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# usercast.py -- example of user defined typecasters
# -*- encoding: latin-1 -*-
#
# Copyright (C) 2001-2010 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
import psycopg2.extensions
import whrandom
# importing psycopg.extras will give us a nice tuple adapter: this is wrong
# because the adapter is meant to be used in SQL IN clauses while we use
# tuples to represent points but it works and the example is about Rect, not
# "Point"
import psycopg2.extras
if len(sys.argv) > 1:
DSN = sys.argv[1]
print "Opening connection using dsn:", DSN
conn = psycopg2.connect(DSN)
print "Initial encoding for this connection is", conn.encoding
curs = conn.cursor()
try:
curs.execute("CREATE TABLE test_cast (p1 point, p2 point, b box)")
except:
conn.rollback()
curs.execute("DROP TABLE test_cast")
curs.execute("CREATE TABLE test_cast (p1 point, p2 point, b box)")
conn.commit()
# this is the callable object we use as a typecast (the typecast is
# usually a function, but we use a class, just to demonstrate the
# flexibility of the psycopg casting system
class Rect(object):
"""Very simple rectangle.
Note that we use this type as a data holder, as an adapter of itself for
the ISQLQuote protocol used by psycopg's adapt() (see __confrom__ below)
and eventually as a type-caster for the data extracted from the database
(that's why __init__ takes the curs argument.)
"""
def __init__(self, s=None, curs=None):
"""Init the rectangle from the optional string s."""
self.x = self.y = self.width = self.height = 0.0
if s: self.from_string(s)
def __conform__(self, proto):
"""This is a terrible hack, just ignore proto and return self."""
if proto == psycopg2.extensions.ISQLQuote:
return self
def from_points(self, x0, y0, x1, y1):
"""Init the rectangle from points."""
if x0 > x1: (x0, x1) = (x1, x0)
if y0 > y1: (y0, y1) = (y1, y0)
self.x = x0
self.y = y0
self.width = x1 - x0
self.height = y1 - y0
def from_string(self, s):
"""Init the rectangle from a string."""
seq = eval(s)
self.from_points(seq[0][0], seq[0][1], seq[1][0], seq[1][1])
def getquoted(self):
"""Format self as a string usable by the db to represent a box."""
s = "'((%d,%d),(%d,%d))'" % (
self.x, self.y, self.x + self.width, self.y + self.height)
return s
def show(self):
"""Format a description of the box."""
s = "X: %d\tY: %d\tWidth: %d\tHeight: %d" % (
self.x, self.y, self.width, self.height)
return s
# here we select from the empty table, just to grab the description
curs.execute("SELECT b FROM test_cast WHERE 0=1")
boxoid = curs.description[0][1]
print "Oid for the box datatype is", boxoid
# and build the user cast object
BOX = psycopg2.extensions.new_type((boxoid,), "BOX", Rect)
psycopg2.extensions.register_type(BOX)
# now insert 100 random data (2 points and a box in each row)
for i in range(100):
p1 = (whrandom.randint(0,100), whrandom.randint(0,100))
p2 = (whrandom.randint(0,100), whrandom.randint(0,100))
b = Rect()
b.from_points(whrandom.randint(0,100), whrandom.randint(0,100),
whrandom.randint(0,100), whrandom.randint(0,100))
curs.execute("INSERT INTO test_cast VALUES ('%(p1)s', '%(p2)s', %(box)s)",
{'box':b, 'p1':p1, 'p2':p2})
print "Added 100 boxed to the database"
# select and print all boxes with at least one point inside
curs.execute("SELECT b FROM test_cast WHERE p1 @ b OR p2 @ b")
boxes = curs.fetchall()
print "Found %d boxes with at least a point inside:" % len(boxes)
for box in boxes:
print " ", box[0].show()
curs.execute("DROP TABLE test_cast")
conn.commit()
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