MyBatis联表查询

MyBatis逆向工程主要用于单表操作，那么需要进行联表操作时，往往需要我们自己去写sql语句。

写sql语句之前，我们先修改一下实体类

Course.java：

 public class Course {
     private Integer id;

     private String cNum;

     private String cName;

     private String remark;

     private Integer status;

     public Integer getId() {
         return id;
     }

     public void setId(Integer id) {
         this.id = id;
     }

     public String getcNum() {
         return cNum;
     }

     public void setcNum(String cNum) {
         this.cNum = cNum == null ? null : cNum.trim();
     }

     public String getcName() {
         return cName;
     }

     public void setcName(String cName) {
         this.cName = cName == null ? null : cName.trim();
     }

     public String getRemark() {
         return remark;
     }

     public void setRemark(String remark) {
         this.remark = remark == null ? null : remark.trim();
     }

     public Integer getStatus() {
         return status;
     }

     public void setStatus(Integer status) {
         this.status = status;
     }

     @Override
     public String toString() {
         return "Course{" +
                 "id=" + id +
                 ", cNum='" + cNum + '\'' +
                 ", cName='" + cName + '\'' +
                 ", remark='" + remark + '\'' +
                 ", status=" + status +
                 '}';
     }
 }

Task.java：

 import java.util.Date;

 public class Task {
     private Integer id;

     private String cid;

     private Integer uid;

     private String filename;

     private String fileUrl;

     private Date created;

     private Date updated;

     private String remark;

     private Integer status;

     //自定义
     private Course course;//联表查询使用

     public Integer getId() {
         return id;
     }

     public void setId(Integer id) {
         this.id = id;
     }

     public String getCid() {
         return cid;
     }

     public void setCid(String cid) {
         this.cid = cid == null ? null : cid.trim();
     }

     public Integer getUid() {
         return uid;
     }

     public void setUid(Integer uid) {
         this.uid = uid;
     }

     public String getFilename() {
         return filename;
     }

     public void setFilename(String filename) {
         this.filename = filename == null ? null : filename.trim();
     }

     public String getFileUrl() {
         return fileUrl;
     }

     public void setFileUrl(String fileUrl) {
         this.fileUrl = fileUrl == null ? null : fileUrl.trim();
     }

     public Date getCreated() {
         return created;
     }

     public void setCreated(Date created) {
         this.created = created;
     }

     public Date getUpdated() {
         return updated;
     }

     public void setUpdated(Date updated) {
         this.updated = updated;
     }

     public String getRemark() {
         return remark;
     }

     public void setRemark(String remark) {
         this.remark = remark == null ? null : remark.trim();
     }

     public Integer getStatus() {
         return status;
     }

     public void setStatus(Integer status) {
         this.status = status;
     }

     //自定义
     public Course getCourse() {
         return course;
     }

     public void setCourse(Course course) {
         this.course = course;
     }

     @Override
     public String toString() {
         return "Task{" +
                 "id=" + id +
                 ", cid='" + cid + '\'' +
                 ", uid=" + uid +
                 ", filename='" + filename + '\'' +
                 ", fileUrl='" + fileUrl + '\'' +
                 ", created=" + created +
                 ", updated=" + updated +
                 ", remark='" + remark + '\'' +
                 ", status=" + status +
                 ", course=" + course +
                 '}';
     }
 }

TaskMapper.java：

 import com.sun123.springboot.entity.Task;
 import com.sun123.springboot.entity.TaskExample;
 import org.apache.ibatis.annotations.Param;

 import java.util.List;

 public interface TaskMapper {
     int countByExample(TaskExample example);

     int deleteByExample(TaskExample example);

     int deleteByPrimaryKey(Integer id);

     int insert(Task record);

     int insertSelective(Task record);

     List<Task> selectByExample(TaskExample example);

     Task selectByPrimaryKey(Integer id);

     int updateByExampleSelective(@Param("record") Task record, @Param("example") TaskExample example);

     int updateByExample(@Param("record") Task record, @Param("example") TaskExample example);

     int updateByPrimaryKeySelective(Task record);

     int updateByPrimaryKey(Task record);

