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64 lines
1.9 KiB
Python
64 lines
1.9 KiB
Python
# cursor.py - how to subclass the cursor type
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#
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# Copyright (C) 2004-2010 Federico Di Gregorio <fog@debian.org>
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#
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# psycopg2 is free software: you can redistribute it and/or modify it
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# under the terms of the GNU Lesser General Public License as published
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# by the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# psycopg2 is distributed in the hope that it will be useful, but WITHOUT
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# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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# License for more details.
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## put in DSN your DSN string
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DSN = 'dbname=test'
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## don't modify anything below this line (except for experimenting)
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import sys
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import psycopg2
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import psycopg2.extensions
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if len(sys.argv) > 1:
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DSN = sys.argv[1]
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print("Opening connection using dsn:", DSN)
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conn = psycopg2.connect(DSN)
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print("Encoding for this connection is", conn.encoding)
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class NoDataError(psycopg2.ProgrammingError):
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"""Exception that will be raised by our cursor."""
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pass
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class Cursor(psycopg2.extensions.cursor):
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"""A custom cursor."""
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def fetchone(self):
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"""Like fetchone but raise an exception if no data is available.
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Note that to have .fetchmany() and .fetchall() to raise the same
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exception we'll have to override them too; even if internally psycopg
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uses the same function to fetch rows, the code path from Python is
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different.
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"""
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d = psycopg2.extensions.cursor.fetchone(self)
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if d is None:
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raise NoDataError("no more data")
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return d
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curs = conn.cursor(cursor_factory=Cursor)
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curs.execute("SELECT 1 AS foo")
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print("Result of fetchone():", curs.fetchone())
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# now let's raise the exception
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try:
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curs.fetchone()
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except NoDataError as err:
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print("Exception caught:", err)
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conn.rollback()
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