One-To-Many Example in NDB

Question

I am trying to create ndb.Model class like Students and subjects

class Subject(ndb.Model):
     name = ndb.StringProperty()

class Student(ndb.Model):
    na         


        

Answer 1

Definition:

class Subject(ndb.Model):
     name = ndb.StringProperty()

class Student(ndb.Model):
    name = ndb.StringProperty()
    subject = ndb.KeyProperty(kind=Subject,repeated=True)

Usage:

subject1 = Subject()
subject1.put()
subject2 = Subject()
subject2.put()
student = Student()
student.subject.append(subject1.key)
student.subject.append(subject2.key)
student.put()

Answer 2

This looks like an old question. In case someone else needs this presently, you should look at Structured Properties https://developers.google.com/appengine/docs/python/ndb/properties#structured. The example is very clear and easy to follow.

Answer 3

When I need 1 to many I use repeated keyProperties. Code:

class Subject(ndb.Model):
     name = ndb.StringProperty()

class Student(ndb.Model):
    name = ndb.StringProperty()
    subjects = ndb.KeyProperty(kind='Subject', repeated=True)

template:

{% for subject in student.subjects %}
  {{subject.get().name}}
{% endfor %}

ndb is nosql so you will not find reference to the parent in the child. However, you could add it like that. Don't forget to set student key value when creating a new subject.

class Subject(ndb.Model):
     name = ndb.StringProperty()
     student = ndb.KeyProperty(kind='Student')

class Student(ndb.Model):
    name = ndb.StringProperty()
    subjects = ndb.KeyProperty(kind='Subject', repeated=True)

Answer 4

Use the subject as a key.

me = Student(key_name='KurzedMetal')
programming = Subject(key_name='Programming')
programming.put()
me.subject = programming.key()
me.put()