def email(cls): return db.Column(db.String(512), nullable=False, unique=True)
def password(cls): return db.Column(db.String(512), nullable=False)
def username(cls): return db.Column(db.String(512), nullable=False, unique=True)
def description(cls): return db.Column(db.String(2048))
def resource_type(cls): return db.Column(db.String(81), nullable=False)
def resource(cls): return db.Column(db.String(1024), nullable=False)
def code(cls): return db.Column(db.String(81), default='0000')