MyBatis Mapper.XML 标签使用说明

 直接将值返回给对象

<select id="list" resultType="com.vipsoft.base.entity.UserInfo">
   SELECT Id,Title FROM User
</select>

如果字段和属性名不一致时，通过 resultMap 做映射

<resultMap id="StudentResult" type="com.mybatis3.domain.Student">
  <id column="stud_id" property="studId"  jdbcType="VARCHAR"/>
  <result column="user_name" property="name"  jdbcType="VARCHAR"/>
  <result column="email"  property="email"  jdbcType="VARCHAR" />
  <result column="phone"  property="phone"  jdbcType="VARCHAR" />
  <result column="status" property="status" jdbcType="INTEGER" />
  <result column="create_time" property="createTime" jdbcType="TIMESTAMP" />
</resultMap>

<select id="findAllStudents" resultMap="StudentResult" >
  SELECT * FROM STUDENTS
</select>

实体引用另一个实体的查询结果返回

<resultMap type="Course" id="CourseResult">
  <id column="course_id" property="courseId"/>
  <result column="name" property="name"/>
  <result column="description" property="description"/>
  <result column="start_date" property="startDate"/>
  <result column="end_date" property="endDate"/>
</resultMap>
  
<resultMap type="Tutor" id="TutorResult">
  <id column="tutor_id" property="tutorId"/>
  <result column="tutor_name" property="name"/>
  <result column="email" property="email"/>
  <collection property="courses" resultMap="CourseResult"/>
</resultMap>
  
<select id="findTutorById" parameterType="int" resultMap="TutorResult">
  SELECT T.TUTOR_ID, T.NAME AS TUTOR_NAME, EMAIL, C.COURSE_ID, C.NAME, DESCRIPTION, START_DATE, END_DATE
  FROM TUTORS T LEFT OUTER JOIN ADDRESSES A ON T.ADDR_ID=A.ADDR_ID
  LEFT OUTER JOIN COURSES C ON T.TUTOR_ID=C.TUTOR_ID
  WHERE T.TUTOR_ID=#{tutorId}
</select>

choose 该方式适用于多个条件中选择一个满足条件的来生成sql

<select id="searchCourses" parameterType="hashmap" resultMap="CourseResult">
  SELECT * FROM COURSES
  <choose>
    <when test="searchBy == 'Tutor'">
      WHERE TUTOR_ID= #{tutorId}
    </when>
    <when test="searchBy == 'CourseName'">
      WHERE name like #{courseName}
    </when>
    <otherwise>
      WHERE TUTOR start_date  &gt;= now()
    </otherwise>
  </choose>
</select>

where 适用于从多个条件中选择所有满足条件的来构成condtions

<select id="searchCourses" parameterType="hashmap" resultMap="CourseResult">
  SELECT * FROM COURSES
  <where>  
    <if test=" tutorId != null ">
      TUTOR_ID= #{tutorId}
    </if>
    <if test="courseName != null">
      AND name like #{courseName}
    </if>
    <if test="startDate != null">
      AND start_date  &gt;= #{startDate}
    </if>
    <if test="endDate != null">
      AND end_date  &lt;= #{endDate}
    </if>
  </where>
</select>

foreach

<select id="selectUserByListId" parameterType="com.ys.vo.UserVo" resultType="com.ys.po.User">
select * from user
  <where>
    <!--
    collection:指定输入对象中的集合属性.该属性的值有三种：list,array,map，根据传入的集合类型而设定该值。
    item:每次遍历生成的对象
    index:当前迭代的次数
    open:开始遍历时的拼接字符串
    close:结束时拼接的字符串
    separator:遍历对象之间需要拼接的字符串
    select * from user where 1=1 and id in (1,2,3)
    -->
    <foreach collection="list" item="id" open="(" separator="," close=")">
     #{id}
    </foreach>
  </where>
</select>

select * from user where id=1 or id=2 or id=3

<select id="selectUserByListId" parameterType="com.ys.vo.UserVo" resultType="com.ys.po.User">
select * from user
  <where>
    <foreach collection="list" item="id" open="and (" close=")" separator="or">
       id=#{id}
    </foreach>
  </where>
</select>