     List<Task> taskList();//联表查询
 }

TaskMapper.xml：（MyBatis逆向工程的基础上进行修改）

 <?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="com.sun123.springboot.mapper.TaskMapper" >
   <resultMap id="BaseResultMap" type="com.sun123.springboot.entity.Task" >
     <id column="id" property="id" jdbcType="INTEGER" />
     <result column="cid" property="cid" jdbcType="VARCHAR" />
     <result column="uid" property="uid" jdbcType="INTEGER" />
     <result column="filename" property="filename" jdbcType="VARCHAR" />
     <result column="file_url" property="fileUrl" jdbcType="VARCHAR" />
     <result column="created" property="created" jdbcType="TIMESTAMP" />
     <result column="updated" property="updated" jdbcType="TIMESTAMP" />
     <result column="remark" property="remark" jdbcType="VARCHAR" />
     <result column="status" property="status" jdbcType="INTEGER" />
   </resultMap>
   <sql id="Example_Where_Clause" >
     <where >
       <foreach collection="oredCriteria" item="criteria" separator="or" >
         <if test="criteria.valid" >
           <trim prefix="(" suffix=")" prefixOverrides="and" >
             <foreach collection="criteria.criteria" item="criterion" >
               <choose >
                 <when test="criterion.noValue" >
                   and ${criterion.condition}
                 </when>
                 <when test="criterion.singleValue" >
                   and ${criterion.condition} #{criterion.value}
                 </when>
                 <when test="criterion.betweenValue" >
                   and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                 </when>
                 <when test="criterion.listValue" >
                   and ${criterion.condition}
                   <foreach collection="criterion.value" item="listItem" open="(" close=")" separator="," >
                     #{listItem}
                   </foreach>
                 </when>
               </choose>
             </foreach>
           </trim>
         </if>
       </foreach>
     </where>
   </sql>
   <sql id="Update_By_Example_Where_Clause" >
     <where >
       <foreach collection="example.oredCriteria" item="criteria" separator="or" >
         <if test="criteria.valid" >
           <trim prefix="(" suffix=")" prefixOverrides="and" >
             <foreach collection="criteria.criteria" item="criterion" >
               <choose >
                 <when test="criterion.noValue" >
                   and ${criterion.condition}
                 </when>
                 <when test="criterion.singleValue" >
                   and ${criterion.condition} #{criterion.value}
                 </when>
                 <when test="criterion.betweenValue" >
                   and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                 </when>
                 <when test="criterion.listValue" >
                   and ${criterion.condition}
                   <foreach collection="criterion.value" item="listItem" open="(" close=")" separator="," >
                     #{listItem}
                   </foreach>
                 </when>
               </choose>
             </foreach>
           </trim>
         </if>
       </foreach>
     </where>
   </sql>
   <sql id="Base_Column_List" >
     id, cid, uid, filename, file_url, created, updated, remark, status
   </sql>
   <select id="selectByExample" resultMap="BaseResultMap" parameterType="com.sun123.springboot.entity.TaskExample" >
     select
     <if test="distinct" >
       distinct
     </if>
     <include refid="Base_Column_List" />
     from task
     <if test="_parameter != null" >
       <include refid="Example_Where_Clause" />
     </if>
     <if test="orderByClause != null" >
       order by ${orderByClause}
     </if>
   </select>
   <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" >
     select
     <include refid="Base_Column_List" />
     from task
     where id = #{id,jdbcType=INTEGER}
   </select>
   <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
     delete from task
     where id = #{id,jdbcType=INTEGER}
   </delete>
   <delete id="deleteByExample" parameterType="com.sun123.springboot.entity.TaskExample" >
     delete from task
     <if test="_parameter != null" >
       <include refid="Example_Where_Clause" />
     </if>
   </delete>
   <insert id="insert" parameterType="com.sun123.springboot.entity.Task" >
     insert into task (id, cid, uid,
       filename, file_url, created,
       updated, remark, status
       )
     values (#{id,jdbcType=INTEGER}, #{cid,jdbcType=VARCHAR}, #{uid,jdbcType=INTEGER},
       #{filename,jdbcType=VARCHAR}, #{fileUrl,jdbcType=VARCHAR}, #{created,jdbcType=TIMESTAMP},
       #{updated,jdbcType=TIMESTAMP}, #{remark,jdbcType=VARCHAR}, #{status,jdbcType=INTEGER}
       )
   </insert>
   <insert id="insertSelective" parameterType="com.sun123.springboot.entity.Task" >
     insert into task
     <trim prefix="(" suffix=")" suffixOverrides="," >
