Mybatis之XML映射文件

<sql id="userColumns"> ${alias}.id,${alias}.username,${alias}.password </sql>

<select
  id="findCustomerById"
  parameterType="Integer"
  resultType="com.itheima.po.Customer"
>
  SELECT * FROM t_customer WHERE id = #{id}
</select>
<insert
  id="addCustomer"
  parameterType="com.itheima.po.Customer"
  keyProperty="id"
  useGeneratedKeys="true"
>
  INSERT INTO t_customer(username,jobs,phone) VALUES (#{username}, #{jobs},
  #{phone})
</insert>
<!-- update和delete和insert实现非常接近 -->

<insert id="addCustomer" parameterType="com.itheima.po.Customer">
  <selectKey keyProperty="id" resultType="Integer" order="BEFORE">
    select if(max(id) is null, 1, max(id)+1) as new newId from t_customer
  </selectKey>
  INSERT INTO t_customer(id,username,jobs,phone) VALUES (#{id},#{username},
  #{jobs}, #{phone})
</insert>

<!-- 普通键值对存储 -->
<!-- 没有显式指定 resultMap -->
<select id="selectUsers" resultType="map">
  select id, username, hashedPassword from some_table where id = #{id}
</select>
<!--  将规范的JavaBean 映射到 ResultSet -->
<select id="selectUsers" resultType="com.someapp.model.User">
  select id, username, hashedPassword from some_table where id = #{id}
</select>
<!-- 如果列名和属性名没有精确匹配(不规范的JavaBean)，可以在 SELECT 语句中对列使用别名 -->
<select id="selectUsers" resultType="com.someapp.model.User">
  select user_id as "id", user_name as "userName", hashed_password as
  "hashedPassword" from some_table where id = #{id}
</select>

<!-- 非常复杂的语句 -->
<select id="selectBlogDetails" resultMap="detailedBlogResultMap">
  select B.id as blog_id, B.title as blog_title, B.author_id as blog_author_id,
  A.id as author_id, A.username as author_username, A.password as
  author_password, A.email as author_email, A.bio as author_bio,
  A.favourite_section as author_favourite_section, P.id as post_id, P.blog_id as
  post_blog_id, P.author_id as post_author_id, P.created_on as post_created_on,
  P.section as post_section, P.subject as post_subject, P.draft as draft, P.body
  as post_body, C.id as comment_id, C.post_id as comment_post_id, C.name as
  comment_name, C.comment as comment_text, T.id as tag_id, T.name as tag_name
  from Blog B left outer join Author A on B.author_id = A.id left outer join
  Post P on B.id = P.blog_id left outer join Comment C on P.id = C.post_id left
  outer join Post_Tag PT on PT.post_id = P.id left outer join Tag T on PT.tag_id
  = T.id where B.id = #{id}
</select>

<!-- 非常复杂的结果映射 -->
<resultMap id="detailedBlogResultMap" type="Blog">
  <constructor>
    <idArg column="blog_id" javaType="int"/>
  </constructor>
  <result property="title" column="blog_title"/>
  <association property="author" javaType="Author">
    <id property="id" column="author_id"/>
    <result property="username" column="author_username"/>
    <result property="password" column="author_password"/>
    <result property="email" column="author_email"/>
    <result property="bio" column="author_bio"/>
    <result property="favouriteSection" column="author_favourite_section"/>
  </association>
  <collection property="posts" ofType="Post">
    <id property="id" column="post_id"/>
    <result property="subject" column="post_subject"/>
    <association property="author" javaType="Author"/>
    <collection property="comments" ofType="Comment">
      <id property="id" column="comment_id"/>
    </collection>
    <collection property="tags" ofType="Tag" >
      <id property="id" column="tag_id"/>
    </collection>
    <discriminator javaType="int" column="draft">
      <case value="1" resultType="DraftPost"/>
    </discriminator>
  </collection>
</resultMap>