若依框架 ------- 三级联动之下拉框查询

联动

因为是查询要放在查询的位置

HTML页面（显示）

<li>
  学生学校：
<!--   <select id="school" name="sysSchool.schoolId">-->
  <select id="school" name="sysGrade.gradeSchool">
    <option value="">请选择学校</option>
  </select>
  学生年级：
<!--   <select id="grade" name="sysGrade.gradeId">-->
  <select id="grade" name="sysClasses.classesGrade">
    <option value="">请选择年级</option>
  </select>
  学生年级：
<!-- <select id="classes" name="sysClasses.classesId">-->
  <select id="classes" name="studentClass">
    <option value="">请选择班级</option>
  </select>
</li>

 js方法（都是重复的，区别：第一个是查全部，之后都是传参查的）

<script type="text/javascript">
  $(document).ready(function() {//页面加载时运行此函数  放在最前端
    $.ajax({
      url: ctx + "system/school/select",
      type: 'GET',
      success:function (data) {
        <!--清空下拉框中的缓存-->
        $("#school").empty();
        <!--避免下拉框的值不变-->
        $("#school").append("<option value=''>请选择学校</option>");
        <!--使用循环解析后端传来的数据，并用使用js动态拼接html语言-->
        for (var i = 0; i < data.length; i++){
          $("#school").append("<option value='" + data[i].schoolId + "'>" + data[i].schoolName + "</option>");
        }
      }
    });
    $("#school").change(function () {//同上面一样
      // alert($("#school").val())
      $.ajax({
        url: ctx + "system/grade/select",
        type: 'GET',
        data: {
          gradeSchool: $("#school").val(),
        },
        success:function (data) {
          $("#grade").empty();
          $("#grade").append("<option value=''>请选择年级</option>");
          for (var i = 0; i < data.length; i++){
            $("#grade").append("<option value='" + data[i].gradeId + "'>" + data[i].gradeName + "</option>");
          }
        }
      });
    });
    $("#grade").change(function () {//同上面一样
      $.ajax({
        url: ctx + "system/classes/select",
        type: 'GET',
        data: {
          classesGrade: $("#grade").val(),
        },
        success:function (data) {
          $("#classes").empty();
          $("#classes").append("<option value=''>请选择班级</option>");
          for (var i = 0; i < data.length; i++){
            $("#classes").append("<option value='" + data[i].classesId + "'>" + data[i].classesName + "</option>");
          }
        }
      })
    });
  })
</script>

controler层
school

@GetMapping("/select")
    @ResponseBody
    public List<SysSchool> select()
    {
        List<SysSchool> list = schoolService.selectSchoolList(new SysSchool());
        return  list;
    }

grade

@GetMapping("/select")
    @ResponseBody
    public List<SysGrade> select(Long gradeSchool)
    {
//        System.out.println("11111111111111111111");
//        System.out.println(gradeSchool);
        List<SysGrade> list1 = gradeService.selectGradeById1(gradeSchool);
        List<SysGrade> list = gradeService.selectGradeList(new SysGrade());
        return  list1;
    }

classes

@GetMapping("/select")
    @ResponseBody
    public List<SysClasses> select(Long classesGrade)
    {
        List<SysClasses> list1 = classesService.selectClassesById1(classesGrade);
        List<SysClasses> list = classesService.selectClassesList(new SysClasses());
        return  list1;
    }

mapper.xml(写sql语句的地方)
方法都一样，这里就不都写了，只写一个grade表的

<select id="selectClassesById1" parameterType="Long" resultMap="SysClassesResult">
    <include refid="selectClassesVo"/>
    where classes_grade = #{classesGrade}
  </select>

mapper.java

public List<SysGrade> selectGradeById1(Long gradeSchool);

service层

public List<SysGrade> selectGradeById1(Long gradeSchool);

serviceImpl层

@Override
    public List<SysGrade> selectGradeById1(Long gradeSchool)
    {
        return gradeMapper.selectGradeById1(gradeSchool);
    }

下拉框查询的传值

要先进行表连接，建立关系，不然怎么查，

表连接的

几个字段，还有SQL语句

<sql id="selectStudentVo">
        SELECT * FROM sys_student
            INNER JOIN sys_classes
            INNER JOIN sys_grade
            INNER JOIN sys_school
                ON sys_student.`student_class` = sys_classes.`classes_id`
                AND sys_classes.`classes_grade` = sys_grade.`grade_id`
                AND sys_grade.`grade_school` = sys_school.`school_id`
    </sql>

下拉框查询的
注意，这里需要改一下id的格式，不然查不了，是一个本人解决不了，或者本身就存在的问题，改字段类型，char，varchar都可以。后期解决会发布，也求大神改正。

<select id="selectStudentList" parameterType="SysStudent" resultMap="SysStudentResult">
    <include refid="selectStudentVo"/>
    <where>
      <if test="studentName != null and studentName != ''">
        AND student_name like concat('%', #{studentName}, '%')
      </if>
      <if test="abs != null and abs != ''">
        AND abs like concat('%', #{abs}, '%')
      </if>
      <if test="sysGrade.gradeSchool != null and sysGrade.gradeSchool != ''">
        AND sys_grade.grade_school =#{sysGrade.gradeSchool}
      </if>
      <if test="sysClasses.classesGrade != null and sysClasses.classesGrade != ''">
        AND sys_classes.classes_grade =#{sysClasses.classesGrade}
      </if>
      <if test="studentClass != null and studentClass != ''">
        AND student_class =#{studentClass}
      </if>
    </where>
    ORDER BY sys_student.`abs` DESC
    ,sys_student.`student_id` ASC
  </select>