MyBatis中的多条件查询讲解

一：使用动态SQL完成多条件查询

a:使用if+where实现多条件查询

首先场景需求，有 个年级和班级表，第一个要求是根据模糊查询姓名，和年龄大小进行条件查询，接口层方法

 public  List<student>  getStudentByIf(student stu);

　　其次是映射文件的配置

 <select id="getStudentByIf" parameterType="stu" resultType="stu">select * from student       <where>   <if test="stuAge!=0">   and stuAge>#{stuAge}       </if> <if test="stuName!=null"> and stuName LIKE '%' #{stuName} '%'             </if>   </where></select>

测试

 studentDao dao = MyBatis.getSessionTwo().getMapper(studentDao.= "z"List<student> list="----------"+

----------zhangyu
----------zy
----------zy
----------zhang

b：choose when 分类

这种方式和java中choose循环结构原理是一样的，判断多种情况，只要修改一下映射文件即可

接口 类

  public List<student> getAllStudentByLike(Map<String, Object> userMap);  //使用map作为参数

映射文件

 <select id="getAllStudentByLike" parameterType="Map" resultType="stu">select * from student<where><choose><when test="stuName!=null"> stuName like CONCAT('%',#{stuName},'%')</when><when test="stuAge!=0"> stuAge> #{stuAge}</when>

<otherwise>
    1=1
</otherwise>

</choose></where></select>

结果

zhangyu
zy
zy
zhang

c:使用foreach完成复杂 查询，有三种方式，

第一种：传入的参数为数组类型

//传一组 xueshengID public List<student> getStudentBystuId_foreach_array(Integer[] ints);




映射文件配置 <!--跟据学生id查询学生Interger-->
    <select id="getStudentBystuId_foreach_array" resultMap="studentList">select * from student<if test="array.length>0">where stuId IN/*数组形式传入学生Id*/<foreach collection="array" item="stu" open="(" separator="," close=")">  #{stu}</foreach>
        </if>
    </select>

测试类

  Integer[] ints = {2,3,4};
        List<student> list = dao.getStudentBystuId_foreach_array(ints);for (student item:list) {
            System.out.println(item.getStuName());
        }

第二种：传入list集合

   public List<student> getStudentBystuId_foreach_list(List<Integer> list);

  <!--跟据学生id查询学生list方式--><select id="getStudentBystuId_foreach_list" resultMap="studentList">select * from student<if test="list.size>0">where stuId IN
        /*集合形式传入学生Id*/<foreach collection="list" item="stu" open="(" separator="," close=")">#{stu}</foreach></if></select>

测试：

 studentDao dao = MyBatis.getSessionTwo().getMapper(studentDao.class);
        Integer ints = 2;
        List<Integer> list = new ArrayList<Integer>();
        list.add(ints);
        List<student> stulist = dao.getStudentBystuId_foreach_list(list);
        for (student item:stulist) {
            System.out.println(item.getStuName());
        }

第三种：根据Map集合

 public List<student> getStudentBystuId_foreach_map(Map<String, Object> stuMap);

 <!--跟据学生id查询学生map方式--><select id="getStudentBystuId_foreach_map" resultMap="studentList">select * from student where stuId IN
        /*集合形式传入学生Id*/<foreach collection="stuId" item="stu" open="(" separator="," close=")">    <!--collection是自己定义的，就是map的key值-->#{stu}</foreach></select>

  Map<String ,Object> stumap = new HashMap<String, Object>();
        List<Integer> listStuId = new ArrayList<Integer>();
        listStuId.add(2);
        listStuId.add(3);
        listStuId.add(4);
        stumap.put("stuId",listStuId);
         List<student> list = dao.getStudentBystuId_foreach_map(stumap);
        for (student item:list
             ) {
            System.out.println(item.getStuName());
        }

打印结果可以执行以下。

d;一对多的两种实现方式

主要是resultMapper里的配置不同

接口方法

 public grade getGradeById(int gradeId);

映射文件配置

 <!--实现一 对多的第一中实现--><resultMap id="gradeMapOne" type="grade"><id column="gradeId" property="gradeId"></id><result column="gradeName" property="gradeName"></result><collection property="gatStudent" ofType="stu"><id column="stuUd" property="stuId"></id><result column="stuName" property="stuName"></result><result column="stuAge" property="stuAge"></result></collection></resultMap><!--实现一 对多的第二中实现--><resultMap id="gradeMap" type="entity.grade"><id column="gradeId" property="gradeId"></id><result column="gradeName" property="gradeName"></result><collection property="gatStudent" ofType="student" select="getStudentById" column="gradeId"></collection>    <!--column的值主要作为下次查询的条件，既查询学生的条件--></resultMap>

    <select id="getGradeById" resultMap="gradeMapOne">select * from grade,student where grade.gradeId = student.stuGrade and gradeId = #{gradeId}</select><!--ddddddddddddddddddd--><select id="getGradeById" resultMap="gradeMap">select * from grade where gradeId=#{gradeId}</select><select id="getStudentById" resultType="entity.student">select * from student where stuGrade = #{stuGrade}</select>

  @Testpublic void  TestConn(){
       gradeDao dao = MyBatis.getSessionTwo().getMapper(gradeDao.class);

       grade grade = dao.getGradeById(1);       for (student item:grade.getGatStudent()            ) {
           System.out.println(item.getStuName());
       }

    }

两种方式都能实现，打印效果

方案一打印效果

==> Preparing: select * from grade,student where grade.gradeId = student.stuGrade and gradeId = ? ============一条sql
==> Parameters: 1(Integer)
<== Columns: gradeId, gradeName, stuId, stuName, stuAge, stuGrade
<== Row: 1, S1297, 2, zhangyu, 19, 1
<== Row: 1, S1297, 3, zy, 20, 1
<== Row: 1, S1297, 4, zy, 21, 1
<== Total: 3
zhangyu
zy
zy

Process finished with exit code 0

方案二打印效果

==> Preparing: select * from grade where gradeId=? ==========第一条sql
==> Parameters: 1(Integer)
<== Columns: gradeId, gradeName
<== Row: 1, S1297
====> Preparing: select * from student where stuGrade = ? ==========第二条sql
====> Parameters: 1(Long)
<==== Columns: stuId, stuName, stuAge, stuGrade
<==== Row: 2, zhangyu, 19, 1
<==== Row: 3, zy, 20, 1
<==== Row: 4, zy, 21, 1
<==== Total: 3
<== Total: 1
zhangyu
zy
zy

Process finished with exit code 0

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