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darrenclarke
 Post subject: Inheritance problem
PostPosted: Tue May 15, 2007 2:58 pm 
Beginner
Beginner

Joined: Thu Jan 25, 2007 3:36 pm
Posts: 25
Hibernate version: 3.2.2
Hibernate Annotations version: 3.3.0.GA
Hibernate EntityManager version: 3.3.0.GA
Database: MySql 5.0.27
JRE: 1.5.0_07 (Java HotSpot(TM) Server VM (build 1.5.0_07-87, mixed mode))


I'm having a problem loading objects where an inheritance hierarchy is involved. I have three entity types:
    Account
    WalletAccount extends Account
    InternalAccount extends WalletAccount

None of these are abstract - an entity can be one of any of these three types.

The ORM specifies a Joined inheritance strategy:

Code:
<entity class="com.blah.Account" access="FIELD">
    <inheritance strategy="JOINED" />

    <attributes>
        <id name="id">
            <generated-value strategy="AUTO" />
        </id>

        <basic name="firstName" optional="false" fetch="EAGER" />
        <basic name="surname" optional="false" fetch="EAGER" />
        [...snip...]
    </attributes>
</entity>

<entity class="com.blah.WalletAccount" access="FIELD">
    <attributes>
        <basic name="walletBalance" optional="false" fetch="EAGER" />
    </attributes>
</entity>


<entity class="com.blah.InternalAccount" access="FIELD">
    <attributes>
        [...snip - more stuff that's not very interesting]
    </attributes>
</entity>




When doing quick finds in order to populate lists I use the EntityManager.find( Class, id ) method, but when I want full details about a particular account I use a query so that I can populate relationships:

Code:
<named-query name="findAccountWithPopulatedRelationships">
    <query>
        SELECT DISTINCT acc
        FROM            Account acc
        LEFT JOIN FETCH acc.accountSystem
        LEFT JOIN FETCH acc.notes
        WHERE           acc.id = :id
    </query>
</named-query>



I have two accounts in the database:
    Account with ID 1 is an InternalAccount (i.e. there is a row in each of the tables Account, WalletAccount and InternalAccount, all of which have id=1).
    Account with ID 2 is a WalletAccount (i.e. there is a row in each of the tables Account and WalletAccount which both have id=2, but no row exists in InternalAccount with this id).

Note that both these accounts have been created via Hibernate too (i.e. via instantiation of new objects and then calling EntityManager.persist()) - they do not exist as a result of dodgy hacking direct to database.


Now, if I start my application and invoke some tests that cause repeated loading (via the query) of the account with ID=1 then it always comes back correctly as an InternalAccount.

If I then invoke a test that causes the loading (via the query) of the account with ID=2 then it comes back correctly as a WalletAccount.

So far so good. Now, if I try to reload the account with ID=1 (again, as before, via the query) it comes back as a WalletAccount, not an InternalAccount. I can check the database and nothing has changed. Furthermore if I restart the application then the account is loaded as an InternalAccount again (until I load a WalletAccount that is, when the problem resurfaces again).

Am I doing something wrong here? I can't understand what's wrong, especially as the entity with ID=1 loads properly until the object with ID=2 is first loaded. I have deliberately missed out a few things from the code above which I don't believe are relevant, but will happily be more verbose if anyone wants more info.

Many thanks
Darren
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darrenclarke
 Post subject:
PostPosted: Thu May 17, 2007 8:35 am 
Beginner
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Joined: Thu Jan 25, 2007 3:36 pm
Posts: 25
I'm still investigating this and have some more diagnostics.

Firstly, when performing the eager find that's causing the problem, I was using a named-query as explained above. I've replaced that with an EntityManager.find( Class, id ), followed by a bunch of Hibernate.initialize() calls to see if that was causing the problem, but that's made no difference.

