(11)hibernate中ManyToMany

傷城~ 2022-05-05 07:58 182阅读 0赞

**1.通过在两个类中分别设置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写的是后者对应的类，column是后者对应的外键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 自动生成的 catch 块
    			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 自动生成的 catch 块
    			e.printStackTrace();
    			s.getTransaction().rollback();
    		}finally {
    			HibernateUtil.closeSession(s);
    		}
    		
    	}

**最佳实践:使用manytomany，无论在哪一端维护关系都较为麻烦，并且有时关联表需要加入其它属性，所以在开发过程中，经常把manytomany改为2个onetomany，即3张表，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("小明老师");
    			s.save(t1);
    			
    			Teacher t2=new Teacher();
    			t2.setName("小红老师");
    			s.save(t2);
    			
    			Course c1=new Course();
    			c1.setName("数据结构");
    			s.save(c1);
    			
    			Course c2=new Course();
    			c2.setName("计算机组成原理");
    			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 自动生成的 catch 块
    			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 自动生成的 catch 块
    			e.printStackTrace();
    			s.getTransaction().rollback();
    		}finally {
    			HibernateUtil.closeSession(s);
    		}
    		
    	}