Question

My App having db class,

class invoice(db.Model):
   location_code = db.StringProperty()
   invoice_no = db.IntegerProperty()
   product_tax_rate = db.FloatProperty()
   basic_tax_rate = db.FloatProperty()
   addl_tax_rate = db.FloatProperty()
   .
   .
   .

In this, i wanted to set product_tax_rate‘s value as default value for property basic_tax_rate‘s property if addl_tax_rate‘s value is 0.

How can i add a generic procedure for this logic in this class method?

Please let me know if you still not getting this requirement.

Answer 1

You can use NDB and ComputedProperty todo something like:

class invoice(ndb.Model):
   product_tax_rate = ndb.ComputedProperty(lambda self: self.basic_tax_rate if self.addl_tax_rate == 0 else ???)
   basic_tax_rate = ndb.FloatProperty()
   addl_tax_rate = ndb.FloatProperty()