(10)hibernate中ManyToMany
阿新 • • 發佈：2018-12-15
1.通過在兩個類中分別設定set完成MnayToMany:
public class Admin { private int id; private String name; private Set<Role> roles; public Admin() { roles=new HashSet<>(); } public void add(Role role) { roles.add(role); } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Set<Role> getRoles() { return roles; } public void setRoles(Set<Role> roles) { this.roles = roles; } }
public class Role { private int id; private String name; private Set<Admin> admins; public Role() { admins=new HashSet<>(); } public void add(Admin admin) { admins.add(admin); } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Set<Admin> getAdmins() { return admins; } public void setAdmins(Set<Admin> admins) { this.admins = admins; } }
<hibernate-mapping> <class name="model.Admin" table="ADMIN"> <id name="id" type="int"> <column name="ID" /> <generator class="native" /> </id> <property name="name" type="java.lang.String"> <column name="NAME" /> </property> <set name="roles" table="ROLE_ADMIN" lazy="extra"> <key> <column name="A_ID" /> </key> <many-to-many class="model.Role" column="R_ID"/> </set> </class> </hibernate-mapping>
注意：（1）.在admin中manytomany意思是admins to roles，class寫的是後者對應的類，column是後者對應的外來鍵id
<hibernate-mapping>
<class name="model.Role" table="ROLE">
<id name="id" type="int">
<column name="ID" />
<generator class="native" />
</id>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
<set name="admins" table="ROLE_ADMIN" lazy="extra">
<key>
<column name="R_ID" />
</key>
<many-to-many class="model.Admin" column="A_ID"/>
</set>
</class>
</hibernate-mapping>
test01:
@Test
void test1() {
Session s=null;
try {
s=HibernateUtil.getSession();
s.beginTransaction();
Admin a1=new Admin();
a1.setName("a1");
s.save(a1);
Admin a2=new Admin();
a2.setName("a2");
s.save(a2);
Role r1=new Role();
r1.setName("小明");
r1.add(a1);
r1.add(a2);
s.save(r1);
Role r2=new Role();
r2.setName("小王");
r2.add(a1);
r2.add(a2);
s.save(r2);
s.getTransaction().commit();
} catch (Exception e) {
// TODO 自動生成的 catch 塊
e.printStackTrace();
s.getTransaction().rollback();
}finally {
HibernateUtil.closeSession(s);
}
}test02:
@Test
void test2() {
Session s=null;
try {
s=HibernateUtil.getSession();
s.beginTransaction();
Admin a=s.load(Admin.class, 1);
System.out.println(a.getName());
for(Role r:a.getRoles()) {
System.out.println(r.getName());
}
s.getTransaction().commit();
} catch (Exception e) {
// TODO 自動生成的 catch 塊
e.printStackTrace();
s.getTransaction().rollback();
}finally {
HibernateUtil.closeSession(s);
}
}最佳實踐:使用manytomany，無論在哪一端維護關係都較為麻煩，並且有時關聯表需要加入其它屬性，所以在開發過程中，經常把manytomany改為2個onetomany，即3張表，如下：
public class Teacher {
private int id;
private String name;
private Set<TeacherCourse> tcs;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<TeacherCourse> getTcs() {
return tcs;
}
public void setTcs(Set<TeacherCourse> tcs) {
this.tcs = tcs;
}
}
public class Course {
private int id;
private String name;
private Set<TeacherCourse> tcs;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<TeacherCourse> getTcs() {
return tcs;
}
public void setTcs(Set<TeacherCourse> tcs) {
this.tcs = tcs;
}
}
public class TeacherCourse {
private int id;
private double ach;
private Teacher teacher;
private Course course;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public double getAch() {
return ach;
}
public void setAch(double ach) {
this.ach = ach;
}
public Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
public Course getCourse() {
return course;
}
public void setCourse(Course course) {
this.course = course;
}
}
<hibernate-mapping>
<class name="model.Teacher" table="TEACHER">
<id name="id" type="int">
<column name="ID" />
<generator class="native" />
</id>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
<set name="tcs" table="TEACHERCOURSE" inverse="true" lazy="extra">
<key>
<column name="T_ID" />
</key>
<one-to-many class="model.TeacherCourse" />
</set>
</class>
</hibernate-mapping>
<hibernate-mapping>
<class name="model.Course" table="COURSE">
<id name="id" type="int">
<column name="ID" />
<generator class="native" />
</id>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
<set name="tcs" table="TEACHERCOURSE" lazy="extra" inverse="true">
<key>
<column name="C_ID" />
</key>
<one-to-many class="model.TeacherCourse" />
</set>
</class>
</hibernate-mapping>
<hibernate-mapping>
<class name="model.TeacherCourse" table="TEACHERCOURSE">
<id name="id" type="int">
<column name="ID" />
<generator class="native" />
</id>
<property name="ach" type="double">
<column name="ACH" />
</property>
<many-to-one name="teacher" class="model.Teacher">
<column name="T_ID" />
</many-to-one>
<many-to-one name="course" class="model.Course">
<column name="C_ID" />
</many-to-one>
</class>
</hibernate-mapping>
test03：
@Test
void test3() {
Session s=null;
try {
s=HibernateUtil.getSession();
s.beginTransaction();
Teacher t1=new Teacher();
t1.setName("小明老師");
s.save(t1);
Teacher t2=new Teacher();
t2.setName("小紅老師");
s.save(t2);
Course c1=new Course();
c1.setName("資料結構");
s.save(c1);
Course c2=new Course();
c2.setName("計算機組成原理");
s.save(c2);
TeacherCourse tc1=new TeacherCourse();
tc1.setAch(88);
tc1.setCourse(c1);
tc1.setTeacher(t1);
s.save(tc1);
tc1=new TeacherCourse();
tc1.setAch(99);
tc1.setCourse(c2);
tc1.setTeacher(t1);
s.save(tc1);
tc1=new TeacherCourse();
tc1.setAch(90);
tc1.setCourse(c2);
tc1.setTeacher(t2);
s.save(tc1);
tc1=new TeacherCourse();
tc1.setAch(90);
tc1.setCourse(c1);
tc1.setTeacher(t2);
s.save(tc1);
s.getTransaction().commit();
} catch (Exception e) {
// TODO 自動生成的 catch 塊
e.printStackTrace();
s.getTransaction().rollback();
}finally {
HibernateUtil.closeSession(s);
}
}test04：
void test4() {
Session s=null;
try {
s=HibernateUtil.getSession();
s.beginTransaction();
Teacher t1=s.load(Teacher.class, 1);
System.out.println(t1.getName()+":");
for(TeacherCourse tc:t1.getTcs()) {
System.out.println(tc.getCourse().getName()+":"+tc.getAch());
}
s.getTransaction().commit();
} catch (Exception e) {
// TODO 自動生成的 catch 塊
e.printStackTrace();
s.getTransaction().rollback();
}finally {
HibernateUtil.closeSession(s);
}
}