add indexes = [] to model meta raises FieldDoesNotExist

[Jonas Kiefer]

I want to create an index on my mptt model like:

class Meta:

verbose_name = _("layer")

verbose_name_plural = _("layers")

indexes = [

models.Index(fields=['lft', 'rght', 'tree_id'],

name="anchestor_search_idx"),

]

but this raises:

raise FieldDoesNotExist(
backend-dev               | django.core.exceptions.FieldDoesNotExist: Layer has no field named 'lft'. The app cache isn't ready yet, so if this is an auto-created related field, it won't be available yet.

How can i add indexes to my model by using the mptt fields.