So, I inspected the SQL that Hibernate generates and found there is no difference between the SQL generated on the first call (which succeeds) and the last call (which returns the wrong type). For reference, here it is (note that the entity names don't match exactly with how I described it before - I previously shortened them for simplicity):

Code:
select  playeracco0_.id                                         as id13_1_,
        playeracco0_.accountSystem_id                           as accountS6_13_1_,
        playeracco0_.failedLoginAttemptCount                    as failedLo2_13_1_,
        playeracco0_.locked                                     as locked13_1_,
        playeracco0_.preferredOutlet_id                         as preferre7_13_1_,
        playeracco0_.suspended                                  as suspended13_1_,
        playeracco0_.username                                   as username13_1_,
        playeracco0_1_.nonWithdrawableBalance                   as nonWithd2_14_1_,
        playeracco0_1_.withdrawableBalance                      as withdraw3_14_1_,
        playeracco0_2_.accountNumber                            as accountN2_15_1_,
        playeracco0_2_.accountSystemId                          as accountS3_15_1_,
        playeracco0_2_.address_id                               as address21_15_1_,
        playeracco0_2_.challengeAnswer                          as challeng4_15_1_,
        playeracco0_2_.challengeQuestion_id                     as challen20_15_1_,
        playeracco0_2_.contactableByOthers                      as contacta5_15_1_,
        playeracco0_2_.contactableByUs                          as contacta6_15_1_,
        playeracco0_2_.dob                                      as dob15_1_,
        playeracco0_2_.email                                    as email15_1_,
        playeracco0_2_.encPin                                   as encPin15_1_,
        playeracco0_2_.firstName                                as firstName15_1_,
        playeracco0_2_.lastName                                 as lastName15_1_,
        playeracco0_2_.over18                                   as over12_15_1_,
        playeracco0_2_.paymentCard_id                           as payment19_15_1_,
        playeracco0_2_.pinIsOneShot                             as pinIsOn13_15_1_,
        playeracco0_2_.registrationDate                         as registr14_15_1_,
        playeracco0_2_.significantDate                          as signifi15_15_1_,
        playeracco0_2_.telephone                                as telephone15_1_,
        playeracco0_2_.termsAndCondsAccepted                    as termsAn17_15_1_,
        playeracco0_2_.title                                    as title15_1_,
        case    when playeracco0_2_.id is not null then 2
                when playeracco0_1_.id is not null then 1
                when playeracco0_.id is not null then 0 end     as clazz_1_,
        accountsys1_.id                                         as id3_0_,
        accountsys1_.adapterClass                               as adapterC2_3_0_,
        accountsys1_.encAdapterClassConfigXml                   as encAdapt3_3_0_,
        accountsys1_.internal                                   as internal3_0_,
        accountsys1_.name                                       as name3_0_,
        accountsys1_.supportsCashDeposits                       as supports6_3_0_,
        accountsys1_.supportsReconciliation                     as supports7_3_0_,
        accountsys1_.tag                                        as tag3_0_

from            PlayerAccount       playeracco0_
left outer join WalletPlayerAccount playeracco0_1_ on playeracco0_.id=playeracco0_1_.id
left outer join InternalPlayerAccount playeracco0_2_ on playeracco0_.id=playeracco0_2_.id
inner join      AccountSystem accountsys1_ on playeracco0_.accountSystem_id=accountsys1_.id
where           playeracco0_.id=?


Next, I stepped through in the debugger...
    1) the first find (an InternalPlayerAccount with ID=1) succeeded as before (repeated 5 times, no problem)
    2) the next find (a WalletPlayerAccount with ID=2) succeeded as before (repeated 5 times, no problem)
    3) the next find (the InternalPlayerAccount with ID=1 again) failed on the first attempt. (Actually, as explained previously, it doesn't *fail* but it returns an entity of type WalletPlayerAccount instead of InternalPlayerAccount.

Whilst in the debugger and immediately prior to step (3) above, I switched to a query tool and executed the SQL above to see if bad data was being returned (specifically whether nulls are returned for the InternalPlayerAccount columns), but everything looked good and valid data was returned from all three *Account tables.


