GQL query for <missing>

Question

When you change data models on the app engine to add new properties those entries without a certain property are listed with the value <missing> in the online data viewer.

What I'm wondering is how can I write a query to find those entries?

Answer 1

There's no way to query the datastore for entities that don't have a given property. You need to iterate over all the entities and check each one - possibly by using the mapreduce API.

Answer 2

There is no direct way to query for older entities with missing attribute, but you can design data model upfront to support this. Add a version attribute to each model class. Version should have a default value, which is increased every time model class is changed and deployed. This way you will be able to query entities by version number.