Question

I believe this is trival but fairly new to Python.

I am trying to create a model using google app engine.

Basically from a E/R point of view
I have 2 objects with a join table (the join table captures the point in time of the join)
Something like this

Person      | Idea     | Person_Idea
-------------------------------
person.key   idea.key    person.key
                         idea.key
                         date_of_idea

my Python code would look like

class Person (db.Model):
  #some properties here....

class Idea(db.Model):
  #some properties here....

class IdeaCreated(db.Model):
  person= db.ReferenceProperty(Person)
  idea= db.ReferenceProperty(Idea)
  created = db.DateTimeProperty(auto_now_add = True)

What I want to be able to do is have a convient way to get all ideas a person has (bypass idea created objects) -sometimes I will need the list of ideas directly.

The only way I can think to do this is to add the follow method on the User class

def allIdeas(self):
  ideas = []
  for ideacreated in self.ideacreated_set:
     ideas.append(ideacreated.idea)
  return ideas

Is this the only way to do this? I is there a nicer way that I am missing?

Also assuming I could have a GQL and bypass hydrating the ideaCreated instances (not sure the exact syntax) but putting a GQL query smells wrong to me.

Answer 1

you should use the person as an ancestor/parent for the idea.

idea = Idea(parent=some_person, other_field=field_value).put()

then you can query all ideas where some_person is the ancestor

persons_ideas = Idea.all().ancestor(some_person_key).fetch(1000)

the ancestor key will be included in the Idea entities key and you won’t be able to change that the ancestor once the entity is created.

i highly suggest you to use ndb instead of db https://developers.google.com/appengine/docs/python/ndb/

with ndb you could even use StructuredProperty or LocalStructuredProperty
https://developers.google.com/appengine/docs/python/ndb/properties#structured

EDIT:
if you need a many to many relationship look in to ListProperties and store the Persons keys in that property. then you can query for all Ideas with that Key in that property.

class Idea(db.Model):
    person = db.StringListProperty()

idea = Idea(person = [str(person.key())], ....).put()

add another person to the idea

idea.person.append(str(another_person.key())).put()

ideas = Idea.filter(person=str(person.key())).fetch(1000)

look into https://developers.google.com/appengine/docs/python/datastore/typesandpropertyclasses#ListProperty