Hibernate Fetching Strategies
- Hibernate uses a fetching strategy to retrieve associated objects if the application needs to navigate the association.
- Fetch strategies can be declared in the O/R mapping metadata, or over-ridden by a particular HQL or Criteria query.
Their are four fetching strategies in hibernate.
- fetch-"select" (default) - Lazy load all the collections and entities.
- fetch-"join" - Disable the lazy loading, always load all the collections and entities.
- batch-size="N" - Fetching up to 'N' collections or entities, Not record.
- fetch-"subselect" = Group its collection into a sub select statement.
Example To Show Fetch-SELECT Strategies With Annotation
Student.java File
@Entity
@Table(name="student")
public class Student {
@Id
@GeneratedValue
private int id;
private String studentName;
@OneToMany(mappedBy="student",
cascade=CascadeType.ALL)
//This annotation is use in one to many relationship
@Fetch(FetchMode.SELECT)
//this annotation declaring fetch mode to select
@BatchSize(size=2) //this define a batch size
private List<Address> address =
new ArrayList<Address>();
public List<Address> getAddress() {
return address;
}
public void setAddress(List<Address> address) {
this.address = address;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
}
Address.java File
@Entity
public class Address {
@Id
@GeneratedValue
private int Id;
private String city;
private String state;
@ManyToOne //this annotation is use
// in many to one relationship
private Student student;
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
public int getId() {
return Id;
}
public void setId(int id) {
Id = id;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
}
Test.java File
public class Test {
public static void main(String[] args)
{
Session session = sessionfactory.openSession();
session.beginTransaction();
Student student=(Student)
session.get(Student.class,1);
System.out.println("Retrieving Data");
System.out.println( student);
System.out.println("Address retrieval initiated");
List<Address> addresses = student.getAddress();
System.out.println("Address retrieval complete");
int i=1;
for (Address address : addresses)
{
System.out.println
("#### individual address: " + i);
System.out.println(address);
System.out.println("#### Address complete");
i++;
}
session.getTransaction().commit();
session.close();
}
}
Output On Console
SLF4J: Failed to load class
"org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation
(NOP) logger implementation
SLF4J: See
http://www.slf4j.org/codes.php#StaticLoggerBinder
for further details.
Hibernate: select student0_.id as
id0_0_, student0_.studentName
as studentN2_0_0_ from student
student0_ where student0_.id=?
Retrieving Data
com.tkhts.Student@e43c6f
Address retrieval initiated.
Address retrieval complete.
Hibernate: select address0_.student_id as
student4_0_1_, address0_.Id
as Id1_, address0_.Id as Id1_0_,
address0_.city as city1_0_,
address0_.state as state1_0_,
address0_.student_id as
student4_1_0_ from Address address0_ where
address0_.student_id=?
#### individual address: 1
com.tkhts.Address@1981537
#### Address complete
#### individual address: 2
com.tkhts.Address@198d2cc
#### Address complete
Example To Show Fetch-JOIN Strategies With Annotation
Student.java File
@Entity
@Table(name="student")
public class Student {
@Id
@GeneratedValue
private int id;
private String studentName;
@OneToMany(mappedBy="student",
cascade=CascadeType.ALL)
//This annotation is use in one to many relationship
@Fetch(FetchMode.JOIN)
//this annotation declaring
//fetch mode to JOIN
@BatchSize(size=2) //this define a batch size
private List<Address> address =
new ArrayList<Address>();
public List<Address> getAddress() {
return address;
}
public void setAddress(List<Address> address) {
this.address = address;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
}
Test.java File
public class Test {
public static void main(String[] args)
{
Session session = sessionfactory.openSession();
session.beginTransaction();
Student student=(Student)
session.get(Student.class,1);
System.out.println("Retrieving Data");
System.out.println( student);
System.out.println("Address retrieval initiated");
List<Address> addresses = student.getAddress();
System.out.println("Address retrieval complete");
int i=1;
for (Address address : addresses)
{
System.out.println
("#### individual address: " + i);
System.out.println(address);
System.out.println("#### Address complete");
i++;
}
session.getTransaction().commit();
session.close();
}
}
Output On Console
SLF4J: Failed to load class
"org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation
(NOP) logger implementation
SLF4J: See
http://www.slf4j.org/codes.php#StaticLoggerBinder
for further details.
Hibernate: select student0_.id as id0_1_,
student0_.studentName
as studentN2_0_1_, address1_.student_id
as student4_0_3_,
address1_.Id as Id3_, address1_.Id as Id1_0_,
address1_.city
as city1_0_, address1_.state as state1_0_,
address1_.student_id
as student4_1_0_ from student
student0_ left outer join
Address address1_ on
student0_.id=address1_.student_id
where student0_.id=?
