Python ORMs with attribute constraints such as required / optional?

Question

Here's what Pony ORM can do:

class Business(db.Entity):
    name        = Required(str)
    latitude    = Optional(float, py_check=lambda val: -90 <= val <= 90)
    longitude   = Optional(float, py_check=lambda val: -180 <= val <= 180)

I'm trying to determine if any of the others (SQLAlchemy, SQLObject, etc.) can do this. And especially, those that can be used as a library in a framework. (So, I'm not sure how much work it'd be to use the Django ORM in a non-Django app.)

I'm having a hard time finding this feature in the various docs, but I'm sure they support it.

So my question: Do these (or other) ORMs support required vs. optional attributes and validations? If so, how?

• SQLAlchemy
• SQLObject
• Storm
• Django
• Peewee

Answer 1

Using SQLAlchemy: Yes

• Required/Optional is done by setting nullable = False/True
• Validations are done using Simple Validators

The code below uses Flask, but pure sqlalchemy code is almost the same:

class Business(db.Model):
    __tablename__ = 'business'
    id = db.Column(db.Integer, primary_key=True)

    name = db.Column(db.String, nullable=False)
    latitude = db.Column(db.Float, nullable=True)
    longitude = db.Column(db.Float, nullable=True)

    @db.validates('latitude')
    def validate_lat(self, key, value):
        assert value is None or (-90 <= value <= 90)
        return value

    @db.validates('longitude')
    def validate_lon(self, key, value):
        assert value is None or (-180 <= value <= 180)
        return value

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As already noted by @kevin-christopher-henry, there is little point using Django ORM with non-Django framework, as well as the other way around: if you use Django, it is much easier to stick to Django ORM.