[1.7.x] Fixed #22411: Throw a more helpful error if contenttypes doesn't exist.

from django.apps import apps

from django.db import models

from django.db.utils import OperationalError, ProgrammingError

from django.utils.translation import ugettext_lazy as _

from django.utils.encoding import smart_text, force_text

from django.utils.encoding import python_2_unicode_compatible

        try:

            ct = self._get_from_cache(opts)

        except KeyError:

            # Load or create the ContentType entry. The smart_text() is

            # needed around opts.verbose_name_raw because name_raw might be a

            # django.utils.functional.__proxy__ object.

            try:

                ct, created = self.get_or_create(

                    app_label=opts.app_label,

                    model=opts.model_name,

                    defaults={'name': smart_text(opts.verbose_name_raw)},

                )

            except (OperationalError, ProgrammingError):

                # It's possible to migrate a single app before contenttypes,

                # as it's not a required initial dependency (it's contrib!)

                # Have a nice error for this.

                raise RuntimeError(

                    "Error creating new content types. Please make sure contenttypes" +

                    " is migrated before trying to migrate apps individually."

                )

            self._add_to_cache(self.db, ct)

        return ct