(12)基于annotation配置ManyToOne

秒速五厘米 2022-05-10 12:34 173阅读 0赞

@Entity
    @Table(name="t_cla")
    public class Classroom {
    private int id;
    private String name;
    private int grade;
    private Set<Student> stus;
    @OneToMany(mappedBy="cla")//表示由对方即多的一方(stu)的cla属性维护关系
    @LazyCollection(LazyCollectionOption.EXTRA)//表示由cla取stus的size时，智能化，使用count
    public Set<Student> getStus() {
    	return stus;
    }
    public void setStus(Set<Student> stus) {
    	this.stus = stus;
    }
    @Id
    @GeneratedValue//相当于native
    public int getId() {
    	return id;
    }
    public void setId(int id) {
    	this.id = id;
    }
    @Column(name="cla_name")//把name在数据库表示为cla_name
    public String getName() {
    	return name;
    }
    public void setName(String name) {
    	this.name = name;
    }
    public int getGrade() {
    	return grade;
    }
    public void setGrade(int grade) {
    	this.grade = grade;
    }
    
    }

@Entity
    @Table(name="t_stu")
    public class Student {
    	private int id;
    private String name;
    private int number;
    private Classroom cla;
    @Id
    @GeneratedValue
    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 int getNumber() {
    	return number;
    }
    public void setNumber(int number) {
    	this.number = number;
    }
    @ManyToOne(fetch=FetchType.LAZY)//由stu取cla时，使用延迟加载
    @JoinColumn(name="c_id")
    public Classroom getCla() {
    	return cla;
    }
    public void setCla(Classroom cla) {
    	this.cla = cla;
    }
    
    }

**hibernate.cfg.xml:**

<hibernate-configuration>
    	<session-factory> 
    	<property name="hibernate.hbm2ddl.auto">update</property>
    	<property name="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</property>
    
    	<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    	<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/hibernate_01</property>
    	<property name="hibernate.connection.username">root</property>
    	<property name="hibernate.connection.password">HZP123</property>
    		<property name="show_sql">true</property>
    		
    		<mapping class="model.Classroom"/>
    		<mapping class="model.Student"/>
    	</session-factory>
    </hibernate-configuration>