python - SQLAlchemy 0.7 - 最大列长度

Question

我正在使用上一个问题 (SQLAlchemy - maximum column length) 中的 SQLAlchemy 最大列长度配方。由于我升级到 SQLAlchemy 0.7，因此无法使用以下表达式安装 LengthValidator:

inst.impl.extensions.insert(0, LengthValidator(col.type.length))

extension 属性未在 SQLAchemy 0.7 中定义。有什么方法可以更改配方以使用 0.7？

Answer 1

下面是用SQLAlchemy的事件系统重写的Ants方案:

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import ColumnProperty
from sqlalchemy import event

def check_string_length(cls, key, inst):
    prop = inst.prop
    # Only interested in simple columns, not relations
    if isinstance(prop, ColumnProperty) and len(prop.columns) == 1:
        col = prop.columns[0]
        # if we have string column with a length, install a length validator
        if isinstance(col.type, String) and col.type.length:
            max_length = col.type.length
            def set_(instance, value, oldvalue, initiator):
                if len(value)>max_length:
                    raise ValueError("Length %d exceeds allowed %d" % \
                                            (len(value), max_length))
            event.listen(inst, 'set', set_)

Base = declarative_base()

event.listen(Base, 'attribute_instrument', check_string_length)