How can I use DB cascade delete in Hibernate?

yevgeny88 · **Joined:** Tue Apr 01, 2008 2:52 pm **Posts:** 6

I have a hierarchy of classes with a single table per hierarchy but with joined secondary tables. Legacy DB schema has tables with cascade on delete. Therefore, to delete a record for a child it was enough to delete the associated record for the parent.
My question is how to tell Hibernate to use this feature?

To illustrate it, I created an example of classes and tables:

This is a parent class

Code:

[color=blue]@javax.persistence.Entity(name="Person")

@javax.persistence.Table(name="person")
@javax.persistence.DiscriminatorColumn(name="type")
@javax.persistence.Inheritance(strategy=InheritanceType.SINGLE_TABLE)
public class Person
{
    int id;
    String type;

    @javax.persistence.Id
    public int getId()
    {
        return id;
    }

    public void setId(int id)
    {
        this.id = id;
    }

    @javax.persistence.Basic
    public String getType()
    {
        return type;
    }

    public void setType(String type)
    {
        this.type = type;
    }

}[/color]

And this is a child

Code:

[color=blue]@Entity(name = "Customer")
@SecondaryTables(@SecondaryTable(name = "customer", pkJoinColumns = {
        @PrimaryKeyJoinColumn(name = "id")}))
@DiscriminatorValue(value = "customer")
public class Customer extends Person
{
    String account;

    @javax.persistence.Basic
    @Column(table = "customer")
    public String getAccount()
    {
        return account;
    }

    public void setAccount(String account)
    {
        this.account = account;
    }

} [/color]

DB Schema looks like:

Code:

[color=blue] CREATE TABLE `person` (
 `id` int(11) NOT NULL,
 `type` varchar(30) default NULL,

 PRIMARY KEY  (`id`)
) ENGINE=InnoDB; 

CREATE TABLE `customer` (
  `id` int(11) NOT NULL,
  `account` varchar(30) default NULL,
  PRIMARY KEY  (`id`),
  FOREIGN KEY (`id`) REFERENCES `person` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB; [/color]

If I issue sql command to DB:

Code:

[color=blue]delete from person where id=1;[/color]

it will delete records from person and from customer tables. I would expect Hibernate to do the same. However, if I execute HQL query through Hibernate:

Code:

[color=blue]delete Person where id=1[/color]

it will generate something like this:

Code:

[color=blue]create temporary table if not exists HT_person (id integer not null);
insert into HT_person select p.id as id from person p left outer join customer p1_ on p.id=c.id where type='customer' and (p.id=1)
delete from customer where (id) IN (select id from HT_person)
delete from person where (id) IN (select id from HT_person)
drop table HT_person[/color]

On large tables with many children it becomes a problem. So one more time, is it possible to teach Hibernate to use DB cascade delete?

Thank you,
Yevgeny

carlolf · **Posted:** Fri Jul 04, 2008 4:08 am

First of all: have a look into the documentation for the Hibernate annotations!

Here is an example to to use cascade delete on db level:

Code:

@OneToMany(mappedBy = "singleParty", cascade = { CascadeType.ALL }, fetch=FetchType.LAZY)   @org.hibernate.annotations.OnDelete(action=OnDeleteAction.CASCADE)
private Set<SingleFinance> finances = new HashSet<SingleFinance>();

Cameron McKenzie · **Posted:** Fri Jul 04, 2008 1:43 pm

Quote:

Hibernate annotations!

And similarly, with JPA annotations.

yevgeny88 · **Joined:** Tue Apr 01, 2008 2:52 pm **Posts:** 6

Probably, I was not clear enough. In my case, there is no any relation of type one-to-many to which I can apply the cascade annotation.
There is only inheritance. One class is derived from another. The derived class is mapped to two tables: the common one and the secondary one.
Naturally, the base class shall not have any references to the derived one.

I want to delete an instance of the derived class. If I used direct JDBC, it would be enough to delete a row from the common table. Cascading will do the rest.
However, Hibernate does an explicit deletion from both classes which is very inefficient.
My question is how to inform Hibernate about DB cascading capability not in case of object relationship but in case of inheritance.

Thanks,
Yevgeny