I have about 50k entities stored in appengine. I am able to look up an individual record via the GQL admin interf开发者_JAVA百科ace with a query like:
SELECT * FROM Pet where __key__ = KEY( 'Pet','Fido')
But I'm having trouble figuring out how to do a batch version of this via JDO. Right now I have this:
PersistenceManager pm = ...;
for(Pet pet : pets) {
for(String k : getAllAliases(pet)) {
keys.add(KeyFactory.createKeyString(Pet.class.getSimpleName(), k));
}
}
Query q = pm.newQuery("select from " + Pet.class.getName() + " where id == :keys");
List<Pet> petlist = (List<Pet>) q.execute(keys);
But though 'Fido' works in the GQL case, it returns nothing when I use that Java + JDO code. What am I doing wrong?
Don't use queries to fetch entities by key - they're inefficient, and require a query for each object retrieved! Instead, get the objects by key. Bulk fetches by key don't appear to be supported by JDO, but fetching them by key one at a time is still going to be a lot more efficient than doing queries for them.
Likely doesn't work in the JDOQL case since it isn't valid JDOQL :-P
Collection keys = ... (create your keys collection) Query q = pm.newQuery("SELECT FROM " + Pet.class.getName() + " WHERE :keys.contains(id)");
i.e the filter uses Java syntax
http://gae-java-persistence.blogspot.com/2009/10/executing-batch-gets.html
I didn't try the JDO version, but the JPA version does work!
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