In case it helps, here is the Hibernate log output. This first extract corresponds to step (1) in the list above, i.e. a successful find:
Code:
2007-05-17 10:40:59.265 FINE    org.hibernate.SQL       select playeracco0_.id as id13_1_,  [snip - see SQL above]
2007-05-17 10:40:59.268 FINE    org.hibernate.jdbc.AbstractBatcher      about to open ResultSet (open ResultSets: 0, globally: 0)
2007-05-17 10:40:59.269 FINE    org.hibernate.loader.Loader     result set row: 0
2007-05-17 10:40:59.271 FINE    org.hibernate.loader.Loader     result row: EntityKey[com.evolvegaming.lgp.AccountSystem#1], EntityKey[com.evolvegaming.lgp.PlayerAccount#1]
2007-05-17 10:40:59.278 FINE    org.hibernate.jdbc.AbstractBatcher      about to close ResultSet (open ResultSets: 1, globally: 1)
2007-05-17 10:40:59.278 FINE    org.hibernate.jdbc.AbstractBatcher      about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
2007-05-17 10:40:59.278 FINE    org.hibernate.jdbc.ConnectionManager    aggressively releasing JDBC connection
2007-05-17 10:40:59.279 FINE    org.hibernate.jdbc.ConnectionManager    releasing JDBC connection [ (open PreparedStatements: 0, globally: 0) (open ResultSets: 0, globally: 0)]
2007-05-17 10:40:59.279 FINE    org.hibernate.engine.TwoPhaseLoad       resolving associations for [com.evolvegaming.lgp.AccountSystem#1]
2007-05-17 10:40:59.280 FINE    org.hibernate.engine.TwoPhaseLoad       done materializing entity [com.evolvegaming.lgp.AccountSystem#1]
2007-05-17 10:40:59.280 FINE    org.hibernate.engine.TwoPhaseLoad       resolving associations for [com.evolvegaming.lgp.InternalPlayerAccount#1]
2007-05-17 10:40:59.282 FINE    org.hibernate.engine.TwoPhaseLoad       done materializing entity [com.evolvegaming.lgp.InternalPlayerAccount#1]
2007-05-17 10:40:59.282 FINE    org.hibernate.engine.StatefulPersistenceContext initializing non-lazy collections
2007-05-17 10:40:59.282 FINE    org.hibernate.loader.Loader     done entity load
2007-05-17 10:40:59.283 FINE    org.hibernate.jdbc.ConnectionManager    aggressively releasing JDBC connection


This second extract corresponds to step (3) in the list above, i.e. a find that returns an entity of the incorrect type.
Code:
2007-05-17 10:41:00.771 FINE    org.hibernate.SQL       select playeracco0_.id as id13_1_, [snip - see SQL above]
2007-05-17 10:41:00.773 FINE    org.hibernate.jdbc.AbstractBatcher      about to open ResultSet (open ResultSets: 0, globally: 0)
2007-05-17 10:41:00.774 FINE    org.hibernate.loader.Loader     result set row: 0
2007-05-17 10:41:00.774 FINE    org.hibernate.loader.Loader     result row: EntityKey[com.evolvegaming.lgp.AccountSystem#1], EntityKey[com.evolvegaming.lgp.PlayerAccount#1]
2007-05-17 10:41:00.777 FINE    org.hibernate.jdbc.AbstractBatcher      about to close ResultSet (open ResultSets: 1, globally: 1)
2007-05-17 10:41:00.778 FINE    org.hibernate.jdbc.AbstractBatcher      about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
2007-05-17 10:41:00.778 FINE    org.hibernate.jdbc.ConnectionManager    aggressively releasing JDBC connection
2007-05-17 10:41:00.778 FINE    org.hibernate.jdbc.ConnectionManager    releasing JDBC connection [ (open PreparedStatements: 0, globally: 0) (open ResultSets: 0, globally: 0)]
2007-05-17 10:41:00.779 FINE    org.hibernate.engine.TwoPhaseLoad       resolving associations for [com.evolvegaming.lgp.AccountSystem#1]
2007-05-17 10:41:00.779 FINE    org.hibernate.engine.TwoPhaseLoad       done materializing entity [com.evolvegaming.lgp.AccountSystem#1]
2007-05-17 10:41:00.780 FINE    org.hibernate.engine.TwoPhaseLoad       resolving associations for [com.evolvegaming.lgp.WalletPlayerAccount#1]
2007-05-17 10:41:00.781 FINE    org.hibernate.engine.TwoPhaseLoad       done materializing entity [com.evolvegaming.lgp.WalletPlayerAccount#1]
2007-05-17 10:41:00.781 FINE    org.hibernate.engine.StatefulPersistenceContext initializing non-lazy collections
2007-05-17 10:41:00.781 FINE    org.hibernate.loader.Loader     done entity load
2007-05-17 10:41:00.781 FINE    org.hibernate.jdbc.ConnectionManager    aggressively releasing JDBC connection


