Checking for nulls with sqlalchemy

Question

I can never seem to get the filter calls right when I want to check for null values.

Is this function unnecessary?

def sqla_false(field):
    if field.type.__class__ == db.String:
        return db.or_(field == None, field == '')
    return field == None

How does sqlalchemy store unset fields? What if one of my wtforms forms sends a "" as a value for one of the fields, would NULL or "" be stored in the database when I call form.populate_obj(obj)?

davidism · Accepted Answer · 2018-05-04 12:05:26Z

1

If you send '', then that is stored and read as the empty string. If you send None, then that is stored as NULL and read as None. Use isinstance(field, db.String) to check for type. Use db.and_(field.isnot(None), field != '') to check that it has a non-empty string value.

edited May 4, 2018 at 12:05

answered Jan 10, 2014 at 16:48

davidism

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