Hibernate: Found two representations of same collection

[Lasse Koskela]

Hi all,

I'm getting a HibernateException saying "Found two representations of same collection: domain.Email.recipients" when updating a class that's holding a java.util.Set of java.lang.Strings. Doing a Session#save() on the same object works perfect. It's just the Session#update() that's making trouble here.

I tried searching the Hibernate forum and found a couple of old threads that discussed the same problem but there were no solutions offered. (I also tried reading the auto-translated Russian Hibernate forum but no luck there either)

Here's all the relevant pieces:

I'm using Hibernate version 2.1.7c against PostgreSQL 8.0.0-rc4 (Win32).

The mapping document:

<hibernate-mapping package="domain">
   <class name="Email" table="EMAIL">
      <id name="id" type="string" column="id" length="32">
         <generator class="uuid.hex" />
      </id>
      <property name="subject" column="subject" type="string" length="255" />
      <property name="body" column="body" type="string" length="10000" />
      <set name="recipients" table="EMAIL_RECIPIENT" cascade="all-delete-orphan">
         <key column="email_id" />
         <element column="recipient_address" type="string" length="100" />
      </set>
   </class>
</hibernate-mapping>

Database tables:

CREATE TABLE email (
  id VARCHAR(32) NOT NULL,
  subject VARCHAR(255),
  body VARCHAR(1000),
  CONSTRAINT email_pkey PRIMARY KEY (id)
);
CREATE TABLE email_recipient (
  email_id VARCHAR(32) NOT NULL,
  recipient_address VARCHAR(100),
  CONSTRAINT fk_email_recipient_to_email FOREIGN KEY (email_id) REFERENCES email (id)
)

The Java class being mapped:

public class Email {
    private String id;
    private String subject;
    private String body;
    private Set recipients; // contains email addresses as strings
 
    ... plus setters and getters for the above
}

The piece of code doing the failing update:

public class EmailStore implements IEmailStore {
    public void update(Email email) {
        // using the Thread Local Session design pattern from
        // <a href="http://www.hibernate.org/42.html" target="_blank" rel="nofollow">http://www.hibernate.org/42.html</a>
        try {
            Session session = HibernateSession.beginTransaction();
            session.update(email);
            session.flush();
            HibernateSession.commitTransaction();
        } catch (HibernateException e) {
            e.printStackTrace(); // this is what prints the below stack trace
            HibernateSession.rollbackTransaction();
            throw new RuntimeException(e);
        }
    }
}

The stack trace of the exception that gets thrown:

net.sf.hibernate.HibernateException: Found two representations of same collection: domain.Email.recipients
   at net.sf.hibernate.impl.SessionImpl.updateReachableCollection(SessionImpl.java:2890)
   at net.sf.hibernate.impl.FlushVisitor.processCollection(FlushVisitor.java:32)
   at net.sf.hibernate.impl.AbstractVisitor.processValue(AbstractVisitor.java:69)
   at net.sf.hibernate.impl.AbstractVisitor.processValues(AbstractVisitor.java:36)
   at net.sf.hibernate.impl.SessionImpl.flushEntity(SessionImpl.java:2612)
   at net.sf.hibernate.impl.SessionImpl.flushEntities(SessionImpl.java:2478)
   at net.sf.hibernate.impl.SessionImpl.flushEverything(SessionImpl.java:2280)
   at net.sf.hibernate.impl.SessionImpl.flush(SessionImpl.java:2259)
   at services.storage.EmailStore.update(EmailStore.java:251)

The generated SQL:

select recipients0_.email_id as email_id__,
       recipients0_.recipient_address as recipien2___
from EMAIL_RECIPIENT recipients0_
where recipients0_.email_id=?

And, finally, the debug level Hibernate log excerpt:

