Mybatis 50_基于嵌套select的1-N关联
50_基于嵌套select的1-N关联
- 嵌套select的1-N关联映射
-
- 基于嵌套select的映射时，可指定如下独有属性：
- 使用@Many注解
- 项目0518基于嵌套select的1-N
- 项目0519基于嵌套select的1-N_注解
嵌套select的1-N关联映射
只要对方是多个对象，都使用
所谓嵌套select，就是指需要一条额外的select语句去获取关联实体
在这种策略下，无论是先拿到主表记录，还是先拿到从表记录，程序都需要执行额外的select语句去获取关联实体。
定义
此时javaType指定集合属性类型（比如List、Set），ofType指定集合元素的类型
基于嵌套select的映射时，可指定如下独有属性：
- select： 指定额外的select语句的ID
- column： 指定将当前实体的哪一列或哪些列传给select语句作为参数
- fetchType：指定抓取策略。延迟加载或立即加载。
延迟加载：只有等到真正去访问关联实体时采取执行额外的select语句。
使用@Many注解
@Many只需要指定select和fetchType,而column依然放在@Result中指定
项目0518基于嵌套select的1-N
主类
package lee;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.itcheng.app.dao.AddressMapper;
import org.itcheng.app.dao.PersonMapper;
import org.itcheng.app.domain.Address;
import org.itcheng.app.domain.Person;
public class PersonManager
{
// SqlSessionFactory应该是应用级别
private static SqlSessionFactory sqlSessionFactory;
public static void main(String[] args) throws IOException
{
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
// 1. 创建SqlSessionFactory
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 2. 打开SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
// findPerson(sqlSession);
/* 结果
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Preparing: select * from person_inf where person_id = ?
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Parameters: 3(Integer)
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson <== Total: 1
* 白鼠精
* -----------------
* DEBUG [main] org.itcheng.app.dao.AddressMapper.getAddressByOwner ==> Preparing: select * from address_inf where owner_id = ?
* DEBUG [main] org.itcheng.app.dao.AddressMapper.getAddressByOwner ==> Parameters: 3(Integer)
* DEBUG [main] org.itcheng.app.dao.AddressMapper.getAddressByOwner <== Total: 1
* 陷空山无底洞
* */
findAddresses(sqlSession);
/* 结果
* DEBUG [main] org.itcheng.app.dao.AddressMapper.findAddressesById ==> Preparing: select * from address_inf where addr_id > ?
* DEBUG [main] org.itcheng.app.dao.AddressMapper.findAddressesById ==> Parameters: 3(Integer)
* DEBUG [main] org.itcheng.app.dao.AddressMapper.findAddressesById <== Total: 2
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Preparing: select * from person_inf where person_id = ?
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Parameters: 3(Integer)
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson <== Total: 1
* 陷空山无底洞-->白鼠精
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Preparing: select * from person_inf where person_id = ?
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Parameters: 4(Integer)
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson <== Total: 1
* 积雷山摩云洞-->玉面狐狸
* -----------------
* */
}
public static void findPerson(SqlSession sqlSession)
{
PersonMapper personMapper = sqlSession.getMapper(PersonMapper.class);
Person p = personMapper.getPerson(3);
System.out.println(p.getName());
System.out.println("-----------------");
// Person获取关联实体是延迟加载，要等到真正访问关联实体时才去执行额外的SELECT语句
List<Address> addresses = p.getAddresses();
addresses.forEach(e -> {
System.out.println(e.getDetail());
});
// 4. 提交事务
sqlSession.commit();
// 5. 关闭资源
sqlSession.close();
}
public static void findAddresses(SqlSession sqlSession)
{
AddressMapper addressMapper = sqlSession.getMapper(AddressMapper.class);
List<Address> addrList = addressMapper.findAddressesById(3);
// 由于Address获取关联实体是立即加载，因此它会立即执行额外的SELECT语句
// 对于立即加载策略,即使不访问关联实体,它也会立即执行额外的SELECT语句
addrList.forEach(e -> {
System.out.println(e.getDetail() + "-->" + e.getPerson().getName());
});
System.out.println("-----------------");
// 4. 提交事务
sqlSession.commit();
// 5. 关闭资源
sqlSession.close();
}
}
接口类
package org.itcheng.app.dao;
import java.util.List;
import org.itcheng.app.domain.Address;
// Mapper组件相当于DAO组件
public interface AddressMapper
{
List<Address> findAddressesById(Integer id);
}
package org.itcheng.app.dao;
import org.itcheng.app.domain.Person;
// Mapper组件相当于DAO组件
public interface PersonMapper
{
Person getPerson(Integer id);
}
配置文件
DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.itcheng.app.dao.AddressMapper">
<select id="findAddressesById" resultMap="addrMap">
select * from address_inf where addr_id > #{id}
select>
<resultMap type="address" id="addrMap">
<id column="addr_id" property="id"/>
<result column="addr_detail" property="detail"/>
<association property="person" select="org.itcheng.app.dao.PersonMapper.getPerson"
column="owner_id" fetchType="lazy"/>
resultMap>
<select id="getAddressByOwner" resultMap="addrMap">
select * from address_inf where owner_id = #{id}
select>
mapper>
DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.itcheng.app.dao.PersonMapper">
<select id="getPerson" resultMap="personMap">
select * from person_inf where person_id = #{id}
select>
<resultMap type="person" id="personMap">
<id column="person_id" property="id"/>
<result column="person_name" property="name"/>
<result column="person_age" property="age"/>
<collection property="addresses"
javaType="ArrayList"
ofType="address"
select="org.itcheng.app.dao.AddressMapper.getAddressByOwner"
column="person_id" fetchType="lazy"/>
resultMap>
mapper>
项目0519基于嵌套select的1-N_注解
主类
package lee;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.itcheng.app.dao.AddressMapper;
import org.itcheng.app.dao.PersonMapper;
import org.itcheng.app.domain.Address;
import org.itcheng.app.domain.Person;
public class PersonManager
{
// SqlSessionFactory应该是应用级别
private static SqlSessionFactory sqlSessionFactory;
public static void main(String[] args) throws IOException
{
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
// 1. 创建SqlSessionFactory
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 2. 打开SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
// findPerson(sqlSession);
/* 结果
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Preparing: select * from person_inf where person_id = ?
