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#------------------------------------------------------------------------------
# Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
#------------------------------------------------------------------------------
#------------------------------------------------------------------------------
# SessionCallback.py
#
# Demonstrate how to use a session callback written in Python. The callback is
# invoked whenever a newly created session is acquired from the pool, or when
# the requested tag does not match the tag that is associated with the
# session. It is generally used to set session state, so that the application
# can count on known session state, which allows the application to reduce the
# number of round trips made to the database.
#
# This script requires cx_Oracle 7.1 and higher.
#------------------------------------------------------------------------------
from __future__ import print_function
import cx_Oracle
import SampleEnv
# define a dictionary of NLS_DATE_FORMAT formats supported by this sample
SUPPORTED_FORMATS = {
"SIMPLE" : "'YYYY-MM-DD HH24:MI'",
"FULL" : "'YYYY-MM-DD HH24:MI:SS'"
}
# define a dictionary of TIME_ZONE values supported by this sample
SUPPORTED_TIME_ZONES = {
"UTC" : "'UTC'",
"MST" : "'-07:00'"
}
# define a dictionary of keys that are supported by this sample
SUPPORTED_KEYS = {
"NLS_DATE_FORMAT" : SUPPORTED_FORMATS,
"TIME_ZONE" : SUPPORTED_TIME_ZONES
}
# define session callback
def InitSession(conn, requestedTag):
# display the requested and actual tags
print("InitSession(): requested tag=%r, actual tag=%r" % \
(requestedTag, conn.tag))
# tags are expected to be in the form "key1=value1;key2=value2"
# in this example, they are used to set NLS parameters and the tag is
# parsed to validate it
if requestedTag is not None:
stateParts = []
for directive in requestedTag.split(";"):
parts = directive.split("=")
if len(parts) != 2:
raise ValueError("Tag must contain key=value pairs")
key, value = parts
valueDict = SUPPORTED_KEYS.get(key)
if valueDict is None:
raise ValueError("Tag only supports keys: %s" % \
(", ".join(SUPPORTED_KEYS)))
actualValue = valueDict.get(value)
if actualValue is None:
raise ValueError("Key %s only supports values: %s" % \
(key, ", ".join(valueDict)))
stateParts.append("%s = %s" % (key, actualValue))
sql = "alter session set %s" % " ".join(stateParts)
cursor = conn.cursor()
cursor.execute(sql)
# assign the requested tag to the connection so that when the connection
# is closed, it will automatically be retagged; note that if the requested
# tag is None (no tag was requested) this has no effect
conn.tag = requestedTag
# create pool with session callback defined
pool = cx_Oracle.SessionPool(SampleEnv.GetMainUser(),
SampleEnv.GetMainPassword(), SampleEnv.GetConnectString(), min=2,
max=5, increment=1, threaded=True, sessionCallback=InitSession)
# acquire session without specifying a tag; since the session returned is
# newly created, the callback will be invoked but since there is no tag
# specified, no session state will be changed
print("(1) acquire session without tag")
conn = pool.acquire()
cursor = conn.cursor()
cursor.execute("select to_char(current_date) from dual")
result, = cursor.fetchone()
print("main(): result is", repr(result))
conn.close()
# acquire session, specifying a tag; since the session returned has no tag,
# the callback will be invoked; session state will be changed and the tag will
# be saved when the connection is closed
print("(2) acquire session with tag")
conn = pool.acquire(tag="NLS_DATE_FORMAT=SIMPLE")
cursor = conn.cursor()
cursor.execute("select to_char(current_date) from dual")
result, = cursor.fetchone()
print("main(): result is", repr(result))
conn.close()
# acquire session, specifying the same tag; since a session exists in the pool
# with this tag, it will be returned and the callback will not be invoked but
# the connection will still have the session state defined previously
print("(3) acquire session with same tag")
conn = pool.acquire(tag="NLS_DATE_FORMAT=SIMPLE")
cursor = conn.cursor()
cursor.execute("select to_char(current_date) from dual")
result, = cursor.fetchone()
print("main(): result is", repr(result))
conn.close()
# acquire session, specifying a different tag; since no session exists in the
# pool with this tag, a new session will be returned and the callback will be
# invoked; session state will be changed and the tag will be saved when the
# connection is closed
print("(4) acquire session with different tag")
conn = pool.acquire(tag="NLS_DATE_FORMAT=FULL;TIME_ZONE=UTC")
cursor = conn.cursor()
cursor.execute("select to_char(current_date) from dual")
result, = cursor.fetchone()
print("main(): result is", repr(result))
conn.close()
# acquire session, specifying a different tag but also specifying that a
# session with any tag can be acquired from the pool; a session with one of the
# previously set tags will be returned and the callback will be invoked;
# session state will be changed and the tag will be saved when the connection
# is closed
print("(4) acquire session with different tag but match any also specified")
conn = pool.acquire(tag="NLS_DATE_FORMAT=FULL;TIME_ZONE=MST", matchanytag=True)
cursor = conn.cursor()
cursor.execute("select to_char(current_date) from dual")
result, = cursor.fetchone()
print("main(): result is", repr(result))
conn.close()
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