Hi i have a question regarding the session-per-application-transaction part of this link.

http://www.hibernate.org/168.html

It claims that

.

I hoped someone could explain it in more detail because I would like to use this design on my system.
I want to open of session for a registration process that span over many requests.
For each request I open a transaction, do some saving and reading from database, commit a transaction,disconnect the session. And when the whole registration process is completed I would like to close the session.

I would like to hold the session for the whole duration of the registration process, because of lazy loading. Is this a bad idea should I instead close the session, and manually lock the object to the new session?


any comments on my approach?

You can use both styles, a Long Session or Detached Objects/Reattachment for each request/response. Keep in mind that you have to close the Long Session at some point, usually at the end of your application transaction.

The atomicity aspect is simple: If you have n database transactions in 1 application transaction, only the last database transaction should write data.

For example, if your registration process has 3 screens and you have the sequence: Screen1(load data), Screen2(load more data), Screen3(save data), your application transaction will be atomar, as Hibernate checks the version of the objects in Screen3 while saving the modifications. If you would also modify data in Screen2 and save, the whole application transaction won't be atomar anymore (no automatic rollback, you would have to do that yourself).

Thanx Christian

So if I want to write to the db in screen 1 or 2 I should use the session per request with detatched objects.

I have another question..
If i want to associate an object already in database, to a new object, will i have to save the new object to database before i make the association?

I'll explain closer:


/**
* @hibernate.class
*/

public class Person() {

private Long personKey;
...
private Set reportedAccidents = new HashSet();

/**
* @hibernate.id generator-class="native" unsaved-value="null"
*/

public Long getPersonKey() {
return personKey;
}

public void setPersonKey(Long _personKey) {
personKey = _personKey;
}

...

/**
* @hibernate.set lazy="true" inverse="true"
* @hibernate.collection-key column="reportedBy"
* @hibernate.collection-one-to-many * class="edu.ncsystem.Nonconformance"
*/
public Set getReportedAccidents() {
return reported;
}

public void setReportedAccidents(Set set) {
reported = set;
}

public void addReportedAccidents(Accident accident) {
reported.add(accident);
}
}

/**
* @hibernate.class
*/

public class Accident() {
private Long accidentKey;
...
private Person reportedBy;

/**
* @hibernate.id generator-class="native" unsaved-value="null"
*/

public Long getAccidentKey() {
return personKey;
}

public void setAccidentKey(Long _personKey) {
personKey = _personKey;
}

.......

/**
* @hibernate.many-to-one
*/
public Person getReportedBy() {
return reportedBy;
}

public void setReportedBy(Person _reportedBy) {
reportedBy = _reportedBy;
}
}

Lets say a person object is in db, and i will register a new accident. I retrieve a person object from db and associates it with my new accident object, wich is not yet saved to db. Then i'll get a net.sf.hibernate.TransientObjectException right?
I wish it was possible to associate an object in database to a object not yet in database so I could use the session per application transaction pattern.
Or is this possible?

Sure, specify a "cascading" option for the Set and cascade the save and/or update operations.