表结构
CREATE TABLE `t_category` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8
CREATE TABLE `t_product` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`typeid` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `FK_7kn4mhej5ccxp2ei4u2he6b8n` (`typeid`),
CONSTRAINT `FK_7kn4mhej5ccxp2ei4u2he6b8n` FOREIGN KEY (`typeid`) REFERENCES `t_category` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8
实体类
package com.yjj.entity;
import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
/**
* 单向一对多
* t_category表字段，id，name
*/
@Table(name = "t_category")
@Entity
public class Category {
@Id
@GeneratedValue
private Integer id;
private String name;
@JoinColumn(name = "typeId")
@OneToMany
private List<Product> products=new ArrayList<>();
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Product> getProducts() {
return products;
}
public void setProducts(List<Product> products) {
this.products = products;
}
@Override
public String toString() {
return "Category{" +
"id=" + id +
", name='" + name + '\'' +
", products=" + products +
'}';
}
}
package com.yjj.entity;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
/**
* 单向一对多
* t_product表字段，id，name，typeId
*/
@Table(name = "t_product")
@Entity
public class Product {
@Id
@GeneratedValue
private Integer id;
private String name;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Product{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
}
Product product=new Product();
product.setName("手机");
Product product1=new Product();
product1.setName("电脑");
Category category=new Category();
category.setName("数码");
category.getProducts().add(product);
category.getProducts().add(product1);
manager.persist(product);
manager.persist(product1);
manager.persist(category);
输出
Hibernate:
insert
into
t_product
(name)
values
(?)
Hibernate:
insert
into
t_product
(name)
values
(?)
Hibernate:
insert
into
t_category
(name)
values
(?)
Hibernate:
update
t_product
set
typeId=?
where
id=?
Hibernate:
update
t_product
set
typeId=?
where
id=?
查询一的一方
Category category=manager.find(Category.class,1);
System.out.println(category);
输出
Hibernate:
select
category0_.id as id1_0_0_,
category0_.name as name2_0_0_
from
t_category category0_
where
category0_.id=?
Hibernate:
select
products0_.typeId as typeId3_0_0_,
products0_.id as id1_2_0_,
products0_.id as id1_2_1_,
products0_.name as name2_2_1_
from
t_product products0_
where
products0_.typeId=?
Category{id=1, name='数码', products=[Product{id=1, name='手机'}, Product{id=2, name='电脑'}]}
先看看数据库吧
image.png
image.png
删除
Category category=manager.find(Category.class,1);
manager.remove(category);
看输出
Hibernate:
select
category0_.id as id1_0_0_,
category0_.name as name2_0_0_
from
t_category category0_
where
category0_.id=?
Hibernate:
update
t_product
set
typeId=null
where
typeId=?
Hibernate:
delete
from
t_category
where
id=?
image.png
删除Category后，Product并没有级联删除，而是把Product中typeid字段置为空，如果想要级联删除
@OneToMany(cascade=CascadeType.REMOVE)
