Java.lang.IllegalArgumentException: References to entities are not allowed

Question

Hi,
I am using Berkely DB(native edition) 5.0.21 version. I have a couple classes as defined below:
Class - 1:
package bdb.test;
import java.util.List;
import com.sleepycat.persist.model.Entity;
import com.sleepycat.persist.model.PrimaryKey;
@Entity
public class Employee {
     @PrimaryKey
     private String id ;
     private String name;
     private List<Employee> reportingManagers ;
     public String getId() {
          return id;
     public void setId(String id) {
          this.id = id;
     public String getName() {
          return name;
     public void setName(String name) {
          this.name = name;
     public List<Employee> getReportingManagers() {
          return reportingManagers;
     public void setReportingManagers(List<Employee> managers) {
          this.reportingManagers = managers;
Class - 2 :
package bdb.test;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.Environment;
import com.sleepycat.db.EnvironmentConfig;
import com.sleepycat.persist.EntityStore;
import com.sleepycat.persist.PrimaryIndex;
import com.sleepycat.persist.StoreConfig;
     public class BDBTest{
          public static void main(String agrs[]){
               Environment myEnv;
               EntityStore store;
               try {
                    EnvironmentConfig myEnvConfig = new EnvironmentConfig();
                    myEnvConfig.setCacheSize(30000);
                    StoreConfig storeConfig = new StoreConfig();
                    myEnvConfig.setAllowCreate(true);
                    myEnvConfig.setInitializeCache(true);
                    storeConfig.setAllowCreate(true);
                    try {
                    // Open the environment and entity store
                    myEnv = new Environment(new File("c:\\BDBTEST\\"), myEnvConfig);
                    store = new EntityStore(myEnv, "MyStore", storeConfig);
                    PrimaryIndex<String, Employee> primaryIndex = store.getPrimaryIndex(String.class, Employee.class);
                    // write Employee
                    Employee employee = buildEmployee("E1", "EMP1");
                    primaryIndex.putNoReturn(employee);
               } catch (FileNotFoundException fnfe) {
                    System.err.println(fnfe.toString());
                    System.exit(-1);
               } catch(DatabaseException dbe) {
                    System.err.println("Error opening environment and store: " +
                    dbe.toString());
                    System.exit(-1);
          public static Employee buildEmployee(String id,String name){
               Employee employee = new Employee();
               employee.setId(id);
               employee.setName(name);
               employee.setManagers(buildManager());
               return employee;
          public static List<Employee> buildManager(){
               List <Employee> managers = new ArrayList<Employee>();
               Employee manager1 = new Employee();
               manager1.setId("M111");
               manager1.setName("Manager1");
               Employee manager2 = new Employee();
               manager2.setId("M222");
               manager2.setName("Manager2");
               managers.add(manager2);
               return managers;
While running the Class 2, I am getting the following exception :
Exception in thread "main" java.lang.IllegalArgumentException: References to entities are not allowed: bdb.test.Employee
     at com.sleepycat.persist.impl.RecordOutput.writeObject(RecordOutput.java:94)
     at com.sleepycat.persist.impl.ObjectArrayFormat.writeObject(ObjectArrayFormat.java:137)
     at com.sleepycat.persist.impl.RecordOutput.writeObject(RecordOutput.java:114)
     at com.sleepycat.persist.impl.ReflectionAccessor$ObjectAccess.write(ReflectionAccessor.java:398)
     at com.sleepycat.persist.impl.ReflectionAccessor.writeNonKeyFields(ReflectionAccessor.java:258)
     at com.sleepycat.persist.impl.ReflectionAccessor.writeNonKeyFields(ReflectionAccessor.java:255)
     at com.sleepycat.persist.impl.ComplexFormat.writeObject(ComplexFormat.java:528)
     at com.sleepycat.persist.impl.ProxiedFormat.writeObject(ProxiedFormat.java:116)
     at com.sleepycat.persist.impl.RecordOutput.writeObject(RecordOutput.java:114)
     at com.sleepycat.persist.impl.ReflectionAccessor$ObjectAccess.write(ReflectionAccessor.java:398)
     at com.sleepycat.persist.impl.ReflectionAccessor.writeNonKeyFields(ReflectionAccessor.java:258)
     at com.sleepycat.persist.impl.ComplexFormat.writeObject(ComplexFormat.java:528)
     at com.sleepycat.persist.impl.PersistEntityBinding.writeEntity(PersistEntityBinding.java:103)
     at com.sleepycat.persist.impl.PersistEntityBinding.objectToData(PersistEntityBinding.java:83)
     at com.sleepycat.persist.PrimaryIndex.putNoOverwrite(PrimaryIndex.java:474)
     at com.sleepycat.persist.PrimaryIndex.putNoOverwrite(PrimaryIndex.java:449)
     at bdb.test.BDBTest.main(BDBTest.java:42)
Question : In the above example reportingManagers is also a list of Employee classes. Can't I self reference a object with in the same object ? How do I store list of reportingManagers in this example? Any help is highly appreciated.
Thanks,
Bibhu

Answer 1

Hi Sandra,
Thanks for the reply.
Is there any restrictions in Berkeley DB to store cyclic referencing objects?
API documentation for Entity annotation talks about cyclic references in one of section but contradicts the same in another section. Please refer the link below:
[ http://download.oracle.com/docs/cd/E17076_02/html/java/com/sleepycat/persist/model/Entity.html]
Following sections of this documentation contradicts each other. I have highlighted both of them in bold.
Other Type Restrictions:
Entity classes and subclasses may not be used in field declarations for persistent types. Fields of entity classes and subclasses must be simple types or non-entity persistent types (annotated with Persistent not with Entity).
If a field of an Entity needs to reference an object, the referenced object should be marked with @Persistent and not with @Entity. So, self referencing is not possible as the main class would have been marked with @Entity.
Embedded Objects
As stated above, the embedded (or member) non-transient non-static fields of an entity class are themselves persistent and are stored along with their parent entity object. This allows embedded objects to be stored in an entity to an arbitrary depth.
There is no arbitrary limit to the nesting depth of embedded objects within an entity; however, there is a practical limit. When an entity is marshalled, each level of nesting is implemented internally via recursive method calls. If the nesting depth is large enough, a StackOverflowError can occur. In practice, this has been observed with a nesting depth of 12,000, using the default Java stack size. This restriction on the nesting depth of embedded objects does not apply to cyclic references, since these are handled specially as described below.
Self referencing is possible.
Object Graphs
When an entity instance is stored, the graph of objects referenced via its fields is stored and retrieved as a graph. In other words, if a single instance is referenced by two or more fields when the entity is stored, the same will be true when the entity is retrieved. When a reference to a particular object is stored as a member field inside that object or one of its embedded objects, this is called a cyclic reference. Because multiple references to a single object are stored as such, cycles are also represented correctly and do not cause infinite recursion or infinite processing loops. If an entity containing a cyclic reference is stored, the cyclic reference will be present when the entity is retrieved.
My question:
In the above first highlighted section says to store a referenced/embedded object it needs be marked with @Persistent and not with @Entity annotation. That rules out storage of cyclic referencing object since the main object would have been already marked with @Entity annotation. The second section indicates having support for cyclic references.
So, Is it possible to store cyclic referencing objects in BDB? if yes, how it should be done?
Thanks,
Bibhu
Edited by: user12848956 on Jan 20, 2011 7:19 AM