< sql >标签
该标签主要定义复用的sql语句片段，在执行的sql语句标签直接引用即可。可以提高编码效率、简化代码和提高可读性。

需要配置id熟悉，表示该sql片段的唯一标识。

引用:通过<include refid=" " / >标签引用，refid的值就是< sql>的id属性的值。

<sql id="Base_Column_List">
  id, question, answer 
</sql>
<select id="selectByPrimaryKey" parameterType="java.lang.Long" resultMap="BaseResultMap">
  select 
  <include refid="Base_Column_List" />
  from java
  where id = #{id,jdbcType=BIGINT}
</select> 

<set> : 主要用来替换sql语句中的set字段，一般在update中使用。

<update>
  update user 
  <set>
    <if test="name != null and name.length()>0">name = #{name},</if>
    <if test="age != null and age .length()>0">age = #{age },</if>
  </set>
  where id = #{id}
</update>　 

批量更新，一次执行多条SQL

<update>
    <foreach collection="list" item="item" index="index" separator=";">
        update user 
        <set>
            <if test="name != null and name.length()>0">name = #{name},</if>
            <if test="age != null and age .length()>0">age = #{age },</if>
        </set>
        <where>
            <if test="id != null and id != ''">
                AND id = #{id,jdbcType=VARCHAR}
            </if>
            <if test="userName != null and userName != ''">
                <bind name="bindUserName" value="'%' + userName + '%'" />
                AND UserName like #{bindUserName}
            </if> 
            <if test="status != null">
                AND Status = #{status,jdbcType=INTEGER}
            </if>
        </where>
    </foreach>
</update>  

<trim> : 是一个格式化的标记，可以完成set或者是where标记的功能。

select * from user 
<trim prefix="WHERE" prefixoverride="AND |OR">
  <if test="name != null and name.length()>0"> AND name=#{name}</if>
  <if test="age != null and age.length()>0"> AND age=#{age}</if>
</trim> 


假如说name和age的值都不为null的话打印的SQL为：select * from user where name = ‘xx’ and age = ‘xx’
在where的后面是不存在第一个and的，上面两个属性的意思如下：
　　prefix：前缀　　　　　　
　　prefixoverride：去掉第一个and或者是or 
 

update user
<trim prefix="set" suffixoverride="," suffix=" where id = #{id} ">
  <if test="name != null and name.length()>0"> name=#{name} , </if>
  <if test="age!= null and age.length()>0"> age=#{age} ,  </if>
</trim>
假如说name和age的值都不为null的话打印的SQL为：update user set name=‘xx’ , age=‘xx’ where id=‘x’

在age='xx’的后面不存在逗号，而且自动加了一个set前缀和where后缀，上面三个属性的意义如下，其中prefix意义如上：
　　 suffixoverride：去掉最后一个逗号（也可以是其他的标记，就像是上面前缀中的and一样）
　 　suffix：后缀 

 choose & foreach list 有一个值，条件=，有多个值 in 

<update id="updateStatus" parameterType="java.util.ArrayList" >
  update User
  set Status = 1,UpdateTime=(select GETDATE())
  <choose>
    <when test="idList != null and idList.size==1">
      WHERE Id= #{id,jdbcType=VARCHAR}
    </when>
    <when test="idList != null and idList.size>1">
      WHERE Id in
      <foreach collection="idList" item="id" open="(" close=")" separator=",">
        <if test="id != null and id != '' ">
          #{id,jdbcType=VARCHAR}
        </if>
      </foreach>
    </when>
    <otherwise>
      WHERE 1=0
    </otherwise>
  </choose>
</update>