psycopg2/examples/lobject.py

# lobject.py - lobject example
#
# Copyright (C) 2001-2006 Federico Di Gregorio  <fog@debian.org>
#
# psycopg2 is free software: you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# psycopg2 is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
# License for more details.

## put in DSN your DSN string

DSN = 'dbname=test'

## don't modify anything below this line (except for experimenting)

import sys
import psycopg2

if len(sys.argv) > 1:
    DSN = sys.argv[1]

print("Opening connection using dsn:", DSN)
conn = psycopg2.connect(DSN)
print("Encoding for this connection is", conn.encoding)

# this will create a large object with a new random oid, we'll
# use it to make some basic tests about read/write and seek.
lobj = conn.lobject()
loid = lobj.oid
print("Created a new large object with oid", loid)

print("Manually importing some binary data into the object:")
data = open("somehackers.jpg").read()
len = lobj.write(data)
print("  imported", len, "bytes of data")

conn.commit()

print("Trying to (re)open large object with oid", loid)
lobj = conn.lobject(loid)
print("Manually exporting the data from the lobject:")
data1 = lobj.read()
len = lobj.tell()
lobj.seek(0, 0)
data2 = lobj.read()
if data1 != data2:
    print("ERROR: read after seek returned different data")
open("somehackers_lobject1.jpg", 'wb').write(data1)
print("  written", len, "bytes of data to somehackers_lobject1.jpg")

lobj.unlink()
print("Large object with oid", loid, "removed")

conn.commit()

# now we try to use the import and export functions to do the same
lobj = conn.lobject(0, 'n', 0, "somehackers.jpg")
loid = lobj.oid
print("Imported a new large object with oid", loid)

conn.commit()

print("Trying to (re)open large object with oid", loid)
lobj = conn.lobject(loid, 'n')
print("Using export() to export the data from the large object:")
lobj.export("somehackers_lobject2.jpg")
print("  exported large object to somehackers_lobject2.jpg")

lobj.unlink()
print("Large object with oid", loid, "removed")

conn.commit()

# this will create a very large object with a new random oid.
lobj = conn.lobject()
loid = lobj.oid
print("Created a new large object with oid", loid)

print("Manually importing a lot of data into the object:")
data = "data" * 1000000
len = lobj.write(data)
print("  imported", len, "bytes of data")

conn.rollback()

print("\nNow try to load the new images, to check it worked!")