MyBatis注解之一对多关联实战

一 领域模型

1 Clazz

package org.fkit.domain; import java.io.Serializable; import java.util.List; public class Clazz implements Serializable { private static final long serialVersionUID = 1L; private Integer id; // 班级id，主键 private String code; // 班级编号 private String name; // 班级名称 // 班级和学生是一对多的关系，即一个班级可以有多个学生 private List<Student> students; public Clazz() { super(); // TODO Auto-generated constructor stub } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getCode() { return code; } public void setCode(String code) { this.code = code; } public String getName() { return name; } public void setName(String name) { this.name = name; } public List<Student> getStudents() { return students; } public void setStudents(List<Student> students) { this.students = students; } @Override public String toString() { return "Clazz [id=" + id + ", code=" + code + ", name=" + name + "]"; } }

2 Student

package org.fkit.domain; import java.io.Serializable; /** * CREATE TABLE tb_clazz( id INT PRIMARY KEY AUTO_INCREMENT, CODE VARCHAR(18), NAME VARCHAR(18) ); INSERT INTO tb_clazz(CODE,NAME) VALUES('j1601','Java就业班'); CREATE TABLE tb_student( id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(18), sex VARCHAR(18), age INT, clazz_id INT, FOREIGN KEY (clazz_id) REFERENCES tb_clazz(id) ); INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('jack','男',23,1); INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('rose','女',18,1); INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('tom','男',21,1); INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('alice','女',20,1); * */ public class Student implements Serializable { private static final long serialVersionUID = 1L; private Integer id; // 学生id，主键 private String name; // 姓名 private String sex; // 性别 private Integer age; // 年龄 // 学生和班级是多对一的关系，即一个学生只属于一个班级 private Clazz clazz; public Student() { super(); // TODO Auto-generated constructor stub } 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 String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public Clazz getClazz() { return clazz; } public void setClazz(Clazz clazz) { this.clazz = clazz; } @Override public String toString() { return "Student [id=" + id + ", name=" + name + ", sex=" + sex + ", age=" + age + "]"; } }

二 会话工厂

package org.fkit.factory; import java.io.InputStream; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; public class FKSqlSessionFactory { private static SqlSessionFactory sqlSessionFactory = null; // 初始化创建SqlSessionFactory对象 static{ try (// 读取mybatis-config.xml文件 InputStream is = Resources.getResourceAsStream("mybatis-config.xml"); ){ sqlSessionFactory = new SqlSessionFactoryBuilder() .build(is); } catch (Exception e) { e.printStackTrace(); } } // 获取SqlSession对象的静态方法 public static SqlSession getSqlSession(){ return sqlSessionFactory.openSession(); } // 获取SqlSessionFactory的静态方法 public static SqlSessionFactory getSqlSessionFactory() { return sqlSessionFactory; } }

三 mapper

1 ClazzMapper

package org.fkit.mapper; import org.apache.ibatis.annotations.Many; import org.apache.ibatis.annotations.Result; import org.apache.ibatis.annotations.Results; import org.apache.ibatis.annotations.Select; import org.apache.ibatis.mapping.FetchType; import org.fkit.domain.Clazz; public interface ClazzMapper { // 根据id查询班级信息 @Select("SELECT * FROM TB_CLAZZ WHERE ID = #{id}") @Results({ @Result(id=true,column="id",property="id"), @Result(column="code",property="code"), @Result(column="name",property="name"), @Result(column="id",property="students", many=@Many( select="org.fkit.mapper.StudentMapper.selectByClazzId", fetchType=FetchType.LAZY)) }) Clazz selectById(Integer id); }

2 StudentMapper

package org.fkit.mapper; import java.util.List; import org.apache.ibatis.annotations.Result; import org.apache.ibatis.annotations.Results; import org.apache.ibatis.annotations.Select; import org.fkit.domain.Student; public interface StudentMapper { // 根据班级id查询班级所有学生 @Select("SELECT * FROM TB_STUDENT WHERE CLAZZ_ID = #{id}") @Results({ @Result(id=true,column="id",property="id"), @Result(column="name",property="name"), @Result(column="sex",property="sex"), @Result(column="age",property="age") }) List<Student> selectByClazzId(Integer clazz_id); }

