Parent/Child and many-to-one in XDoclet

mraible · **Joined:** Sun Oct 05, 2003 9:07 am **Posts:** 47

I have read the parent/child section in the documentation and this *should* be easy, but it just ain't workin. I have a Position object and a PositionSkills object. The Position object can have 0-n skills. Therefore, I have this XDoclet code on my getter:

Code:

    /**
     * @return a list of skills associated with this position
     *
     * @hibernate.bag name="skills" table="position_skill" inverse="false"
     *   cascade="all-delete-orphan"
     * @hibernate.collection-key column="position_id"
     * @hibernate.collection-one-to-many
     *   class="us.co.adams.apptracker.persistence.PositionSkill"
     */
    public List getSkills() {
        return skills;
    }

My PositionSkill object merely has a positionId column with the following:

Code:

     * @hibernate.property column="position_id" 
     */
    public Long getPositionId() {
        return positionId;
    }

If I add an addSkill() method to my Position object, to set the positionId when adding a new skill to the Position, everything works as expected.

Here's where the problem comes into play. The documentation says I should let the PositionSkill class handle it's parent. So I change inverse to "false" on the getSkills() mapping and I add a parent property + getters/setters to the PositionSkill object. Then I map it with the following:

Code:

    /**
     * Return the position that requires these skills
     *
     * @return Position - the position that holds these skills
     * @hibernate.many-to-one name="position" column="position_id" not-null="true"
     */
    public Position getPosition() {
        return position;
    }

I have to change the getPositionId's mapping to have update="false" and insert="false". I also change the Position.addSkill method to use setParent(this) instead of setParentId(this.id). Everything *looks* right, but I get a "java.lang.StackOverflowError" when i try to run a simple test to add a positionSkill to a Position.

Any ideas?

emmanuel · **Posted:** Tue Dec 16, 2003 5:18 am

PositionId is useless since it's handled by the position object. Remove it.

the table attribute in bag is useless since one-to-many does not need extra tables. Remove it

If you use a many-to-one on the other side, inverse="true" on the one-to-many side is recommended http://www.hibernate.org/Documentation/InsideExplanationOfInverseTrue

The position addSkill should look like

Code:

public addSkill(Skill skill) {
  _skills.add(skill);
  skill.setPosition(this);
}

Any composite-id ? If yes, implements equals and hashCode

Otherwise try the mapping contained in the doc and change it until it looks like yours, then try to use xdoclet

mraible · **Joined:** Sun Oct 05, 2003 9:07 am **Posts:** 47

I tried your suggestions and I just get a StackOverFlow error again. Here's my generated mapping for position:

Code:

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class
        name="us.co.adams.apptracker.persistence.Position"
        table="position"
        dynamic-update="false"
        dynamic-insert="false"
    >

        <id
            name="id"
            column="id"
            type="java.lang.Long"
            unsaved-value="null"
        >
            <generator class="native">
            </generator>
        </id>

        <property
            name="closingDate"
            type="java.util.Date"
            update="true"
            insert="true"
            column="closing_date"
        />

        <property
            name="name"
            type="java.lang.String"
            update="true"
            insert="true"
            column="name"
            length="100"
        />

        <property
            name="comments"
            type="java.lang.String"
            update="true"
            insert="true"
            column="comments"
            length="2000"
        />

        <property
            name="department"
            type="java.lang.String"
            update="true"
            insert="true"
            column="department"
            length="30"
            not-null="true"
        />

        <property
            name="description"
            type="java.lang.String"
            update="true"
            insert="true"
            column="description"
            length="2000"
            not-null="true"
        />

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

        <property
            name="jobNumber"
            type="java.lang.String"
            update="true"
            insert="true"
            column="job_number"
            length="9"
            not-null="true"
        />

        <property
            name="location"
            type="java.lang.String"
            update="true"
            insert="true"
            column="location"
            length="30"
            not-null="true"
        />

        <property
            name="requirements"
            type="java.lang.String"
            update="true"
            insert="true"
            column="requirements"
            length="2000"
            not-null="true"
        />

        <property
            name="salary"
            type="java.lang.Integer"
            update="true"
            insert="true"
            column="salary"
        />

        <property
            name="salaryType"
            type="java.lang.String"
            update="true"
            insert="true"
            column="salary_type"
            length="10"
        />

        <bag
            name="skills"
            lazy="false"
            inverse="true"
            cascade="all-delete-orphan"
        >

              <key
                  column="position_id"
              />

              <one-to-many
                  class="us.co.adams.apptracker.persistence.PositionSkill"
              />
        </bag>

    </class>

</hibernate-mapping>

And the mapping for PositionSkill:

Code:

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class
        name="us.co.adams.apptracker.persistence.PositionSkill"
        table="position_skill"
        dynamic-update="false"
        dynamic-insert="false"
    >

        <id
            name="id"
            column="id"
            type="long"
            unsaved-value="null"
        >
            <generator class="native">
            </generator>
        </id>

