## org.springframework.orm.jdo
Interface JdoCallback<T>

    public interface JdoCallback<T>

Callback interface for JDO code. To be used with `JdoTemplate`'s execution methods, often as anonymous classes within a method implementation. A typical implementation will call PersistenceManager CRUD to perform some operations on persistent objects.

Note that JDO works on bytecode-modified Java objects, to be able to perform dirty detection on each modification of a persistent instance field. In contrast to Hibernate, using returned objects outside of an active PersistenceManager poses a problem: To be able to read and modify fields e.g. in a web GUI, one has to explicitly make the instances "transient". Reassociation with a new PersistenceManager, e.g. for updates when coming back from the GUI, isn't possible, as the JDO instances have lost their identity when turned transient. This means that either value objects have to be used as parameters, or the contents of the outside-modified instance have to be copied to a freshly loaded active instance on reassociation.

Since:
  03.06.2003
Author:
  Juergen Hoeller
See Also:
  `JdoTemplate`, `JdoTransactionManager`

Method Summary
`T` `doInJdo(javax.jdo.PersistenceManager pm)` Gets called by `JdoTemplate.execute` with an active JDO `PersistenceManager`.

Method Detail

### doInJdo

    T doInJdo(javax.jdo.PersistenceManager pm)
              throws javax.jdo.JDOException

  Gets called by `JdoTemplate.execute` with an active JDO `PersistenceManager`. Does not need to care about activating or closing the `PersistenceManager`, or handling transactions.

  Note that JDO callback code will not flush any modifications to the database if not executed within a transaction. Thus, you need to make sure that JdoTransactionManager has initiated a JDO transaction when the callback gets called, at least if you want to write to the database.

  Allows for returning a result object created within the callback, i.e. a domain object or a collection of domain objects. A thrown custom RuntimeException is treated as an application exception: It gets propagated to the caller of the template.

  Parameters:
    `pm` - active PersistenceManager
  Returns:
    a result object, or `null` if none
  Throws:
    `javax.jdo.JDOException` - if thrown by the JDO API
  See Also:
    `JdoTemplate.execute(org.springframework.orm.jdo.JdoCallback<T>)`, `JdoTemplate.executeFind(org.springframework.orm.jdo.JdoCallback<?>)`