Mapping
Collections via *.hbm.xml and @ Annotations
Before start giving
details just note some basics about various collections
1. Java.util.List :
i.
Contains
heterogeneous elements.
ii.
Elements
are placed as per insertion order.
iii.
Can be
accessed via index, where set maintain its index.
2. Java.util.Set :
ii.
Contains
heterogeneous elements.
iii.
Elements
are placed in random order.
iv.
Can’t be
accessed via index.
3. Java.util.Map :
i.
Contains
key-value pairs.
ii.
Contains
heterogeneous values, can contain heterogeneous values.
iii.
Elements
are placed as per key.
iv.
Can be
accessed via index, here key act as an index.
4. Arrays :
i.
Can contain
only homogeneous values.
ii.
Elements
are placed as per insertion order.
iii.
Can be
accessed via index where index is internally maintained.
How to map
collection to database in hibernate :
As each collection
can hold multiple values i.e if a person is having emails, so a person can hold
multiple email id, while mapping these things to database we will be having
problem that a column can contain a single value.
In above case if we
are having a single table named ‘PERSON’ it will raise problem of having
multiple email values for ‘EMAIL’ column.
So to map
collection values, we have to create a separate table for column having
multiple values( EMAIL column will be carved out from PERSON table and a fresh
new table named EMAILS will be created to hold EMAIL values) and we have to link the primary table and
child table ( PERSON – EMAILS ) using foreign key constraint.
As few Collection
type also maintains their order so to maintain that we have to keep a column
named INDEX in database table.
Collection Type
|
*.hbm.xml
|
Annotation
|
List
|
<list name="emails"
table="emails">
<key
column="sid"/>
<index
column=”idx”/>
<element
column="email" type="string"/>
</list>
|
@CollectionOfElements
@JoinTable(name="emails", joinColumns=@JoinColumn(name="sid"))
@IndexColumn(name="idx")
@Column(name="email")
|
Set
|
<set
name="phones" table="phones">
<key
column="sid"/>
<element
column ="phones" type="long"/>
</set>
|
@CollectionOfElements
@JoinTable(name="phones", joinColumns=@JoinColumn(name="sid"))
@Column(name="phone")
Set<Long> phones;
|
Map
|
<map
name="refs" table="refs">
<key column="sid"/>
<index column="rname"
type="string"/>
<element column="rphone"
type="string"/>
</map>
|
@CollectionOfElements
@JoinTable(name="refs", joinColumns=@JoinColumn(name="sid"))
@IndexColumn(name="rname")
@Column(name="rphone")
Map<String,String> refs;
|
Arrays
|
<array name="courses" table="courses">
<key column="sid"/>
<index column="idx"/>
<element column="cname"
type="string"/>
</array>
|
@CollectionOfElements
@JoinTable(name="courses", joinColumns=@JoinColumn(name="sid"))
@IndexColumn(name="idx")
@Column(name="course")
String [] courses;
|
Let’s See Examples
for both type of mappings:
1. Mapping various Collections via *.hbm.xml
1. Mapping various Collections via *.hbm.xml
Points to ponder :
I am asking hibernate to create tables for me so no need to create tables separately.
I am asking hibernate to create tables for me so no need to create tables separately.
