Question

I have an appengine app which has been running for about a year now, i have mainly been using JDO queries until now, but i am trying to collect stats and the queries are taking too long. I have the following entity (Device)

public class Device implements Serializable{
    ...
    @Persistent
    private Set<Key> feeds;// Key for the Feed entity
    ...
}

So I want to get a count of how many Devices have a certain Feed. I was doing it in JDOQL before as such (uses javax.jdo.Query):

Query query = pm.newQuery("select from Device where feeds.contains(:feedKey)");
Map<String, Object> paramsf = new HashMap<String, Object>();
paramsf.put("feedKey",feed.getId());
List<Device> results = (List<Device>) query.executeWithMap(paramsf);

Though this code times out now. I was trying to use the Datastore API so I could set chunk size,etc to see if i could speed the query up or use a cursor, but I am unsure how to search in a Set field. I was trying this (uses com.google.appengine.api.datastore.Query)

Query query = new Query("Device");
query.addFilter("feeds", FilterOperator.IN, feed.getId());
query.setKeysOnly();
final FetchOptions fetchOptions = FetchOptions.Builder.withPrefetchSize(100).chunkSize(100);
QueryResultList<Entity> results = dss.prepare(query).asQueryResultList(fetchOptions);

Essentially i am unsure how to search in the one-to-many filed (feeds) for a single key. Is it possible to index it somehow?

hope it makes sense….

Answer 1

Lists (and other things that are implemented as lists, like sets) are indexed individually. As a result, you can simply use an equality filter in your query, the same as if you were filtering on a single value rather than a list. A record will be returned if any of the items in the list match.