gistfile1.py

class CourseEnrollment(models.Model):
    """
    Represents a Student's Enrollment record for a single Course. You should
    generally not manipulate CourseEnrollment objects directly, but use the
    classmethods provided to enroll, unenroll, or check on the enrollment status
    of a given student.

    We're starting to consolidate course enrollment logic in this class, but
    more should be brought in (such as checking against CourseEnrollmentAllowed,
    checking course dates, user permissions, etc.) This logic is currently
    scattered across our views.
    """
    MODEL_TAGS = ['course_id', 'is_active', 'mode']

    user = models.ForeignKey(User)
    course_id = CourseKeyField(max_length=255, db_index=True)
    created = models.DateTimeField(auto_now_add=True, null=True, db_index=True)

    _course_overview = models.ForeignKey(CourseOverview,
                            on_delete=models.DO_NOTHING,
                            db_column='course_id',
                            related_name='+',
                            db_index=False,
                            db_constraint=False,
                        )

gistfile2.txt

ERRORS:
student.CourseEnrollment: (models.E007) Field '_course_overview' has column name 'course_id' that is used by another field.
	HINT: Specify a 'db_column' for the field.