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# cursor.py - how to subclass the cursor type
#
# Copyright (C) 2004 Federico Di Gregorio <fog@debian.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY
# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
# for more details.
## put in DSN your DSN string
DSN = 'dbname=test'
## don't modify anything below this line (except for experimenting)
import sys
import psycopg
import psycopg.extensions
if len(sys.argv) > 1:
DSN = sys.argv[1]
print "Opening connection using dsn:", DSN
conn = psycopg.connect(DSN)
print "Encoding for this connection is", conn.encoding
class NoDataError(psycopg.ProgrammingError):
"""Exception that will be raised by our cursor."""
pass
class Cursor(psycopg.extensions.cursor):
"""A custom cursor."""
def fetchone(self):
"""Like fetchone but raise an exception if no data is available.
Note that to have .fetchmany() and .fetchall() to raise the same
exception we'll have to override them too; even if internally psycopg
uses the same function to fetch rows, the code path from Python is
different.
"""
d = psycopg.extensions.cursor.fetchone(self)
if d is None:
raise NoDataError("no more data")
return d
curs = conn.cursor(factory=Cursor)
curs.execute("SELECT 1 AS foo")
print "Result of fetchone():", curs.fetchone()
# now let's raise the exception
try:
curs.fetchone()
except NoDataError, err:
print "Exception caugth:", err
conn.rollback()
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