Hibernate "must knows"

hibernate.md

@Entity, @Id, @Table

Create a hibernate.cfg.xml file first, then add a line for mapping

<mapping class="demo.terrytsao.model.StudentInfo" />

import javax.persistence.*;

@Entity
@Table(name="SomeTableNameIfYouDontWantItToBeTheDefaultClassName")
public class StudentInfo {

    @Id @GeneratedValue(strategy = GenerationType.AUTO)
    private int rollNo;

    @Column(name="username", nullable=false)
    private String name;

    @Transient
    private String attrToIgnore;

    @Temporal(TemporalType.DATE)
    private Date dateWithoutTime;

    // the rest
}


public class Main {
    public static void main(String[] args) {
        StudentInfo student = new StudentInfo();

        SessionFactory sf = new AnnotationConfiguration().configure();
        Session sss = sf.openSession();

        sss.beginTransaction();

        sss.save(student);

        sss.getTransaction().commit();
        sss.close();
        sf.close();
    }
}

one to one mapping

@Entity
public class Student {

    @Id @GeneratedValue
    private int id;
}

@Entity
public class StudentDetail {

    @Id @GeneratedValue(generator = "newGenerator")
    @GenericGenerator(name="newGenerator", strategy = "foreign", 
            parameters = {@Parameter(value = "student", name="property")})
    private int id;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "student_id")
    private Student student;
}

// in main, save studentDetail object after setStudent method call

one to many mapping

@Entity
public class Student {

    @Id @GeneratedValue
    private int id;

    @ManyToOne(cascade = CascadeType.ALL) 
    private StudentAddress studentAddress;

    // getters and setters
}

@Entity
public class StudentAddress {

    @Id @GeneratedValue
    private int id;

    // for bidirection
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "studentAddress")
    private Set<Student> students = new HashSet<>(0);
    
    // getters and setters
}

// in main, save student object

many to many mapping

@Entity
public class Student {

    @Id @GeneratedValue
    private int id;

    @ManyToMany(cascade = CascadeType.ALL) 
    private Set<StudentCert> studentCert = new HashSet<>(0);

    // getters and setters
}

@Entity
public class StudentCert {

    @Id @GeneratedValue
    private int id;

    // for bidirection
    @ManyToMany(cascade = CascadeType.ALL, mappedBy = "studentCert")
    private Set<Student> students = new HashSet<>(0);
    
    // getters and setters
}

CRUD

public static void main(String[] args) {
    // Save
    session.save(student);

    // Get
    student = (Student) session.get(Student.class, 1);

    // Update
    student.setSth("Sth");
    session.update(student);

    // Delete
    session.delete(student);

}