

for name, fullname in session.query(User.name, User.fullname): 
    print name, fullname

对于有效的Hello World表,这似乎非常复杂,特别是与大致相似的SQLObject代码相比:

from sqlobject import SQLObject, StringCol, sqlhub, connectionForURI

sqlhub.processConnection = connectionForURI('sqlite:/:memory:')

class Person(SQLObject):
    fname = StringCol()
    mi = StringCol(length=1, default=None)
    lname = StringCol()

Person.createTable()

p = Person(fname="John", lname="Doe")
p.mi = 'Q'
p2 = Person.get(1)
print p2
print p2 is p

我理解SQLAlchemy"更强大",但这种力量似乎需要付出代价,或者我错过了什么？

Answer 1

好吧,有一件事你缺少:你提到的教程没有"构建"一个完整的例子,不同的代码片段并不意味着连接成一个源文件.相反,它们描述了可以使用库的不同方式.无需尝试自己一遍又一遍地做同样的事情.

从示例中省略实际使用的orm部分,代码可能如下所示:

from sqlalchemy import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, scoped_session

engine = create_engine('sqlite:///:memory:', echo=True)
Base = declarative_base(bind=engine)
Session = scoped_session(sessionmaker(engine))

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    password = Column(String)

Base.metadata.create_all()

"声明式"扩展负责定义表并将其映射到您的类,因此您不需要声明users_table自己.User类还允许使用关键字参数进行实例化,例如User(name="foo")(但不是位置参数).我还添加了scoped_session的使用,这意味着您可以直接使用Session而无需实际实例化它(如果当前线程中还没有一个会话,它将实例化一个新会话,否则重用现有的会话)

Answer 2

你提供的代码示例不是苹果对苹果.SQLAlchemy版本可能会减少一点:

from sqlalchemy import create_engine
from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

engine = create_engine('sqlite:///:memory:', echo=True)
Base = declarative_base()

class User(Base):
    __tablename__ = 'users'

    id = Column('id', Integer, primary_key=True)
    name = Column('name', String)
    fullname = Column('fullname', String)
    password = Column('password', String)

    def __repr__(self):
       return "" % (self.name, self.fullname, self.password)

Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)
session = Session()

# actually using the ORM isn't too bad..
ed_user = User(name='ed', fullname='Ed Jones', password='edspassword')
session.add(ed_user)

our_user = session.query(User).filter_by(name='ed').first()

session.add_all([
    User(name='wendy', fullname='Wendy Williams', password='foobar'),
    User(name='mary', fullname='Mary Contrary', password='xxg527'),
    User(name='fred', fullname='Fred Flinstone', password='blah')])

ed_user.password = 'f8s7ccs'

session.flush()

for instance in session.query(User).order_by(User.id):
    print instance.name, instance.fullname

for name, fullname in session.query(User.name, User.fullname):
    print name, fullname

您可能还会发现Elixir更像SQLObject(但由于我没有使用过,这只是猜测).

根本没有使用过SQLObject,我无法评论SA究竟做得更好.但是我在SA方面有很好的经验,特别是在处理复杂的,真实的遗留模式时.默认情况下,它可以很好地提供良好的SQL查询,并且有很多方法可以调整它们.

我发现SQLAlchemy作者的电梯间距在实践中保持得相当好.