（十八）Mybatis自关联多对一查询方式

版权声明：如需转载，敬请标明出处。 https://blog.csdn.net/Aphysia/article/details/81071442

注：代码已托管在GitHub上，地址是：https://github.com/Damaer/Mybatis-Learning ，项目是mybatis-14-oneself-many2one，需要自取，需要配置maven环境以及mysql环境(sql语句在resource下的test.sql中)，觉得有用可以点个小星星，小菜鸟在此Thanks~
现在有个需求，给出当前的栏目的id，希望查出父辈栏目，父辈的父辈栏目等等信息。
数据表设计如下：

实体类设计：

package beans;

import java.util.Set;

public class NewsLabel {
  private Integer id;
  private String name;
  private NewsLabel parent;
  public Integer getId() {
    return id;
  }
  public void setId(Integer id) {
    this.id = id;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public NewsLabel getParent() {
    return parent;
  }
  @Override
  public String toString() {
    return "NewsLabel [id=" + id + ", name=" + name + ", parent=" + parent
            + "]";
  }
  public void setParent(NewsLabel parent) {
    this.parent = parent;
  }

}

sql接口定义：

public interface INewsLabelDao {
  NewsLabel selectParentByParentId(int pid);
}

mapper.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="dao.INewsLabelDao">
    <resultMap type="NewsLabel" id="newsLabelMapper">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <association property="parent"
                     javaType="NewsLabel"
                     select="selectParentByParentId"
                     column="pid"/>
    </resultMap>
    <select id="selectParentByParentId" resultMap="newsLabelMapper">
        select id,name,pid from newslabel where id=#{xxx}
    </select>
</mapper>

测试类：

public class MyTest {
  private INewsLabelDao dao;
  private SqlSession sqlSession;
  @Before
  public void Before(){
    sqlSession=MyBatisUtils.getSqlSession();
    dao=sqlSession.getMapper(INewsLabelDao.class);
  }
  @Test
  public void TestselectMinisterById(){
    NewsLabel children=dao.selectParentByParentId(7);

    System.out.println(children);

  }
  @After
  public void after(){
    if(sqlSession!=null){
      sqlSession.close();
    }
  }

}

查询出来结果：

[service] 2018-07-16 11:54:10,123 - dao.INewsLabelDao.selectParentByParentId -683  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - ==>  Preparing: select id,name,pid from newslabel where id=? 
[service] 2018-07-16 11:54:10,154 - dao.INewsLabelDao.selectParentByParentId -714  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - ==> Parameters: 7(Integer)
[service] 2018-07-16 11:54:10,174 - dao.INewsLabelDao.selectParentByParentId -734  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - ====>  Preparing: select id,name,pid from newslabel where id=? 
[service] 2018-07-16 11:54:10,174 - dao.INewsLabelDao.selectParentByParentId -734  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - ====> Parameters: 4(Integer)
[service] 2018-07-16 11:54:10,181 - dao.INewsLabelDao.selectParentByParentId -741  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - ======>  Preparing: select id,name,pid from newslabel where id=? 
[service] 2018-07-16 11:54:10,181 - dao.INewsLabelDao.selectParentByParentId -741  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - ======> Parameters: 2(Integer)
[service] 2018-07-16 11:54:10,183 - dao.INewsLabelDao.selectParentByParentId -743  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - ========>  Preparing: select id,name,pid from newslabel where id=? 
[service] 2018-07-16 11:54:10,183 - dao.INewsLabelDao.selectParentByParentId -743  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - ========> Parameters: 0(Integer)
[service] 2018-07-16 11:54:10,184 - dao.INewsLabelDao.selectParentByParentId -744  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - <========      Total: 0
[service] 2018-07-16 11:54:10,184 - dao.INewsLabelDao.selectParentByParentId -744  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - <======      Total: 1
[service] 2018-07-16 11:54:10,184 - dao.INewsLabelDao.selectParentByParentId -744  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - <====      Total: 1
[service] 2018-07-16 11:54:10,184 - dao.INewsLabelDao.selectParentByParentId -744  [main] DEBUG dao.INewsLabelDao.selectParentByParentId  - <==      Total: 1
NewsLabel [id=7, name=北京金瓯, parent=NewsLabel [id=4, name=CBA, parent=NewsLabel [id=2, name=体育新闻, parent=null]]]