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#------------------------------------------------------------------------------

# subclassing.py

# Demonstrate how to subclass connections and cursors in order to add

# additional functionality (like logging) or create specialized interfaces for

# paticular applications.

#------------------------------------------------------------------------------

import cx_Oracle as oracledb

import sample_env

# sample subclassed connection which overrides the constructor (so no

# parameters are required) and the cursor() method (so that the subclassed

# cursor is returned instead of the default cursor implementation)

class Connection(oracledb.Connection):

def __init__(self):

connect_string = sample_env.get_main_connect_string()

print("CONNECT to database")

super().__init__(connect_string)

def cursor(self):

return Cursor(self)

# sample subclassed cursor which overrides the execute() and fetchone()

# methods in order to perform some simple logging

class Cursor(oracledb.Cursor):

def execute(self, statement, args):

print("EXECUTE", statement)

print("ARGS:")

for arg_index, arg in enumerate(args):

print(" ", arg_index + 1, "=>", repr(arg))

return super().execute(statement, args)

def fetchone(self):

print("FETCH ONE")

return super().fetchone()

# create instances of the subclassed connection and cursor

connection = Connection()

cursor = connection.cursor()

# demonstrate that the subclassed connection and cursor are being used

cursor.execute("select count(*) from ChildTable where ParentId = :1", (30,))

count, = cursor.fetchone()

print("COUNT:", int(count))

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