I am using MySQL
and database named ‘testdb2’. Please create a database ‘testdb2’ using command
Create database testdb2;
Project Structure:
Hibernate.cfg.xml
:
<?xml
version="1.0" encoding="UTF-8"?>
<!DOCTYPE
hibernate-configuration PUBLIC
"-//Hibernate/Hibernate
Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory name="collectionMapping">
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.password">admin</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/testdb2</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hbm2ddl.auto">update<?xml-stylesheet
type="text/xsl" href=""?></property>
<mapping resource="com/sushil/hibernate/model/student.hbm.xml"/>
</session-factory>
</hibernate-configuration>
student.hbm.xml
<?xml version="1.0" encoding="utf-8"?>
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE
hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping
DTD//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.sushil.hibernate.model">
<class name="Student" table="student_details">
<id name="sid">
<generator
class="increment"/>
</id>
<property name="sname"/>
<property name="dob"/>
<property name="qual" />
<array name="courses" table="courses">
<key
column="sid"/>
<index
column="idx"/>
<element
column="cname" type="string"/>
</array>
<list name="emails" table="emails">
<key
column="sid"/>
<index/>
<element
column="email" type="string"/>
</list>
<bag name="marks" table="marks">
<key
column="sid"/>
<element
column="marks" type="int"/>
</bag>
<set name="phones" table="phones">
<key
column="sid"/>
<element
column ="phones" type="long"/>
</set>
<map
name="refs" table="refs">
<key
column="sid"/>
<index
column="rname" type="string"/>
<element
column="rphone" type="string"/>
</map>
</class>
</hibernate-mapping>
Student.java
package
com.sushil.hibernate.model;
import
java.util.*;
public class
Student {
int sid;
String sname;
String dob;
String qual;
String [] courses;
List<String> emails;
List<Integer> marks;
Set<Long> phones;
Map<String,String> refs;
public Student() {}
public Student(String sname,
String dob, String qual, String[] courses,
List<String>
emails, List<Integer> marks, Set<Long> phones,
Map<String,
String> refs) {
super();
this.sname =
sname;
this.dob = dob;
this.qual = qual;
this.courses =
courses;
this.emails =
emails;
this.marks =
marks;
this.phones =
phones;
this.refs = refs;
}
public int getSid() {
return sid;
}
public void setSid(int
sid) {
this.sid = sid;
}
public String getSname() {
return sname;
}
public void
setSname(String sname) {
this.sname =
sname;
}
public String getDob() {
return dob;
}
public void
setDob(String dob) {
this.dob = dob;
}
public String getQual() {
return qual;
}
public void
setQual(String qual) {
this.qual = qual;
}
public String[] getCourses()
{
return courses;
}
public void
setCourses(String[] courses) {
this.courses =
courses;
}
public List<String>
getEmails() {
return emails;
}
public void
setEmails(List<String> emails) {
this.emails =
emails;
}
public List<Integer>
getMarks() {
return marks;
}
public void
setMarks(List<Integer> marks) {
this.marks =
marks;
}
public Set<Long>
getPhones() {
return phones;
}
public void
setPhones(Set<Long> phones) {
this.phones =
phones;
}
public Map<String,
String> getRefs() {
return refs;
}
public void
setRefs(Map<String, String> refs) {
this.refs = refs;
}
@Override
public String toString() {
return "Student
[sid=" + sid + ", sname=" + sname + ", dob=" + dob
+
", qual=" + qual + ", courses=" + Arrays.toString(courses)
+
", emails=" + emails + ", marks=" + marks + ",
phones="
+
phones + ", refs=" + refs + "]";
}
}
HibernateUtil.java
package
com.sushil.hibernate.util;
import
org.hibernate.SessionFactory;
import
org.hibernate.cfg.Configuration;
public
class HibernateUtil {
static SessionFactory fact;
static {
Configuration cfg=new
Configuration();
cfg=cfg.configure();
fact=cfg.buildSessionFactory();
}
public static SessionFactory
getFactory(){
return fact;
}
}
Client.java
package
com.sushil.hibernate.client;
import
java.util.*;
import
org.hibernate.*;
import
com.sushil.hibernate.model.Student;
import
com.sushil.hibernate.util.HibernateUtil;
public
class Client {
public static void main(String[]
args) {
SessionFactory
fact=HibernateUtil.getFactory();
List<String>
emails =new ArrayList<String>();
emails.add("a@hi.com");
emails.add("b@hi.com");
emails.add("c@hi.com");
emails.add("d@hi.com");
List<Integer>
marks =new ArrayList<Integer>();
marks.add(20);
marks.add(30);
marks.add(40);
