Fetching strategy in hibernate

 what  are  fetching  strategy  in Hibernate?  

To optimize   the   Hibernate select statement, efficiently   Hibernate defines fetching strategies

Hibernate has four type of fetching strategies.

1. fetch-“join” = Disable the lazy loading, always load all the collections and entities.

2. fetch-“select” (default) = Lazy load all the collections and entities.

3. batch-size=”N” = Fetching up to ‘N’ collections or entities, *Not record*.

4. fetch-“subselect” = Group its collection into a sub select statement.

  Here is   example how to declare   fetching   strategies. In  (**.hbm.xml ) file   and

 annotation.

Mapping   based   declaration

<hibernate-mapping>

    <class name="com.bksoft.emp" table="stock">

        <set name="empattndsRecords"  cascade="all" inverse="true"

            table="empattnds_record" batch-size="10" fetch="select">

            <key>

                <column name="emp_id" not-null="true" />

            </key>

            <one-to-many class="com.bksoft.common.empRecords" />

        </set>

    </class>

</hibernate-mapping>

  

 Annotation based declaration..

 @Entity

@Table(name = "emp", catalog = "xyz")

public class Stock implements Serializable{

...

                @OneToMany(fetch = FetchType.LAZY, mappedBy = "empRecords")

                @Cascade(CascadeType.ALL)

                @Fetch(FetchMode.SELECT)

               @BatchSize(size = 10)

                public Set< empattndsRecords > getEmpAttendenceRecords() {

                                return EmpAttendenceRecords();

                }