如何在Mybatis中实现一个连接查询与嵌套查询功能

#表一：地址国家表
CREATE TABLE address(aid INT AUTO_INCREMENT PRIMARY KEY,aname VARCHAR(20));

INSERT INTO address VALUES(NULL,"魏国");
INSERT INTO address VALUES(NULL,"蜀国");
INSERT INTO address VALUES(NULL,"吴国");


#表二：出场人物表
CREATE TABLE person(
	pid INT AUTO_INCREMENT PRIMARY KEY,
	pname VARCHAR(20),
	paid INT,
	CONSTRAINT pafk FOREIGN KEY person(paid) REFERENCES address(aid) ON UPDATE CASCADE ON DELETE CASCADE
	);
	
INSERT INTO person VALUES(1,"曹操",1);
INSERT INTO person VALUES(2,"荀彧",1);
INSERT INTO person VALUES(3,"张辽",1);

INSERT INTO person VALUES(4,"刘备",2);
INSERT INTO person VALUES(5,"关羽",2);
INSERT INTO person VALUES(6,"张飞",2);
INSERT INTO person VALUES(7,"诸葛亮",2);

INSERT INTO person VALUES(8,"孙权",3);
INSERT INTO person VALUES(9,"周瑜",3);
INSERT INTO person VALUES(10,"陆逊",3);

INSERT INTO person VALUES(11,"公孙瓒",NULL);


#表三：交通工具表
CREATE TABLE tool(tid INT AUTO_INCREMENT PRIMARY KEY,tname VARCHAR(20));
INSERT INTO tool VALUES(1,"马");
INSERT INTO tool VALUES(2,"船");


#表四：地址国家——交通工具 多对多关系表
CREATE TABLE aandt(
	a_aid INT,
	a_tid INT,
	PRIMARY KEY(a_aid,a_tid),#联合主键，是指多个字段组成一个组合，该组合在数据表中唯一
	CONSTRAINT FOREIGN KEY aandt(a_aid) REFERENCES address(aid) ON UPDATE CASCADE ON DELETE CASCADE,
	CONSTRAINT FOREIGN KEY aandt(a_tid) REFERENCES tool(tid) ON UPDATE CASCADE ON DELETE CASCADE
);

INSERT INTO aandt VALUES(1,1);
INSERT INTO aandt VALUES(2,1);
INSERT INTO aandt VALUES(2,2);
INSERT INTO aandt VALUES(3,2);

<!--多对一的数据库-->
 <mapper namespace="com.fh.dao.PersonDao">
 	<!--该映射的id为map1，该映射的内容为：将查询到的字段的结果值，按照本映射的对应关系，分别封装在Person实体类下的各个属性上，整体构成Person-->
 <resultMap id="map1" type="com.fh.domain.Person">
  <id column="pid" property="pid"/><!--id：主键映射； column：数据库表字段； property：类中对应属性名-->
  <result column="pname" property="pname"/><!--result：非主键映射-->
  <result column="paid" property="paid"/>
  <association property="address" javaType="com.fh.domain.Address"><!--association：在查询到多，然后对应出一时，用于关联对应出一的一方； property：查询类中包含的子对象属性; javaType：子对象属性封装对应的类-->
   <id column="aid" property="aid"/>
   <result column="aname" property="aname"/>
  </association>
 </resultMap>
 <select id="findAllPerson" resultMap="map1">/*resultMap:自己编写的结果集，本查询的返回值正是该结果集所对应的映射组构成的Person*/
--   查询所有人及其对应的地址，以人为主，则对人侧外连接
  SELECT * FROM person p LEFT OUTER JOIN address a ON p.paid = a.aid
 </select>
</mapper>

<!--一对多的数据库-->
 <mapper namespace="com.fh.dao.AddressDao">
 <resultMap id="map2" type="com.fh.domain.Address">
  <id column="aid" property="aid"/>
  <result column="aname" property="aname"/>
  <collection property="personList" ofType="com.fh.domain.Person"><!--collection：查询到一，接着关联对应出多时，指向多的一方； foType：集合中每个元素所属的映射类-->
   <id column="pid" property="pid"/>
   <result column="pname" property="pname"/>
   <result column="paid" property="paid"/>
  </collection>
 </resultMap>
 <select id="findAllAddress" resultMap="map2">
  SELECT * FROM address a LEFT OUTER JOIN person p ON a.aid = p.paid;
 </select>
</mapper>

<mapper namespace="com.fh.dao.ToolDao">
 <resultMap id="map3" type="com.fh.domain.Tool">
  <id column="tid" property="tid"/>
  <result column="tname" property="tname"/>
  <collection property="addressList" ofType="com.fh.domain.Address">
   <id column="aid" property="aid"/>
   <result column="aname" property="aname"/>
  </collection>
 </resultMap>
 <select id="findAllTool" resultMap="map3">
  SELECT t.*,a.* FROM tool AS t LEFT OUTER JOIN aandt AS a_t ON t.`tid` = a_t.`a_tid` LEFT OUTER JOIN address AS a ON a_t.`a_aid` = a.`aid`;
 </select>

//查询所有人，以及其对应的地址
 List<Person> findPersonFromAddress();

<!--多对一的数据库-->
 <mapper namespace="com.fh.dao.PersonDao">
 <!--person映射的基本属性对应下面person的结果集，本结果集内部再继续进行处理-->
 <resultMap id="map1" type="com.fh.domain.Person">
  <id column="pid" property="pid"/>
  <result column="pname" property="pname"/>
  <result column="paid" property="paid"/>
  <!--
  对应到person内的子属性对象，column内为person对应到address的外键，由此外键，传入select内的方法进行二次嵌套查询，交由AddressDao在其中的指定方法进行处理
  即要求查询目标为：Address.aid = Person.paid
  -->
  <association property="address" column="paid" select="com.fh.dao.AddressDao.findAddressById"/>
 </resultMap>
 <!--第一次查询为只查询主要对象，自定义结果集-->
 <select id="findPersonFromAddress" resultMap="map1">
  select * from person
 </select>
</mapper>

//按照id查询Address
List<Address> findAddressById(Integer id);

 <mapper namespace="com.fh.dao.AddressDao">
 <!--根据id对address查询-->
 <select id="findAddressById" resultType="com.fh.domain.Address">
  SELECT * FROM address WHERE aid = #{aid}
 </select>

List<Address> findAddressWithPerson();

<resultMap id="map2" type="com.fh.domain.Address">
  <id column="aid" property="aid"/>
  <result column="aname" property="aname"/>
  <collection property="personList" column="aid" select="com.fh.dao.PersonDao.findPersonById"/>
 </resultMap>
 <select id="findAddressWithPerson" resultMap="map2">
  select * from address
 </select>

 List<Person> findPersonById(Integer id);

<select id="findPersonById" resultType="com.fh.domain.Person">
  select * from person where pid = #{pid}
 </select>

<settings>
  <setting name="lazyLoadingEnable" value="true"/>
  <setting name="lazyLoadTriggerMethods" value="true"/><!--本条设置表示将包括原本不会延迟加载的equals/clone/hashCode/toString在内所有方法进行延迟加载-->
 </settings>