Sets in hibernate?

[Bobby Anderson]

When creating a complete new Set of entities and storing that set using the entity's set method I thought that hibernate would pick up that fact that since this is a new set all other elements in the old set (db rows) will be deleted.

I.E. A document contains many text items

   
@Entity
@Table(name = "DOC")
public class Doc implements java.io.Serializable {

	
	private long docId;
	private String title;
	private Set<TextItem> textItems = new HashSet<TextItem>(0);


	public Doc() {
	}


	@Id
	@Column(name = "DOC_ID", unique = true, nullable = false, scale = 0)
	@GeneratedValue( strategy=GenerationType.SEQUENCE, generator="GS_DOC_GEN" )
	@SequenceGenerator( name="GS_DOC_GEN", sequenceName="GS_DOC", allocationSize=1 )
	public long getDocId() {
		return this.docId;
	}

	public void setDocId(long docId) {
		this.docId = docId;
	}

	@Column(name = "TITLE")
	public String getTitle() {
		return this.title;
	}

	public void setTitle(String title) {
		this.title = title;
	}


	@OneToMany(fetch = FetchType.LAZY, mappedBy = "doc", cascade = CascadeType.ALL)
	public Set<TextItem> getTextItems() {
		return this.textItems;
	}

	public void setTextItems(Set<TextItem> tgTextitems) {
		this.textItems = tgTextitems;
	}
}

   
@Entity
//@Indexed(index = "text")
@Table(name = "TG_TEXTITEM")
public class TextItem implements java.io.Serializable {

	private long textItemId;
	private String textBody;
	private Doc doc;

	public TextItem() {
	}

	public TextItem(long textItemId) {
		this.textItemId = textItemId;
	}

	public TextItem(long textItemId, String textBody, Doc doc) {
		this.textItemId = textItemId;
		this.textBody = textBody;
		this.doc = doc;
	}

	@Id
	@Column(name = "TEXTITEM_ID", unique = true, nullable = false, scale = 0)
	@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "GS_TEXTITEM_GEN")
	@SequenceGenerator(name = "GS_TEXTITEM_GEN", sequenceName = "GS_TEXTITEM", allocationSize = 1)
	public long getTextitemId() {
		return this.textItemId;
	}

	public void setTextitemId(long textitemId) {
		this.textItemId = textitemId;
	}

	@Lob
	@Column(name = "TEXTBODY")
	public String getTextBody() {
		return this.textBody;
	}

	public void setTextBody(String textBody) {
		this.textBody = textBody;
	}

	@ManyToOne(fetch = FetchType.LAZY)
	@JoinColumn(name = "DOC_ID", nullable = false)
	public Doc getDoc() {
		return this.doc;
	}

	public void setDoc(Doc doc) {
		this.doc = doc;
	}

}

I want to be able to store text items for a doc and have hibernate delete all old text items for that doc.

I.E.

    
// Get a doc from the DB
Doc doc = em.find(12);  // This doc has 10 text items in it

Set<TextItem> textItems = new HashSet<TextItem>();
TextItem textItem = new TextItem();
textItem.setText("Hello");
textItems.add(textItem);

//This should be a new set with only one element
doc.setTextItems(textItems); 

// Once this is persisted this doc only has one text item in it
// yet the db now shows 11

Why is this not deleting the 10 old text items since I used a new set with just one item in it?

Is this a problem because the relationship is bi-directional.

[Jaikiran Pai]

Do not change the "reference" of the set that is already present:

// Get a doc from the DB
Doc doc = em.find(12);  // This doc has 10 text items in it
// get existing text items and work on that set reference
Set<TextItem> textItems = doc.getTextItems();
// remove all existing text items from the set.
textItems.clear();

// now add a new text item
TextItem textItem = new TextItem();
textItem.setText("Hello");
textItems.add(textItem);


// Once this is persisted this doc only has one text item in it

[xsunil kumar]

Please relook in hibernate.cfg.xml

[Bobby Anderson]

I am confused the setTextItems(Set<TextItem> items) takes a Set object. I thought that the old set would be completely overridden when you set a new object of type Set.

I.E.

    
     public void setTextItems(Set<TextItem> tgTextitems) {  
         this.textItems = tgTextitems;  
     }  

I am replacing the entire set not just one element, right? When debugging I can see the object change, but hibernate is not deleting all the old TextItems that were in the old list. Also the code posted as a solution does not work either, i.e. just clearing the list. I actually have to iterate though the list and remove all the textItems from the db.

I think this is due to the bidirectional dependency. I.E. a TextItem has a reference back to a Doc and a Doc has a set of text items.

Also what does

Please relook in hibernate.cfg.xml

mean???

Thanks

[denis sorn]

You could eventually use Session merge method. I.e.

  session.merge(yourChangedObject)  

.

[EDIT]

Forget it. I have not read what you wrote. Sorry.

[Patricia Hall]

This is a JPA "feature". There is a Hibernate annotation that supports automatic deletion of orphan records, however it is not supported by JPA, so it is Hibernate specific. Unfortunately, I don't know what the annotation is, because where I work we try to stick with JPA code.

The items that were in the set, but no longer are, are not deleted from the database. JPA only breaks the link between the parent entity and the data record in the child entity.

We have to put in code that deletes the orphans. Hope this helps.