12:57:46,576 DEBUG Loader:611 - Initializing object from ResultSet: 1
12:57:46,626 DEBUG Loader:680 - Hydrating entity: domain.Email#1
12:57:46,626 DEBUG StringType:68 - returning 'subject' as column: subject
12:57:46,626 DEBUG StringType:68 - returning 'subject' as column: subject
12:57:46,626 DEBUG StringType:68 - returning 'body' as column: body
12:57:46,626 DEBUG StringType:68 - returning 'body' as column: body
12:57:46,746 DEBUG Loader:294 - done processing result set (1 rows)
12:57:46,746 DEBUG BatcherImpl:210 - done closing: 0 open PreparedStatements, 0 open ResultSets
12:57:46,756 DEBUG BatcherImpl:272 - closing statement
12:57:46,756 DEBUG Loader:314 - total objects hydrated: 1
12:57:46,756 DEBUG SessionImpl:2215 - resolving associations for [domain.Email#1]
12:57:46,766 DEBUG SessionImpl:3982 - creating collection wrapper:[domain.Email.recipients#1]
12:57:46,786 DEBUG SessionImpl:2246 - done materializing entity [domain.Email#1]
12:57:46,786 DEBUG SessionImpl:3149 - initializing non-lazy collections
12:57:46,786 DEBUG SessionImpl:3295 - initializing collection [domain.Email.recipients#1]
12:57:46,786 DEBUG SessionImpl:3296 - checking second-level cache
12:57:46,786 DEBUG SessionImpl:3302 - collection not cached
12:57:46,796 DEBUG BatcherImpl:203 - about to open: 0 open PreparedStatements, 0 open ResultSets
12:57:46,796 DEBUG SQL:229 - select recipients0_.email_id as email_id__,
 recipients0_.recipient_address as recipien2___
 from EMAIL_RECIPIENT recipients0_ where recipients0_.email_id=?
12:57:46,796 DEBUG SQL:229 - select recipients0_.email_id as email_id__,
 recipients0_.recipient_address as recipien2___
 from EMAIL_RECIPIENT recipients0_ where recipients0_.email_id=?
12:57:46,796 DEBUG BatcherImpl:252 - preparing statement
12:57:46,796 DEBUG StringType:46 - binding '1' to parameter: 1
12:57:46,796 DEBUG StringType:46 - binding '1' to parameter: 1
12:57:46,806 DEBUG Loader:402 - result set contains (possibly empty) collection: [domain.Email.recipients#1]
12:57:46,806 DEBUG SessionImpl:3038 - uninitialized collection: initializing
12:57:46,816 DEBUG Loader:277 - processing result set
12:57:46,816 DEBUG Loader:480 - result row:
12:57:46,816 DEBUG StringType:68 - returning '1' as column: email_id__
12:57:46,816 DEBUG StringType:68 - returning '1' as column: email_id__
12:57:46,816 DEBUG Loader:367 - found row of collection: [domain.Email.recipients#1]
12:57:46,816 DEBUG SessionImpl:3061 - reading row
12:57:46,816 DEBUG StringType:68 - returning '[e-mail]' as column: recipien2___
12:57:46,816 DEBUG StringType:68 - returning '[e-mail]' as column: recipien2___
12:57:46,816 DEBUG Loader:480 - result row:
12:57:46,826 DEBUG StringType:68 - returning '1' as column: email_id__
12:57:46,826 DEBUG StringType:68 - returning '1' as column: email_id__
12:57:46,826 DEBUG Loader:367 - found row of collection: [domain.Email.recipients#1]
12:57:46,826 DEBUG SessionImpl:3061 - reading row
12:57:46,826 DEBUG StringType:68 - returning '[e-mail]' as column: recipien2___
12:57:46,826 DEBUG StringType:68 - returning '[e-mail]' as column: recipien2___
12:57:46,826 DEBUG Loader:294 - done processing result set (2 rows)
12:57:46,826 DEBUG BatcherImpl:210 - done closing: 0 open PreparedStatements, 0 open ResultSets
12:57:46,826 DEBUG BatcherImpl:272 - closing statement
12:57:46,826 DEBUG SessionImpl:3097 - 1 collections were found in result set
12:57:46,826 DEBUG SessionImpl:3128 - collection fully initialized: [domain.Email.recipients#1]
12:57:46,826 DEBUG SessionImpl:3131 - 1 collections initialized
12:57:46,836 DEBUG SessionImpl:3304 - collection initialized
12:57:47,447 DEBUG JDBCTransaction:37 - begin
12:57:47,447 DEBUG JDBCTransaction:41 - current autocommit status:false
12:57:47,447 DEBUG SessionImpl:1449 - updating [domain.Email#1]
12:57:47,467 DEBUG SessionImpl:1296 - collection dereferenced while transient [domain.Email.recipients#1]
12:57:47,477 DEBUG Cascades:497 - processing cascades for: domain.Email
12:57:47,487 DEBUG Cascades:506 - done processing cascades for: domain.Email
12:57:47,497 DEBUG SessionImpl:2266 - flushing session
12:57:47,497 DEBUG Cascades:497 - processing cascades for: domain.Email
12:57:47,497 DEBUG Cascades:506 - done processing cascades for: domain.Email
12:57:47,497 DEBUG SessionImpl:2459 - Flushing entities and processing referenced collections
12:57:47,537 DEBUG SessionImpl:2553 - Updating entity: [domain.Email#1]
12:57:47,567 DEBUG JDBCTransaction:82 - rollback
12:57:47,567 DEBUG SessionImpl:594 - transaction completion
12:57:47,567 DEBUG SessionImpl:576 - closing session
12:57:47,567 DEBUG SessionImpl:3371 - disconnecting session
12:57:47,567 DEBUG SessionImpl:594 - transaction completion

