Do not require non-NULL field (allow empty strings) in FormAlchemy
formalchemy, pylons, python, sqlalchemy, validation
Solution
Finally found a kludge, but it seems this is the only sane way to do it:
fs.serial_number.validators.remove(formalchemy.validators.required)
fs.mac.validators.remove(formalchemy.validators.required)
For the validator function, that FA will completely skip all validation when the value is `None`, because, by convention, it won't pass `None` to validators (except for when `validators.required` is set, which is hard-coded). I've filed an enhancement request ticket trying to solve this.
Problem
I'm fairly novice to FormAlchemy and it seems that I don't get something. I have a SQLAlchemy model defined like this: ``` ... class Device(meta.Base): __tablename__ = 'devices' id = sa.Column('id_device', sa.types.Integer, primary_key=True) serial_number = sa.Column('sn', sa.types.Unicode(length=20), nullable=False) mac = sa.Column('mac', sa.types.Unicode(length=12), nullable=False) ipv4 = sa.Column('ip', sa.types.Unicode(length=15), nullable=False) type_id = sa.Column('type_id', sa.types.Integer, sa.schema.ForeignKey('device_types.id')) type = orm.relation(DeviceType, primaryjoin=type_id == DeviceType.id) ... ``` Then in my (Pylons) controller I create a FormAlchemy form like this: ``` c.device = model.meta.Session.query(model.Device).get(device_id) fs = FieldSet(c.device, data=request.POST or None) fs.configure(options=[fs.ipv4.label(u'IP').readonly(), fs.type.label(u'Type').with_null_as((u'—', '')), fs.serial_number.label(u'S/N'), fs.mac.label(u'MAC')]) ``` The documentation says that "By default, NOT NULL columns are required. You can only add required-ness, not remove it.", but I want to allow non-NULL empty strings, which `validators.required` disallows. Is there something like `blank=True, null=False` in Django? To be more precise, I want a custom validator like one below, to either allow empty strings with `type=None` or all values to be set non-NULL and non-empty: ``` # For use on fs.mac and fs.serial_number. # I haven't tested this code yet. def required_when_type_is_set(value, field): type_is_set = field.parent.type.value is not None: if value is None or (type_is_set and value.strip() = ''): raise validators.ValidationError(u'Please enter a value') ``` If possible, I'd like to refrain from monkey-patching `formalchemy.validators.required` or other kludges. I don't want to set `nullable=True` on model fields, because it doesn't seems to be proper solution too. What's the correct way to validate form in such case? Thanks for any suggestions in advance.