       <if test="id != null" >
         id,
       </if>
       <if test="cid != null" >
         cid,
       </if>
       <if test="uid != null" >
         uid,
       </if>
       <if test="filename != null" >
         filename,
       </if>
       <if test="fileUrl != null" >
         file_url,
       </if>
       <if test="created != null" >
         created,
       </if>
       <if test="updated != null" >
         updated,
       </if>
       <if test="remark != null" >
         remark,
       </if>
       <if test="status != null" >
         status,
       </if>
     </trim>
     <trim prefix="values (" suffix=")" suffixOverrides="," >
       <if test="id != null" >
         #{id,jdbcType=INTEGER},
       </if>
       <if test="cid != null" >
         #{cid,jdbcType=VARCHAR},
       </if>
       <if test="uid != null" >
         #{uid,jdbcType=INTEGER},
       </if>
       <if test="filename != null" >
         #{filename,jdbcType=VARCHAR},
       </if>
       <if test="fileUrl != null" >
         #{fileUrl,jdbcType=VARCHAR},
       </if>
       <if test="created != null" >
         #{created,jdbcType=TIMESTAMP},
       </if>
       <if test="updated != null" >
         #{updated,jdbcType=TIMESTAMP},
       </if>
       <if test="remark != null" >
         #{remark,jdbcType=VARCHAR},
       </if>
       <if test="status != null" >
         #{status,jdbcType=INTEGER},
       </if>
     </trim>
   </insert>
   <select id="countByExample" parameterType="com.sun123.springboot.entity.TaskExample" resultType="java.lang.Integer" >
     select count(*) from task
     <if test="_parameter != null" >
       <include refid="Example_Where_Clause" />
     </if>
   </select>
   <update id="updateByExampleSelective" parameterType="map" >
     update task
     <set >
       <if test="record.id != null" >
         id = #{record.id,jdbcType=INTEGER},
       </if>
       <if test="record.cid != null" >
         cid = #{record.cid,jdbcType=VARCHAR},
       </if>
       <if test="record.uid != null" >
         uid = #{record.uid,jdbcType=INTEGER},
       </if>
       <if test="record.filename != null" >
         filename = #{record.filename,jdbcType=VARCHAR},
       </if>
       <if test="record.fileUrl != null" >
         file_url = #{record.fileUrl,jdbcType=VARCHAR},
       </if>
       <if test="record.created != null" >
         created = #{record.created,jdbcType=TIMESTAMP},
       </if>
       <if test="record.updated != null" >
         updated = #{record.updated,jdbcType=TIMESTAMP},
       </if>
       <if test="record.remark != null" >
         remark = #{record.remark,jdbcType=VARCHAR},
       </if>
       <if test="record.status != null" >
         status = #{record.status,jdbcType=INTEGER},
       </if>
     </set>
     <if test="_parameter != null" >
       <include refid="Update_By_Example_Where_Clause" />
     </if>
   </update>
   <update id="updateByExample" parameterType="map" >
     update task
     set id = #{record.id,jdbcType=INTEGER},
       cid = #{record.cid,jdbcType=VARCHAR},
       uid = #{record.uid,jdbcType=INTEGER},
       filename = #{record.filename,jdbcType=VARCHAR},
       file_url = #{record.fileUrl,jdbcType=VARCHAR},
       created = #{record.created,jdbcType=TIMESTAMP},
       updated = #{record.updated,jdbcType=TIMESTAMP},
       remark = #{record.remark,jdbcType=VARCHAR},
       status = #{record.status,jdbcType=INTEGER}
     <if test="_parameter != null" >
       <include refid="Update_By_Example_Where_Clause" />
     </if>
   </update>
   <update id="updateByPrimaryKeySelective" parameterType="com.sun123.springboot.entity.Task" >
     update task
     <set >
       <if test="cid != null" >
         cid = #{cid,jdbcType=VARCHAR},
       </if>
       <if test="uid != null" >
         uid = #{uid,jdbcType=INTEGER},
       </if>
       <if test="filename != null" >
         filename = #{filename,jdbcType=VARCHAR},
       </if>
       <if test="fileUrl != null" >
         file_url = #{fileUrl,jdbcType=VARCHAR},
       </if>
       <if test="created != null" >
         created = #{created,jdbcType=TIMESTAMP},
       </if>
       <if test="updated != null" >
         updated = #{updated,jdbcType=TIMESTAMP},
       </if>
       <if test="remark != null" >
         remark = #{remark,jdbcType=VARCHAR},
       </if>
       <if test="status != null" >
         status = #{status,jdbcType=INTEGER},
       </if>
     </set>
     where id = #{id,jdbcType=INTEGER}
   </update>
   <update id="updateByPrimaryKey" parameterType="com.sun123.springboot.entity.Task" >
     update task
     set cid = #{cid,jdbcType=VARCHAR},
       uid = #{uid,jdbcType=INTEGER},
       filename = #{filename,jdbcType=VARCHAR},
       file_url = #{fileUrl,jdbcType=VARCHAR},
       created = #{created,jdbcType=TIMESTAMP},
       updated = #{updated,jdbcType=TIMESTAMP},
       remark = #{remark,jdbcType=VARCHAR},
       status = #{status,jdbcType=INTEGER}
     where id = #{id,jdbcType=INTEGER}
   </update>

