flairhq_migration.py

from pymongo import MongoClient
from bson.objectid import ObjectId
db = MongoClient('mongodb://localhost:27017/').fapp
username_map = {}
reverse_map = {}
initial_list_of_users = []
print "Beginning database migration.\nAccounting for users..."
for user in db.user.find({}):
	username_map[str(user['_id'])] = user['name']
	reverse_map[user['name']] = str(user['_id'])
	initial_list_of_users.append(user)
print "Finished accounting for users.\nMigrating users..."
for user in initial_list_of_users:
	previous_id = str(user['_id'])
	if previous_id in username_map and reverse_map[username_map[previous_id]] == previous_id:
		user['_id'] = username_map[previous_id]
		db.user.insert_one(user)
	db.user.remove({'_id': ObjectId(previous_id)})
db.user.update_many({}, {'$unset': {'name': 1, 'uid': 1}})
print "Finished migrating users.\nMigrating comments..."
for comment in db.comment.find({}):
	if 'user' in comment and comment['user'] in username_map:
		db.comment.update_one({'_id': comment['_id']}, {'$set': {'user': username_map[comment['user']]}})
	else:
		print 'Warning: The following comment contains an invalid/missing userid, so it will be deleted.'
		print comment
		db.comment.delete_one({'_id': comment['_id']})
print "Finished migrating comments.\nMigrating games..."
for game in db.game.find({}):
	if 'user' in game and game['user'] in username_map:
		db.game.update_one({'_id': game['_id']}, {'$set': {'user': username_map[game['user']]}})
	else:
		print 'Warning: The following game contains an invalid/missing userid, so it will be deleted.'
		print game
		db.game.delete_one({'_id': game['_id']})
print "Finished migrating games.\nMigrating references..."
for reference in db.reference.find({}):
	if 'user' in reference and reference['user'] in username_map and reference['user2']:
		if reference['user2'][:3] == '/u/':
			new_user2 = reference['user2'][3:]
		else:
			new_user2 = reference['user2']
		db.reference.update_one({'_id': reference['_id']}, {'$set': {'user': username_map[reference['user']], 'user2': new_user2}})
	else:
		print 'Warning: The following reference contains an invalid/missing userid, so it will be deleted.'
		print reference
		db.reference.delete_one({'_id': reference['_id']})
print "Finished migrating references.\nMigrating modnotes..."
for modnote in db.modnote.find({}):
	if 'refUser' in modnote and modnote['refUser'] in username_map:
		db.modnote.update_one({'_id': modnote['_id']}, {'$set': {'refUser': username_map[modnote['refUser']]}})
	else:
		print 'Warning: The following modnote contains an invalid/missing userid, so it will be deleted.'
		print modnote
		db.modnote.delete_one({'_id': modnote['_id']})
print "Finished migrating modnotes.\nMigrating events..."
db.event.update_many({}, {'$rename': {'userName': 'user'}})
print "Finished migrating events.\nDeleting sessions..."
db.sessions.drop()
print "Finished deleting sessions.\nMigration is now complete."

Update: Now it shouldn't crash if it encounters malformed database entries.

Update 2: Now it removes the /u/ in front of the user2 field in References.

Update 3: Now it won't crash if there are duplicate entries for the same username.

Update 4: No more iteration issues, hopefully

Update 5: Now it won't delete references where the user2 field doesn't begin with /u/.

Update 6: Rename userName property of Events to user