models.py

class Project(models.Model):
    project_code = models.CharField(max_length=7, unique=True)


class Hole(models.Model):
    hole_number = models.CharField(max_length=16)
    project = models.ForeignKey('Project', on_delete=models.CASCADE,
                                blank=True, null=True, related_name='holes', verbose_name='Project')


class Description(models.Model):
    depth_top = models.DecimalField(max_digits=5, decimal_places=2)
    depth_base = models.DecimalField(max_digits=5, decimal_places=2)
    content = models.CharField(max_length=512)
    hole = models.ForeignKey('Hole', on_delete=models.CASCADE, blank=True,
                             null=True, related_name='descriptions', verbose_name='Hole')


def get_by_proj(proj_id, hole_id, depth_top, depth_base):
    p = Description.objects.filter(hole__project__project_code=proj_id) \
            .filter(hole__hole_number=hole_id) \
            .filter(depth_top=float(depth_top), depth_base=float(depth_base)) \
            .first()  # working up from bottom to top
    print(p)
    return {
        'project_id': p.hole.project.project_code,
        'hole_id': p.hole.hole_number,
        'depth_top': p.depth_top,
        'depth_base': p.depth_base,
        'content': p.content,
    }