   <resultMap id="TaskResultMap" type="com.sun123.springboot.entity.Task" extends="BaseResultMap">
     <association property="course" resultMap="com.sun123.springboot.mapper.CourseMapper.BaseResultMap"></association>
   </resultMap>
   <select id="taskList" resultMap="TaskResultMap">
     SELECT t.*,c.* FROM task t LEFT JOIN course c ON t.cid=c.c_num
   </select>

 </mapper>

<association property="course" resultMap="com.sun123.springboot.mapper.CourseMapper.BaseResultMap"></association>这种写法直接引入了CourseMApper.xml中的字段信息，不需要再次定义，比较简洁。

接下来以Bootstrap table分页插件为例，实现完整的调用

StuService.java：

 //bootstrap table分页插件，数据返回
 BootstrapPage showTask(int offset, int limit,String search);

StuServiceImpl.java：

     /**
      * @Description //bootstrap table分页插件，数据返回
      * @Date 2019-04-04 19:54
      * @Param [limit, offset]
      * @return com.sun123.springboot.entity.bootstrap.PageHelper
      **/
     @Override
     public BootstrapPage showTask(int offset, int limit,String search) {
         BootstrapPage bootstrapPage = new BootstrapPage();
                     //pageNumber    pageSize
         Page pages = PageHelper.startPage(offset, limit);

         List<Task> taskList = taskMapper.taskList();
         bootstrapPage.setRows(taskList);
         bootstrapPage.setTotal((int)pages.getTotal());
         return bootstrapPage;
     }

StuController.java：

     @GetMapping("pageInfo")
     @ResponseBody
     public BootstrapPage pageInfo(int offset, int limit, String search){
         System.out.println("======"+offset+"==="+limit+"====="+search+"=====");
         BootstrapPage page = stuService.showTask(offset, limit,search);
         return page;
     }

后台查询结果：

 Task{id=25, cid='04021611', uid=3, filename='呵呵呵', fileUrl='http://192.168.83.133/images/2019/03/24/1 - 副本1553391128920311.jpg', created=Sun Mar 24 09:32:11 CST 2019, updated=Sun Mar 24 09:32:11 CST 2019, remark='5263', status=0,
  course=Course{id=25, cNum='04021611', cName='Hadoop数据分析平台Ⅰ', remark='5263', status=0}}

表格展示时，操作如下：

 $(function() {
                 $('#table').bootstrapTable({
                     url: 'pageInfo',
                     pagination: true, //是否显示分页（*）
                     sortable: false, //是否启用排序
                     sortOrder: "asc", //排序方式
                     //toolbar: '#toolbar', //工具按钮用哪个容器
                     //method:'post',
                     //sortable: true,//排序
                     showColumns: true,//是否显示 内容列下拉框
                     //clickToSelect: true,//点击选中checkbox
                     sidePagination: "server", //分页方式：client客户端分页，server服务端分页（*）
                     pageNumber: 1, //初始化加载第一页，默认第一页
                     pageSize: 5, //每页的记录行数（*）
                     pageList: [5, 10, 50, 100], //可供选择的每页的行数（*）
                     showRefresh: true,//是否显示刷新按钮
                     showToggle: true,//是否显示详细视图和列表视图的切换按钮
                     //search: true, //是否显示表格搜索，此搜索是客户端搜索，不会进服务端，所以，个人感觉意义不大
                     //queryParamsType: "", //默认值为 'limit' ,在默认情况下 传给服务端的参数为：offset,limit,sort
                     // 设置为 ''  在这种情况下传给服务器的参数为：pageSize,pageNumber
                     showExport: true,//是否显示导出
                     columns: [{
                         field: 'course.cName',
                         title: '课程名称'
                     }, {
                         field: 'filename',
                         title: '文件名称'
                     }, {
                         field: 'remark',
                         title: '说明'
                     },{
                         field: 'created',
                         title: '上传时间'
                     },{
                         field: 'fileUrl',
                         title: '下载地址'
                     }, ]
                 });
             })

说明：course对象属性的使用需要多写一层，例如：course.cName