SQLAlChemy没有内置这一点,因为它将DBAPI/数据库作为最好、最有效的值验证和强制源.
要构建您自己的验证,通常使用TypeDecorator或ORM级别的验证.TypeDecorator的优势在于它在核心运行,并且可以相当透明,尽管它只在实际发出SQL时发生.
为了更快地进行验证和强制,这是在ORM级别.
验证可以是临时的,在ORM层,通过@validates
:
http://docs.sqlalchemy.org/en/latest/orm/mapped_attributes.html#simple-validators个
@valiates use的事件系统也可以直接使用.您可以编写一个通用解决方案,将您 Select 的验证器链接到要映射的类型:
from sqlalchemy import Column, Integer, String, DateTime
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import event
import datetime
Base= declarative_base()
def validate_int(value):
if isinstance(value, basestring):
value = int(value)
else:
assert isinstance(value, int)
return value
def validate_string(value):
assert isinstance(value, basestring)
return value
def validate_datetime(value):
assert isinstance(value, datetime.datetime)
return value
validators = {
Integer:validate_int,
String:validate_string,
DateTime:validate_datetime,
}
# this event is called whenever an attribute
# on a class is instrumented
@event.listens_for(Base, 'attribute_instrument')
def configure_listener(class_, key, inst):
if not hasattr(inst.property, 'columns'):
return
# this event is called whenever a "set"
# occurs on that instrumented attribute
@event.listens_for(inst, "set", retval=True)
def set_(instance, value, oldvalue, initiator):
validator = validators.get(inst.property.columns[0].type.__class__)
if validator:
return validator(value)
else:
return value
class MyObject(Base):
__tablename__ = 'mytable'
id = Column(Integer, primary_key=True)
svalue = Column(String)
ivalue = Column(Integer)
dvalue = Column(DateTime)
m = MyObject()
m.svalue = "ASdf"
m.ivalue = "45"
m.dvalue = "not a date"
也可以使用TypeDecorator在类型级别构建验证和强制,尽管这仅在发出SQL时进行,例如下面的示例将UTF-8字符串强制为Unicode:
http://docs.sqlalchemy.org/en/latest/core/custom_types.html#coercing-encoded-strings-to-unicode个