Ternary Associations are baffling me!

markmansour · **Posted:** Sun Apr 04, 2004 2:11 am

I have a simple ternary association I would like to persist and query
involving 3 persitable objects - Image, Author and Contribution. I
also have a type to represent an association, my AuthorContribution
type.

I don't really care if I use a Set, Map, composite-element or anything
else to represent this relationship.

I have a table that represents the association between the three
object (IMAGE_AUTHOR_CONTRIBUTION).

The problem is the association table (IMAGE_AUTHOR_CONTRIBUTION) is never updated althought each of the classes (IMAGE, AUTHOR, CONTRIBUTION) write to the database successfully!

Also, I was also expecting that during the creation of the
IMAGE_AUTHOR_CONTRIBUTION table that a primary key of (IMAGE_ID,
AUTHOR_ID, CONTRIBUTION_ID) would have been created and instead there
was no primary key.

Any help would be GREATLY appreciated.

I am using Hibernate 2.1, hsqldb v1.7.1

Here is the code I use to persist my data:

Code:

        Image image = new Image( "Mona Lisa" );
        Author author = new Author( "Leonardo De Vinci" );
        Contribution contribution = new Contribution( "Painter" );

        AuthorContribution ac = new AuthorContribution( author, contribution );
        Set acs = new HashSet();
        acs.add( ac );
        image.setAuthorContributions( acs );

        Session session = sessions.openSession();
        session.save( contribution );
        session.save( author );
        session.save( image );
        session.close();

Here are my mapping files:

--- (Image.hbm.xml)

Code:

    <class name="Image" table="IMAGE">
        <id name="id" column="IMAGE_ID" type="java.lang.Integer" unsaved-value="-99">
            <generator class="native"/>
        </id>
        <set name="authorContributions" table="IMAGE_AUTHOR_CONTRIBUTION" inverse="false" cascade="all">
            <key column="IMAGE_ID" />
            <composite-element class="AuthorContribution">
                <many-to-one name="author" class="Author" column="AUTHOR_ID"/>
                <many-to-one name="contribution" class="Contribution" column="CONTRIBUTION_ID"/>
            </composite-element>
        </set>
        <property name="name" type="java.lang.String" column="NAME" not-null="true"/>
    </class>

--- (Author.hbm.xml)

Code:

    <class name="Author" table="AUTHOR">
        <id name="id" column="AUTHOR_ID" type="java.lang.Integer" unsaved-value="-99">
            <generator class="native"/>
        </id>
        <property name="name" type="java.lang.String" column="NAME" not-null="true"/>
    </class>

--- (Contribution.hbm.xml)

Code:

    <class name="Contribution" table="CONTRIBUTION">
        <id name="id" column="CONTRIBUTION_ID" type="java.lang.Integer" unsaved-value="-99" >
            <generator class="native"/>
        </id>
        <property name="name" type="java.lang.String" column="NAME" not-null="true" />
    </class>

Here are my java files:

--- (Image.java)

Code:

public class Image
{
    protected Integer id = new Integer( 0 );
    protected String name;
    protected Set authorContributions;

    private Image() { }
    public Image( String name ) { this.name = name; }
    public Set getAuthorContributions() { return authorContributions; }
    public void setAuthorContributions( Set authorContributions ) { this.authorContributions = authorContributions; }
    public Integer getId() { return id; }
    public void setId( Integer id ) { this.id = id; }
    public String getName() { return name; }
    public void setName( String name ) { this.name = name; }

    public boolean equals( Object o ) 
    {
        if( this == o ) return true;
        if( !( o instanceof Image ) ) return false;

        final Image image = ( Image ) o;

        if( !authorContributions.equals( image.authorContributions ) ) return false;
        if( !name.equals( image.name ) ) return false;

        return true;
    }

    public int hashCode()
    {
        int result;
        result = name.hashCode();
        result = 29 * result + authorContributions.hashCode();
        return result;
    }
}

--- (Author.java)

Code:

import java.util.Set;

public class Author
{
    protected Integer id = new Integer( 0 );
    protected String name;

    private Author(){}
    public Author( String name ) { this.name = name; }
    public Integer getId() { return id; }
    public void setId( Integer id ) { this.id = id; }
    public String getName() { return name; }
    public void setName( String name ) { this.name = name; }
    public boolean equals( Object o )
    {
        if( this == o ) return true;
        if( !( o instanceof Author ) ) return false;

        final Author author = ( Author ) o;

        if( !name.equals( author.name ) ) return false;

        return true;
    }

    public int hashCode() { return name.hashCode(); }
}

--- (Contribution.java)

