学习过Hibernate框架的伙伴们很容易就能简单的配置各种映射关系(Hibernate框架的映射关系在我的blogs中也有详细的讲解)，但是在Mybatis框架中我们又如何去实现
一对多的关系映射呢？ 其实很简单
首先我们照常先准备前期的环境(具体解释请 参考初识Mybatis进行增、删、改、查 blogs )这里我就直接上代码了
主配置文件：Configuration.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"> <configuration> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"> <property name="" value=""/> </transactionManager> <dataSource type="UNPOOLED"> <property name="driver" value="oracle.jdbc.OracleDriver"/> <property name="url" value="jdbc:oracle:thin:@localhost:1521:orcl"/> <property name="username" value="practice"/> <property name="password" value="123"/> </dataSource> </environment> </environments> <mappers> <mapper resource="config/Student.xml"/> <mapper resource="config/Grade.xml"/> </mappers> </configuration>
背景：学生和班级是一个典型的一对多的关系，一个班级可以对应着多个学生，所以我们随即创建了学生对象和班级对象
学生类：Student
package entity; /* * 学生类 * */ public class Student { //学生编号 private Integer sid; //学生名称 private String sname; //学生性别 private String sex; public Student() { } public Student(String sname, String sex) { this.sname = sname; this.sex = sex; } public Integer getSid() { return sid; } public void setSid(Integer sid) { this.sid = sid; } public String getSname() { return sname; } public void setSname(String sname) { this.sname = sname; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } }
班级类：Grade
package entity; import java.util.HashSet; import java.util.Set; /* * 班级类 * */ public class Grade { //班级编号 private Integer gid; //班级名称 private String gname; //班级描述 private String gdesc; //班级下的学生信息 private Set<Student> stus=new HashSet<Student>(); public Set<Student> getStus() { return stus; } public void setStus(Set<Student> stus) { this.stus = stus; } public Grade() { } public Grade(Integer gid, String gname, String gdesc) { this.gid = gid; this.gname = gname; this.gdesc = gdesc; } public Integer getGid() { return gid; } public void setGid(Integer gid) { this.gid = gid; } public String getGname() { return gname; } public void setGname(String gname) { this.gname = gname; } public String getGdesc() { return gdesc; } public void setGdesc(String gdesc) { this.gdesc = gdesc; } }
实体类准备完了的话，我们就可以开始看配置文件了，也是最关键的一部分
首先讲简单点的学生实体类对应的配置文件
Student.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="Student"> <resultMap type="entity.Student" id="StudentResult"> <id column="sid" jdbcType="INTEGER" property="sid"/> <result column="sname" jdbcType="VARCHAR" property="sname"/> <result column="sex" jdbcType="VARCHAR" property="sex"/> </resultMap> </mapper>
然后就是最关键的班级实体的配置文件了
Grade.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="Grade"> <resultMap type="entity.Grade" id="GradeResult"> <id column="gid" jdbcType="INTEGER" property="gid"/> <result column="gname" jdbcType="VARCHAR" property="gname"/> <result column="gdesc" jdbcType="VARCHAR" property="gdesc"/> <!-- 一对多关系 --> <collection property="stus" resultMap="Student.StudentResult"></collection> </resultMap> <!-- 查询所有信息 --> <select id="selectAllInfo" resultMap="GradeResult"> <!-- select sid,sname,sex,g.gid,gname,gdesc from Student s,Grade g where s.gid=g.gid --> select sid,sname,sex,g.gid,gname,gdesc from Student s left join Grade g on s.gid=g.gid </select> </mapper>
以上就是对配置文件的解释了
接下来我们就可以进行一道测试了
