Python/postgres/psycopg2: getting ID of row just inserted
PythonPostgresqlPsycopg2Python Problem Overview
I'm using Python and psycopg2 to interface to postgres.
When I insert a row...
sql_string = "INSERT INTO hundred (name,name_slug,status) VALUES ("
sql_string += hundred_name + ", '" + hundred_slug + "', " + status + ");"
cursor.execute(sql_string)
... how do I get the ID of the row I've just inserted? Trying:
hundred = cursor.fetchall()
returns an error, while using RETURNING id:
sql_string = "INSERT INTO domes_hundred (name,name_slug,status) VALUES ("
sql_string += hundred_name + ", '" + hundred_slug + "', " + status + ") RETURNING id;"
hundred = cursor.execute(sql_string)
simply returns None.
UPDATE: So does currval (even though using this command directly into postgres works):
sql_string = "SELECT currval(pg_get_serial_sequence('hundred', 'id'));"
hundred_id = cursor.execute(sql_string)
Can anyone advise?
thanks!
Python Solutions
Solution 1 - Python
cursor.execute("INSERT INTO .... RETURNING id")
id_of_new_row = cursor.fetchone()[0]
And please do not build SQL strings containing values manually. You can (and should!) pass values separately, making it unnecessary to escape and SQL injection impossible:
sql_string = "INSERT INTO domes_hundred (name,name_slug,status) VALUES (%s,%s,%s) RETURNING id;"
cursor.execute(sql_string, (hundred_name, hundred_slug, status))
hundred = cursor.fetchone()[0]
See the psycopg docs for more details: http://initd.org/psycopg/docs/usage.html#passing-parameters-to-sql-queries
Solution 2 - Python
I ended up here because I had a similar problem, but we're using Postgres-XC, which doesn't yet support the RETURNING ID clause. In that case you can use:
cursor.execute('INSERT INTO ........')
cursor.execute('SELECT LASTVAL()')
lastid = cursor.fetchone()['lastval']
Just in case it was useful for anyone!
Solution 3 - Python
Consider a RETURNING clause http://www.postgresql.org/docs/8.3/static/sql-insert.html