Python/postgres/psycopg2: getting ID of row just inserted

Question

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!

Asked By: AP257

||

Source

Answer 1

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

Answered By: ThiefMaster

Answer 2

Consider a RETURNING clause http://www.postgresql.org/docs/8.3/static/sql-insert.html

Answered By: Mike Graham

Answer 3

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!

Answered By: Jamie Brown

Answer 4

For me, neither ThiefMaster’s answer worked nor Jamie Brown’s. What worked for me was a mix of both, and I’d like to answer here so it can help someone else.

What I needed to do was:

cursor.execute('SELECT LASTVAL()')
id_of_new_row = cursor.fetchone()[0]

The statement lastid = cursor.fetchone()['lastval'] didn’t work for me, even after cursor.execute('SELECT LASTVAL()'). The statement id_of_new_row = cursor.fetchone()[0] alone didn’t work either.

Maybe I’m missing something.

Answered By: Paulo

Answer 5

ThiefMaster’s approach worked for me, for both INSERT and UPDATE commands.

If cursor.fetchone() is called on a cursor after having executed an INSERT/UPDATE command but lacked a return value (RETURNING clause) an exception will be raised: ProgrammingError('no results to fetch'))


insert_query = """
    INSERT INTO hundred (id, name, name_slug, status)
        VALUES (DEFAULT, %(name)s, %(name_slug)s, %(status)s)
        RETURNING id;
"""

insert_query_values = { 
    "name": "",
    "name_slug": "",
    "status": ""
}

connection = psycopg2.connect(host="", port="", dbname="", user="", password="")

try:
    with connection:
        with connection.cursor() as cursor:
            cursor.execute(insert_query, insert_query_values)
            num_of_rows_affected = cursor.rowcount
            new_row_id = cursor.fetchone()

except psycopg2.ProgrammingError as ex:
    print("...", ex)
    raise ex

finally:
    connection.commit()
    connection.close()

Answered By: danrodz

Python/postgres/psycopg2: getting ID of row just inserted

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