On 4/20/07, Mike H <[EMAIL PROTECTED]> wrote:
> It seems to be working well for the developers here, so here's hoping
> it's useful for some other people too :)
This is interesting-- migrating django apps using django. Are there
cases where Django or the DB could become so broken that the migrator
couldn't run? I wasn't sure, so I took the coward's way.
I'm attaching my db_upgrade.py for comparison. (I've attached it
on-list a time or two before, but there are many migration threads.
:)) It uses numbers instead of names for migrations, and has a custom
db_version table (no django model for it). It supports only python
upgrade steps, but those steps are handed a connection to work with if
they want to use SQL directly. Finally, it runs against Ye Olde
Django (0.91) and probably needs some tweaks to run against 0.96.
If I'm reading your code right, the migrations could be applied out of
order, depending on which ones you have already run. Since schema is
stateful, I think strict order is better.
Consider developers Mike and Jeremy, starting with the same DB. Mike
creates a migration, "HalfPrice" and runs it locally. Jeremy creates
a migration, "FullPrice" and runs it locally. Each then update their
checkouts and run syncdb.
The migrator conflict is update like this, say:
migrations = [
"HalfPrice",
"FullPrice"
]
The changes of FullPrice will be run for Mike (since that's not in the
applied list in his DB), and the changes of HalfPrice will be run for
Jeremy (for the same reason).
Now, this probably isn't an issue outside of development, but it was
this situation that led me to use migration numbers rather than names
and have my migration script halt if the DB rev was at or higher than
the highest migration step.
Cheers,
Jeremy
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#!/usr/bin/python
import sys, os
import psycopg
from django.core.db import db
from django.conf.settings import DATABASE_USER, DATABASE_NAME, DATABASE_HOST, DATABASE_PORT, DATABASE_PASSWORD, DEBUG, TIME_ZONE, UPGRADE_STEPS_PATH, DEBUG
def usage():
sys.stderr.write("%s [--nobackup] \n Expects DJANGO_SETTINGS_MODULE to be set.\n")
if len(sys.argv) == 1:
do_backup = True
else:
if sys.argv[1] == "--nobackup":
do_backup = False
else:
usage()
sys.exit()
try:
os.environ['DJANGO_SETTINGS_MODULE']
except KeyError:
usage()
sys.exit()
def get_conn_string():
if DATABASE_NAME == '':
from django.core.exceptions import ImproperlyConfigured
raise ImproperlyConfigured, "You need to specify DATABASE_NAME in your Django settings file."
conn_string = "dbname=%s" % DATABASE_NAME
if DATABASE_USER:
conn_string = "user=%s %s" % (DATABASE_USER, conn_string)
if DATABASE_PASSWORD:
conn_string += " password='%s'" % DATABASE_PASSWORD
if DATABASE_HOST:
conn_string += " host=%s" % DATABASE_HOST
if DATABASE_PORT:
conn_string += " port=%s" % DATABASE_PORT
return conn_string
def get_db():
log("Opening DB for upgrade")
cur = db.cursor()
conn = db.connection
return conn, cur
def get_current_version(cur):
"""
Assumes:
create table db_version (branch varchar(50), version integer);
insert into db_version values ('trunk', 1);
"""
try:
cur.execute('select branch, version from db_version')
except psycopg.ProgrammingError, e:
logerr("Couldn't find db_version \n====%s\n====:\n perhaps you forgot to restore a DB dump or should create the table with ('trunk', 1)?" % e)
return cur.fetchone()
def log(s):
sys.stderr.write('info: %s\n' % s)
def logerr(s):
sys.stdout.write('error: %s\n' % s)
sys.stdout.write('error: You probably want to restore the DB!\nQuitting.\n')
sys.exit()
def backup_db(init, final) :
import subprocess
from time import gmtime, strftime
dumpfile = "db_preupgrade_%s_from_%d_to_%d_at_%s_dump" % \
(DATABASE_NAME, init, final, strftime("%Y%m%dT%H%M%S", gmtime()))
log("If you're asked for the DB password, it's: %s" % DATABASE_PASSWORD)
#FIXME: use subprocess.Popen and tie pg_dump output to gzip input.
ret = subprocess.call(["pg_dump", "-f", dumpfile, "-U", DATABASE_USER, "-h", DATABASE_HOST, DATABASE_NAME])
if ret != 0:
raise RuntimeError, "Failed to create pg_dump %d" % ret
return dumpfile
if __name__ == '__main__':
sys.path.insert(0, UPGRADE_STEPS_PATH)
import upgrade_steps
conn, cur = get_db()
label, initial_version = get_current_version(cur)
log("Starting at version %d of db branch %s." % (initial_version, label))
steps = []
version = initial_version
while True:
try:
version += 1
func_name = '%s%d' % (label, version)
steps.append(getattr(upgrade_steps, func_name))
if not callable(steps[-1]):
logerr("%s is not callable, quitting." % func_name)
sys.exit()
except SystemExit:
raise
except:
break
final_version = version-1
if initial_version == final_version:
log("No DB upgrade to do. Already at %s version %d." % (label, initial_version))
log("Quitting.")
sys.exit()
log("Upgrading from %d to %d on %s" % (initial_version, final_version, label))
if do_backup:
try:
log("Backing up existing db.")
dumpfile = backup_db(initial_version, final_version)
except RuntimeError, e:
logerr(e)
log("Backed up to %s" % dumpfile)
else:
log("skipping backup")
version = initial_version
for step in steps:
try:
version += 1
# FIXME: a successful Django ORM .save() causes a commit in the transaction
# thereby committing something we really don't want to
step(conn, cur)
cur.execute("update db_version set version = %d", [version])
if DEBUG: #commit changes from each step to aid in debugging.
conn.commit()
log("Done with version %s" % version)
except psycopg.ProgrammingError, e:
logerr("SQL failed in db upgrade to version %d:%s" % (version, e))
except Exception, e:
logerr("Unknown error updating on to version %d: %s" % (version, e))
conn.commit() #final commit with all steps completed.
log("Successfully completed upgrade from %d to %d" % (initial_version, final_version))
