Question

I have written the following function using sqlalchemy (my underlying db is PostgreSQL 8.4).
I have the following schema:

CREATE TABLE temporary_data_key (
                        id                          SERIAL PRIMARY KEY,
                        key                         VARCHAR(36) NOT NULL
                        );
CREATE UNIQUE INDEX idxu_temp_data_nm ON temporary_data_key (key);


CREATE TABLE temporary_data (
                        key_id                      INTEGER REFERENCES temporary_data_key(id) ON UPDATE CASCADE ON DELETE RESTRICT NOT NULL,
                        id_value                    INTEGER CHECK (id_value > 0) NOT NULL
                        );

I expect the function to clean up after itself (i.e. remove the generated key in temporary_table_key table) if an error occurs – for some reason, the table is not been cleared when an exception occurs.

Here is the function:

def storeIdsInTemporaryTable(dbinfo, id_list):
    conn = dbinfo['db_connection']
    metadata = dbinfo['metadata']
    tableinfo = Table('temporary_data', metadata, autoload=True)
    datarows = []

    temp_dbinfo = {'db_connection': conn, 'table': tableinfo, 'datarows': datarows }

    guid = genutils.getGUID()

    sql = "INSERT INTO temporary_data_key (key) VALUES ('{0}') RETURNING id".format(guid)
    key_id = executeSQLonDbConnection(temp_dbinfo, sql, return_field='id')

    for id_value in id_list:
        datarows.append( { 'key_id': key_id, 'id_value': id_value } )

    try:
        insertToDb(temp_dbinfo)
    except Exception as e:
        print 'ERROR:',e
        guid = None # to indicate an error occured
        if key_id:
            conn.execute("DELETE FROM temporary_data_key WHERE key='{0}'".format(key_id))

    return guid

Can anyone spot why the function is not cleaning up the temporary_data key as part of exception handling?

Answer 1

I found the solution.

The last line should be:

if key_id:
    conn.execute("DELETE FROM temporary_data_key WHERE key='{0}'".format(guid))