The best way to map @OneToOne

The best way to map @OneToOne

   June 29, 2021       Ravi Yasas

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@OneToOne

The best approach to bidirectional @OneToOne is to use @MapsId

Student entity

@Entity

@Data

@Table(name = "students")

public class Student implements Serializable {

    @Id

    @GeneratedValue

    private Integer id;

    private String name;

    private String email;

    @OneToOne(mappedBy = "student", cascade = CascadeType.ALL)

    private StudentDetails studentDetails;

}

StudentDetails entity

@Entity

@Data

@Table(name = "student_details")

public class StudentDetails implements Serializable {

    @Id

    @GeneratedValue(strategy = GenerationType.AUTO)

    private Integer id;

    private String studentDetailsInfo;

    @OneToOne

    @JoinColumn(name = "student_id")

    @MapsId

    private Student student;

}

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The best way to map @ManyToMany

The best way to map @ManyToMany

   June 29, 2021       Ravi Yasas

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@ManyToMany

Many to many relationships can be easily mapped by creating another table using @JoinTable as follows.

Student entity

@Data

@Table(name = "Student")

@Entity

public class Student implements Serializable {

    @Id

    @GeneratedValue(strategy = GenerationType.AUTO)

    private Integer id;

    private String studentName;

    @ManyToMany

    @JoinTable(

        name = "student_task",

        joinColumns = @JoinColumn(name = "task_id"),

        inverseJoinColumns = @JoinColumn(name = "student_id")

    )

    private Set<Task> tasks = new HashSet<>();

}

Task entity

@Entity

@Data

@Table(name = "tasks")

public class Task implements Serializable {

    @Id

    @GeneratedValue(strategy = GenerationType.AUTO)

    private Integer id;

    private String taskName;

    @ManyToMany(mappedBy = "tasks")

    private Set<Student> students = new HashSet<>();

}

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States of an object in Hibernate

States of an object in Hibernate

   June 26, 2021       Ravi Yasas

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Hibernate object states

There are three states

• Transient 
• If the object just created, no primary key and not associate with a session, then the object is in the transient state
• Persistent 
• If a session is open, the object is in the persistent state
• Detached 
• If a session is closed, the object is in the detached state

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