Hibernate 一对多关系操作

这里使用类别Category和产品Product举例。

Category与Product属于1:m 的关系，数据库如下：

那么，实体设计如下：

package com.sasa.domain;

import java.util.Date;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class Category {

    public Category() {}
    
    private Integer id;
    private String c_name;
    private String descr;
    private Date create_tm;
    
    private Set<Product> Products = new HashSet<Product>();
    
    
    public Set<Product> getProducts() {
        return Products;
    }
    public void setProducts(Set<Product> products) {
        Products = products;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getC_name() {
        return c_name;
    }
    public void setC_name(String c_name) {
        this.c_name = c_name;
    }
    public String getDescr() {
        return descr;
    }
    public void setDescr(String descr) {
        this.descr = descr;
    }
    public Date getCreate_tm() {
        return create_tm;
    }
    public void setCreate_tm(Date create_tm) {
        this.create_tm = create_tm;
    }
    @Override
    public String toString() {
        return "Category [id=" + id + ", c_name=" + c_name + ", descr=" + descr + ", create_tm=" + create_tm
                + ", Products=" + Products + "]";
    }
    
}

package com.sasa.domain;

import java.time.LocalDateTime;

public class Product {
    
    public Product() {}
    
    private Integer pid;
    private String pname;
    private Double price;
    private LocalDateTime create_tm;
    private Category category;
    
    public Category getCategory() {
        return category;
    }
    public void setCategory(Category category) {
        this.category = category;
    }
    public Integer getPid() {
        return pid;
    }
    public void setPid(Integer pid) {
        this.pid = pid;
    }
    public String getPname() {
        return pname;
    }
    public void setPname(String pname) {
        this.pname = pname;
    }
    public Double getPrice() {
        return price;
    }
    public void setPrice(Double price) {
        this.price = price;
    }
    
    public LocalDateTime getCreate_tm() {
        return create_tm;
    }
    public void setCreate_tm(LocalDateTime create_tm) {
        this.create_tm = create_tm;
    }
    @Override
    public String toString() {
        return "Product [pid=" + pid + ", pname=" + pname + ", price=" + price + ", create_tm=" + create_tm
                + ", category=" + category + "]";
    }
    
    
    
}

配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping package="com.sasa.domain">
        <class name="Category" table="category">
            <id name="id" column="id">
                <generator class="native"></generator>
            </id>
            <property name="c_name"></property>
            <property name="descr"></property>
            <property name="create_tm"></property>
            <set name="products">
                <key column="category_id"></key>
                <one-to-many class="Product"/>
            </set>
        </class>
    </hibernate-mapping>
    

name：引用属性名

column：外键名称

class：与此类相关的类的完整类名

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
    <hibernate-mapping package="com.sasa.domain">
        <class name="Product" table="product">
            <id name="pid" column="pid">
                <generator class="native"></generator>
            </id>
            <property name="pname"></property>
            <property name="price"></property>
            <property name="create_tm"></property>
            <many-to-one name="category" column="category_id" class="Category"></many-to-one>
        </class>
    </hibernate-mapping>
    

当设计好之后，就可以书写代码测试了：

package com.sasa.service;

import java.time.LocalDateTime;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.junit.Test;

import com.sasa.domain.Category;
import com.sasa.domain.Product;
import com.sasa.utils.HibernateUtils;

public class CategoryService {
    @Test
    //新增类别和产品
    public void addCategorys(){
        Session session = HibernateUtils.getCurrentSession();
        Transaction tran = session.beginTransaction();
    //========================================
        Category category = new Category();
        category.setC_name("运动器材");
        category.setDescr("sport");
        
        Product p1 = new Product();
        p1.setPname("足球");
        p1.setPrice(100.00);
        
        Product p2 = new Product();
        p2.setPname("篮球");
        p2.setPrice(90.00);
        
        //一对多
        category.getProducts().add(p1);
        category.getProducts().add(p2);
        
        //多对一
        p1.setCategory(category);
        p2.setCategory(category);
        
        session.save(category);
        session.save(p1);
        session.save(p2);
    //==========================================    
        tran.commit();
        session.close();
        
    }
    
    
    //为类别增加产品
    public void addProductByCategory() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tran = session.beginTransaction();
        
        //====================================
        
        //1、获得要操作的类别  2、创建产品  3、将产品添加到类别，将类别设置到产品  4、执行保存
        Category category = session.get(Category.class, 9);
        
        Product product = new Product();
        product.setPname("羽毛球");
        product.setCreate_tm(LocalDateTime.now());
        product.setPrice(40.50);
        
        category.getProducts().add(product);
        product.setCategory(category);
        
        session.save(product);
        
        //====================================
        
        tran.commit();
        session.close();
    }
    
    
    //删除产品
    public void delProductByCategory() {
        Session session = HibernateUtils.getCurrentSession();
        Transaction tran = session.beginTransaction();
        
        //====================================
        
        //1、获得要操作的类别  2、获得要移除的产品  3、将产品从类别集合中移除 
        Category category = session.get(Category.class, 9);
        
        Product product = session.get(Product.class, 35);
        
        category.getProducts().remove(product);
        product.setCategory(null);//注意：数据库外键需设计为可空 这里的删除是将外键设置为null， 执行的是update，不执行delete
        
        //====================================
        //
        tran.commit();
        session.close();
    }

}

HibernateUtils.java:

package com.sasa.utils;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class HibernateUtils {

    private static SessionFactory sessionFac;
    
    static {
        // Configuration 配置加载类，加载主配置，orm元数据加载
                Configuration conf = new Configuration().configure();
                // SessionFactory 创建用于操作数据库的Session工厂
                // SessionFactory 负责保存和使用所有配置，消耗内存资源非常大
                // 线程安全
                // 保证在web项目中，只创建一个SessionFactory
             sessionFac = conf.buildSessionFactory();
    }
    
    //获得Session
    //打开一个全新的Session
    public static Session openSession() {
        Session session = sessionFac.openSession();
        return session;
    }

    //获得线程上绑定的Session
    public static Session getCurrentSession() {
        Session session = sessionFac.getCurrentSession();
        return session;
    }

}