mybatis的3种关联映射（1）：一对一

以你之姓@ 2022-05-24 02:05 207阅读 0赞

### 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" />
    
        
        <association property="course" column="cid" resultMap="springboot.mapper.CourseMapper.BaseResultMap"></association>
    
    
      </resultMap>
      <sql id="Base_Column_List" >
        tid, tname, tphone, taddr, cid
      </sql>
    
      
       
      <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}

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