Find by multiple ids in datastore using jpa 2.0 - google-app-engine

Question

Here is my JPA query:
String jpql = "SELECT a FROM Account a WHERE a.id IN :list";
TypedQuery<Account> q = mgr.createQuery(jpql, Account.class);
q.setParameter("list", list);
return q.getResultList();
Here is the error log:
Cannot find type of (part of) a.id since symbol has no type; implicit variable?
org.datanucleus.exceptions.NucleusUserException: Cannot find type of (part of) a.id since symbol has no type; implicit variable?
at org.datanucleus.query.expression.PrimaryExpression.bind(PrimaryExpression.java:274)
at org.datanucleus.query.expression.DyadicExpression.bind(DyadicExpression.java:87)
at org.datanucleus.query.compiler.JavaQueryCompiler.compileFilter(JavaQueryCompiler.java:480)
at org.datanucleus.query.compiler.JPQLCompiler.compile(JPQLCompiler.java:81)
at org.datanucleus.store.query.AbstractJPQLQuery.compileInternal(AbstractJPQLQuery.java:271)
at org.datanucleus.store.query.Query.setImplicitParameter(Query.java:799)
at org.datanucleus.api.jpa.JPAQuery.setParameter(JPAQuery.java:437)
at org.datanucleus.api.jpa.JPAQuery.setParameter(JPAQuery.java:57)
at com.example.game.dao.impl.AccountDaoImpl.findByIds(AccountDaoImpl.java:42)
at com.example.game.gameApi.sendPuzzle(gameApi.java:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.google.appengine.tools.development.agent.runtime.Runtime.invoke(Runtime.java:115)
at com.google.api.server.spi.SystemService.invokeServiceMethod(SystemService.java:304)
at com.google.api.server.spi.SystemServiceServlet.execute(SystemServiceServlet.java:161)
at com.google.api.server.spi.SystemServiceServlet.doPost(SystemServiceServlet.java:120)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:123)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:61)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at com.google.appengine.tools.development.DevAppServerServersFilter.doFilter(DevAppServerServersFilter.java:106)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:94)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:421)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
Also, account looks like this
#Entity
public class Account implements java.io.Serializable{
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;
private String name;
public Account(long id, name) {
super();
Key key = KeyFactory.createKey(Account.class.getSimpleName(), id);
this.key = key;
this.name = name
}
//getters and setters
}
For a counterpart, in python the datastore supports multi key queries similar to
list_of_keys = ndb.put_multi(list_of_entities)
list_of_entities = ndb.get_multi(list_of_keys)
ndb.delete_multi(list_of_keys)
And as suggested by the tutorial, using a loop would be inefficient.

Answer 1

I think you want your query to be:
String jpql = "SELECT a FROM Account a WHERE a.key IN :list";
since the variable is named key, not id.

Answer 2

I don't know if JPA allows for what you are seeking, but you can definitely do it using a DatastoreService object, as in
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
From there, you can use your python app-engine knowledge to guide you. If you have been developing for long, then you have probably had to use Hibernate to supplement JPA. If you really want to code to the interface, then you may not like this answer. But it is a solution no different than using Hibernate.