MyBatis - 映射配置文件：SQL编写（案例）

MyBatis - 映射配置文件：SQL编写

一般性CRUD

1 查询所有：selectAll

<mapper namespace="StudentMapper">
	<!--
        select：查询功能的标签
        id属性：唯一标识
        resultType属性：指定结果映射对象类型，可以不写
        parameterType属性：指定参数映射对象类型，可以不写
    -->
    <select id="selectAll" resultType="student">
        SELECT * FROM student
    </select>
</mapper>

对应java语句：
List<Student> list = sqlSession.selectList("StudentMapper.selectAll");
sqlSession.close();

2 依据id查询：selectById

<mapper namespace="StudentMapper">
	<select id="selectById" resultType="student" parameterType="int">
        SELECT * FROM student WHERE id = #{id}
    </select>
</mapper>

对应java语句：
Student stu = sqlSession.selectOne("StudentMapper.selectById", 3);
sqlSession.close();

3 模糊查询：姓名含有“张” - 三种方式

<mapper namespace="StudentMapper">
	<select id="findByName" resultType="com.itheima.domain.Student" parameterType="String">
        <!-- 1 -->
        select * from student where name like '%${value}%'
        <!-- 2 -->
        select * from student where name like concat{'%', #{name}, '%'}
        <!-- 3 -->
        select * from student where name like #{name}
    </select>
</mapper>

对应java语句：
<!-- 1 -->
List<Student> list = sqlSession.selectList("StudentMapper.findByName", "张");
<!-- 2 -->
List<Student> list = sqlSession.selectList("StudentMapper.findByName", "张");
<!-- 3 -->
List<Student> list = sqlSession.selectList("StudentMapper.findByName", "%张%");
sqlSession.close();

4 查询student表记录数

<mapper namespace="StudentMapper">
	<select id="findCount" resultType="int">
        select count(*) from student
    </select>
</mapper>

对应java语句：
int count = sqlSession.selectOne("StudentMapper.findCount");
sqlSession.close();

5 插入数据

<mapper namespace="StudentMapper">
	<insert id="insert" parameterType="student">
        INSERT INTO student VALUES (#{id},#{name},#{age})
    </insert>
</mapper>

对应java语句：
int result = sqlSession.insert("StudentMapper.insert", stu);
sqlSession.commit();
sqlSession.close();

6 插入数据，并返回添加数据的主键id

<mapper namespace="StudentMapper">
	<!--
        keyColumn: 获取哪个字段的值
        keyProperty: 将查询结果封装到对象的哪个属性
        useGeneratedKeys: 是否返回最后添加数据的主键id值
    -->
    <insert id="saveUserReturnId2" keyColumn="id" keyProperty="id" useGeneratedKeys="true">
        insert into student values(#{id},#{name},#{age})
    </insert>
</mapper>

对应java语句：
sqlSession.insert("StudentMapper.saveUserReturnId2", student);
sqlSession.commit();
sqlSession.close();

7 修改数据：依据id设置student 的 name、age

<mapper namespace="StudentMapper">
	<update id="update" parameterType="student">
        UPDATE student SET name = #{name},age = #{age} WHERE id = #{id}
    </update>
</mapper>

对应java语句：
int result = sqlSession.update("StudentMapper.update",stu);
sqlSession.commit();
sqlSession.close();

8 依据id删除数据

<mapper namespace="StudentMapper">
	<delete id="delete" parameterType="int">
        DELETE FROM student WHERE id = #{id}
    </delete>
</mapper>

对应java语句：
int result = sqlSession.delete("StudentMapper.delete",5);
sqlSession.commit();
sqlSession.close();

动态SQL

9 多条件查询（可缺少部分条件）

<mapper namespace="StudentMapper">
	<!--第一个AND会被自动去除-->
    <select id="selectCondition" resultType="student" parameterType="student">
        <include refid="select"/>
        <where>
            <if test="id != null">
                AND id = #{id}
            </if>
            <if test="name != null">
                AND name = #{name}
            </if>
            <if test="age != null">
                AND age = #{age}
            </if>
        </where>
    </select>
</mapper>

