【Mybatis】动态SQL

查询条件不确定，需要根据情况产生SQL语法，这种情况叫动态SQL

StudentMapper.xml

<?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="cn.qblank.entity.Student">
<!-- 当表名和字段名不一样的时候可以设置resultMap进行映射 -->
<resultMap type="student" id="studentMap">
<id property="id" column="stu_id"/>
<result property="name" column="stu_name"/>
<result property="sal" column="stu_sal"/>
</resultMap>

<!-- 批量添加学生 -->
<select id="addAll" parameterType="student" resultMap="studentMap">
insert into t_students(stu_id,stu_name,stu_sal) values(#{id},#{name},#{sal})
</select>

<!-- 动态查询学生 -->
<!-- mybatis会将查询出来的表记录和studentMap这个id所对应的映射结果相互匹配 -->
<select id="dynafindAll" parameterType="map" resultMap="studentMap">
select stu_id,stu_name,stu_sal from t_students
<where>
<if test="pid!=null">
and stu_id = #{pid}
</if>
<if test="pname!=null">
and stu_name = #{pname}
</if>
<if test="psal!=null">
and stu_sal = #{psal}
</if>
</where>
</select>

<!-- 动态更新 -->
<update id="dynaUpdate" parameterType="map">
update t_students
<set>
<if test="uname!=null">
stu_name = #{uname},
</if>
<if test="usal!=null">
stu_sal = #{usal},
</if>
</set>
where stu_id = #{uid}
</update>

<!-- 动态删除(数组) -->
<delete id="dynaDeleteArray" parameterType="int">
delete from t_students where stu_id in
<!-- foreach用于迭代数组元素
collection:表示容器
open表示开始符号
close表示结束符合
separator表示元素间的分隔符
item表示迭代的数组，属性值可以任意，但提倡与方法的数组名相同
#{ids}表示数组中的每个元素值
-->
<foreach collection="array" open="(" close=")" item="ids" separator=",">
#{ids}
</foreach>
</delete>
<!-- 动态删除(集合) -->
<delete id="dynaDeleteList" parameterType="int">
delete from t_students where stu_id in
<foreach collection="list" open="(" close=")" item="ids" separator=",">
#{ids}
</foreach>
</delete>

<!-- 动态添加 -->
<insert id="dynaAdd" parameterType="student">
insert into t_students(<include refid="key"/>) values(<include refid="value"/>)
</insert>
<!-- sql片段对应字段名,id属性值任意 -->
<sql id="key">
<!-- 去掉最后一个, -->
<trim suffixOverrides=",">
<if test="id!=null">
stu_id,
</if>
<if test="name!=null">
stu_name,
</if>
<if test="sal!=null">
stu_sal,
</if>
</trim>
</sql>
<!-- sql片段对应字段名,id属性值任意 -->
<sql id="value">
<!-- 去掉最后一个, -->
<trim suffixOverrides=",">
<if test="id!=null">
#{id},
</if>
<if test="name!=null">
#{name},
</if>
<if test="sal!=null">
#{sal},
</if>
</trim>
</sql>
</mapper>

然后在dao层StudentDao封装相应的方法

/**
* 动态添加
* @param student
*/
public void dynaAdd(Student student){
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
int rows = sqlSession.insert(Student.class.g
d293
etName() +".dynaAdd",student);
System.out.println("更新了" + rows + "行");
sqlSession.commit();
} catch (Exception e) {
e.printStackTrace();
sqlSession.rollback();
throw e;
}finally{
MybatisUtil.closeSqlSession();
}
}

/**
* 动态更新
* @param id
* @param name
* @param sal
*/
public void dynaUpdate(Integer id,String name,Double sal){
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
Map<String, Object> map = new LinkedHashMap<>();
map.put("uid", id);
map.put("uname", name);
map.put("usal", sal);
int rows = sqlSession.update(Student.class.getName() +".dynaUpdate",map);
System.out.println("更新了" + rows + "行");
sqlSession.commit();
} catch (Exception e) {
e.printStackTrace();
sqlSession.rollback();
throw e;
}finally{
MybatisUtil.closeSqlSession();
}
}

/**
* 动态查询
* @return
*/
public List<Student> dynafindAll(Integer id,String name,Double sal){
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
Map<String, Object> map = new LinkedHashMap<>();
map.put("pid", id);
map.put("pname", name);
map.put("psal", sal);
return sqlSession.selectList(Student.class.getName() +".dynafindAll",map);
} catch (Exception e) {
e.printStackTrace();
throw e;
}finally{
MybatisUtil.closeSqlSession();
}
}

/**
* 动态删除(根据ID批量删除学生(数组版本))
* @param id
* @param name
* @param sal
*/
public void dynaDeleteArray(int...ids){
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
int rows = sqlSession.update(Student.class.getName() +".dynaDeleteArray",ids);
System.out.println("更新了" + rows + "行");
sqlSession.commit();
} catch (Exception e) {
e.printStackTrace();
sqlSession.rollback();
throw e;
}finally{
MybatisUtil.closeSqlSession();
}
}
/**
* 动态批量删除(集合)
* @param ids
*/
public void dynaDeleteList(List<Integer> ids){
SqlSession sqlSession = null;
try {
sqlSession = MybatisUtil.getSqlSession();
int rows = sqlSession.update(Student.class.getName() +".dynaDeleteList",ids);
System.out.println("更新了" + rows + "行");
sqlSession.commit();
} catch (Exception e) {
e.printStackTrace();
sqlSession.rollback();
throw e;
}finally{
MybatisUtil.closeSqlSession();
}
}

这样就实现了mybatis的动态SQL,使代码变得更加灵活。