mybatis学习

https://www.w3cschool.cn/mybatis/7zy61ilv.html

1. 常见的语法

• <select>
  <select id= "getId" paramerType="com.xx.xx" resultType="com.xx.xx">
  select id
  from a
  where id = #{id}
  </select>

• <insert>
  --支持返回自增组件id
  </insert id="insertId" parameterType="com.xx.xx" useGeneratedKeys="true" keyProperty="xx.id">
  insert into table_name (id,
  )
  values(#{xx.id,jdbcType=xx})
  </insert>

• <update>
  <update id="updateid">
  update table_name
  <set>
  id = #{id}
  </set>
  where id = #{id}
  </update>

• <delete id="delete" parameterType="com.xx">
  <delete>
  delete from table_name where id=#{id}
  </delete>
  1.1 参数引用
  参数引用使用格式：#{name}
  对象参数引用格式：#{object.name}
  如果引用的值在动态sql中，那么就不需要加#
  2 resultMap --定义mysql格式和输出格式的定义方式
  两个基本属性，id标记resultMap的名称，type表示映射之后的类名称
  <resultMap id="myMap" type="com.xx.xx">
  <id column="id" > </id>
  <result column="abc" property="ABC" jdbcType="varchar" javaType="java.Lang.String"></result>
  <resultMap>
  resultMap的使用方式
  <select id="select" resultMap="myMap">
  select id from table_name
  </select>

3. sql 复用
   <sql id = "baseColumns">
   id,gmt_create
   </sql>
   定义的sql复用格式举例：<include refid="baseColumns"></include>
   <select id="">
   select <include refid="baseColumns"></include>
   from a
   </select>
4. 动态sql

• <if> if动态判断
  举例
  <select>
  select id
  from a
  where status =0
  <if test='title != null'>title like #{title}</if>
  </select>

• <choose> // case when 判断

• <where> //消除where中多余的and

• <set> //消除动态语句中的，
  <update>
  update table
  <set>
  <if test="name != null">name=#{name} </if>
  </set>
  where id = #{id}
  </update>
• foreach //遍历数组
  <select>
  select if
  from table
  where id in
  <foreach item="item" index="index" collection="list" open="(" separator="," close=")">
  #{item}
  </foreach>
  </select>
  list传参：注意点：foreach中collection的属性值名称是传参的名称