Retrieving Data
com.tkhts.Student@1eb6e46
Address retrieval initiated.
Address retrieval complete.
#### individual address: 1
com.tkhts.Address@209b8c
#### Address complete
#### individual address: 2
com.tkhts.Address@26b13c
#### Address complete
Example To Show batch-size="2" Strategies With Annotation
Student.java File
@Entity
@Table(name="student")
public class Student {
@Id
@GeneratedValue
private int id;
private String studentName;
@OneToMany(mappedBy="student",
cascade=CascadeType.ALL)
//This annotation is use in one to many relationship
@BatchSize(size=2) //this define a batch size
private List<Address> address =
new ArrayList<Address>();
public List<Address> getAddress() {
return address;
}
public void setAddress(List<Address> address) {
this.address = address;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
}
Test.java File
public class Test {
public static void main(String[] args)
{
Session session = sessionfactory.openSession();
session.beginTransaction();
Student student=(Student)
session.get(Student.class,1);
System.out.println("Retrieving Data");
System.out.println( student);
System.out.println("Address retrieval initiated");
List<Address> addresses = student.getAddress();
System.out.println("Address retrieval complete");
int i=1;
for (Address address : addresses)
{
System.out.println
("#### individual address: " + i);
System.out.println(address);
System.out.println("#### Address complete");
i++;
}
session.getTransaction().commit();
session.close();
}
}
Output On Console
SLF4J: Failed to load class
"org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation
(NOP) logger implementation
SLF4J: See
http://www.slf4j.org/codes.php#StaticLoggerBinder
for further details.
Hibernate: select student0_.id as
id0_0_, student0_.studentName
as studentN2_0_0_ from student
student0_ where student0_.id=?
Retrieving Data
com.tkhts.Student@1d69131
Address retrieval initiated.
Address retrieval complete.
Hibernate: select address0_.student_id
as student4_0_1_, address0_.Id
as Id1_, address0_.Id as Id1_0_,
address0_.city as city1_0_,
address0_.state as state1_0_, address0_.student_id as
student4_1_0_ from Address address0_
where address0_.student_id=?
#### individual address: 1
com.tkhts.Address@743d2c
#### Address complete
#### individual address: 2
com.tkhts.Address@15c1703
#### Address complete
Note : In above example of batch-size fetch strategy the 'batch-size=2' indicate that per-fetch 2 records from collection. The batch-size fetching strategy is not define
how many records inside in the collections are loaded. Instead, it defines how many collections should be loaded.
Example To Show Fetch-SUBSELECT Strategies With Annotation
Student.java File
@Entity
@Table(name="student")
public class Student {
@Id
@GeneratedValue
private int id;
private String studentName;
@OneToMany(mappedBy="student",
cascade=CascadeType.ALL)
//This annotation is use in one to many relationship
@Fetch(FetchMode.SUBSELECT)
//this annotation declaring fetch mode to JOIN
@BatchSize(size=2) //this define a batch size
private List<Address> address =
new ArrayList<Address>();
public List<Address> getAddress() {
return address;
}
public void setAddress(List<Address> address) {
this.address = address;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
}
Test.java File
public class Test {
public static void main(String[] args)
{
Session session = sessionfactory.openSession();
session.beginTransaction();
Student student=(Student)
session.get(Student.class,1);
System.out.println("Retrieving Data");
System.out.println( student);
System.out.println("Address retrieval initiated");
List<Address> addresses = student.getAddress();
System.out.println("Address retrieval complete");
int i=1;
for (Address address : addresses)
{
System.out.println
("#### individual address: " + i);
System.out.println(address);
System.out.println("#### Address complete");
i++;
}
session.getTransaction().commit();
session.close();
}
}
Output On Console
SLF4J: Failed to load class
"org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation
(NOP) logger implementation
SLF4J: See
http://www.slf4j.org/codes.php#StaticLoggerBinder
for further details.
Hibernate: select student0_.id as id0_0_,
student0_.studentName
as studentN2_0_0_ from student
student0_ where student0_.id=?
Retrieving Data
com.tkhts.Student@100362a
Address retrieval initiated.
Address retrieval complete.
Hibernate: select address0_.student_id
as student4_0_1_,
address0_.Id as Id1_, address0_.Id
as Id1_0_, address0_.city
as city1_0_, address0_.state as state1_0_,
address0_.student_id
as student4_1_0_ from Address address0_
where address0_.student_id=?
#### individual address: 1
com.tkhts.Address@236c40
#### Address complete
#### individual address: 2
com.tkhts.Address@1981537
#### Address complete
