psycopg2/examples/usercast.py

# 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 dns:", 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()