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# usercast.py -- example of user defined typecasters
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# -*- encoding: latin-1 -*-
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# Copyright (C) 2001-2005 Federico Di Gregorio <fog@debian.org>
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by the
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# Free Software Foundation; either version 2, or (at your option) any later
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY
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# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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## put in DSN your DSN string
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## don't modify anything below tis line (except for experimenting)
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import psycopg2.extensions
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# importing psycopg.extras will give us a nice tuple adapter: this is wrong
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# because the adapter is meant to be used in SQL IN clauses while we use
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# tuples to represent points but it works and the example is about Rect, not
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import psycopg2.extras
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print "Opening connection using dns:", DSN
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conn = psycopg2.connect(DSN)
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print "Initial encoding for this connection is", conn.encoding
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curs.execute("CREATE TABLE test_cast (p1 point, p2 point, b box)")
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curs.execute("DROP TABLE test_cast")
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curs.execute("CREATE TABLE test_cast (p1 point, p2 point, b box)")
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# this is the callable object we use as a typecast (the typecast is
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# usually a function, but we use a class, just to demonstrate the
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# flexibility of the psycopg casting system
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"""Very simple rectangle.
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Note that we use this type as a data holder, as an adapter of itself for
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the ISQLQuote protocol used by psycopg's adapt() (see __confrom__ below)
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and eventually as a type-caster for the data extracted from the database
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(that's why __init__ takes the curs argument.)
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def __init__(self, s=None, curs=None):
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"""Init the rectangle from the optional string s."""
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self.x = self.y = self.width = self.height = 0.0
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if s: self.from_string(s)
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def __conform__(self, proto):
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"""This is a terrible hack, just ignore proto and return self."""
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if proto == psycopg2.extensions.ISQLQuote:
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def from_points(self, x0, y0, x1, y1):
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"""Init the rectangle from points."""
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if x0 > x1: (x0, x1) = (x1, x0)
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if y0 > y1: (y0, y1) = (y1, y0)
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def from_string(self, s):
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"""Init the rectangle from a string."""
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self.from_points(seq[0][0], seq[0][1], seq[1][0], seq[1][1])
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"""Format self as a string usable by the db to represent a box."""
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s = "'((%d,%d),(%d,%d))'" % (
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self.x, self.y, self.x + self.width, self.y + self.height)
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"""Format a description of the box."""
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s = "X: %d\tY: %d\tWidth: %d\tHeight: %d" % (
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self.x, self.y, self.width, self.height)
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# here we select from the empty table, just to grab the description
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curs.execute("SELECT b FROM test_cast WHERE 0=1")
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boxoid = curs.description[0][1]
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print "Oid for the box datatype is", boxoid
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# and build the user cast object
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BOX = psycopg2.extensions.new_type((boxoid,), "BOX", Rect)
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psycopg2.extensions.register_type(BOX)
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# now insert 100 random data (2 points and a box in each row)
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p1 = (whrandom.randint(0,100), whrandom.randint(0,100))
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p2 = (whrandom.randint(0,100), whrandom.randint(0,100))
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b.from_points(whrandom.randint(0,100), whrandom.randint(0,100),
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whrandom.randint(0,100), whrandom.randint(0,100))
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curs.execute("INSERT INTO test_cast VALUES ('%(p1)s', '%(p2)s', %(box)s)",
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{'box':b, 'p1':p1, 'p2':p2})
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print "Added 100 boxed to the database"
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# select and print all boxes with at least one point inside
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curs.execute("SELECT b FROM test_cast WHERE p1 @ b OR p2 @ b")
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boxes = curs.fetchall()
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print "Found %d boxes with at least a point inside:" % len(boxes)
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print " ", box[0].show()
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curs.execute("DROP TABLE test_cast")
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examples/usercast.py
