使用MyBatis(八)一对一关联（嵌套查询，嵌套结果）

1.创建2张表，建立主外键关系

2.建立实体类

package com.yw.test06;


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

package com.yw.test06;

public class Student
{
	private int id;
	private String name;
	private int age;
	private Class c;
	
	public int getId()
	{
		return id;
	}
	public void setId(int id)
	{
		this.id = id;
	}
	public String getName()
	{
		return name;
	}
	public void setName(String name)
	{
		this.name = name;
	}
	public int getAge()
	{
		return age;
	}
	public void setAge(int age)
	{
		this.age = age;
	}
	public Class getC()
	{
		return c;
	}
	public void setC(Class c)
	{
		this.c = c;
	}
	@Override
	public String toString()
	{
		return "Student [id=" + id + ", name=" + name + ", age=" + age + ", c=" + c + "]";
	}

	
	
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
	<properties resource="config.properties">
	</properties>
	<typeAliases>
		<!-- <typeAlias type="com.yw.test06.StudentMapper" alias="Student" />
		<typeAlias type="com.yw.test06.ClassMapper" alias="Class" /> -->
		<package name="com.yw.test06"/>
	</typeAliases>
	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="${driver}" />
				<property name="url" value="${url}" />
				<property name="username" value="${username}" />
				<property name="password" value="${password}" />
			</dataSource>
		</environment>
	</environments>
	<mappers>
		<!-- <mapper resource="org/mybatis/example/BlogMapper.xml"/> -->
		<mapper resource="com/yw/test06/StudentMapper.xml" />
	</mappers>

</configuration>

1）嵌套查询

<?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="com.yw.test07.StudentMapper">

	<select id="selectStudent" resultMap="studentResult">
		SELECT * FROM student s
		WHERE s.ID = #{id}
	</select>
	<resultMap type="Student" id="studentResult">
		<association property="c" column="c_id" javaType="Class"
			select="selectClass" />
	</resultMap>

	<select id="selectClass" resultType="Class">
		SELECT * FROM class WHERE ID= #{id}
	</select>

</mapper>

<?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="com.yw.test06.StudentMapper">

    
    <resultMap id="studentResult" type="com.yw.test06.Student">
        <id property="id" column="id"/>
        <result property="name"  column="name"/>
        <result property="age"  column="age"/>

        <association property="c" resultMap="classResult"
            javaType="Class"></association>

    </resultMap>
    <resultMap type="com.yw.test06.Class" id="classResult">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
    </resultMap>
 
    <select id="selectStudent" resultMap="studentResult"> 
        SELECT s.id,c.id,s.name,s.age,c.name from student s  left join class c on c.id=s.c_id where s.id=#{id}
    </select>



</mapper>

package com.yw.test06;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class Test01
{
	public static void main(String[] args) throws IOException
	{
		
		String resource = "com/yw/test06/mybatis-config.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
		
		SqlSession session = sqlSessionFactory.openSession(false);
		try {
		  Student user = (Student) session.selectOne("com.yw.test06.StudentMapper.selectStudent", 1);
		  System.out.println(user);			
			
		} finally {
		  session.close();
		}
	}
}

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