hibernate--ID生成策略_联合主键

约定不等于承诺〃 2024-02-18 14:45 84阅读 0赞

一：XML格式

首先需要将作为联合主键的属性重新封装成一个对象。如将teacher类中的id,name取出重新封装:

package com.bean;
    
    import java.io.Serializable;
    
    public class TeacherPK implements Serializable{
    	private int id;
    	private String name;
    	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;
    	}
    	@Override
    	public int hashCode() {
    		return this.name.hashCode();
    	}
    	@Override
    	public boolean equals(Object obj) {
    		if(obj instanceof TeacherPK){
    			TeacherPK teac = (TeacherPK)obj;
    			if(this.id == teac.getId() && this.name.equals(teac.getName())){
    				return true;
    			}
    		}
    		return false;
    	}
    	
    }

teacher.java:

package com.bean;
    
    public class teacher {
        private TeacherPK pk;
    	private String title;
    	public TeacherPK getPk() {
    		return pk;
    	}
    
    	public void setPk(TeacherPK pk) {
    		this.pk = pk;
    	}
    
    	public String getTitle() {
    		return title;
    	}
    
    	public void setTitle(String title) {
    		this.title = title;
    	}
    
    }

另外映射文件hbm.xml文件的id标签做如下修改：

<composite-id name = "pk" class = "com.bean.TeacherPK">
            <key-property name="id"/>
            <key-property name="name"/>
         </composite-id>

必须得实现序列化接口Serializable , 并重写equeal() 和 hashCode()方法。

测试类：

package com.action;
    
    import org.hibernate.Session;
    import org.hibernate.SessionFactory;
    import org.hibernate.cfg.Configuration;
    import org.hibernate.service.ServiceRegistryBuilder;
    
    import com.bean.TeacherPK;
    import com.bean.teacher;
    
    public class test {
       public static void main(String []agrs){
    	   Configuration cfg = new Configuration();
    	   cfg.configure(); //加载hibernate配置文件
    	   SessionFactory sessionFactory = cfg.buildSessionFactory(new ServiceRegistryBuilder().applySettings(cfg.getProperties()).buildServiceRegistry());	   
    	   Session session = sessionFactory.openSession();
    	   
    	   teacher teach = new teacher();
    	   TeacherPK pk = new TeacherPK();
    	   pk.setId(3);
    	   pk.setName("LDW");
    	   teach.setTitle("研究生");
    	   teach.setPk(pk);
    	   
    	   session.beginTransaction();  //开启事务
    	   session.save(teach);    //执行数据库添加操作
    	   session.getTransaction().commit(); // 事务提交
    	   System.out.println("the end");
    	}
    }

二：Annotation:

一）在主键类注解@Embeddable 如：StudentPK.java

package com.bean;
    
    import java.io.Serializable;
    
    import javax.persistence.Embeddable;
    
    @Embeddable
    public class StudentPK implements Serializable{
    	private int id;
    	private String name;
    	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;
    	}
    	@Override
    	public int hashCode() {
    		return this.name.hashCode();
    	}
    	@Override
    	public boolean equals(Object obj) {
    		if(obj instanceof StudentPK){
    			StudentPK teac = (StudentPK)obj;
    			if(this.id == teac.getId() && this.name.equals(teac.getName())){
    				return true;
    			}
    		}
    		return false;
    	}
    	
    }

然后在进行@Id注解 如：

@Id
    	public StudentPK getPk() {
    		return pk;
    	}

二）不需要在主键类中注解 ， 只需在注解@EmbeddedId 即可 ，如：

@Entity
    public class Student {
    	private String password;
        private StudentPK pk ;
        
        @EmbeddedId
    	public StudentPK getPk() {
    		return pk;
    	}

三）通过注解@Id @IdClass 如：

package com.bean;
    
    import javax.persistence.EmbeddedId;
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.GenerationType;
    import javax.persistence.Id;
    import javax.persistence.IdClass;
    import javax.persistence.TableGenerator;
    
    @Entity
    @IdClass(value=StudentPK.class)
    public class Student {
    	private String password;
        private String name ;
        private int id;
    
        @Id
    	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;
    	}
    
    	public String getPassword() {
    		return password;
    	}
    
    	public void setPassword(String password) {
    		this.password = password;
    	}
    
    }

同样StudentPK.java主键类不变（因为往数据库中load()等操作的时候需要主键）