MyBatis多条件查询

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.class);
        student stu = new student();
        stu.setStuName("z");
       // stu.setStuAge(19);
        List<student> list=  dao.getStudentByIf(stu);
       
        for (student item:list) {
            System.out.println("----------"+item.getStuName());
        }


  打印效果

----------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>

  @Test
    public 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