Google App Engine数据存储模型参考另一类

Question

So that you can understand the data model, I basically have cities and within each one I'll have categories and then inside each category I'll have listings. Here's what I have so far.

from google.appengine.ext import db

class City(db.Model):
    name = db.StringProperty(required=True)
    connections = db.ListProperty()
    categories = db.ListProperty()

So Next, I want to add:

class Category(db.Model)
    name = db.StringProperty(required=True)

But do I need to specify that only Category should be in categories or something to that effect?

Answer 1

You want to look at a custom property named KeyListProperty in App Engine Patch . That will give you the sort of many-to-many relationship you want.

Answer 2

You need to throw the categories property from your City and use a ReferenceProperty in your Category class:

class Category(db.Model)
    name = db.StringProperty(required=True)
    city = db.ReferenceProperty(City, collection_name = 'categories')

This will also automatically add categories collection for your City model.