如何使用SQLAlchemy创建SQL视图？

Question

是否有“ Pythonic”方式（我的意思是，没有“ pure SQL”查询）来使用SQLAlchemy定义SQL视图？

Answer 1

更新：
又见SQLAlchemy的使用配方这里

据我所知，开箱即用不支持创建（只读非实例化）视图。但是在SQLAlchemy
0.7中添加此功能非常简单（类似于我在此处给出的示例）。您只需要编写一个编译器扩展即可
CreateView。使用此扩展名，您可以编写（假设这t是一个带有列的表对象id）

createview = CreateView('viewname', t.select().where(t.c.id>5))
engine.execute(createview)

v = Table('viewname', metadata, autoload=True)
for r in engine.execute(v.select()):
    print r

这是一个工作示例：

from sqlalchemy import Table
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.sql.expression import Executable, ClauseElement

class CreateView(Executable, ClauseElement):
    def __init__(self, name, select):
        self.name = name
        self.select = select

@compiles(CreateView)
def visit_create_view(element, compiler, **kw):
    return "CREATE VIEW %s AS %s" % (
         element.name,
         compiler.process(element.select, literal_binds=True)
         )

# test data
from sqlalchemy import MetaData, Column, Integer
from sqlalchemy.engine import create_engine
engine = create_engine('sqlite://')
metadata = MetaData(engine)
t = Table('t',
          metadata,
          Column('id', Integer, primary_key=True),
          Column('number', Integer))
t.create()
engine.execute(t.insert().values(id=1, number=3))
engine.execute(t.insert().values(id=9, number=-3))

# create view
createview = CreateView('viewname', t.select().where(t.c.id>5))
engine.execute(createview)

# reflect view and print result
v = Table('viewname', metadata, autoload=True)
for r in engine.execute(v.select()):
    print r

如果需要，您也可以专门学习方言，例如

@compiles(CreateView, 'sqlite')
def visit_create_view(element, compiler, **kw):
    return "CREATE VIEW IF NOT EXISTS %s AS %s" % (
         element.name,
         compiler.process(element.select, literal_binds=True)
         )