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In many to many, it creates three tables in total.
Student,Teacher,Student_teacher
In our example, all mappings are done in teacher class
1.Annotation
Teacher:
we create @ManyToMany @JoinTable(name="xx",@JoinColumns={@JoinColumn()},@inverseJoinColumns={@JoinColumn()})
@JoinColumns links its pk to the junction table
Why are we using @JoinColumns not @JoinColumn directly?
B/c we could have composite primary keys, thus, we should use @JoinColumns;
@inverseJoinColumns links second table‘s pk to the junction table
@Entity public class Teacher { private String name; private int id; private Set<Student> students; @ManyToMany @JoinTable(name="t_s", //join column points to this.id; joinColumns={@JoinColumn(name="teacher_id")}, //inverseJoinColumns points to id of student class inverseJoinColumns={@JoinColumn(name="stu_id")} ) public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Id public int getId() { return id; } public void setId(int id) { this.id = id; } } @Entity @Table(name="t_student") public class Student { private int age; private int classID; private String name; private int id;
public int getClassID() { return classID; } public void setClassID(int classID) { this.classID = classID; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Id public int getId() { return id; } public void setId(int id) { this.id = id; } }
2.XML
Teacher class:
<Key> appears anywhere the parent mapping element defines a join to a new table that references the primary key of the original table. It also defines the foreign key in the joined table
<key column="xx"> xx is the id of this.class;
<many-to-many class="student" column="xx"> xx is the id of student class
<hibernate-mapping package="com.hibernate.model"> <class name="Teacher" table="T_Teacher"> <id name="id"></id> <property name="name"></property> <!-- table="xx" xx is name of junction table --> <set name="students" table="tea_stu"> <key column="teacher_Id"></key> <many-to-many class="com.hibernate.model.Student" column="stu_id"/> </set> </class> <hibernate-mapping package="com.hibernate.model"> <class name="Student" table ="S_Student"> <id name="id"></id> <property name="name"></property> <property name="age"></property> <property name="classID"></property> </class>
Hibernate Many-to-Many Unidirectional mapping
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原文地址：http://www.cnblogs.com/fifi043/p/4906183.html
