I have some problems with Datastore in Google AppEngine.
I have 2 Models in the datastore which are:
name = StringProperty(required=True)
category = KeyProperty(kind=Category)
description = TextProperty(required=True)
price = IntegerProperty(required=True)
SELECT * FROM Product WHERE category = 'CertainName';
The following should perform what your sql query is doing:
query = Product.query(Product.category == "CertainName") # Note the "=="
I just realized you need to filter by key(thank you @mgilson). The query changes a little. Basically you just need to first get your category_entity and then apply the filter like this:
query = Product.query(Product.category == category_entity.key)
Refer to https://github.com/GoogleCloudPlatform/python-docs-samples/blob/master/appengine/standard/ndb/queries/snippets.py for more info (look at query_purchases_for_customer_via_key)