/* * 1.1 查询所有的班级和班级下的所有学生(一对多) * */ @Test public void selectAllStu() throws Exception{ //通过配置文件获取到数据库连接信息 Reader reader = Resources.getResourceAsReader("config/Configuration.xml"); //通过配置信息构建一个SessionFactory工厂 SqlSessionFactory sqlsessionfactory=new SqlSessionFactoryBuilder().build(reader); //通过SessionFaction打开一个回话通道 SqlSession session = sqlsessionfactory.openSession(); /*SqlSession session =MybatisUtil.getSession();*/ //调用配置文件中的sql语句 List<Grade> list = session.selectList("Grade.selectAllInfo"); //遍历查询出来的结果 for (Grade grade : list) { System.out.println("班级："+grade.getGname()); for (Student stu : grade.getStus()) { System.out.println("学生："+stu.getSname()); } } session.close(); }
执行后，查询出来的结果是
以上是第一种一对多关系映射的方式，下面是第二种一对多映射的方法，其他的所有步骤和上面的都是一样的只有相对应的配置文件不同，所以我就只贴小配置了
Grade.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="Grade"> <resultMap type="entity.Grade" id="GradeResult"> <id column="gid" jdbcType="INTEGER" property="gid"/> <result column="gname" jdbcType="VARCHAR" property="gname"/> <result column="gdesc" jdbcType="VARCHAR" property="gdesc"/> <!-- 一对多关系 --> <!-- <collection property="stus" resultMap="Student.StudentResult"></collection> --> <collection property="stus" javaType="entity.Student"> <id property="sid" column="sid"/> <result property="sname" column="sname"/> <result property="sex" column="sex"/> </collection> </resultMap> <!-- 查询所有信息 --> <select id="selectAllInfo" resultMap="GradeResult"> <!-- select sid,sname,sex,g.gid,gname,gdesc from Student s,Grade g where s.gid=g.gid --> select sid,sname,sex,g.gid,gname,gdesc from Student s left join Grade g on s.gid=g.gid </select> <!-- 新增班级并同时新增班级下的学生 --> <!--useGeneratedKeys=true 表明采用主键生成策略 keyProperty="gid" 表明将生成的主键添加到parameterType类中的那个属性值中去 --> <!-- <insert id="" useGeneratedKeys="true" keyProperty="gid" parameterType="entity.Grade"> </insert> --> </mapper>
接下来就可以在多的一方配置一的关联关系了
Student.xml
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="Student"> <resultMap type="entity.Student" id="StudentResult"> <id column="sid" jdbcType="INTEGER" property="sid"/> <result column="sname" jdbcType="VARCHAR" property="sname"/> <result column="sex" jdbcType="VARCHAR" property="sex"/> <!-- 多对一 --> <!-- <association property="grade" resultMap="Grade.GradeResult"></association> --> <association property="grade" javaType="entity.Grade"> <id property="gid" column="gid"/> <result property="gname" column="gname"/> <result property="gdesc" column="gdesc"/> </association> </resultMap> <!-- 使用别名 --> <sql id="cloums"> s.sid,s.sname,s.sex ,g.gid,g.gname,g.gdesc </sql> <!-- 多对一查询学生的班级 --> <select id="selectGradeByStu" resultMap="StudentResult"> select <include refid="cloums"/> from Student s ,Grade g where s.gid=g.gid </select> <!-- 简单查询所有信息 --> <select id="selectAllStu" resultMap="StudentResult"> select sid,sname,sex,gid from Student </select> <!--动态拼接Sql --> <select id="selectAllStuByWhere" parameterType="entity.Student" resultMap="StudentResult"> select sid,sname,sex,gid from Student where 1=1 <if test="sname!=null and !"".equals(sname.trim())"> <!-- and sname like '%'|| #{sname}|| '%' --> <!-- 模糊查询 --> and sname like '%${sname}%'<!-- 模糊查询 --> <!-- and sname = #{sname} --> </if> </select> <!-- 新增学生信息 --> <insert id="InsertStuInfo" parameterType="entity.Student" > insert into Student values(SEQ_NUM.Nextval,#{sname},#{sex},1) </insert> <!-- 删除学生信息 --> <insert id="DeleteStuBySid" parameterType="int"> delete from Student where sid=#{sid} <!--或者是 delete from Student where sid=#{_parameter} --> </insert> <!-- 根据SID修改学生信息 --> <update id="UpdateStuBySid" parameterType="entity.Student" > update Student set sname=#{sname},sex=#{sex} where sid=#{sid} </update> </mapper>
这样就已经完成了Mybatis框架中的简单的双向一对多的配置了，怎么样，是不是没有想象中的难呢？希望对大家有点帮助吧！