MyBatis - 對映配置檔案：SQL編寫

一般性CRUD

1 查詢所有：selectAll

<mapper namespace="StudentMapper">
	<!--
        select：查詢功能的標籤
        id屬性：唯一標識
        resultType屬性：指定結果對映物件型別，可以不寫
        parameterType屬性：指定引數對映物件型別，可以不寫
    -->
    <select id="selectAll" resultType="student">
        SELECT * FROM student
    </select>
</mapper>

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

2 依據id查詢：selectById

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

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

3 模糊查詢：姓名含有“張” - 三種方式

<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>

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

4 查詢student表記錄數

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

對應java語句：
int count = sqlSession.selectOne("StudentMapper.findCount");
sqlSession.close();

5 插入資料

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

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

6 插入資料，並返回新增資料的主鍵id

<mapper namespace="StudentMapper">
	<!--
        keyColumn: 獲取哪個欄位的值
        keyProperty: 將查詢結果封裝到物件的哪個屬性
        useGeneratedKeys: 是否返回最後新增資料的主鍵id值
    -->
    <insert id="saveUserReturnId2" keyColumn="id" keyProperty="id" useGeneratedKeys="true">
        insert into student values(#{id},#{name},#{age})
    </insert>
</mapper>

對應java語句：
sqlSession.insert("StudentMapper.saveUserReturnId2", student);
sqlSession.commit();
sqlSession.close();

7 修改資料：依據id設定student 的 name、age

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

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

8 依據id刪除資料

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

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

動態SQL

9 多條件查詢（可缺少部分條件）

<mapper namespace="StudentMapper">
	<!--第一個AND會被自動去除-->
    <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>

對應java程式碼：
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 實現 SELECT * FROM student WHERE id IN (1,2,5) - 引數型別list

<mapper namespace="StudentMapper">
	<!--  
		collection：引數容器型別， (list-集合， array-陣列)。
		open：開始的 SQL 語句。
		close：結束的 SQL 語句。
		item：引數變數名。
		separator：分隔符。
	-->
    <!-- 範圍查詢: 查詢條件是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>

對應java程式碼：
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 實現 SELECT * FROM student WHERE id IN (1,2,5) - 引數型別array

<mapper namespace="StudentMapper">
	<!--注意: 引數型別為陣列, parameterType型別必須設定為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>

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

12 動態更新(修改)資料（可缺少部分引數）

<mapper namespace="StudentMapper">
	<update id="updateStu">
       update student set
       <set>
           <!-- 判斷條件, 控制set後面的引數 逗號會自動控制 建議都寫-->
            <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>

對應java程式碼：
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片段簡化編寫

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

等價於： 

<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>

資料表字段 與 JavaBean類屬性 名稱不一致

<mapper namespace="StudentMapper">
	<!--
		查詢的【資料庫中表列名】和實體類的【JavaBean類屬性】名稱不一致情況
		id標籤：主鍵
		result標籤：非主鍵
		property: 配置為實體類的屬性名
		column: 配置為SQL列名
		若物件屬性和列名一致時, 可以不配置. 但是為了程式碼的閱讀性,建議都配置上.
	-->
	<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>
    對應：
    <select id="findAll" resultMap="userMap">
		select * from user
	</select>
</mapper>