Hibernate is a powerful Object-Relational Mapping (ORM) framework that simplifies database interactions by mapping Java objects to database tables. In this section, we’ll cover the basics of Hibernate CRUD operations (Create, Read, Update, Delete) and how to handle different types of entity mappings: One-to-One, One-to-Many, and Many-to-Many.
Hibernate CRUD Operations
Create: To insert a new record into the database, you can use session.save() or session.persist(). These methods add a new entity into the database.
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Session session = sessionFactory.openSession(); Transaction transaction = session.beginTransaction(); session.save(newEntity); transaction.commit(); session.close(); |
Read: You can retrieve an entity using session.get() or session.load().
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MyEntity entity = session.get(MyEntity.class, id); |
Update: To update an existing entity, Hibernate uses session.update() or session.merge().
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entity.setName("New Name"); session.update(entity); |
Delete: To delete an entity, use session.delete()
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session.delete(entity); |
Hibernate Entity Mappings
One-to-One Mapping: In a one-to-one relationship, one entity is associated with exactly one instance of another entity. For example, a person has one passport.
Mapping Example:
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@Entity public class Person { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @OneToOne(mappedBy = "person") private Passport passport; } @Entity public class Passport { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @OneToOne @JoinColumn(name = "person_id") private Person person; } |
One-to-Many Mapping: A one-to-many relationship means one entity is associated with multiple instances of another entity. For example, one department has many employees.
Mapping Example:
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@Entity public class Department { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @OneToMany(mappedBy = "department") private List<Employee> employees; } @Entity public class Employee { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @ManyToOne @JoinColumn(name = "department_id") private Department department; } |
Many-to-Many Mapping: A many-to-many relationship means that multiple instances of one entity are related to multiple instances of another entity. For example, students and courses.
Mapping Example:
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@Entity public class Student { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @ManyToMany @JoinTable( name = "student_course", joinColumns = @JoinColumn(name = "student_id"), inverseJoinColumns = @JoinColumn(name = "course_id") ) private List<Course> courses; } @Entity public class Course { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @ManyToMany(mappedBy = "courses") private List<Student> students; } |
