How to model a unique constraint in GAE ndb

Question

I want to have several \"bundles\" (Mjbundle), which essentially are bundles of questions (Mjquestion). The Mjquestion has an integer \"index\" property which needs to be unique

Answer 1

When you use a StructuredProperty, all of the entities that type are stored as part of the containing entity - so when you fetch your bundle, you have already fetched all of the questions. If you stick with this way of storing things, iterating to check in code is the solution.