Hibernate: Updating OneToMany relationship

Question

I have a parent with a list of child mapped.

May I know how do I update the list of child when I update the parent

Example:

A parent P1 have child AB C.

I decided to delete B and add D

so parent P1 have child ACD in the database.

currently I merely delete all child that belongs to parent P1 and repopulate chid(ACD) again... I believe there is a more simple way of doing so.

I know this task is quite sensitive, please be kind enough to let me know what I need to set to ensure the child is inserted and deleted properly.

New Question:

1) Is there a way to lazy update/delete a relationship? I have a list that is FetchType.Lazy, when I am updating the data, I might not wish to load the relationship or update it.

2) If a list have item ABC, I removed item C and do a dto.save(). Will item C be deleted?

Answer 1

Here is the mapping to update child using parent -

@Entity
@Table(name = "COMPANY")
@SequenceGenerator(name="CompanySeq", sequenceName="COMPANYseq", allocationSize=1)
public class Company implements Serializable {

    private static final long serialVersionUID = 1L;

    /*
     * Customer Company Details 
     */

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "CompanySeq")
    @Column(name = "COMPANY_ID")
    private Integer id;

    @Column(name="COMPANY_NAME")
    private String name;

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumn(name = "COMPANY_ID",nullable=false)
    @OrderBy(clause = "PRODUCT_NAME" )
    @ForeignKey(name = "fk_company_product")     
    private List<Product> products = new ArrayList<Product>();    

 }



 @Entity
@Table(name = "PRODUCT")
@SequenceGenerator(name="CompanyProductSeq", sequenceName="COMPANY_PRODUCT",  allocationSize=1)
public class Product implements Serializable{

    /**
     * SerialVersion ID
     */
    private static final long serialVersionUID = 4073418246832063389L;

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "CompanyProductSeq")
    @Column(name = "PRODUCT_ID")
    private Integer id;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name = "COMPANY_ID", updatable = false, insertable = false, nullable=false)  
    private Company companyId;

        @Column(name = "PRODUCT_NAME")
    private String name;

    }

Answer 2

1+ for Promod as he provided very good code to understand it. The functionality you want is all about Hibernate Cascade . By the use of cascade you just need to update parent bean object and the list of its child objects and Cascade will do the rest.

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
@JoinColumn(name = "COMPANY_ID",nullable=false)
@OrderBy(clause = "PRODUCT_NAME" )
@ForeignKey(name = "fk_company_product")     
private List<Product> products = new ArrayList<Product>();    

In upper example given by Pramod, Company is keeping all data about Products as it's children. Here

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)

cascadeType.All will perform all parental operation on child too ie Insertion/Updation on Company will perform the same on Product, If you want to update Products of a Company, You just need to fetch the loaded Company bean with products ( FetchType.EAGER ), modify or add new products in the bean and saveUpdate the Company. It will save/update Company and its Products too.