Question

Ok so I’m having bit of a problem with my Hibernate mappings and getting the desired behavior.

Basically what I have is the following Hibernate mapping:

<hibernate-mapping>
    <class name="com.package.Person" table="PERSON" schema="MYSCHEMA" lazy="false">
        <id name="personId" column="PERSON_ID" type="java.lang.Long">
            <generator class="sequence">
                <param name="sequence">PERSON_ID_SEQ</param>
            </generator>
        </id>

        <property name="firstName" type="string" column="FIRST_NAME">
        <property name="lastName" type="string" column="LAST_NAME">
        <property name="age" type="int" column="AGE">

        <set name="skills" table="PERSON_SKILL" cascade="all-delete-orphan">
            <key>
                <column name="PERSON_ID" precision="12" scale="0" not-null="true"/>
            </key>
            <many-to-many column="SKILL_ID" unique="true" class="com.package.Skill"/>
        </set>
    </class>
</hibernate-mapping>


<hibernate-mapping>
    <class name="com.package.Skill" table="SKILL" schema="MYSCHEMA">
        <id name="skillId" column="SKILL_ID" type="java.lang.Long">
            <generator class="sequence">
                <param name="sequence">SKILL_ID_SEQ</param>
            </generator>
        </id>
        <property name="description" type="string" column="DESCRIPTION">
    </class>
</hibernate-mapping>

So lets assume that I have already populated the Skill table with some skills in it. Now when I create a new Person I want to associate them with a set of skills that already exist in the skill table by just setting the ID of the skill. For example:

Person p = new Person();
p.setFirstName("John");
p.setLastName("Doe");
p.setAge(55);

//Skill with id=2 is already in the skill table
Skill s = new Skill()
s.setSkillId(2L);

p.setSkills(new HashSet<Skill>(Arrays.asList(s)));
PersonDao.saveOrUpdate(p);

If I try to do that however I get an error saying:

WARN (org.slf4j.impl.JCLLoggerAdapter:357) - SQL Error: 1407, SQLState: 72000
ERROR (org.slf4j.impl.JCLLoggerAdapter:454) - ORA-01407: cannot update ("MYSCHEMA"."SKILL"."DESCRIPTION") to NULL

ERROR (org.slf4j.impl.JCLLoggerAdapter:532) - Could not synchronize database state with session
org.hibernate.exception.GenericJDBCException: Could not execute JDBC batch update

The reason I am getting this error I think is because Hibernate sees that the Skill with Id 2 has ‘updated’ its description to null (since I never set it) and tries to update it. But I don’t want Hibernate to update this. What I want it to do is insert the new Person p and insert a record into the join table, PERSON_SKILL, that matches p with the skill in the SKILL table with id=2 without touching the SKILL table.

Is there anyway to achieve this behavior?

Answer 1

Instead of creating the Skill object yourself:

//Skill with id=2 is already in the skill table
Skill s = new Skill()
s.setSkillId(2L);
p.setSkills(new HashSet<Skill>(Arrays.asList(s)));

You should be retrieving it from the Hibernate Session:

Skill s = (Skill) session.get(Skill.class, 2L);
p.setSkills(new HashSet<Skill>(Arrays.asList(s)));

This way the Session thinks that the skill contained in p.skills is persistent, and not transient.