association的使用

association----------第6条使用

1.目录结构

2.Mybatis-config.xml配置

<!DOCTYPE configuration  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-config.dtd">  <!-- xml核心配置 -->
<configuration>
<!-- 日志的具体实现 --><settings><setting name="logImpl" value="LOG4J"/></settings><!-- 环境配置 --><environments default="mysql"><environment id="mysql"><!-- 指定事务回滚 --><transactionManager type="JDBC"></transactionManager><!-- 指数据源配置 --><dataSource type="POOLED"><property name="driver" value="com.mysql.jdbc.Driver"/><property name="url" value="jdbc:mysql://127.0.0.1:3306/user"/><property name="username" value="root"/><property name="password" value="123456"/></dataSource></environment></environments>
<!-- 告诉mybatis去哪里找映射文件 --><mappers><!-- <mapper resource="org/mapper/UserMapper.xml"/> --><mapper resource="org/mapper/studentMapper.xml"/></mappers>
</configuration>

3.班级类

package org.domain;public class ClassGrade {private int id;           private String code;   //班级编号public ClassGrade() {super();
}
public ClassGrade(int id, String code) {super();this.id = id;this.code = code;
}
public int getId() {return id;
}
public void setId(int id) {this.id = id;
}
public String getCode() {return code;
}
public void setCode(String code) {this.code = code;
}}

4.学生类

package org.domain;
public class student {private int id;private String name;private String sex;private int age;private int class_id;private ClassGrade classGrade;public student() {super();}public student(int id, String name, String sex, int age) {super();this.id = id;this.name = name;this.sex = sex;this.age = age;}public student(int id, String name, String sex, int age, int class_id) {super();this.id = id;this.name = name;this.sex = sex;this.age = age;this.class_id = class_id;}public student(int kid, String name, String sex, int age,ClassGrade classGrade) {super();this.name = name;this.sex = sex;this.age = age;this.classGrade = classGrade;}public int getId() {return id;}public void setId(int id) {this.id = id;}public int getClass_id() {return class_id;}public void setClass_id(int class_id) {this.class_id = class_id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public ClassGrade getClassGrade() {return classGrade;}public void setClassGrade(ClassGrade classGrade) {this.classGrade = classGrade;}
}

sqlSessionFactory类

package org.factory;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 sqlSessionFactory {//SqlSessionFactory:单个数据库的映射关系编译之后的内存镜像//功能：是创建SqlSession 的工厂private static SqlSessionFactory factory=null;/** 获取 SqlSessionFactory对象的方法*/static {//读取mybatis-config.xml文件InputStream input = null;try {input = Resources.getResourceAsStream("mybatis-config.xml");} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}//初始化mybatisfactory=new SqlSessionFactoryBuilder().build(input);}/** 获取sqlSession对象*/public static SqlSession getSqlSession() {return  factory.openSession(); }/** 获取sqlSessionFactory*/public static SqlSessionFactory getSqlSessionFactory() {return factory;}}

6.studentMapper.xml配置

(配置文件中每一个select针对各自的表)

第一种方式select嵌套：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE  mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.mapper.studentMapper"><!-- 对象result  tMap学生映射--><resultMap id="studentResultMap" type="org.domain.student" ><id property="id" column="id"/><result property="name" column="name"/><result property="sex" column="sex"/><result property="age" column="age"/><association property="classGrade"  column="class_id" javaType="org.domain.ClassGrade" select="selectClasses"><result property="id" column="id"/><result property="code" column="code"/></association></resultMap><!--班级查询  --><select id="selectClasses"  resultType="org.domain.ClassGrade">select * from class_tb where id=#{id}</select><!--学生查询语句  --><select id="selectStudents" resultMap="studentResultMap">select * from student</select></mapper>

(配置文件中每一个select针对连接一个以上的表)

第二种方式resultMap嵌套：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE  mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.mapper.studentMapper"><!-- 对象result  tMap学生映射--><resultMap id="studentResultMap" type="org.domain.student" ><id property="id" column="id"/><result property="name" column="name"/><result property="sex" column="sex"/><result property="age" column="age"/><association property="classGrade"  column="class_id" resultMap="class"/>  </resultMap><resultMap  id="class"  type="org.domain.ClassGrade"><result property="id" column="id"/><result property="code" column="code"/></resultMap><!--关联查询学生及班级  --><select id="aSelect"  resultMap="studentResultMap">select  student.id,student.name,student.sex,student.age,class_tb.id as oid,class_tb.codefrom student left outer join class_tb  on student.class_id=class_tb.id; </select>
</mapper>

第三种方式对象嵌套（跟第二种方式没有太大差别只是对象也不需要再关联查询）：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE  mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.mapper.studentMapper"><!-- 对象result  tMap学生映射--><resultMap id="studentResultMap" type="org.domain.student" ><id property="id" column="id"/><result property="name" column="name"/><result property="sex" column="sex"/><result property="age" column="age"/><association property="classGrade"  column="class_id" javaType="org.domain.ClassGrade">  <result property="id" column="id"/><result property="code" column="code"/></association></resultMap><!--关联查询学生及班级  --><select id="aSelect"  resultMap="studentResultMap">select  student.id,student.name,student.sex,student.age,class_tb.id as oid,class_tb.codefrom student left outer join class_tb  on student.class_id=class_tb.id; </select>
</mapper>

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