Question

I need orders / purchases that allow many items for instance something like

class Purchase(db.Model):
  '''a completed transaction'''
  item = db.ReferenceProperty(Item, repeated=True))

Is the repeated keyword legal and used in the correct manner here? What are my other options? Should I do it with a repeated stringproperty instead?

item_ids = model.StringProperty(repeated=True)
or with repeated KeyProperties?
Thanks

Answer 1

There is a ListProperty:

class Purchase(db.Model):
    items = db.ListProperty(db.Key)

It is used like a python list:

p = Purchase()
p.items = [item1.key(), item2.key(), item3.key()]

In queries however it looks like a single-valued field. Every value of ListProperty is indexed separately.

Query below will return all purchases which contain the item1:

Purchase.all().filter('items =', item1.key())

Query below will return all purchases which contain either item1 or item2:

Purchase.all().wilter('items IN', [item1.key(), item2.key()])

If you will ever need to index more than one ListProperty don’t forget to familiarize your self with exploding-indexes.