CODEWITHSUNDEEP
pythongoogle-app-engineapp-engine-ndb
Dave
Dave

Reputation: 3570

NDB Caching When Using Projected Queries

Could not find this specific question asked before yet. How does App Engine's NDB handle caching when using projected queries vs. full entity queries?

For example, if I do a projected query first..

MyModel.query().get(projected=['name'])

...and then do a regular query next...

MyModel.query().get()

...what will I get? The full entity? If so, was ANY part of first query automatically cached by NDB? Or is NDB able to make the distinction well, so the next time I run the projected query it is potentially pulled from cache?

Upvotes: 1

Views: 278

Answers (2)

Guido van Rossum
Guido van Rossum

Reputation: 16890

Projection query results are never cached. It would not be right if a get by key were to ever return a projection result. So no worries.

Upvotes: 3

Rob Curtis
Rob Curtis

Reputation: 2265

As far as I'm aware, query results are only cached in in-context cache, but results are not fetched from cache for queries.

key.get() will be cached and retrieved from cache, but query.get() won't be retrieved from cache.

https://developers.google.com/appengine/docs/python/ndb/cache

From the docs: Queries do not look up values in any cache. However, query results are written back to the in-context cache if the cache policy says so (but never to Memcache).

To answer the question regarding what you'll be getting, in both queries it appears that the results will be fetched from the datastore and not from cache.

Upvotes: 4

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