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Parameters: 3(Integer)
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson <== Total: 1
* 白鼠精
* -----------------
* DEBUG [main] org.itcheng.app.dao.AddressMapper.getAddressByOwner ==> Preparing: select * from address_inf where owner_id = ?
* DEBUG [main] org.itcheng.app.dao.AddressMapper.getAddressByOwner ==> Parameters: 3(Integer)
* DEBUG [main] org.itcheng.app.dao.AddressMapper.getAddressByOwner <== Total: 2
* 陷空山无底洞
* 灵山大雷音寺
* */
findAddresses(sqlSession);
/* 结果
* DEBUG [main] org.itcheng.app.dao.AddressMapper.findAddressesById ==> Preparing: select * from address_inf where addr_id > ?
* DEBUG [main] org.itcheng.app.dao.AddressMapper.findAddressesById ==> Parameters: 3(Integer)
* DEBUG [main] org.itcheng.app.dao.AddressMapper.findAddressesById <== Total: 6
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Preparing: select * from person_inf where person_id = ?
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Parameters: 1(Integer)
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson <== Total: 1
* 斜月三星洞-->孙悟空
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Preparing: select * from person_inf where person_id = ?
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Parameters: 2(Integer)
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson <== Total: 1
* 福陵山云栈洞-->猪八戒
* 高老庄-->猪八戒
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Preparing: select * from person_inf where person_id = ?
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Parameters: 3(Integer)
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson <== Total: 1
* 陷空山无底洞-->白鼠精
* 灵山大雷音寺-->白鼠精
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Preparing: select * from person_inf where person_id = ?
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson ==> Parameters: 4(Integer)
* DEBUG [main] org.itcheng.app.dao.PersonMapper.getPerson <== Total: 1
* 积雷山摩云洞-->玉面狐狸
* -----------------
* */
}
public static void findPerson(SqlSession sqlSession)
{
PersonMapper personMapper = sqlSession.getMapper(PersonMapper.class);
Person p = personMapper.getPerson(3);
System.out.println(p.getName());
System.out.println("-----------------");
// Person获取关联实体是延迟加载，要等到真正访问关联实体时才去执行额外的SELECT语句
List<Address> addresses = p.getAddresses();
addresses.forEach(e -> {
System.out.println(e.getDetail());
});
// 4. 提交事务
sqlSession.commit();
// 5. 关闭资源
sqlSession.close();
}
public static void findAddresses(SqlSession sqlSession)
{
AddressMapper addressMapper = sqlSession.getMapper(AddressMapper.class);
List<Address> addrList = addressMapper.findAddressesById(3);
// 由于Address获取关联实体是立即加载，因此它会立即执行额外的SELECT语句
// 对于立即加载策略,即使不访问关联实体,它也会立即执行额外的SELECT语句
addrList.forEach(e -> {
System.out.println(e.getDetail() + "-->" + e.getPerson().getName());
});
System.out.println("-----------------");
// 4. 提交事务
sqlSession.commit();
// 5. 关闭资源
sqlSession.close();
}
}
接口类
package org.itcheng.app.dao;
import java.util.List;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.ResultMap;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.mapping.FetchType;
import org.itcheng.app.domain.Address;
// Mapper组件相当于DAO组件
public interface AddressMapper
{
@Select("select * from address_inf where addr_id > #{id}")
@Results(id = "addrMap", value = {
@Result(column="addr_id", property="id", id=true),
@Result(column="addr_detail", property="detail"),
@Result(property="person", column="owner_id",
one=@One(select="org.itcheng.app.dao.PersonMapper.getPerson",
fetchType=FetchType.LAZY))
})
List<Address> findAddressesById(Integer id);
@Select("select * from address_inf where owner_id = #{id}")
@ResultMap("addrMap") // 该注解表明引用一个已有ResultMap的id
List<Address> getAddressByOwner(Integer ownerId);
}
package org.itcheng.app.dao;
import java.util.ArrayList;
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.mapping.FetchType;
import org.itcheng.app.domain.Person;
// Mapper组件相当于DAO组件
public interface PersonMapper
{
@Select("select * from person_inf where person_id = #{id}")
@Results({ @Result(column = "person_id", property = "id", id = true),
@Result(column = "person_name", property = "name"),
@Result(column = "person_age", property = "age"),
@Result(property="addresses", column="person_id",
javaType = ArrayList.class,
many = @Many(select = "org.itcheng.app.dao.AddressMapper.getAddressByOwner",
fetchType = FetchType.LAZY))
})
Person getPerson(Integer id);
}