四 配置文件

1 db.properties

driver=com.mysql.jdbc.Driver url=jdbc:mysql://127.0.0.1:3306/mybatis username=root password=123456

2 log4j.xml

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd"> <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"> <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender"> <layout class="org.apache.log4j.PatternLayout"> <param name="ConversionPattern" value="%5p [%t] %m%n" /> </layout> </appender> <logger name="org.fkit.mapper"> <level value="DEBUG" /> </logger> <root> <level value="ERROR" /> <appender-ref ref="STDOUT" /> </root> </log4j:configuration>

3 mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <!-- XML 配置文件包含对 MyBatis 系统的核心设置 --> <configuration> <properties resource="db.properties"/> <!-- 指定 MyBatis 所用日志的具体实现 --> <settings> <setting name="logImpl" value="LOG4J"/> <!-- 要使延迟加载生效必须配置下面两个属性 --> <setting name="lazyLoadingEnabled" value="true"/> <setting name="aggressiveLazyLoading" value="false"/> </settings> <environments default="mysql"> <!-- 环境配置，即连接的数据库。 --> <environment id="mysql"> <!-- 指定事务管理类型，type="JDBC"指直接简单使用了JDBC的提交和回滚设置 --> <transactionManager type="JDBC"/> <!-- dataSource指数据源配置，POOLED是JDBC连接对象的数据源连接池的实现。 --> <dataSource type="POOLED"> <property name="driver" value="${driver}"/> <property name="url" value="${url}"/> <property name="username" value="${username}"/> <property name="password" value="${password}"/> </dataSource> </environment> </environments> <!-- mappers告诉了MyBatis去哪里找持久化类的映射文件 --> <mappers> <mapper class="org.fkit.mapper.ClazzMapper"/> <mapper class="org.fkit.mapper.StudentMapper"/> </mappers> </configuration>

五 测试

package org.fkit.test; import org.apache.ibatis.session.SqlSession; import org.fkit.domain.Clazz; import org.fkit.factory.FKSqlSessionFactory; import org.fkit.mapper.ClazzMapper; public class OneToManyTest { public static void main(String[] args) { // 定义SqlSession变量 SqlSession sqlSession = null; try { // 创建SqlSession实例 sqlSession = FKSqlSessionFactory.getSqlSession(); // 获取ClazzMapper实例 ClazzMapper cm = sqlSession.getMapper(ClazzMapper.class); // 根据id查询Clazz对象 Clazz clazz = cm.selectById(1); // 查看查询到的Clazz对象 System.out.println(clazz.getId() + " "+ clazz.getCode() + " "+clazz.getName()); // 查看关联的学生集合，因为配置使用的是LAZY懒加载，所以当使用时才执行SQL语句 clazz.getStudents().forEach(student->System.out.println(student)); // 提交事务 sqlSession.commit(); } catch (Exception e) { // 回滚事务 sqlSession.rollback(); e.printStackTrace(); }finally { // 关闭SqlSession if(sqlSession != null) sqlSession.close(); } } }

测试结果

DEBUG [main] ==> Preparing: SELECT * FROM TB_CLAZZ WHERE ID = ? DEBUG [main] ==> Parameters: 1(Integer) DEBUG [main] <== Total: 1 1 j1601 Java就业班 DEBUG [main] ==> Preparing: SELECT * FROM TB_STUDENT WHERE CLAZZ_ID = ? DEBUG [main] ==> Parameters: 1(Integer) DEBUG [main] <== Total: 4 Student [id=1, name=jack, sex=男, age=23] Student [id=2, name=rose, sex=女, age=18] Student [id=3, name=tom, sex=男, age=21] Student [id=4, name=alice, sex=女, age=20]