In this example you will learn how to map many-to-one relationship using Hibernate Annotations. Consider the following relationship between Student and Address entity.
According to the relationship many students can have the same address.
To create this relationship you need to have a STUDENT and ADDRESS table. The relational model is shown below.
To create the STUDENT and ADDRESS table you need to create the following Java classes with hibernate annotations.
Student class is used to create the STUDENT table.
01.
package
com.vaannila.student;
02.
03.
import
javax.persistence.CascadeType;
04.
import
javax.persistence.Column;
05.
import
javax.persistence.Entity;
06.
import
javax.persistence.GeneratedValue;
07.
import
javax.persistence.Id;
08.
import
javax.persistence.ManyToOne;
09.
import
javax.persistence.Table;
10.
11.
@Entity
12.
@Table
(name =
"STUDENT"
)
13.
public
class
Student {
14.
15.
private
long
studentId;
16.
private
String studentName;
17.
private
Address studentAddress;
18.
19.
public
Student() {
20.
}
21.
22.
public
Student(String studentName, Address studentAddress) {
23.
this
.studentName = studentName;
24.
this
.studentAddress = studentAddress;
25.
}
26.
27.
@Id
28.
@GeneratedValue
29.
@Column
(name =
"STUDENT_ID"
)
30.
public
long
getStudentId() {
31.
return
this
.studentId;
32.
}
33.
34.
public
void
setStudentId(
long
studentId) {
35.
this
.studentId = studentId;
36.
}
37.
38.
@Column
(name =
"STUDENT_NAME"
, nullable =
false
, length =
100
)
39.
public
String getStudentName() {
40.
return
this
.studentName;
41.
}
42.
43.
public
void
setStudentName(String studentName) {
44.
this
.studentName = studentName;
45.
}
46.
47.
@ManyToOne
(cascade = CascadeType.ALL)
48.
public
Address getStudentAddress() {
49.
return
this
.studentAddress;
50.
}
51.
52.
public
void
setStudentAddress(Address studentAddress) {
53.
this
.studentAddress = studentAddress;
54.
}
55.
56.
}
Address class is used to create the ADDRESS table.
01.
package
com.vaannila.student;
02.
03.
import
javax.persistence.Column;
04.
import
javax.persistence.Entity;
05.
import
javax.persistence.GeneratedValue;
06.
import
javax.persistence.Id;
07.
import
javax.persistence.Table;
08.
09.
@Entity
10.
@Table
(name =
"ADDRESS"
)
11.
public
class
Address {
12.
13.
private
long
addressId;
14.
private
String street;
15.
private
String city;
16.
private
String state;
17.
private
String zipcode;
18.
19.
public
Address() {
20.
}
21.
22.
public
Address(String street, String city, String state, String zipcode) {
23.
this
.street = street;
24.
this
.city = city;
25.
this
.state = state;
26.
this
.zipcode = zipcode;
27.
}
28.
29.
@Id
30.
@GeneratedValue
31.
@Column
(name =
"ADDRESS_ID"
)
32.
public
long
getAddressId() {
33.
return
this
.addressId;
34.
}
35.
36.
public
void
setAddressId(
long
addressId) {
37.
this
.addressId = addressId;
38.
}
39.
40.
@Column
(name =
"ADDRESS_STREET"
, nullable =
false
, length=
250
)
41.
public
String getStreet() {
42.
return
this
.street;
43.
}
44.
45.
public
void
setStreet(String street) {
46.
this
.street = street;
47.
}
48.
49.
@Column
(name =
"ADDRESS_CITY"
, nullable =
false
, length=
50
)
50.
public
String getCity() {
51.
return
this
.city;
52.
}
53.
54.
public
void
setCity(String city) {
55.
this
.city = city;
56.
}
57.
58.
@Column
(name =
"ADDRESS_STATE"
, nullable =
false
, length=
50
)
59.
public
String getState() {
60.
return
this
.state;
61.
}
62.
63.
public
void
setState(String state) {
64.
this
.state = state;
65.
}
66.
67.
@Column
(name =
"ADDRESS_ZIPCODE"
, nullable =
false
, length=
10
)
68.
public
String getZipcode() {
69.
return
this
.zipcode;
70.
}
71.
72.
public
void
setZipcode(String zipcode) {
73.
this
.zipcode = zipcode;
74.
}
75.
76.
}
01.
<?
xml
version
=
"1.0"
encoding
=
"UTF-8"
?>
02.
<!DOCTYPE hibernate-configuration PUBLIC
03.
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
05.
<
hibernate-configuration
>
06.
<
session-factory
>
07.
<
property
name
=
"hibernate.connection.driver_class"
> org.hsqldb.jdbcDriver</
property
>
08.
<
property
name
=
"hibernate.connection.url"
> jdbc:hsqldb:hsql://localhost<;/
property
>
09.
<
property
name
=
"hibernate.connection.username"
>sa</
property
>
10.
<
property
name
=
"connection.password"
></
property
>
11.
<
property
name
=
"connection.pool_size"
>1</
property
>
12.
<
property
name
=
"hibernate.dialect"
> org.hibernate.dialect.HSQLDialect</
property
>
13.
<
property
name
=
"show_sql"
>true</
property
>
14.
<
property
name
=
"hbm2ddl.auto"
>create</
property
>
15.
<
mapping
class
=
"com.vaannila.student.Student"
/>
16.
<
mapping
class
=
"com.vaannila.student.Address"
/>
17.
</
session-factory
>
18.
</
hibernate-configuration
>
01.
package
com.vaannila.student;
02.
03.
import
org.hibernate.HibernateException;
04.
import
org.hibernate.Session;
05.
import
org.hibernate.Transaction;
06.
07.
import
com.vaannila.util.HibernateUtil;
08.
09.
public
class
Main {
10.
11.
public
static
void
main(String[] args) {
12.
Session session = HibernateUtil.getSessionFactory().openSession();
13.
Transaction transaction =
null
;
14.
try
{
15.
transaction = session.beginTransaction();
16.
Address address =
new
Address(
"OMR Road"
,
"Chennai"
,
"TN"
,
"600097"
);
17.
//By using cascade=all option the address need not be saved explicitly when the student object is persisted the address will be automatically saved.
18.
//session.save(address);
19.
Student student1 =
new
Student(
"Eswar"
, address);
20.
Student student2 =
new
Student(
"Joe"
, address);
21.
session.save(student1);
22.
session.save(student2);
23.
transaction.commit();
24.
}
catch
(HibernateException e) {
25.
transaction.rollback();
26.
e.printStackTrace();
27.
}
finally
{
28.
session.close();
29.
}
30.
31.
}
32.
33.
}
The Student table has two records.
The Address table has one record.
Both the student records points to the same address record, this illustrates the many-to-one mapping.
The folder structure of the example is shown below.