Big thanks for reading this far!
[ January 16, 2005: Message edited by: Lasse Koskela ]

[Ilja Preuss]

Were there *any* replies to the threads you found? I don't have the slightest idea what that error message even means...

My first idea would be to take a look at the source code where the exception is thrown. Perhaps I will find the time to do that tomorrow at work...

[Lasse Koskela]

There were replies alright but none that helped, unfortunately.
I'll also dig inside Hibernate tomorrow. Remind me to report back my findings if you don't hear from me...

[Lasse Koskela]

Should I perhaps specify a primary key for the email_recipient table?
E.g.

CREATE TABLE email (
  id VARCHAR(32) NOT NULL,
  subject VARCHAR(255),
  body VARCHAR(1000),
  CONSTRAINT email_pkey PRIMARY KEY (id)
);
CREATE TABLE email_recipient (
  email_id VARCHAR(32) NOT NULL,
  recipient_address VARCHAR(100),
  CONSTRAINT fk_email_recipient_to_email FOREIGN KEY (email_id) ,
  CONSTRAINT pk_email_recipient PRIMARY KEY (email_id, recipient_address)
)

It just occurred to me that Hibernate might check for this since the semantics of a Set not containing duplicate entries would effectively translate to such a primary key in the database. Does it (check such things)?

I'm not in a place where I could try it out right now so I'll have to report back later after trying that... In the meanwhile, I'd appreciate a confirmation one way or the other, of course.

[Paul Sturrock]

Should I perhaps specify a primary key for the email_recipient table

Absolutely. I've not seen the error you are getting before, but I'd suspect its because you have a table with no PK. The Hibernate developers are very strict about a relational value requiring a PK, because they (quite correctly) state that without one its not a relational value. Given their assumption, I would imagine that somewhere in their code your model is causing identity problems, hence the error.

[Ilja Preuss]

The code is a little bit, well, obscure:

CollectionEntry ce = getCollectionEntry(coll);
if (ce==null) {
  // refer to comment in addCollection()
 throw new HibernateException(
    "Found two representations of same collection: " + coll.getCollectionSnapshot().getRole());
}

I didn't find any comment in an addCollection method, though. :roll: Well, what do you expect from a 3000 line class...

It's doubly confusing because getCollectionEntry just looks it up in a Map and null means that *it wasn't found at all*, as far as I can tell. I don't have the slightest idea what that has to do with *more* than one representation...

Lasse, all I can advice you to do is running the code through your preferred debugger, crossing fingers and execrating the hibernate developers...
[ January 17, 2005: Message edited by: Ilja Preuss ]

[Lasse Koskela]

Okay. I might try some garlic and exorcism if that doesn't help.

[Lasse Koskela]

Originally posted by Paul Sturrock:
Absolutely. I've not seen the error you are getting before, but I'd suspect its because you have a table with no PK. The Hibernate developers are very strict about a relational value requiring a PK, because they (quite correctly) state that without one its not a relational value. Given their assumption, I would imagine that somewhere in their code your model is causing identity problems, hence the error.

Nope. I added a primary key (email_id, email_recipient) to the table but that didn't help. I also let Hibernate auto-create the table and it didn't work with that either (and it didn't create a primary key for that table, by the way).

[Lasse Koskela]

I also downgraded to 2.1.6 and the problem persists.

[Denys Mitin]

Ilja Preuss wrote:I didn't find any comment in an addCollection method, though.

You probably looked on wrong version of source code or wrong variant of method.
For me it looks like there is enough information

if ( old != null ) {
	if (old==coll) throw new AssertionFailure("bug adding collection twice");
	// or should it actually throw an exception?
	old.unsetSession(session);
	collectionEntries.remove(old);
	// watch out for a case where old is still referenced
	// somewhere in the object graph! (which is a user error)
}

[Jaikiran Pai]

Denys, welcome to CodeRanch!

The thread is 9 year old so it's possible that the version which Ilja looked at didn't have those comments at that time and the newer version probably has it.