mybatis的3种关联映射（1）：一对一

mybatis的3种关联映射有：一对一，一对多，多对多。

在实际项目开发中经常遇到一对一的关联，比如老师和课程一对一的关系。

在mapper.xml中写法：

<mapper namespace="springboot.mapper.TeacherMapper" > <resultMap id="BaseResultMap" type="springboot.model.Teacher" > <id column="tid" property="tid" jdbcType="INTEGER" /> <result column="tname" property="tname" jdbcType="VARCHAR" /> <result column="tphone" property="tphone" jdbcType="VARCHAR" /> <result column="taddr" property="taddr" jdbcType="VARCHAR" /> <result column="cid" property="cid" jdbcType="INTEGER" /> <!-- 一对一的关联关系 column="cid"两个表的关联点 --> <association property="course" column="cid" resultMap="springboot.mapper.CourseMapper.BaseResultMap"></association> </resultMap> <sql id="Base_Column_List" > tid, tname, tphone, taddr, cid </sql> <!--一对一的关联sql语句，cid作为2个表的外键--> <select id="findTeacher" resultMap="BaseResultMap" parameterType="java.lang.Integer"> SELECT t.* ,c.* FROM teacher t,course c WHERE t.cid=c.cid and t.tid = #{tid,jdbcType=INTEGER} </select>

dao层写法：

public interface TeacherMapper {   //老师跟课程一对一的关联   Teacher findTeacher(Integer id); }

注：在dao层的方法名findTeacher要跟mapper.xml中的select id中的值保持一致，不一致会报错

model层：

public class Teacher { private Integer tid; private String tname; private String tphone; private String taddr; private Integer cid;     //新增的课程属性 private Course course; public Course getCourse() { return course; } public void setCourse(Course course) { this.course = course; } public Integer getTid() { return tid; } public void setTid(Integer tid) { this.tid = tid; } public String getTname() { return tname; } public void setTname(String tname) { this.tname = tname; } public String getTphone() { return tphone; } public void setTphone(String tphone) { this.tphone = tphone; } public String getTaddr() { return taddr; } public void setTaddr(String taddr) { this.taddr = taddr; } public Integer getCid() { return cid; } public void setCid(Integer cid) { this.cid = cid; } @Override public String toString() { return "Teacher{" + "tid=" + tid + ", tname='" + tname + '\'' + ", tphone='" + tphone + '\'' + ", taddr='" + taddr + '\'' + ", cid=" + cid + '}'; } }

springboot测试类：

@SpringBootApplication @MapperScan("springboot.mapper") public class Application { public static void main( String[] args ) { ApplicationContext context = SpringApplication.run(Application.class, args); TeacherMapper teacherMapper=context.getBean(TeacherMapper.class); System.out.println("老师和课程一对一联系："); Teacher teacher1=teacherMapper.findTeacher(2); System.out.println(teacher1.getTname()+"------"+teacher1.getCourse().toString()); }

测试效果：

老师和课程一对一联系： DEBUG [main] - Creating a new SqlSession DEBUG [main] - SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@4b3a45f1] was not registered for synchronization because synchronization is not active DEBUG [main] - Fetching JDBC Connection from DataSource DEBUG [main] - JDBC Connection [ProxyConnection[PooledConnection[com.mysql.jdbc.JDBC4Connection@78a287ed]]] will not be managed by Spring DEBUG [main] - ==> Preparing: SELECT t.* ,c.* FROM teacher t,course c WHERE t.cid=c.cid and t.tid = ? DEBUG [main] - ==> Parameters: 2(Integer) DEBUG [main] - <== Total: 1 DEBUG [main] - Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@4b3a45f1] DEBUG [main] - Returning JDBC Connection to DataSource 老王------Course{cid=2, cname='C语言', ctime=56}

我的座右铭：不会，我可以学；落后，我可以追赶；跌倒，我可以站起来；我一定行。