批处理

  <select id="getAdsByGroupIds" resultMap="adInfoWithGroupId">
	  SELECT
		ai.*, gam.group_id
	  FROM
		group_ad_mapping AS gam
	  LEFT JOIN
		ad_info AS ai
	  ON
		gam.creative_id = ai.creative_id
	  WHERE
		gam.group_id in
	  <foreach collection="list" item="item" index="index" separator="," open="(" close=")">
		  #{item}
	  </foreach>
	  ORDER BY
		ai.create_at DESC
  </select>

一对多

java类

public class SalesLead {
    private Long id;
    private Long clientId;
    private Integer userId;
    private Integer salesUserId;
    private Integer agentUserId;
    private Integer saleStatus = 0;
    private Integer isDeal = 0;
    private Integer isRead = 0;
    private BigDecimal totalMoney = new BigDecimal("0");
    private BigDecimal prepaid = new BigDecimal("0");
    private String memo = "";
    private String fromOpenid = "";
    private String toOpenid = "";
    private String des = "";
    private String title = "";
    private Timestamp createTime = new Timestamp(System.currentTimeMillis());
    private Timestamp updateTime = new Timestamp(System.currentTimeMillis());
    private Timestamp closeTime;

    private List<SalesLeadFollow> follows;
    //getter and settter
}

    <resultMap id="salesLeadMap" type="com.company.sales.pojo.SalesLead">
        <id property="id" column="id"/>
        <result property="clientId" column="client_id"/>
        <result property="userId" column="user_id"/>
        <result property="salesUserId" column="sales_user_id"/>
        <result property="agentUserId" column="agent_user_id"/>
        <result property="saleStatus" column="sale_status"/>
        <result property="isDeal" column="is_deal"/>
        <result property="isRead" column="is_read"/>
        <result property="totalMoney" column="total_money"/>
        <result property="prepaid" column="prepaid"/>
        <result property="memo" column="memo"/>
        <result property="fromOpenid" column="from_openid"/>
        <result property="toOpenid" column="to_openid"/>
        <result property="des" column="des"/>
        <result property="title" column="title"/>
        <result property="createTime" column="create_time"/>
        <result property="updateTime" column="update_time"/>
        <result property="closeTime" column="close_time"/>

        <collection property="follows" ofType="com.company.sales.pojo.SalesLeadFollow" column="id" select="selectFollow" />
    </resultMap>

    <resultMap id="salesLeadFollowMap" type="com.company.sales.pojo.SalesLeadFollow">
        <id property="id" column="id"/>
        <result property="userId" column="user_id"/>
        <result property="followUserId" column="follow_user_id"/>
        <result property="followType" column="follow_type"/>
        <result property="salesLeadId" column="sales_lead_id"/>
        <result property="timeline" column="timeline"/>
        <result property="createTime" column="create_time"/>
    </resultMap>

    <select id="selectFollow" resultMap="salesLeadFollowMap">
        SELECT * from sales_lead_follow WHERE sales_lead_id = #{id} ORDER BY id DESC
    </select>

一对一

public class WbStatus extends BasePojo implements Serializable {
    private static final Logger log = LoggerFactory.getLogger(WbStatus.class);
    private static final long serialVersionUID = 1L;
    private Integer id;
    private Long sid = 0L;
    private String idstr = "";
    private Long mid = 0L;
    private Long userId = 0L;
    private String userScreenName = "";
    private String userProfileImageUrl = "";
    private String text = "";
    private String source = "";
    private String thumbnailPic = "";
    private String bmiddlePic = "";
    private String originalPic = "";
    private String retweetedStatusId = "";
    private String geo = "";
    private Integer repostsCount = 0;
    private Integer commentsCount = 0;
    private Integer attitudesCount = 0;
    private String visible = "";
    private String picUrls = "";
    private Timestamp createAt;
    private Timestamp updateAt;
    private String ad = "";
    private Integer isDeleted = 0;

    //逻辑字段，不是DB字段.
    private WbUser wbUser;


    public WbStatus() {
    }

Mybatis的代码片段:

    <resultMap id="wbStatusResultMap" type="com.weibosdk.pojo.WbStatus">
        <id property="id" column="id"/>
        <result property="sid" column="sid"/>
        <result property="idstr" column="idstr"/>
        <result property="mid" column="mid"/>
        <result property="userId" column="user_id"/>
        <result property="userScreenName" column="user_screen_name"/>
        <result property="userProfileImageUrl" column="user_profile_image_url"/>
        <result property="text" column="text"/>
        <result property="source" column="source"/>
        <result property="thumbnailPic" column="thumbnail_pic"/>
        <result property="bmiddlePic" column="bmiddle_pic"/>
        <result property="originalPic" column="original_pic"/>
        <result property="retweetedStatusId" column="retweeted_status_id"/>
        <result property="geo" column="geo"/>
        <result property="repostsCount" column="reposts_count"/>
        <result property="commentsCount" column="comments_count"/>
        <result property="attitudesCount" column="attitudes_count"/>
        <result property="visible" column="visible"/>
        <result property="picUrls" column="pic_urls"/>
        <result property="createAt" column="create_at"/>
        <result property="updateAt" column="update_at"/>
        <result property="ad" column="ad"/>
        <result property="isDeleted" column="is_deleted"/>
        <association property="wbUser" javaType="com.weibosdk.pojo.WbUser" select="selectWbUser" column="user_id">
        </association>
    </resultMap>

    <select id="selectWbUser" resultMap="com.weibosdk.dao.mapper.WbUserMapper.wbUserResultMap">
      SELECT * from wb_user WHERE u_id = #{userId} limit 1
    </select>

自定义 TypeHandler

@MappedJdbcTypes(JdbcType.VARCHAR)
@MappedTypes(Object.class)
public class JsonObjectTypeHandler implements TypeHandler {
    @Override
    public void setParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType) throws SQLException {
        if (parameter == null) {
            ps.setString(i, "");
            return;
        }
        ps.setString(i, Constants.GSON.toJson(parameter));
    }

    @Override
    public Object getResult(ResultSet rs, String columnName) throws SQLException {
        return rs.getString(columnName);
    }

    @Override
    public Object getResult(ResultSet rs, int columnIndex) throws SQLException {
        return rs.getString(columnIndex);
    }

    @Override
    public Object getResult(CallableStatement cs, int columnIndex) throws SQLException {
        return cs.getString(columnIndex);
    }
}

注册application.properties

mybatis.type-handlers-package=com.your.package.hanlders

使用

<result property="urlObjects" column="url_objects" typeHandler="com.your.package.hanlders.JsonObjectTypeHandler"/>

在 insert 语句中使用

#{s.urlObjects, typeHandler=com.your.package.hanlders.JsonObjectTypeHandler}

常见问题

Cannot define both nestedQueryId and nestedResultMapId

这是因为重复定义了. 典型的错误写法如下

<resultMap>
  <association property="user" resultMap="userMap" select="getByUid" column="user_id" />
</resultMap>

<select id="getByUid" resultMap="userMap">
  select * from wb_user where u_id = #{uid}
</select>

正确的写法

<association property="user" resultMap="userMap" select="getByUid" column="user_id" /> 修改为

<association property="user" select="getByUid" column="user_id" />