In this example, the Google App Engine documentation makes the Customer the entity group parent of the AccountInfo entity. Wouldn't AccountInfo encapsulate Customer rather than the other way around? Normally I would think of an AccountInfo class as including all of the information about the Customer.

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;

@PersistenceCapable
public class AccountInfo {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key key;

    public void setKey(Key key) {
        this.key = key;
    }
}

// ...
        KeyFactory.Builder keyBuilder = new KeyFactory.Builder(Customer.class.getSimpleName(), "custid985135");
        keyBuilder.addChild(AccountInfo.class.getSimpleName(), "acctidX142516");
        Key key = keyBuilder.getKey();

        AccountInfo acct = new AccountInfo();
        acct.setKey(key);
        pm.makePersistent(acct);