Hibernate 双向一对一&双向一对多

叁歲伎倆 2022-08-21 06:54 175阅读 0赞

***纸上得来终觉浅***

**1.双向一对多**

双向一对多与双向多对一是相同的。  这中情况下B有多个A，B能够加载A，A也能够加载B：

package roadArchitectWeb;
    
    import java.util.HashSet;
    import java.util.Set;
    
    public class Teacher {
    	private Integer Id;
    	private String Name;
    	private String PhoneNum;
    	private Set<Student> Students = new HashSet<>();
    
    	public Set<Student> getStudents() {
    		return Students;
    	}
    	public void setStudents(Set<Student> students) {
    		Students = students;
    	}
    	public Integer getId() {
    		return Id;
    	}
    	public void setId(Integer id) {
    		Id = id;
    	}
    	public String getName() {
    		return Name;
    	}
    	public void setName(String name) {
    		Name = name;
    	}
    	public String getPhoneNum() {
    		return PhoneNum;
    	}
    	public void setPhoneNum(String phoneNum) {
    		PhoneNum = phoneNum;
    	}
    	public  Teacher() {
    	}
    	@Override
    	public String toString() {
    		return "Teacher [Id=" + Id + ", Name=" + Name + ", PhoneNum=" + PhoneNum + ", Students=" + Students + "]";
    	}
    }

package roadArchitectWeb;
    
    public class Student {
    	private Integer Id;
    	private String sName;
    	private String Age;
    	private Teacher teacher;
    	public Teacher getTeacher() {
    		return teacher;
    	}
    	public void setTeacher(Teacher teacher) {
    		this.teacher = teacher;
    	}
    	public Integer getId() {
    		return Id;
    	}
    	public void setId(Integer id) {
    		Id = id;
    	}
    	public String getsName() {
    		return sName;
    	}
    	public void setsName(String sName) {
    		this.sName = sName;
    	}
    	public String getAge() {
    		return Age;
    	}
    	public void setAge(String age) {
    		Age = age;
    	}
    	@Override
    	public String toString() {
    		return "Student [Id=" + Id + ", sName=" + sName + ", Age=" + Age + ", teacher=" + teacher + "]";
    	}
    	public Student(){
    	}
    }

<?xml version="1.0"?>
    <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
    
    <hibernate-mapping>
        <class name="roadArchitectWeb.Teacher" table="TEACHER">
            <id name="Id" type="java.lang.Integer">
                <column name="ID" />
                <generator class="native" />
            </id>
            <property name="Name" type="java.lang.String">
                <column name="NAME" />
            </property>
            <property name="PhoneNum" type="java.lang.String">
                <column name="PHONENUM" />
            </property>
            <set name="Students" table="STUDENT">
    
            <key column="teacherId"></key>
            <one-to-many class="roadArchitectWeb.Student"/>
            </set>
        </class>
    </hibernate-mapping>

<?xml version="1.0"?>
    <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
    
    <hibernate-mapping package="roadArchitectWeb">
        <class name="Student" table="STUDENT">
            <id name="Id" type="java.lang.Integer">
                <column name="ID" />
                <generator class="native">
                </generator>
            </id>
            <property name="sName" type="java.lang.String">
                <column name="SNAME" />
            </property>
            <property name="Age" type="java.lang.String">
                <column name="AGE" />
            </property>
            <many-to-one name="teacher" class="Teacher"
            column="teacherId">
            </many-to-one>
        </class>
    </hibernate-mapping>

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE hibernate-configuration PUBLIC
    		"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    		"http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
    <hibernate-configuration>
        <session-factory>
        <property name="connection.username">root</property>
        <property name="connection.password">123456</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost/roadarchitectweb</property>
        
        <property name="dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <property name="hbm2ddl.auto">update</property>
        
        <property name="hibernate.c3p0.max_size">10</property>
        <property name="hibernate.c3p0.min_size">5</property>
        <property name="c3p0.acquire_increment">2</property>
        
        <property name="c3p0.idle_test_period">2000</property>
        <property name="c3p0.timeout">2000</property>
        
        <property name="c3p0.max_statements">10</property>
        
        <property name="hibernate.temp.use_jdbc_metadata_defaults">false</property>
        <mapping resource="roadArchitectWeb/Student.hbm.xml"/>
        <mapping resource="roadArchitectWeb/Teacher.hbm.xml"/>
        </session-factory>
    </hibernate-configuration>

package roadArchitectWeb;
    import org.hibernate.Session;
    import org.hibernate.SessionFactory;
    import org.hibernate.Transaction;
    import org.hibernate.cfg.Configuration;
    import org.junit.Test;
    
    import com.mysql.jdbc.interceptors.ServerStatusDiffInterceptor;
    public class HibernateTest {
    	@Test
    	public void test() {
    		SessionFactory sessionFactory = null;
    		Configuration configuration = new Configuration().configure();
    		sessionFactory = configuration.buildSessionFactory();
    		Session session = sessionFactory.openSession();
    		Transaction transaction = session.beginTransaction();
    		
    		/*begin*/
    		Teacher teacher = new Teacher();
    		Student student = new Student();
    		teacher.setName("chenT");
    		teacher.setPhoneNum("18788837117");
    		student.setsName("ma");
    		student.setAge("11");
    		student.setTeacher(teacher);
    		teacher.getStudents().add(student);
    		
    		session.save(student);
    		session.save(teacher);
    		
    //		student = (Student)session.get(Student.class, 1);
    //		teacher = (Teacher)session.get(Teacher.class,1);
    //		System.out.println("HibernateTest.test()S:"+student.getTeacher().getName());
    //		System.out.println("HibernateTest.test()T:"+teacher.getStudents().size());
    		
    		transaction.commit();
    		session.close();
    		sessionFactory.close();
    	}
    }

**2.双向一对一**

一对一双向关联就是在一对一外键关联的基础上，在另一个类中在加上对方的属性；

接着之前做的的一对一外键的基础上：

在B（Teacher）中增加A的属性，同时设置one-to-one标签即可；这样的话就可以互相加载。  
**3.另外学习过程中注意到了下面一点：一和多，一的一方设置对象的属性，多的一方设置Set集合属性。**