Do I need to add a db_index to this Django model?

class Comments(models.Model):
    content = models.ForeignKey(Content)

Do I need to add a db_index to "co开发者_Go百科ntent"? Or would that automatically be indexed because it's a foreign key?

Unless specified otherwise, an index will be created for a ForeignKey. Relevant source code:

class ForeignKey(RelatedField, Field):
    # snip
    def __init__(self, to, to_field=None, rel_class=ManyToOneRel, **kwargs):
        # snip
        if 'db_index' not in kwargs:
            kwargs['db_index'] = True