Code:

import java.util.Set;

public class Contribution
{
    protected Integer id = new Integer( 0 );
    protected String name;

    private Contribution(){}
    public Contribution( String name ) { this.name = name; }
    public Integer getId() { return id; }
    public void setId( Integer id ) { this.id = id; }
    public String getName() { return name; }
    public void setName( String name ) { this.name = name; }
    public boolean equals( Object o )
    {
        if( this == o ) return true;
        if( !( o instanceof Contribution ) ) return false;

        final Contribution author = ( Contribution ) o;

        if( !name.equals( author.name ) ) return false;

        return true;
    }

    public int hashCode() { return name.hashCode(); }
}

--- (AuthorContribution.java)

Code:

public class AuthorContribution
{
    protected Author author;
    protected Contribution contribution;

    private AuthorContribution() { }

    public AuthorContribution( Author author, Contribution contribution )
    {
        this.author = author;
        this.contribution = contribution;
    }

    public Author getAuthor() { return author; }
    public void setAuthor( Author author ) { this.author = author; }
    public Contribution getContribution() { return contribution; }
    public void setContribution( Contribution contribution ) { this.contribution = contribution; }

    public boolean equals( Object o )
    {
        if( this == o ) return true;
        if( !( o instanceof AuthorContribution ) ) return false;

        final AuthorContribution authorContribution = ( AuthorContribution ) o;

        if( !author.equals( authorContribution.author ) ) return false;
        if( !contribution.equals( authorContribution.contribution ) ) return false;

        return true;
    }

    public int hashCode()
    {
        int result;
        result = author.hashCode();
        result = 29 * result + contribution.hashCode();
        return result;
    }
}

markmansour · **Posted:** Tue Apr 06, 2004 1:30 am

If this question is unclear please let me know and I will rephrase it.

Thanks

emmanuel · **Posted:** Wed Apr 07, 2004 6:32 am

This should work AFAIK, give more info (log).
Have a look at http://www.hibernate.org/109.html just in case.

markmansour · **Posted:** Thu Apr 08, 2004 5:18 am

Hi Emmanuel,

Thanks for the response. I really appreciate any time you can give here.

Now here is the strange thing. I simply added a session.flush() and the IMAGE_AUTHOR_CONTRIBUTION table was updated.

Code:

        Image image = new Image( "Mona Lisa" );
        Author author = new Author( "Leonardo De Vinci" );
        Contribution contribution = new Contribution( "Painter" );

        AuthorContribution ac = new AuthorContribution( author, contribution );
        Set acs = new HashSet();
        acs.add( ac );
        image.setAuthorContributions( acs );

        Session session = sessions.openSession();
        session.save( contribution );
        session.save( author );
        session.save( image );
        session.flush();            //  <---- HERE!!!
        session.close();

I read the equals()/hashcode() page and I think I am doing everything correctly - I've included the equals and hashcode methods in the original post and all they are doing is checking for equality on the 'name' attribute of each class. Nothing fancy.

I also tried removing any reference to AuthorContribution from the equals and hashcode methods of Image class, but that made no difference.

So... Is flush necessary or have I make a mistake somewhere?

Mark

anthony · **Posted:** Thu Apr 08, 2004 5:27 am

?????
where is the commit?

emmanuel · **Posted:** Thu Apr 08, 2004 8:50 am

This is the correct behavior
An impelmentation detail force Hibernate to do the insert of entities wo explicit request.
Since you don't use hibernate tx.commit() you need to explicitly flush before closing.

markmansour · **Posted:** Mon Apr 12, 2004 8:00 pm

Emmanuel,

Thanks for the clarification. Either surrounding the action in a transaction or calling flush works like a treat. I've decided to surround the action in a transaction.

Thanks for taking the time to look at this.

Mark

aismail · **Joined:** Wed Mar 11, 2009 4:37 am **Posts:** 9

Hi all,

I've stumbled upon the same problem as emmanuel, only 5 years later. I don't understand why a flush / commit is necessary to persist the ternary association to the database (in his case, stored in the table IMAGE_AUTHOR_CONTRIBUTION). Can anyone explain?

Thanks,
Andrei

nordborg · **Posted:** Wed Mar 11, 2009 6:25 am

This is how Hibernate works. It has nothing to do with the ternary association as such. Hibernate keep things in memory until there is a reason to synchronize with the database.
flush() or commit() are examples of such reasons. The save() method is an exception to the general rule. Depending on what kind of id generator you are using it may trigger an insert into the database, or it may not. In any case, the insert doesn't mean that other updates also happen.

For example, if markmansour had used the 'assigned' id generator instead of 'native' the save() wouldn't have triggered an insert and without the flush() nothing would have been inserted.

See http://www.hibernate.org/hib_docs/v3/re ... shing.html