package com.dx.jpa.singlemanytoone;import java.util.Date;
import java.util.HashSet;
import java.util.Set;import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.Transient;@Entity
@Table(name = "jpa_customer")
public class Customer {private Integer id;private String fullName;private Integer age;private Date birth;private Date createDate;private Set<Order> orders = new HashSet<>();@Id@GeneratedValue(strategy = GenerationType.AUTO)public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}@Column(name = "FULL_NAME", length = 64, nullable = false)public String getFullName() {return fullName;}public void setFullName(String fullName) {this.fullName = fullName;}public Integer getAge() {return age;}public void setAge(Integer age) {this.age = age;}@Temporal(TemporalType.DATE)public Date getBirth() {return birth;}public void setBirth(Date birth) {this.birth = birth;}@Temporal(TemporalType.TIMESTAMP)public Date getCreateDate() {return createDate;}public void setCreateDate(Date createDate) {this.createDate = createDate;}// 映射一对多的关联关系// @JoinColumn 用来映射一对多的关联关系// @OneToMany 用来映射外键列@JoinColumn(name = "CUSTOMER_ID")@OneToMany(fetch=FetchType.EAGER,cascade=CascadeType.REMOVE)public Set<Order> getOrders() {return orders;}public void setOrders(Set<Order> orders) {this.orders = orders;}// 帮助方法，不希望保存到数据库，但是需要动态获取Customer对象的属性。
    @Transientpublic String getCustomerInfo() {return "username:" + fullName + ",age:" + age;}
}

package com.dx.jpa.singlemanytoone;import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;@Entity
@Table(name = "jpa_order")
public class Order {private Integer id;private String name;private Customer Customer;@Id@GeneratedValue(strategy = GenerationType.AUTO)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;}@JoinColumn(name = "CUSTOMER_ID")@ManyToOne(fetch = FetchType.LAZY)public Customer getCustomer() {return Customer;}public void setCustomer(Customer customer) {Customer = customer;}
}

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"><persistence-unit name="Jpa-helloword"transaction-type="RESOURCE_LOCAL"><!-- 配置使用什么 ORM 产品来作为 JPA 的实现 --><provider>org.hibernate.jpa.HibernatePersistenceProvider</provider><!-- 添加持久化类 --><class>com.dx.jpa.singlemanytoone.Customer</class><class>com.dx.jpa.singlemanytoone.Order</class><properties><!-- 数据库的相关配置 --><property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" /><property name="javax.persistence.jdbc.url" value="jdbc:mysql://127.0.0.1:3306/jpa" /><property name="javax.persistence.jdbc.user" value="root" /><property name="javax.persistence.jdbc.password" value="root" /><!-- 指定方言 MySQL                org.hibernate.dialect.MySQLDialectMySQL with InnoDB    org.hibernate.dialect.MySQLInnoDBDialectMySQL with MyISAM    org.hibernate.dialect.MySQLMyISAMDialectMySQL5                org.hibernate.dialect.MySQL5DialectMySQL5 with InnoDB    org.hibernate.dialect.MySQL5InnoDBDialect--><property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect" /><property name="hibernate.show_sql" value="true" /><property name="hibernate.format_sql" value="true" /><!-- create：每次加载hibernate时都会删除上一次的生成的表，然后根据你的model类再重新来生成新表，哪怕两次没有任何改变也要这样执行，这就是导致数据库表数据丢失的一个重要原因。<br>create-drop ：每次加载hibernate时根据model类生成表，但是sessionFactory一关闭,表就自动删除。<br>update：最常用的属性，第一次加载hibernate时根据model类会自动建立起表的结构（前提是先建立好数据库），以后加载hibernate时根据 model类自动更新表结构，即使表结构改变了但表中的行仍然存在不会删除以前的行。要注意的是当部署到服务器后，表结构是不会被马上建立起来的，是要等 应用第一次运行起来后才会。<br>validate ：每次加载hibernate时，验证创建数据库表结构，只会和数据库中的表进行比较，不会创建新表，但是会插入新值。 <br> --><property name="hibernate.hbm2ddl.auto" value="update" />            </properties></persistence-unit>
</persistence>

Hibernate: selectnext_val as id_val fromhibernate_sequence for updateHibernate: updatehibernate_sequence setnext_val= ? wherenext_val=?
Hibernate: selectnext_val as id_val fromhibernate_sequence for updateHibernate: updatehibernate_sequence setnext_val= ? wherenext_val=?
Hibernate: selectnext_val as id_val fromhibernate_sequence for updateHibernate: updatehibernate_sequence setnext_val= ? wherenext_val=?
Hibernate: insert intojpa_customer(age, birth, createDate, FULL_NAME, id) values(?, ?, ?, ?, ?)
Hibernate: insert intojpa_order(CUSTOMER_ID, name, id) values(?, ?, ?)
Hibernate: insert intojpa_order(CUSTOMER_ID, name, id) values(?, ?, ?)
Hibernate: updatejpa_order setCUSTOMER_ID=? whereid=?
Hibernate: updatejpa_order setCUSTOMER_ID=? whereid=?