How does Hibernate handle many-to-many mapping relationships?

There are three ways to implement many-to-many mapping relationships in Hibernate: by using the @ManyToMany annotation, by using union tables, and by using association tables. In this example, the @ManyToMany annotation is used, the mappedBy attribute is used in EntityA to specify the fields associated with the mapping in EntityB, and the @ManyToMany annotation is used in EntityB to represent the many-to-many mapping relationship with EntityA.

Hibernate many-to-many mapping relationship processing method

Introduction

Hibernate is An object-relational mapping (ORM) framework for mapping between Java objects and relational databases. A many-to-many mapping is a type of relationship in which one entity can be associated with multiple entities and vice versa.

Implementing many-to-many mapping

In Hibernate, many-to-many mapping can be achieved by using the @ManyToMany annotation, as shown below:

// EntityA.java
@Entity
public class EntityA {
    @Id
    private Long id;

    @ManyToMany(mappedBy = "entitiesA")
    private Set<EntityB> entitiesB;
}

// EntityB.java
@Entity
public class EntityB {
    @Id
    private Long id;

    @ManyToMany
    private Set<EntityA> entitiesA;
}

In EntityA, the entitiesB field represents the collection of EntityB associated with EntityA. The mappedBy attribute specifies the field in EntityB associated with this map. In EntityB, the entitiesA field represents the collection of EntityA associated with EntityB.

Practical Case

Question: Suppose we have a student and tutor system. Each student can have multiple tutors, and each tutor can teach multiple students. Design the Hibernate mapping to represent this relationship.

Solution:

// Student.java
@Entity
public class Student {
    @Id
    private Long id;
    private String name;

    @ManyToMany(mappedBy = "students")
    private Set<Tutor> tutors;
}

// Tutor.java
@Entity
public class Tutor {
    @Id
    private Long id;
    private String name;

    @ManyToMany
    private Set<Student> students;
}

Note:

• In the Student entity, The tutors field represents the collection of tutors associated with the student. The mappedBy attribute specifies the field in the Tutor entity that is associated with this map.
• In the Tutor entity, the students field represents the collection of students associated with the tutor.

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