        <many-to-one
            name="position"
            class="us.co.adams.apptracker.persistence.Position"
            cascade="none"
            outer-join="auto"
            update="true"
            insert="true"
            column="position_id"
            not-null="true"
        />

        <property
            name="lastUsed"
            type="java.lang.String"
            update="true"
            insert="true"
            column="last_used"
            not-null="true"
        />

        <property
            name="yearsExperience"
            type="java.lang.Integer"
            update="true"
            insert="true"
            column="years_experience"
            not-null="true"
        />

        <property
            name="name"
            type="string"
            update="true"
            insert="true"
            column="name"
            not-null="true"
            unique="false"
        />

    </class>

</hibernate-mapping>

gavin · **Posted:** Tue Dec 16, 2003 10:29 am

It really helps an incredible amount to show the stack trace.

emmanuel · **Posted:** Tue Dec 16, 2003 10:29 am

Sounds good to me. Show you code, stacktrace and log as said in
http://www.hibernate.org/ForumMailinglists/HowToAskForHelp

mraible · **Joined:** Sun Oct 05, 2003 9:07 am **Posts:** 47

Hmmmm, you guys are clever. My stackTrace was going into an infinite loop on my toString method, so I replaced it with ToStringBuilder.reflectionToString(this) and it fixed the issue. I don't know what's wrong with my toString() method, but it usually works fine. Any ideas?

public String toString() {
//return ToStringBuilder.reflectionToString(this);
StringBuffer results = new StringBuffer();

results.append(getClass().getName() + "\n");

// get super class as String
results.append(getClassAsString(getClass().getSuperclass()));

// get this class as String
results.append(getClassAsString(getClass()));

return results.toString();
}

private StringBuffer getClassAsString(Class clazz) {
StringBuffer results = new StringBuffer();

Field[] fields = clazz.getDeclaredFields();

try {
AccessibleObject.setAccessible(fields, true);

for (int i = 0; i < fields.length; i++) {
results.append("\t" + fields[i].getName() + "=" +
fields[i].get(this) + "\n");
}
} catch (Exception e) {
// ignored!
}

return results;
}

After all this - it's good to know how to do this, but I don't think I'll use it. On my UI, I need to do CRUD on PositionSkill - and I don't feel like storing all the position values in hidden fields. I guess I could put it into session scope or something.

Thanks for you help,

Matt

gavin · **Posted:** Tue Dec 16, 2003 10:57 am

I hope you realize that reflectionToString() is not circular-reference-safe!

mraible · **Joined:** Sun Oct 05, 2003 9:07 am **Posts:** 47

Nevermind, toString() was getting called on the class itself - please disregard.

mraible · **Joined:** Sun Oct 05, 2003 9:07 am **Posts:** 47

reflectionToString() seems to work a heckuva lot better than my toString method. I replaced mine with:

public String toString() {
return ToStringBuilder.reflectionToString(this,
ToStringStyle.MULTI_LINE_STYLE);
}

And now everything works as expected (and desired).

Matt

stolley · **Posted:** Tue Dec 16, 2003 6:49 pm

gavin wrote:

I hope you realize that reflectionToString() is not circular-reference-safe!

It wasn't in 1.0 but is in 2.0.

stolley · **Posted:** Tue Dec 16, 2003 6:56 pm

mraible wrote:

And now everything works as expected (and desired).

No it doesn't, you just think it does :)

Seriously, I use ToStringBuilder and it works well, but what you have to watch out for is lazy collections and proxy classes.

The new version of ToStringBuilder is not only circular-reference safe, but allows customization so that you can deal with this.

Here's the code that I have on my base persistent class (it relies on knowledge of my base class and it's getID() abstract method, but you can figure it out for yourself from there):

Code:

    /**
     * Uses the commons-lang ReflectionToStringBuilder to output something
     * useful (a bit verbos though).  Does some work to avoid initializing
     * proxied/lazied hibernate objects.
     * <p>
     * There's no reason not to write your own toString() method if you want
     * to output something a bit more precise.  Watch out for Hibernate
     * proxy objects though.
     */
    public String toString() {
        ReflectionToStringBuilder builder =
            new ReflectionToStringBuilder(this) {
                public ToStringBuilder append(
                    String fieldName, Object fieldValue)
                {
                    if( 
                        fieldValue != null && 
                        fieldValue instanceof PersistentEntity 
                    ){
                        PersistentEntity entity = (PersistentEntity)
                            fieldValue;
                        if( !Hibernate.isInitialized(fieldValue) ){
                            return 
                                super.append(
                                    "{proxy}"+fieldName+".id", 
                                    entity.getId() ); 
                        }
                    }
                    
                    return super.append(fieldName, fieldValue);
                }
            };
        return builder.toString();
    }
    

-Yves- · **Joined:** Fri Jun 03, 2005 4:08 am **Posts:** 12

Just spent almost a day with this problem too after following the Parent/Child section of the documentation.

Maybe that section of the document can be updated to warn future newbies about the pitfall of toString() in a bi-directional association!

-Yves-