### PL/pgSQL

class ExcHandler(BasicObject):

    def __init__(self, exc, handler=None):

        if handler != None: handler = as_Code(handler)

        self.exc = exc

        self.handler = handler

    def to_str(self, db, body):

        body = as_Code(body)

        if self.handler != None: handler_str = '\n'+self.handler.to_str(db)

        else: handler_str = ' NULL;'

        str_ = '''\

BEGIN

'''+body.to_str(db)+'''

EXCEPTION

    WHEN '''+self.exc+''' THEN'''+handler_str+'''

END;\

'''

        return str_

unique_violation_handler = ExcHandler('unique_violation')