13.3.3 List Implementation
Folder class will have a list of files so we need to design the Folder class as below. Since list is ordered collection , we need to specify a column name in <list-index> attribute to store the index of the list elements.
Folder.java
package com.tutorial.hibernate;
import java.util.ArrayList;
import java.util.List;
public class Folder {
private int folderId;
private String folderName;
private List<File> files = new ArrayList<File>();
public int getFolderId() {
return folderId;
}
public void setFolderId(int folderId) {
this.folderId = folderId;
}
public String getFolderName() {
return folderName;
}
public void setFolderName(String folderName) {
this.folderName = folderName;
}
public List<File> getFiles() {
return files;
}
public void setFiles(List<File> files) {
this.files = files;
}
}
We will use <list> tag to define the Folder and File classes in component-mapping.hbm.xml .
- <key column> tag will create a column with the given name in the table configured in <set> and it will be a foreign key column for the primary key of Folder table. No need to create property in Object corresponding to this column as Hibernate does manages it internally.
- <list-index > is used to specify the column which will store the index to maintain the order. No need to create a property in Object corresponding to this column as Hibernate does manages it internally.
- <composite-element> tag defines the class name and its properties.
<?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>
<class name="com.tutorial.hibernate.Folder" table="Folder">
<id name="folderId" type="int" column="folder_id">
<generator class="native"/>
</id>
<property name="folderName" column="name" type="string"/>
<list name="files" table="Files" >
<key column="folderIdForeignKey"></key>
<list-index column="position"></list-index>
<composite-element class="com.tutorial.hibernate.File">
<property name="name" type="string" column="file_name"/>
<property name="size" type= "int" column="file_size"/>
<property name="extension" type="string" column="file_ext"/>
</composite-element>
</list>
</class>
</hibernate-mapping>
Create Tables
CREATE TABLE 'folder' (
'folder_id' int(11) NOT NULL AUTO_INCREMENT,
'name' varchar(255) DEFAULT NULL,
PRIMARY KEY ('folder_id')
);
CREATE TABLE 'files' (
'folderIdForeignKey' int(11) NOT NULL,
'file_name' varchar(255) DEFAULT NULL,
'file_size' int(11) DEFAULT NULL,
'file_ext' varchar(255) DEFAULT NULL,
'position' int(11) NOT NULL,
PRIMARY KEY ('folderIdForeignKey','position'),
CONSTRAINT 'FK_n1d8h7ymasle0im3hk2dtxswt' FOREIGN KEY ('folderIdForeignKey') REFERENCES 'folder' ('folder_id')
)
Test Program
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.SortedSet;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import com.tutorial.hibernate.File;
import com.tutorial.hibernate.Folder;
public class Test {
public static void main(String args[])
{
Configuration cfg = new Configuration().configure();
SessionFactory factory = cfg.buildSessionFactory();
Session session= factory.openSession();
Transaction tx = session.beginTransaction();
Folder folder = new Folder();
folder.setFolderName("folder1");
List<File> files = new ArrayList<File>();
File f1= new File();
f1.setExtension(".txt");
f1.setName("sample");
f1.setSize(102);
File f2= new File();
f2.setExtension(".xls");
f2.setName("data");
f2.setSize(1024);
files.add(f1);
files.add(f2);
folder.setFiles(files);
session.save(folder);
Query q = session.createQuery("from Folder");
Folder f =(Folder) q.uniqueResult();
System.out.println(f.getFiles());
tx.commit();
session.close();
factory.close();
}
}
Run Test Program. Database state will be as below
13.3.4 Collection Implementation
To support unordered and duplicated values , we can use Collection interface and ArrayList as an implementation . Hibernate does provide <bag> and <idbag> tags to map the Collections.
Folder class will have a collections of files (with arraylist as implementation ) so we need to design the Folder class as below.
Folder.java
package com.tutorial.hibernate;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
public class Folder {
private int folderId;
private String folderName;
private Collection<File> files = new ArrayList<File>();
public int getFolderId() {
return folderId;
}
public void setFolderId(int folderId) {
this.folderId = folderId;
}
public String getFolderName() {
return folderName;
}
public void setFolderName(String folderName) {
this.folderName = folderName;
}
public Collection<File> getFiles() {
return files;
}
public void setFiles(Collection<File> files) {
this.files = files;
}
}
We will use <bag> tag to define the Folder and File classes in component-mapping.hbm.xml .
- <key column> tag will create a column with given name in the table configured in <bag> and it will be a foreign key column for the primary key of Folder table. No need to create property in Object corresponding to this column as Hibernate does manages it internally.
- <composite-element> tag defines the class name and its properties.
<?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>
<class name="com.tutorial.hibernate.Folder" table="Folder">
<id name="folderId" type="int" column="folder_id">
<generator class="native"/>
</id>
<property name="folderName" column="name" type="string"/>
<bag name="files" table="Files" >
<key column="folderIdForeignKey"></key>
<composite-element class="com.tutorial.hibernate.File">
<property name="name" type="string" column="file_name"/>
<property name="size" type= "int" column="file_size"/>
<property name="extension" type="string" column="file_ext"/>
</composite-element>
</bag>
</class>
</hibernate-mapping>
Create Tables
CREATE TABLE 'folder' (
'folder_id' int(11) NOT NULL AUTO_INCREMENT,
'name' varchar(255) DEFAULT NULL,
PRIMARY KEY ('folder_id')
);
CREATE TABLE 'files' (
'folderIdForeignKey' int(11) NOT NULL,
'file_name' varchar(255) DEFAULT NULL,
'file_size' int(11) DEFAULT NULL,
'file_ext' varchar(255) DEFAULT NULL,
KEY 'FK_n1d8h7ymasle0im3hk2dtxswt' ('folderIdForeignKey'),
CONSTRAINT 'FK_n1d8h7ymasle0im3hk2dtxswt' FOREIGN KEY ('folderIdForeignKey') REFERENCES 'folder' ('folder_id')
);
Test Program
import java.util.ArrayList;
import java.util.Collection;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import com.tutorial.hibernate.File;
import com.tutorial.hibernate.Folder;
public class Test {
public static void main(String args[])
{
Configuration cfg = new Configuration().configure();
SessionFactory factory = cfg.buildSessionFactory();
Session session= factory.openSession();
Transaction tx = session.beginTransaction();
Folder folder = new Folder();
folder.setFolderName("folder1");
Collection<File> files = new ArrayList<File>();
File f1= new File();
f1.setExtension(".txt");
f1.setName("sample");
f1.setSize(102);
File f2= new File();
f2.setExtension(".xls");
f2.setName("data");
f2.setSize(1024);
files.add(f1);
files.add(f2);
folder.setFiles(files);
session.save(folder);
Query q = session.createQuery("from Folder");
Folder f =(Folder) q.uniqueResult();
System.out.println(f.getFiles());
tx.commit();
session.close();
factory.close();
}
}