对应java代码：
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
Student stu = new Student();
stu.setId(2);
stu.setName("李四");
List<Student> list = mapper.selectCondition(stu);
for (Student student : list) {
   System.out.println(student);
}
sqlSession.close();
inputStream.close();

10 实现 SELECT * FROM student WHERE id IN (1,2,5) - 参数类型list

<mapper namespace="StudentMapper">
	<!--  
		collection：参数容器类型， (list-集合， array-数组)。
		open：开始的 SQL 语句。
		close：结束的 SQL 语句。
		item：参数变量名。
		separator：分隔符。
	-->
    <!-- 范围查询: 查询条件是List -->
    <select id="selectByIds" resultType="student" parameterType="list">
        <include refid="select"/>
        <where>
            <foreach collection="list" open="id IN (" close=")" item="id" separator=",">
                #{id}
            </foreach>
        </where>
    </select>
</mapper>

对应java代码：
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
List<Integer> ids = new ArrayList<>();
ids.add(1);
ids.add(2);
ids.add(5);
List<Student> list = mapper.selectByIds(ids);
for (Student student : list) {
   System.out.println(student);
}
sqlSession.close();
inputStream.close();

11 实现 SELECT * FROM student WHERE id IN (1,2,5) - 参数类型array

<mapper namespace="StudentMapper">
	<!--注意: 参数类型为数组, parameterType类型必须设置为list-->
    <select id="findByIdsArray" resultType="Student" parameterType="list">
        SELECT * FROM student
        <where>
            <foreach collection="array" open="id in (" item="id" separator="," close=")">
                #{id}
            </foreach>
        </where>
    </select>
</mapper>

对应java代码：
Integer[] ids = {1,2,3};
List<Student> students = dao.findByIdsArray(ids);
for (Student s : students) {
   System.out.println(s);
}
sqlSession.close();
inputStream.close();

12 动态更新(修改)数据（可缺少部分参数）

<mapper namespace="StudentMapper">
	<update id="updateStu">
       update student set
       <set>
           <!-- 判断条件, 控制set后面的参数 逗号会自动控制 建议都写-->
            <if test="name !=null and name!=''">
                name = #{name},
            </if>
           <if test="age !=null and age!=0">
               age = #{age},
           </if>
       </set>
       <where>
           <if test="id!=null and id!=0">
               id=#{id}
           </if>
       </where>
   </update>
</mapper>

对应java代码：
Student stu = new Student();
stu.setId(1);
stu.setName("武2郎");
stu.setAge(18);
dao.updateStu(stu);
sqlSession.commit();
sqlSession.close();
inputStream.close();

抽取sql片段简化编写

<mapper namespace="StudentMapper">
   <select id="selectById" resultType="student" parameterType="int">
        SELECT * FROM student WHERE id = #{id}
   </select>
</mapper>

等价于： 

<mapper namespace="StudentMapper">
   <sql id="selectStudent">select * from student</sql>
   <select id="findById" parameterType="int" resultType="student">
       <include refid="selectStudent"></include> where id=#{id}
   </select>
</mapper>

数据表字段 与 JavaBean类属性 名称不一致

<mapper namespace="StudentMapper">
	<!--
		查询的【数据库中表列名】和实体类的【JavaBean类属性】名称不一致情况
		id标签：主键
		result标签：非主键
		property: 配置为实体类的属性名
		column:  配置为SQL列名
		若对象属性和列名一致时, 可以不配置. 但是为了代码的阅读性,建议都配置上.
	-->
	<resultMap id="userMap" type="com.itheima.domain.User">
  		<id property="userId" column="id"></id>
  		<result property="userName" column="username"></result>
  		<result property="userAddress" column="address"></result>
  		<result property="userSex" column="sex"></result>
  		<result property="userBirthday" column="birthday"></result>
	</resultMap>
    对应：
    <select id="findAll" resultMap="userMap">
 		select * from user
	</select>
</mapper>