What causes Hiberante to issue a SQL update command

[ying lam]

I have the following code which just query an object from the database.
But when I turn on hibernate sql output. it causes 2 sqls:
1. query
2. update

My question is why hibernate generate the 2nd update command? I did not modify the cat object at all in my transaction?


private static Cat getCat(String name, Home home) {
Session session = HibernateUtil.getSessionFactory().getCurrentSession();

session.beginTransaction();

// cause hibernate to create 1 query. This is expected
Query query = session
.createQuery(
"from Cat as cat where cat.name= :name and cat.home.id = :homeid");

List result = query.setString("name", name).setLong("homeid",
home.getId().longValue()).list();

// why hibernate caused a sql update query here? I did not modify
// any of the persistent object
session.getTransaction().commit();

if (result.size() == 1) {
return (Cat) result.get(0);
}
}



Here is my mapping file:



<class name="com.testproject.model.Cat" table="BUILDS"
lazy="true">
<id name="id" column="CAT_ID">
<generator class="native" />
</id>
<version name="version" column="version"
type="java.lang.Integer" />


<property name="name" not-null="true" />

<many-to-one name="home" column="HOME_ID"
class="com.testproject.model.Home" not-null="true" />


</class>

Is there a way to disable it? I would like to minimize Hibernate sql if possible. The object that I get from the database should be 'clean' instead of 'dirty' so hibernate shouldn't need to update it. Right?

Thank you.

[Mark Spritzler]

"yinglcs",
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[Mark Spritzler]

First the code is tough to read. There is a CODE button below Add Reply button to put CODE tags in your post so that you can put your actual code in between them and keep its indentation.

But I am thinking that there must be more to your code that you didn't post.

If you had loaded an object, made a change, then run a query, Hibernate will execute the update for the changed object when the query is run because in order for Hibernate to be sure that th query will return the correct results it needs to update/insert/delete data that might be changed that needs to be changed in the database so that the query gets the correct data.

Mark

[ying lam]

Thanks. Here is the code and mapping file. I appreciate if you can tell me why hibernate issues an UPDATE command. And how can I avoid it?

Code:

   
private static Cat getCat(String name, Home home) {
   Session session = HibernateUtil.getSessionFactory().getCurrentSession();
 
   session.beginTransaction();
Query query = session.createQuery("from Cat as cat where  cat.name= :name and cat.home.id = :homeid");


   query.setString("name", name).setLong("homeid",
      home.getId().longValue());
 
   List result = query.list();
   session.getTransaction().commit();
 
   if (result.size() == 1) {
return (Cat) result.get(0);
   } else {
       return null;
}
 
 

Mapping file:

    
<hibernate-mapping>
 
<class name="com.testproject.model.Cat" table="CATS"
lazy="true">
<id name="id" column="CAT_ID">
<generator class="native" />
</id>
<version name="version" column="version"
type="java.lang.Integer" />
 
<property name="name" not-null="true" />
 
<property name="description" />
 
<many-to-one name="home" column="HOME_ID"
class="com.testproject.model.Home" update="false" cascade="none" not-null="true"/>
 
</class>
</hibernate-mapping>
 
<hibernate-mapping>
 
<class name="com.testproject.model.Home" table="HOMES"
lazy="true">
 
<id name="id" column="HOME_ID">
<generator class="native" />
</id>
<version name="version" column="version"
type="java.lang.Integer" />
 

<!--  parent/child relationship from hibernate-in-action book -->
<set name="cats" cascade="all-delete-orphan" inverse="true"
lazy="true">
<key column="HOME_ID" />
<one-to-many class="com.testproject.Cat" />
</set>
 
</class>
</hibernate-mapping>
 

sql generate by hibernate

    
 
Hibernate: select cat0_.CAT_ID as CAT1_0_, cat0_.version as version0_, cat0_.name as name0_, cat0_.description as descript7_0_, cat0_.HOME_ID as HOME8_0_ from CATS cat0_ where cat0_.name=? and cat0_.HOME_ID=?
 
# I don't understand where this comes from. I just get the Cat object. no update
Hibernate: update CATS set version=?, name=?, description=? where CAT_ID=? and version=?
 

[ying lam]

Here is the code I execute the query:

From the code, I did not modify the object I get from the query. So I don't understand why hibernate issues an update command.

Any help is appreciated.

Thank you.

    
private static Cat getCat(String name, Home home) {
   Session session = HibernateUtil.getSessionFactory().getCurrentSession();
 
   session.beginTransaction();
Query query = session.createQuery("from Cat as cat where  cat.name= :name and cat.home.id = :homeid");


   query.setString("name", name).setLong("homeid",
      home.getId().longValue());
 
   List result = query.list();
   session.getTransaction().commit();
 
   if (result.size() == 1) {
return (Cat) result.get(0);
   } else {
       return null;
}

[Scott Johnson]

Why are you committing the transaction after the call to list()?

Which line appears to be triggering the update sql to execute. (Is it happening during the commit?)

What was the value of version in the database before the select? Was it null?

Set the Hibernate log level to DEBUG. You should see some log entries that specify which property of cat is dirty. (Search for "dirty".)

[ying lam]

Thank you for your help.

>> Why are you committing the transaction after the call to list()?
This is because I just get the presistent object thru the query. And I return from the getCat() method , as a result, I commit the transaction before I return the 'Cat'.

>> Which line appears to be triggering the update sql to execute. (Is it happening during the commit?)

Yes, it happens during commit.

>> What was the value of version in the database before the select? Was it null?
It was 0


>> Set the Hibernate log level to DEBUG. You should see some log entries that specify which property of cat is dirty. (Search for "dirty".)

Okay, i will try that.

[Scott Johnson]

[ying]It was 0

I'll bet that's the issue. Manually run an sql to set the version to 1 and see if the update still happens.

I think Hibernate sees the 0 and thinks it's a default value and that the object has never been persisted.
[ November 05, 2006: Message edited by: Scott Johnson ]

[pascal betz]

>> Which line appears to be triggering the update sql to execute. (Is it happening during the commit?)

Yes, it happens during commit.

SQL statements are only sent to the DB when flushing (which is done automatically when commiting) the session.

But the versioning seems to be a good candidate .

Pascal

[Scott Johnson]

[Pascal]SQL statements are only sent to the DB when flushing (which is done automatically when commiting) the session.

Hibernate does not guarantee that the only time sqls are executed is when the session is flushed.

[pascal betz]

Hibernate does not guarantee that the only time sqls are executed is when the session is flushed.

Point taken :-)