psycopg2/examples/lobject.py

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# lobject.py - lobject example
#
# Copyright (C) 2001-2006 Federico Di Gregorio <fog@debian.org>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY
# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 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 dns:", DSN
conn = psycopg2.connect(DSN)
print "Encoding for this connection is", conn.encoding
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# 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.
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lobj = conn.lobject()
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loid = lobj.oid
print "Created a new large object with oid", loid
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print "Manually importing some binary data into the object:"
data = open("somehackers.jpg").read()
len = lobj.write(data)
print " imported", len, "bytes of data"
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conn.commit()
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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()
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print "\nNow try to load the new images, to check it worked!"