Persistance JDO - How to query a property of a collection with JDOQL?

Question

I want to build an application where a user identified by an email address can have several application accounts. Each account can have one or more users. I am trying to use the JDO Storage capabilities with Google App Engine Java. Here is my attempt:

@PersistenceCapable
@Inheritance(strategy = InheritanceStrategy.NEW_TABLE)
public class AppAccount {
     @PrimaryKey
     @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
     private Long id;

    @Persistent
    private String companyName;

    @Persistent
    List<Invoices> invoices = new ArrayList<Invoices>();

    @Persistent
    List<AppUser> users = new ArrayList<AppUser>();

    // Getter Setters and Other Fields
}

@PersistenceCapable
@EmbeddedOnly
public class AppUser {

    @Persistent
    private String username;

    @Persistent
    private String firstName;

    @Persistent
    private String lastName;

     // Getter Setters and Other Fields
}

When a user logs in, I want to check how many accounts he belongs to. If he or she belongs to more than one then he or she will be presented with a dashboard where he/she can click which account he/she wants to load. This is my code to retrieve a list of app accounts where he/she is registered.

public static List<AppAccount> getUserAppAccounts(String username) {
    PersistenceManager pm = JdoUtil.getPm();
    Query q = pm.newQuery(AppAccount.class);
    q.setFilter("users.username == usernameParam");
    q.declareParameters("String usernameParam");
    return (List<AppAccount>) q.execute(username);
}

But I get the next error:

SELECT FROM invoices.server.AppAccount WHERE users.username == usernameParam PARAMETERS String usernameParam: Encountered a variable expression that isn't part of a join.  Maybe you're referencing a non-existent field of an embedded class.
org.datanucleus.store.appengine.FatalNucleusUserException: SELECT FROM com.softamo.pelicamo.invoices.server.AppAccount WHERE users.username == usernameParam PARAMETERS String usernameParam: Encountered a variable expression that isn't part of a join.  Maybe you're referencing a non-existent field of an embedded class.
    at org.datanucleus.store.appengine.query.DatastoreQuery.getJoinClassMetaData(DatastoreQuery.java:1154)
    at org.datanucleus.store.appengine.query.DatastoreQuery.addLeftPrimaryExpression(DatastoreQuery.java:1066)
    at org.datanucleus.store.appengine.query.DatastoreQuery.addExpression(DatastoreQuery.java:846)
    at org.datanucleus.store.appengine.query.DatastoreQuery.addFilters(DatastoreQuery.java:807)
    at org.datanucleus.store.appengine.query.DatastoreQuery.performExecute(DatastoreQuery.java:226)
    at org.datanucleus.store.appengine.query.JDOQLQuery.performExecute(JDOQLQuery.java:85)
    at org.datanucleus.store.query.Query.executeQuery(Query.java:1489)
    at org.datanucleus.store.query.Query.executeWithArray(Query.java:1371)
    at org.datanucleus.jdo.JDOQuery.execute(JDOQuery.java:243)
    at com.softamo.pelicamo.invoices.server.Store.getUserAppAccounts(Store.java:82)
    at com.softamo.pelicamo.invoices.test.server.StoreTest.testgetUserAppAccounts(StoreTest.java:39)
    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 org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:76)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:46)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Any ideas?

Am I getting JDO persistance totally wrong?

score 5 · Answer 1 · answered Apr 04 '10 at 23:18

The AppAccount class has a users variable that is a List. The List does not have a username property directly.

You need to do something like this:

@PersistenceCapable
@EmbeddedOnly
public class AppUser {

    @Persistent
    private String username;

    @Persistent
    private String firstName;

    @Persistent
    private String lastName;

    //override equals method for List .contains
    @Override
    public boolean equals(AppUser au) {
        return au.getUsername().equals(this.username);
    } 

     // Getter Setters and Other Fields
}

Query q = pm.newQuery(AppAccount.class);
//the : denotes an implicit variable will be passed to query execute method
q.setFilter("users.contains(:username)");
//create a new AppUser with the username you want to check, this query will find the AppAccount with any AppUser with the same username, because the .equals method of AppUser has been overridden to return true based on the username member variable
List<AppAccount> results = (List<AppAccount>)query.execute(new AppUser(username));

How does this work when there is no 1-arg constructor for the class AppUser? Thanks :) — jamesmortensen, Jan 16 '12 at 19:02
Google provides [some documentation](https://developers.google.com/appengine/docs/java/datastore/jdo/queries#Filters) for filtering on collection contents. jmort253: it doesn't matter what the constructor parameters for AppUser are. What matters is that the "username" filter parameter provided to [query.execute()](http://db.apache.org/jdo/api30/apidocs/javax/jdo/Query#execute()) is equals() to the AppUser you want your resulting AppAccount values to have in their users collections. This is what Finbarr has done here by overriding the .equals() method. — dmiller309, Jul 31 '13 at 23:04

Persistance JDO - How to query a property of a collection with JDOQL?

1 Answers1