Question

On Google App Engine in Python, I have a Visit entity that has a parent of Patient. A Patient may have multiple visits.

I need to set the most_recent_visit (and some auxiliary visit data) somewhere for later querying, probably in another child entity that Brett Slatkin might call a “relationship index entity.”

I wish to do so in a bulk style as follows:

1. get 100 Patient keys
2. get all Visits that have any of the Patients from 1 as an ancestor
3. go through the Visits and get the latest for each Patient

Is there any way to perform step 2 in a bulk get?

I know there is a way to bulk get entities from a list of keys, and there is a way to match a single entity by its ancestor.

Answer 1

There’s no way in the datastore to to the kind of query you’re looking for; it’s a join, which isn’t supported. Step 2 is going to require 100 queries.

You could store a list of Visit keys in each Patient entity, and then be able to do a simple bulk get all of these entities based on their keys.