Cascades in Hibernate – overview

Let us understand Cascades in Hibernate with examples

In previous articles, we have understood about Association or Mapping between entities like One To One, One To Many and Many to Many.

In these associations, one entity will be the relationship owner and other one is just a mapped entity.

We want to save mapped entity automatically without writing any code whenever the relationship owner entity is saved.

To achieve this, we need to use Cascade in Hibernate mapping.

What is Cascade ?

Cascade is the feature provided by hibernate to automatically manage the state of mapped entity whenever the state of its relationship owner entity is affected.

In other words,
When relationship owner is saved,then associated mapped entity should also be saved and when relationship owner is deleted, associated mapped entity should also be deleted etc.

Various Cascade operations supported in Hibernate

none (default)

save

update

save-update

delete

delete-orphan

all

Let us understand How cascade is used in Hibernate with One to Many relation

We can use Cascade for all types of relation(One to One,One to Many and Many to Many)

Consider the relation between Applicant and Address

One applicant will have many addresses like Permanent and Current address

Relation looks as below

As shown in the above ER diagram,Relation between Applicant and Address is One To Many.

Address_Id is the primary key for Address table

Applicant_Id is the primary key for Applicant table

We can see that Applicant_Id which is the primary key at One side(Applicant) has become the Foreign key on the Many side(Address).

In this relation, We will make Applicant as the relation owner.

Whenever we save or update the Applicant entity , its related entity Address should also be affected automatically.

Suppose we create one Applicant object and 2 address objects and associate these 2 address objects to Applicant object

Now if we save Applicant object ,corresponding 2 Address objects should also be saved in DB.

This way we are cascading the operation performed on Owner entity to the related entity.

Cascade is supported in both XML and annotation mapping

Cascade with XML

We just need to declare the cascade with required options in the associated entity as below

applicant.hbm.xml

<set name="addresses" table="Address" 
                inverse="true" lazy="true" fetch="select" cascade="save-update, delete">
            <key>
                <column name="Applicant_Id" not-null="true" />
            </key>
            <one-to-many class="Address" />
        </set>

Cascade with Annotation

We just need to declare the cascade with required options in the associated entity using @Cascade annotation as below.

Applicant.java

@OneToMany(mappedBy="applicant")

@Cascade({CascadeType.SAVE_UPDATE, CascadeType.DELETE})

    private Set<Address> addresses;

CascadeType is used to specify the type of Cascade.

Raj

Founder of javainsimpleway.com
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