String courses[] =
{"Core Java","Spring","Hibernate","Data
Structure"};
Set<Long>
phones=new HashSet<Long>();
phones.add(93456198291L);
phones.add(87634178191L);
phones.add(98561432671L);
Map<String,String>
refs=new HashMap<String,String>();
refs.put("aaa",
"bbb");
refs.put("ccc",
"ddd");
refs.put("eee",
"fff");
try{
Session
ses=fact.openSession();
Transaction
tx=ses.beginTransaction();
Student st= new
Student("Sushil", "12-07-1985", "MCA", courses,
emails, marks, phones, refs);
ses.save(st);
tx.commit();
}catch( Exception e){
e.printStackTrace();
}
System.out.print("All
Tables Created");
}
}
Ouptut
:
2. Mapping various
Collections via @ Annotations
Project Structure:
Hibernate.cfg.xml
<?xml
version="1.0" encoding="UTF-8"?>
<!DOCTYPE
hibernate-configuration PUBLIC
"-//Hibernate/Hibernate
Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory name="collectionMapping">
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.password">admin</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/HiberAnnotestdb</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hbm2ddl.auto">update<?xml-stylesheet
type="text/xsl" href=""?></property>
<mapping class="com.sushil.hibernate.model.Student"/>
</session-factory>
</hibernate-configuration>
Student.java
package
com.sushil.hibernate.model;
import
java.util.*;
import
javax.persistence.*;
import
org.hibernate.annotations.CollectionOfElements;
import
org.hibernate.annotations.IndexColumn;
@Entity
@Table(name="student")
public class
Student {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name="sid")
int sid;
@Column(name="sname")
String sname;
@Column(name="dob")
String dob;
@Column(name="qual")
String qual;
@CollectionOfElements
@JoinTable(name="courses",
joinColumns=@JoinColumn(name="sid"))
@IndexColumn(name="idx")
@Column(name="course")
String [] courses;
@CollectionOfElements
@JoinTable(name="emails",
joinColumns=@JoinColumn(name="sid"))
@IndexColumn(name="idx")
@Column(name="email")
List<String> emails;
@CollectionOfElements
@JoinTable(name="marks",
joinColumns=@JoinColumn(name="sid"))
@IndexColumn(name="idx")
@Column(name="marks")
List<Integer> marks;
@CollectionOfElements
@JoinTable(name="phones",
joinColumns=@JoinColumn(name="sid"))
@Column(name="phone")
Set<Long> phones;
@CollectionOfElements
@JoinTable(name="refs",
joinColumns=@JoinColumn(name="sid"))
@IndexColumn(name="rname")
@Column(name="rphone")
Map<String,String> refs;
public
Student() { }
public Student(String sname,
String dob, String qual, String[] courses,
List<String>
emails, List<Integer> marks, Set<Long> phones,
Map<String,
String> refs) {
super();
this.sname =
sname;
this.dob = dob;
this.qual = qual;
this.courses =
courses;
this.emails =
emails;
this.marks =
marks;
this.phones =
phones;
this.refs = refs;
}
public int getSid() {
return sid;
}
public void setSid(int
sid) {
this.sid = sid;
}
public String getSname() {
return sname;
}
public void
setSname(String sname) {
this.sname =
sname;
}
public String getDob() {
return dob;
}
public void
setDob(String dob) {
this.dob = dob;
}
public String getQual() {
return qual;
}
public void
setQual(String qual) {
this.qual = qual;
}
public String[] getCourses()
{
return courses;
}
public void
setCourses(String[] courses) {
this.courses =
courses;
}
public List<String>
getEmails() {
return emails;
}
public void
setEmails(List<String> emails) {
this.emails =
emails;
}
public List<Integer>
getMarks() {
return marks;
}
public void
setMarks(List<Integer> marks) {
this.marks =
marks;
}
public Set<Long>
getPhones() {
return phones;
}
public void
setPhones(Set<Long> phones) {
this.phones =
phones;
}
public Map<String,
String> getRefs() {
return refs;
}
public void
setRefs(Map<String, String> refs) {
this.refs = refs;
}
@Override
public String toString() {
return "Student
[sid=" + sid + ", sname=" + sname + ", dob=" + dob
+
", qual=" + qual + ", courses=" + Arrays.toString(courses)
+
", emails=" + emails + ", marks=" + marks + ",
phones="
+
phones + ", refs=" + refs + "]";
}
}
HibernateUtil.java
package
com.sushil.hibernate.util;
import
org.hibernate.SessionFactory;
import
org.hibernate.cfg.AnnotationConfiguration;
import
org.hibernate.cfg.Configuration;
public class
HibernateUtil {
static SessionFactory fact;
static {
Configuration cfg=new
AnnotationConfiguration();
cfg=cfg.configure();
fact=cfg.buildSessionFactory();
}
public static
SessionFactory getFactory(){
return fact;
}
}
Client.java
Same
as in previous example.
Ouput :
