Optimistic Locking in a Webapp

larry · **Joined:** Fri Jan 23, 2004 4:29 pm **Posts:** 39

How should I implement optimistic locking in a webapp?
Any feedback is welcome.

I'm using the following frameworks:

Here's how I planned on doing it.

1. Set optimistic-lock to version and dynamic-update to true

Code:

<class
    optimistic-lock="version"
    dynamic-update="true"
/>

The documentation states

Quote:

If you enable dynamic-update, you will have a choice of optimistic locking strategies

2. Add the version tag to the class and create the column in the database

The class has a field called version which is used for versioning.

Code:

java.lang.Integer version

Code:

<version
        column="version"
        name="version"
        type="integer"
        unsaved-value="null"
/>

If the field is null it means we have a transient object which needs to be saved.

3. Add version and id to the HTML form

Code:

<input type="text" name="name" value="$!object.name"/>
<input type="hidden" name="id" value="$!object.id"/>
<input type="hidden" name="version" value="$!object.version"/>

I'm using Velocity so if the object is null the id and version fields would be null and
a new object would be inserted by hibernate.

4. Read version and id in WebWork2 action

When the user submits the data to the action I get the id and version
and create the object as follows.

Code:

Object object = new Object();
object.setVersion(version);
object.setId(version);
object.setName(name);

I then call:

Code:

session.saveOrUpdate(object);

saveOrUpdate would insert a new object into the database if id and version are null.
Or update the existing object if id and version are set to non-null values.

5. Hibernate takes care of the rest

Hibernate increments the version number and checks that a non stale object is being updated.

If the database contains version 15 of object and user submits data with version 0 hibernate will
detect this and throw a StaleObjectException.

emmanuel · **Posted:** Tue Jun 01, 2004 3:14 am

Correct except for the first one:
No need for dynamic-update="true" when using optimistic-locking="version"

larry · **Joined:** Fri Jan 23, 2004 4:29 pm **Posts:** 39

emmanuel wrote:

Correct except for the first one:
No need for dynamic-update="true" when using optimistic-locking="version"

Could you explain why dynamic-update is not needed when optimistic-locking="version".

In the documentation it says:

Quote:

If you enable dynamic-update, you will have a choice of optimistic locking strategies:

*

version check the version/timestamp columns
*

all check all columns
*

dirty check the changed columns
*

none do not use optimistic locking

The documentation makes it sound like you are required to have dynamic-update enabled to have optimistic locking.

michael · **Posted:** Tue Jun 01, 2004 7:05 am

It is only required to use dynamic-update to have a choice, not to have optimistic locking at all :) You can use version/timestamp without dyanmic-update, too.