Computed fields from multiple columns
I'm new to programming and have a question
How can I make a computed field that adds up from another table
depending on the contents of the first table?
eg A multi choice exam has the results entered by formfactory.
The answers and their scores are stored in a separate table
db
table:answers
answers.question, answers.answer, answers.score
1. 3rd planet, a. mars, 0
1. 3rd planet, b. Earth, 10
1. 3rd planet, c. Pluto, 0
2. Best movie, a. Toy Story 3, 5
2. Best movie, b. Casablanka, 10
3. Best movie, c. Twilight, -1000
db
table:exam
exam.id exam.name exam.score exam.question01 exam.question02
1 Fred Smith 20 b. Earth
b.Casablanka
2 Sarah Smith 15 b. Earth
a.Toy Story 3
As can be seen, the exam score is the sum of the answer scores given.
My difficulty is in the model...
m = DAL ('sqlite://storage.sqlite')
from gluon.tools import *
crud = Crud(globals(),m)
m.define_table('answers',
Field('question'),
Field('answer'),
Field('score',int))
m.define_table('exam',
Field('name'),
Field('score',compute=lambda
r:m(m.answers.answer==r.question01).select()[0].score
+m(m.answers.answer==r.question02).select()[0].score),
Field('question01'),
Field('question02'))
It reads the score quite well if checking only one question, but if
adding both, it returns None.
How could I modify it to add up from multiple questions?
You help is greatly appreciated.
