django slick report and nested categories - django

Question

I am using in django the following models.py:
class Expense(models.Model):
name = models.CharField(max_length=50)
date = models.DateField(unique=False, blank=False)
slug = models.SlugField(unique=True, null=True, default='')
price = models.DecimalField(default=0.0, blank=True, max_digits = 20, decimal_places = 2)
category = models.ForeignKey(
'Category',
related_name="Expense",
on_delete=models.CASCADE
)
account = models.ForeignKey(Account, on_delete=models.CASCADE, verbose_name=u"Account", help_text=u"account")
def __str__(self):
return '{},{},{}'.format(self.name, self.date, self.price)
def save(self, *args, **kwargs):
self.slug = slugify(self.name)
super(Expense,self).save(*args, **kwargs)
def get_absolute_url(self):
return self.slug
class Category(MPTTModel):
name = models.CharField(max_length=200)
slug = models.SlugField(unique=True, null=True, default='')
parent = TreeForeignKey(
'self',
blank=True,
null=True,
related_name='child',
on_delete=models.CASCADE
)
class Meta:
unique_together = ('slug', 'parent',)
verbose_name_plural = "categories"
def __str__(self):
full_path = [self.name]
k = self.parent
while k is not None:
full_path.append(k.name)
k = k.parent
return ' -> '.join(full_path[::-1])
The TreeForeignKey allows me to define nested categories, such as Home -> Electricity and so on.
I am using the following Slick Report view.py:
class TotalExpenses(SlickReportView):
report_model = Expense
date_field = 'date'
group_by = 'category'
columns = ['name', SlickReportField.create(method=Sum, field='price', name='price__sum', verbose_name=('Total category $'))]
charts_settings = [
{
'type': 'bar',
'data_source': 'price__sum',
'title_source': 'name',
},
]
It works but I would like to sum only level 1 categories. Do you know how this might be possible?