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    <p>SQLAlchemy doesn't build this in as it defers to the DBAPI/database as the best and most efficient source of validation and coercion of values.</p> <p>To build your own validation, usually TypeDecorator or ORM-level validation is used. TypeDecorator has the advantage that it operates at the core and can be pretty transparent, though it only occurs when SQL is actually emitted.</p> <p>To do validation and coercion sooner, this is at the ORM level.</p> <p>Validation can be ad-hoc, at the ORM layer, via <code>@validates</code>:</p> <p><a href="http://docs.sqlalchemy.org/en/latest/orm/mapped_attributes.html#simple-validators" rel="nofollow noreferrer">http://docs.sqlalchemy.org/en/latest/orm/mapped_attributes.html#simple-validators</a></p> <p>The event system that @validates uses is also available directly. You can write a generalized solution that links validators of your choosing to the types being mapped:</p> <pre><code>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" </code></pre> <p>Validation and coercion can also be built at the type level using TypeDecorator, though this is only when SQL is being emitted, such as this example which coerces utf-8 strings to unicode:</p> <p><a href="http://docs.sqlalchemy.org/en/latest/core/custom_types.html#coercing-encoded-strings-to-unicode" rel="nofollow noreferrer">http://docs.sqlalchemy.org/en/latest/core/custom_types.html#coercing-encoded-strings-to-unicode</a></p>
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    1. POHow can I verify Column data types in the SQLAlchemy ORM?
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    1. USIlja Everilä
    1. USzzzeek
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    1. POHow can I verify Column data types in the SQLAlchemy ORM?
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    1. COThank you zzzeek. I had not used the event system before. Great example that shows where and how to hook into it.
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