Client Defined Transactions

[haninaguib]

Hi I have a general problem I am trying to resolve and have got my self all confused so I thought I
would try to get some help.

The problem revolves around user-defined transactions. Let me explain this by defining a simplication
of my application. The 'server' in this example provides 2 services, UserManager and QueryManager.

UserManager lets say has the following methods:
- addUser(User)
- removeUser(String login)

QueryManager lets say has the following methods:
- Object[] query(String hqlQuery, Map params);

As it stands these methods are transactional, using TransactionProxyFactoryBean / HibernateTransactionManager
I use hibernate to implement my DAO interfaces behind the scene.

So far so good. Now I want to give users of my server the ability to define their own
transactions: Here is sort of what I want them to do:

TransactionManager.beginTransaction();
Object[] user = queryManager.query("some query that returns a list of user ids I want to delete",params);
for (int x=0;x<user.length;x++)
userMan.removeUser(user[x].toString());
TransactionManager.endTransaction();

Now I know this example is not very smart, and you may say why not have a userManager.removeUsers(String hqlQuery,Map params), or
a try/catch around the removeUser etc...
But the point is I cannot predict what the user will be doing in his transaction, and I thought giving them the ability to define their transactions
would be useful.

So what I want to do is to somehow have a TransactionManager class that would open a transaction, (which my service classes and dao hibernate
classes would participate in) until I closed it.

Is their an existing way of doing this? Or am I completly off the mark here?

Thanks,
Hani

[irbouho]

Hani,

What TransactionManager implementation are you using here? Local / JTA? Also, where will "uers' be calling this code? view layer?
Any error? stackTrace?

[dvoytenko]

You can always get a PlatformTransactionManager as defined in any example using transactions, for instance:

  <bean id="transactionManager"
class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource">
      <ref local="dataSource"/>
    </property>
  </bean>

In java, you can get access to such manager (injection or otherwise) and use it to start/end transaction. Of course, a lot will depend on the transaction definitions of the specific methods you will be calling (i.e. if a method specifies "PROPAGATION_REQUIRES_NEW", this will not help).

  PlatformTransactionManager txMan = ....;
  ...
  ...
  TransactionDefinition txDef = new DefaultTransactionDefinition(...);
  TransactionStatus tx = txMan.getTransaction(txDef);
  try {
    ...
    // invoke transactional methods
    ...
    txMan.commit(txDef);
  } catch (...) {
    txMan.rollback(txDef);
  }

This should work, but there're a lot of nuances here, such as proper exception handling, etc.

Another way is to use TransactionTemplate and TransactionCallback from transaction.support package.

  <bean id="txTemplate"
class="org.springframework.transaction.support.TransactionTemplate">
    <property name="transactionManager">
      <ref local="transactionManager"/>
    </property>
  </bean>

  public void setTxTemplate(TransactionTemplate txTemplate) {
    this.txTemplate = txTemplate;
  }

  ...
  ...
  txTemplate.execute(new TransactionCallback() {
     public Object doInTransaction(TransactionStatus status) {
        // invoke transactional methods
     }
  });

[Costin Leau]

does the user work directly on the code w/o the ability to work on Spring configuration? are you doing a framework using Spring? Why not allow the user to directly define TransactionDefinitions using properties (declaratively through XML or programatically)?

[dvoytenko]

As far as I understood Hani is trying to accomplish some sort of Command Pattern implementation within a transaction, i.e. to run undefined commands within a transaction.