Bulk update PostgreSQL from Python dict

问题

In an existing PostgreSQL table, I would like to UPDATE several existing columns with values from a dictionary lookup (see dict below). Somewhat like described in this nice blog post. However, I can't figure out how to do that with a Python dictionary. Here comes the terrible pseudo-code:

d = {10:'chair', 11:'table', 12:'lamp', 
    20:'english ivy', 21:'peace lily', 22:'spider plant'}

curs.execute("""
    UPDATE my_table t
    SET furniture = %(t.furniture)s,
    SET plant = %(t.plant)s""",
    d)

The original table would look somewhat like this:

gid | furniture | plant
-----------------------
 0  |    10     |  21
 1  |    11     |  20
 ...

After the operation it should look like this:

gid | furniture |    plant
-----------------------------
 0  |   chair   | peace lily
 1  |   table   | english ivy
 ...

Is this possible or will I have to loop through the table?

回答1:

try this:

rows = (
    {'gid': 10, 'furniture': 10, 'plant': 10},
    {'gid': 20, 'furniture': 20, 'plant': 20}
)
cur.executemany(
    '''
        UPDATE myTable 
        SET
            furniture = %(furniture)s,
            plant = %(plant)s
        WHERE
            gid = %(gid)s
    ''',
    rows
)

回答2:

The approach of catver works. However, I found that creating a temporary table proved to be more efficient.

import psycopg2
from psycopg2.extensions import AsIs

rows = zip(d.keys(), d.values())
curs.execute("""
    CREATE TEMP TABLE codelist(DKEY INTEGER, DVALUE TEXT) 
    ON COMMIT DROP""")

curs.executemany("""
  INSERT INTO codelist (DKEY, DVALUE)
  VALUES(%s, %s)""",
  rows)

for i in [(AsIs('furniture'), AsIs('furniture')), (AsIs('plant'), AsIs('plant'))]:
    curs.execute("""
        UPDATE my_table
        SET %s = codelist.DVALUE
        FROM codelist
        WHERE codelist.DKEY = my_table.%s;
        """, i)

NB: This example may not quite work because I am replacing INTEGER with TEXT values. This may throw the error ERROR: operator does not exist: integer = character varying. In that case, this answer might help.

来源：https://stackoverflow.com/questions/30162121/bulk-update-postgresql-from-python-dict

标签

python

postgresql

dictionary

psycopg2