sqlalchemy 的 ORM 方式使用示例

知乎： 使用 sqlalchemy 的 orm 方式運算元據庫是一種怎樣的體驗？

答： 酸爽！

這是 sqlalchemy 的層級圖。不難發現，其中 orm 是最頂級的封裝。

orm 基本操作步驟如下：

from sqlalchemy importcreate_engine

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

from sqlalchemy.orm importsession

session = session(engine)

from sqlalchemy.ext.declarative import

declarative_base
base = declarative_base()

from sqlalchemy import

column, integer, foreignkey
from sqlalchemy.orm import
relationship
class
parent(base):
__tablename__ = '
parent
'id = column(integer, primary_key=true)
children = relationship("
child")
def__repr__
(self):
return""
.format(self.id, self.children)
class
child(base):
__tablename__ = '
child
'id = column(integer, primary_key=true)
parent_id = column(integer, foreignkey('
parent.id'))
def__repr__
(self):
return
"".format(self.id, self.parent_id)

base.metadata.drop_all(engine)

base.metadata.create_all(engine) 
#生產環境只需執行一次！！！！

session.add_all([parent(children=[child() for j in range(5)]) for i in range(2)])

session.commit()

#

懶載入 (lazyload)
#load everything, no eager loading.
for parent in
session.query(parent):
print
(parent.children)
#聯合載入 (joinedload)
#load everything, joined eager loading.
for parent in session.query(parent).options(joinedload("
children
")):
parent.children
#子查詢載入 (subqueryload)
#load everything, subquery eager loading.
for parent in session.query(parent).options(subqueryload("
children
")):
parent.children

from sqlalchemy import

create_engine
from sqlalchemy.orm import
session
from sqlalchemy.ext.declarative import
declarative_base
from sqlalchemy import
column, integer, foreignkey
from sqlalchemy.orm import
relationship
from sqlalchemy.orm import
joinedload, subqueryload
#建立連線
engine = create_engine('
sqlite:///:memory:
', echo=true)
#建立會話
session =session(engine)
#宣告基類
base =declarative_base()
#定義表（繼承基類）
class
parent(base):
__tablename__ = '
parent
'id = column(integer, primary_key=true)
children = relationship("
child")
def__repr__
(self):
return""
.format(self.id, self.children)
class
child(base):
__tablename__ = '
child
'id = column(integer, primary_key=true)
parent_id = column(integer, foreignkey('
parent.id'))
def__repr__
(self):
return""
.format(self.id, self.parent_id)
#生成表
base.metadata.drop_all(engine)
base.metadata.create_all(engine) 
#生產環境只需執行一次！！！！
#新增記錄
session.add_all([parent(children=[child() for j in range(5)]) for i in range(2)])
session.commit()#查詢
#lazyload
#load everything, no eager loading.
for parent in
session.query(parent):
print
(parent.children)
#joinedload
#load everything, joined eager loading.
for parent in session.query(parent).options(joinedload("
children
")):
parent.children
#subqueryload
#load everything, subquery eager loading.
for parent in session.query(parent).options(subqueryload("
children
")):
parent.children

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