What is the purpose of the @ManyToMany annotation in JPA?

A) To map a many-to-many relationship between entities

B) To map a one-to-one relationship between entities

C) To configure database caching

D) To define a foreign key relationship

Answer:

A) To map a many-to-many relationship between entities

Explanation:

The @ManyToMany annotation in JPA is used to map a many-to-many relationship between entities. This type of relationship occurs when multiple entities of one type are associated with multiple entities of another type, such as “many students can enroll in many courses.”

For example:


@Entity
public class Student {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    @ManyToMany
    @JoinTable(
        name = "student_course",
        joinColumns = @JoinColumn(name = "student_id"),
        inverseJoinColumns = @JoinColumn(name = "course_id")
    )
    private List<Course> courses;

    // Getters and setters
}

In this example, the Student entity has a @ManyToMany relationship with the Course entity. The @JoinTable annotation is used to define the join table that maps the relationship between students and courses. The joinColumns attribute specifies the foreign key column in the join table that refers to the Student entity, and the inverseJoinColumns attribute specifies the foreign key column that refers to the Course entity.

The @ManyToMany annotation is crucial for representing complex relationships in JPA, ensuring that the associations between entities are correctly mapped and maintained in the database.

Reference links:

Spring Data JPA Tutorial