SQLAlchemy 0.7 - maximum column length

Question

I am using SQLAlchemy maximum column length recipe from my previous question (SQLAlchemy - maximum column length). Since I upgraded to SQLAlchemy 0.7, the LengthValidator cannot be installed using the following expression:

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

The extension attribute is not defined in SQLAchemy 0.7. Is there any way how to change the recipe to work with 0.7?

Answer 1

Below is Ants' solution rewritten with event system of SQLAlchemy:

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)

Answer 2

You can use sqlalchemy.orm.validates decorator:

@validates('name')
def validate_name(self, key, name):
    assert len(name) <= 50
    return name