MyBatis结果集映射的实现示例

<resultMap id="BaseResultMap" type="com.lilith.entity.User">
  <id column="id" property="id" />
  <result column="user_name" property="userName" />
  <result column="real_name" property="realName" />
  <result column="sex" property="sex" />
</resultMap>

<id property="id" column="user_id" javaType="int" jdbcType="INTEGER" />

<result property="name" column="user_name" javaType="String" jdbcType="VARCHAR" />

<association property="address" javaType="Address" column="address_id" select="selectAddressById" />

<collection property="posts" javaType="ArrayList" column="id" ofType="Post" select="selectPostsForBlog"/>

<!-- 1️⃣、定义 resultMap -->
<resultMap id="userResultMap" type="User">
	<id property="id" column="user_id"/>
	<result property="userName" column="user_name"/>
	<result property="password" column="user_pwd"/>
</resultMap>
<!-- 2️⃣、在查询中引用 resultMap -->
<select id="selectUserById" resultMap="userResultMap" parameterType="int">
	SELECT user_id, user_name, user_pwd FROM users WHERE user_id = #{id}
</select>

<resultMap id="addressMap" type="org.dllwh.mybatis.model.Address">
  <id property="id" column="addr_id"/>
  <result property="street" column="street"/>
  <result property="city" column="city"/>
  <result property="zipCode" column="zipCode"/>
</resultMap>
<resultMap id="userWithAddressMap" type="User">
  <id property="id" column="id"/>
  <result property="userName" column="userName"/>
  <result property="nickName" column="nickName"/>
  <!-- 一对一关联：使用 association 标签 -->
  <association property="address" resultMap="addressMap" />
</resultMap>
<select id="selectUserWithAddress" resultMap="userWithAddressMap" parameterType="int">
	select suu.*, a.* from sys_upms_user suu
	left join address a on suu.id = a.user_id
	where id = #{userId}
</select>

<!--
	select属性：指定用哪个查询来查询当前属性的数据
	column属性：设置当前结果集中哪列的数据作为select属性指定的查询方法需要参数
-->
<resultMap id="userWithAddressMap" type="User">
  <id property="id" column="user_id"/>
  <result property="userName" column="user_name"/>
  <result property="password" column="user_pwd"/>
  <!-- 关联映射，通过 user_id 关联地址 -->
  <association property="address" column="id" select="selectAddressByUserId"/>
</resultMap>
<!-- 1️⃣、根据userId查询用户 -->
<select id="selectUserWithAddress" resultMap="userWithAddressMap" parameterType="int">
    SELECT user_id, user_name, user_pwd FROM users WHERE user_id = #{id}
</select>
<!-- 2️⃣、根据userId查询所具有的地址信息 -->
<!-- 定义查询地址的 SQL -->
<select id="selectAddressByUserId" resultType="Address" parameterType="int">
    SELECT addr_id AS id, street, city, zip_code AS zipCode FROM address WHERE user_id = #{userId}
</select>

<!--定义User基本属性映射规则-->
<resultMap id="userMap" type="org.dllwh.mybatis.model.SysUser">
  <id property="id" column="id"/>
  <result property="username" column="username" />
	<result property="age" column="age" />
	<result property="address" column="address" />
  <collection property="roles" resultMap="userRoleMap"/>
</resultMap>

<resultMap id="userRoleMap" type="org.dllwh.mybatis.model.SysRole" >
  <id property="id" column="roleId"/>
  <result property="roleName" column="roleName"/>
  <result property="roleCode" column="roleCode"/>
</resultMap>

<select id="getUserLst" resultMap="userMap">
  SELECT suu.*, sur.*
  from sys_upms_user suu
  LEFT JOIN sys_upms_user_role suur on suur.userId = suu.id
  LEFT JOIN sys_upms_role sur on suur.roleId = sur.id
</select>

public interface TypeHandler<T> {
	// 将数据库类型转换为Java类型
	T fromDatabaseType(Object databaseValue);
	// 将Java类型转换为数据库类型
	Object toDatabaseType(T javaObject);
}

<resultMap id="userResultMap" type="User">
	<result column="name" property="name" typeHandler="com.example.MyCustomTypeHandler"/>
</resultMap>

public class MyCustomTypeHandler implements TypeHandler<String> {
  @Override
  public String fromDatabaseType(Object databaseValue) {
    // 将数据库类型转换为Java类型
    return (String) databaseValue;
  }
  @Override
  public Object toDatabaseType(String javaObject) {
    // 将Java类型转换为数据库类型
    return javaObject;
  }
}