first pass on a migrate_to_split Django command

cms/djangoapps/contentstore/management/commands/migrate_to_split.py

+"""
+Django management command to migrate a course from the old Mongo modulestore
+to the new split-Mongo modulestore.
+"""
+from django.core.management.base import BaseCommand, CommandError
+from django.contrib.auth.models import User
+from xmodule.modulestore import Location
+from xmodule.modulestore.django import modulestore
+from xmodule.modulestore.split_migrator import SplitMigrator
+from xmodule.modulestore import InvalidLocationError
+
+
+class Command(BaseCommand):
+    help = "Migrate a course from old-Mongo to split-Mongo"
+    args = "location email <locator>"
+
+    def parse_args(self, *args):
+        """
+        Return a three-tuple of (location, user, locator_string).
+        If the user didn't specify a locator string, the third return value
+        will be None.
+        """
+        if len(args) < 2:
+            raise CommandError(
+                "migrate_to_split requires at least two arguments: "
+                "a location and a user identifier (email or ID)"
+            )
+
+        try:
+            location = Location(args[0])
+        except InvalidLocationError:
+            raise CommandError("Invalid location string {}".format(args[0]))
+
+        user_id = None
+        email = None
+        try:
+            user_id = int(args[1])
+        except ValueError:
+            email = args[1]
+        if user_id:
+            try:
+                user = User.objects.get(pk=user_id)
+            except User.DoesNotExist:
+                raise CommandError("No user exists with ID {}".format(user_id))
+        else:
+            try:
+                user = User.objects.get(email=email)
+            except User.DoesNotExist:
+                raise CommandError("No user exists with email {}".format(email))
+
+        assert user, "User doesn't exist! That shouldn't happen..."
+
+        try:
+            locator_string = args[2]
+        except IndexError:
+            locator_string = None
+
+        return location, user, locator_string
+
+    def handle(self, *args, **options):
+        location, user, locator_string = self.parse_args(*args)
+
+        draft = modulestore('default')
+        direct = modulestore('direct')
+        split = modulestore('split')
+
+        migrator = SplitMigrator(
+            draft_modulestore=draft,
+            direct_modulestore=direct,
+            split_modulestore=split,
+            loc_mapper=split.loc_mapper,
+        )
+
+        migrator.migrate_mongo_course(location, user, locator_string)