hibernate_map.txt

Persisting Map
--------------

Map is used when we want to persist a collection of key/value pairs where the key is always unique. Some common implementations of java.util.Map are java.util.HashMap, java.util.LinkedHashMap, and so on. For this recipe, we will use java.util.HashMap.

Now, let's assume that we have a scenario where we are going to implement Map<String, String>; here, the String key is the e-mail address label, and the value String is the e-mail address. For example, we will try to construct a data structure similar to <"Personal e-mail", "emailaddress2@provider2.com">, <"Business e-mail", "emailaddress1@provider1.com">. This means that we will create an alias of the actual e-mail address so that we can easily get the e-mail address using the alias and can document it in a more readable form. This type of implementation depends on the custom requirement; here, we can easily get a business e-mail using the Business email key.

Tables:

CREATE TABLE `email` (
  `Employee_id` BIGINT(20) NOT NULL,
  `emails` VARCHAR(255) DEFAULT NULL,
  `emails_KEY` VARCHAR(255) NOT NULL DEFAULT '',
  PRIMARY KEY (`Employee_id`,`emails_KEY`),
  KEY `FK5C24B9C38F47B40` (`Employee_id`),
  CONSTRAINT `FK5C24B9C38F47B40` FOREIGN KEY (`Employee_id`) REFERENCES `employee` (`id`)
);


CREATE TABLE `employee` (
  `id` BIGINT(20) NOT NULL AUTO_INCREMENT,
  `name` VARCHAR(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
);

Employee.java
-------------

@Entity
@Table(name = "employee")
public class Employee {

  @Id
  @GeneratedValue
  @Column(name = "id")
  private long id;

  @Column(name = "name")
  private String name;

  @ElementCollection
  @CollectionTable(name = "email")
  private Map<String, String> emails;

  public long getId() {
    return id;
  }

  public void setId(long id) {
    this.id = id;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public Map<String, String> getEmails() {
    return emails;
  }

  public void setEmails(Map<String, String> emails) {
    this.emails = emails;
  }

  @Override
  public String toString() {
    return "Employee" 
        + "\n\tId: " + this.id
        + "\n\tName: " + this.name
        + "\n\tEmails: " + this.emails;
  }
}


Here, we will consider how to work with Map and its manipulation operations, such as inserting, retrieving, deleting, and updating.

Main Class:

Configuration cfg = new Configuration().configure();
		
			SessionFactory sessionFactory = cfg.buildSessionFactory();
			Session session = sessionFactory.openSession();
			Transaction transaction = session.beginTransaction();
		
		  Employee employee = new Employee();
		  employee.setName("yogesh");
		    
		  Map<String, String> emails = new HashMap<String, String>();
		  emails.put("Business email", "emailaddress1@provider1.com");
		  emails.put("Personal email", "emailaddress2@provider2.com");
		  employee.setEmails(emails);

		  session.save(employee);
		  transaction.commit();
		  session.close();
		  
		  

For Array:
------------------------------

  @ElementCollection
  @IndexColumn(name="email_index")
  @CollectionTable(name = "email")
  private String[] emails;
  
  
  
 Employee employee = new Employee();
employee.setName("Pankaj");
employee.setEmails (new String []{"emailaddress1@provider1.com", "emailaddress2@provider2.com", "emailaddress3@provider3.com", "emailaddress4@provider4.com"});