Hi,

I have a problem with optimistic locking using timestamp. I am using MySQL.

My hbm file looks like this:

<hibernate-mapping>

<class name="package.Clazz"
table="THE_TABLEr">

<!--id name="id"
type="int"
column="ID">
<generator class="identity"/>
</id-->

<id name="id"
type="int"
column="ID"
unsaved-value="null">
<generator class="identity"/>
</id>

<version name="timeOfLastUpdate"
column="TIME_OF_LAST_UPDATE"
type="timestamp"/>

<property name="name"
type="java.lang.String"
column="name"
not-null="true"
length="50"/>

<property name="homePage"
type="java.lang.String"
column="homePage"
length="100"/>

</class>

</hibernate-mapping>

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The Java code:
ses.saveOrUpdate( obj );
ses.flush();
ses.connection().commit();

---------------------------------------------------------------------------------

I query a record in my JSP page, change the name and then push my Save button. I then get the error:

13:16:02,850 INFO [STDOUT] Hibernate: insert into MY_TABLE (TIME_OF_LAST_UPDATE, name, homePage) values (?, ?, ?)
13:16:02,870 WARN [JDBCExceptionReporter] SQL Error: 1062, SQLState: S1009
13:16:02,870 ERROR [JDBCExceptionReporter] Invalid argument value, message from server: "Duplicate entry 'a' for key 2"
13:16:02,880 WARN [JDBCExceptionReporter] SQL Error: 1062, SQLState: S1009
13:16:02,880 ERROR [JDBCExceptionReporter] Invalid argument value, message from server: "Duplicate entry 'a' for key 2"
13:16:02,880 ERROR [JDBCExceptionReporter] could not insert: [com.betservant.model.Bookmaker]
java.sql.SQLException: Invalid argument value, message from server: "Duplicate entry 'a' for key 2"
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:1651)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:889)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:956)

----------------------------------------------------------------------------------
The database column TIME_OF_LAST_UPDATE is of type datetime.

The thing is that I don't want it to do an insert since it is a change of an existing database record. If i change the version tag like this:

<version name="updateVersion"
column="updateVersion"
type="long"/>

then it works. The default value in the database for updateVersion is 0 and it gets accumulated nicely each update. Is it something I missed with dealing with timestamps? Or have I misunderstood something with saveOrUpdate? Do I have to manually set the timestamp on my object before passing it to saveOrUpdate?


Best regards
Lasse

Use <timestamp> instead of <version> for timestamp versioning.

Him


Thanks. Why is that? Something wrong with version?`

Lasse

What I am thinking is what it says in Chapter 5.1.8 of the reference:



Best regards

Lasse

Version is for version (version + 1 when updated)
timestamp is for... timestamp

Ok, so what is <version type="timestamp"> used for?

Best regards
Lasse

For nothing. It is nonesense. IMHO Hibernate should complain about this.

Well, the reason is that any Type can actually be used as a version type, as long as the Type also implements VersionType. It is all poymorphic internally.

But could this really be the reason why Hibernate didn't recognize my record as persistent and therefore tried to do an insert? I mean having <version type="timestamp"....

Best regards

Lasse

Probably rather a problem with your unsaved-value mapping. But timestamp for a version property is wrong too.

Hi gloeglm,

1st thing
When I used this

<version name="updateVersion"
column="updateVersion"
type="long"/>

it worked. In both cases I use the unsaved-value="null". But, what does that have to do with the version column? Hmm, feel puzzled here.

=================================

2nd thing
I then look into the adminapp-0.9.2 example which is downloadable on hibernate.org. If you look into src/java/org/hibernate/admin/model/User.hbm.xml you'll find the following:

<id name="id" column="USER_ID"
unsaved-value="null">
<!-- Wrapper Long, so use
unsaved-value="null" instead of "0". -->
<generator class="increment"/></id>

and

<!-- Use a timestamp for optimistic
locking -->
<version name="timeOfLastUpdate"
column="TIME_OF_LAST_UPDATE"
type="calendar"/>


This must be working musn't it?
I haven't tested the adminapp application but I think I will today.

What I also wonder if I choose to use <timestamp> for optimistic locking, do I have to set the value of the database column myself?

When I used the column of type LONG it had an initial value of 0, zero, in the database.

Best regards


Lasse

Solved....

I just wanted to say that I solved it. The solution really indicates that my question really really was posted in the correct group, i.e. Beginners.

The thing I missed to do was to carry the value of the timestamp-version field all the way up to the web-clien and then down to the server when the user made a submit in the web form.

In my case I use Struts, so the thing I added was to carry the timeOfLastUpdate value in my ActionForm object ... and then assigned the timeOfLastUpdate to the value object, i.e. the object which is coupled to the hbm.xml file.

I got it to work with the <timestamp>-tag. I did not test it with the <version>-tag and type=timestamp. But that should also work.

Best regards and Thanx a lot for all your help. You are great people!

As a general rule, do you think is correct to put such important datas on the presentation tier ?
I usually put there only the identifier of my objects, to be sure no one can change on the client so important data.
Ciao.

Hi,

Well, first my intention of this thread was optimistic locking. What I then wonder is what field you would use to accomplish optimistic locking? By definition, it has to be a field that can change. I suppose that your id's never change.

Second, the fields that I used in this example are not exposed in the web browser, they only travel along with the ActionForm object. How do you mean that the fields can be changed?

Best regards

Lasse