The most interesting bits to my mind are the last two org.hibernate.engine.TwoPhaseLoad entries in each extract - in the first extract it resolves/materializes com.evolvegaming.lgp.InternalPlayerAccount and in the second extract com.evolvegaming.lgp.WalletPlayerAccount

I'm going to continue investigating, but if this is ringing bells for anyone, I'd really appreciate any thoughts/comments/suggestions.

Darren
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darrenclarke
 Post subject:
PostPosted: Thu May 17, 2007 10:26 am 
Beginner
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Joined: Thu Jan 25, 2007 3:36 pm
Posts: 25
More info...

I said below that I'm reproducing the problem consistently by performing the following steps:

    1) Finding an InternalPlayerAccount with ID=1 succeeds (repeated 5 times, no problem)
    2) Finding a WalletPlayerAccount with ID=2 succeeds (repeated 5 times, no problem)
    3) Finding the InternalPlayerAccount with ID=1 again returns an entity of type WalletPlayerAccount instead of InternalPlayerAccount on the first attempt.

The actual logic looks something like this:
Code:
int outerLoopLimit = 5;
int innerLoopLimit = 5;
try {
    for( int h=0; h<outerLoopLimit; h++ ) {

        for( int i=0 ; i<innerLoopLimit; i++ ) {
            findPlayerAccount(1); //i.e. the InternalPlayerAccount with id=1
        }

        for( int i=0 ; i<innerLoopLimit; i++ ) {
            findPlayerAccount(2); //i.e. the WalletPlayerAccount with id=2
        }

    }
} catch( Throwable t ) {
    t.printStackTrace();
}


When I execute this, the code gets through the first inner loop all five times without a problem. It then gets through the second inner loop OK and starts to re-iterate the outer loop. It then fails on the first execution of findPlayerAccount(1).


So, I tried playing with the values of innerLoopLimit. If I increase it, the behaviour described above is always the same - first outer iteration succeeds, then the first iteration of the first inner loop fails.

However, if I decrease the innerLoopLimit to two, I find this isn't the case - loading the account with id=1 succeeds even on the second iteration of the outer loop until the 6th time in total, at which point it fails as before. I decrease the innerLoopLimit to one and see the same - I get 5 good finds of account with id=1 (even after loading a WalletPlayerAccount), then fail on the 6th.

This seemed fishy, I looked through my persistence.xml and noticed c3p0's connection pool min_size=5
Code:
  <property name="hibernate.c3p0.min_size"       value="5" />
  <property name="hibernate.c3p0.max_size"       value="20" />
  <property name="hibernate.c3p0.timeout"        value="1800" />
  <property name="hibernate.c3p0.max_statements" value="100" />


I tried removing the c3p0-related properties from configuration altogether and my problem dissapears!


So, does anybody think this could be a C3P0 bug, or could it still be something I'm doing wrong (in which case all suggestions appreciated!)

Darren
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darrenclarke
 Post subject:
PostPosted: Fri May 18, 2007 5:58 am 
Beginner
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Joined: Thu Jan 25, 2007 3:36 pm
Posts: 25
I've realised that this is probably the wrong forum for this post and have moved it:

http://forum.hibernate.org/viewtopic.php?p=2351862

Thanks,
Darren
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