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>
<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
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