010_Spring Data JPA一对多关系

1. 一对多的关联关系

1.1. 角色和用户是一对多的关联关系

角色类(对应表名: t_role): 一方

用户类(对应表名: t_user): 多方

1.2. 角色表

1.3. 用户表 

2. 一对多的关联关系例子

2.1. 创建一个名为spring-data-jpa-one2many的Java项目, 同时添加相关jar包, 并添加JUnit能力。

 

2.2. 新建Role.java 

package com.bjbs.pojo;import java.io.Serializable; import java.util.HashSet; import java.util.Set; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.OneToMany; import javax.persistence.Table;@Entity // 指定该类是实体类 @Table(name = "t_role") // 指定数据库表名(表名和实体类对应) public class Role implements Serializable {private static final long serialVersionUID = 1L;@Id // 指定为主键@GeneratedValue(strategy = GenerationType.IDENTITY) // 指定主键生成策略@Column(name = "id") // 指定表中列名(列名和属性名对应)private Integer id;@Column(name = "name")private String name; // 角色名@OneToMany(mappedBy="role")private Set<User> users = new HashSet<User>();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 Set<User> getUsers() {return users;}public void setUsers(Set<User> users) {this.users = users;}@Overridepublic String toString() {return "Role [id=" + id + ", name=" + name + "]";}}

2.3. 新建User.java

package com.bjbs.pojo;import java.io.Serializable; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; 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 // 指定该类是实体类 @Table(name = "t_user") // 指定数据库表名(表名和实体类对应) public class User implements Serializable {private static final long serialVersionUID = 1L;@Id // 指定为主键@GeneratedValue(strategy = GenerationType.IDENTITY) // 指定主键生成策略@Column(name = "id") // 指定表中列名(列名和属性名对应)private Integer id;@Column(name = "name")private String name; // 用户名@ManyToOne(cascade=CascadeType.PERSIST)// @JoinColumn: 就是维护一个外键@JoinColumn(name="r_id")private Role role;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 Role getRole() {return role;}public void setRole(Role role) {this.role = role;}@Overridepublic String toString() {return "User [id=" + id + ", name=" + name + "]";}}

2.4. 新建UserRepository.java

package com.bjbs.dao;import org.springframework.data.jpa.repository.JpaRepository; import com.bjbs.pojo.User;/*** 参数一T: 当前需要映射的实体; 参数二 T: 当前映射的实体中的id的类型*/ public interface UserRepository extends JpaRepository<User, Integer> {}

2.5. 新建TestUserRepository.java

package com.bjbs.test;import org.junit.Test; import org.junit.runner.RunWith; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.test.context.ContextConfiguration; import org.springframework.test.context.junit4.SpringJUnit4ClassRunner; import com.bjbs.dao.UserRepository; import com.bjbs.pojo.Role; import com.bjbs.pojo.User;@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration("classpath:applicationContext.xml") public class TestUserRepository {@Autowiredprivate UserRepository userRepository;@Testpublic void findOne() {User user = userRepository.findOne(2);System.out.println(user);Role role = user.getRole();System.out.println(role);}@Testpublic void save() {// 新建用户User user = new User();user.setName("翠花");// 新建角色Role role = new Role();role.setName("测试人员");// 建立关系role.getUsers().add(user);user.setRole(role);// 保存用户userRepository.save(user);} }

2.6. 在src下新建application.properties

spring.datasource.driverClassName=com.mysql.cj.jdbc.Driver spring.datasource.url=jdbc:mysql://192.168.25.138:3306/StudyMybatis?useSSL=true&useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai spring.datasource.username=root spring.datasource.password=lyw123456

2.7. 在src下新建applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns="http://www.springframework.org/schema/beans"xmlns:context="http://www.springframework.org/schema/context"xmlns:tx="http://www.springframework.org/schema/tx"xmlns:jpa="http://www.springframework.org/schema/data/jpa"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsdhttp://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd"><!-- 配置读取properties文件的工具类 --><context:property-placeholder location="classpath:application.properties" /><!-- 配置c3p0数据库连接池 --><bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"><property name="jdbcUrl" value="${spring.datasource.url}" /><property name="driverClass" value="${spring.datasource.driverClassName}" /><property name="user" value="${spring.datasource.username}" /><property name="password" value="${spring.datasource.password}" /></bean><!-- Spring整合JPA 配置EntityManagerFactory --><bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"><property name="dataSource" ref="dataSource" /><property name="jpaVendorAdapter"><bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"><!-- hibernate相关的属性的注入 --><!-- 配置数据库类型 --><property name="database" value="MYSQL" /><!-- 正向工程 自动创建表 --><!-- <property name="generateDdl" value="true" /> --><!-- 显示执行的SQL --><property name="showSql" value="true" /></bean></property><!-- 扫描实体的包 --><property name="packagesToScan"><list><value>com.bjbs.pojo</value></list></property></bean><!-- 配置Hibernate的事务管理器 --><bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager"><property name="entityManagerFactory" ref="entityManagerFactory" /></bean><!-- 配置开启注解事务处理 --><tx:annotation-driven transaction-manager="transactionManager" /><!-- 配置springIOC的注解扫描 --><context:component-scan base-package="com.bjbs.service" /><!-- Spring Data JPA 的配置 --><!-- base-package: 扫描dao接口所在的包 --><jpa:repositories base-package="com.bjbs.dao" /> </beans>

2.8. 查询一个用户

2.9. 保存一个用户 

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