11.2 注解的使用示例3 一对多关联关系

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11.2 注解的使用示例3 一对多关联关系

例如班级和学生是一对多的关联关系,则在查询学生的时候使用@one注解来关联查询班级.
查询班级的时候,使用@Many注解来查询该班级的所有学生.示例项目如下所示:

示例:一对多关联关系

项目结构

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G:\workspace_web2\MyAOneToManyTest
├─src
│ ├─db.properties
│ ├─domain
│ │ ├─Clazz.java
│ │ └─Student.java
│ ├─fractory
│ │ └─SqlSessionFactoryTools.java
│ ├─log4j.xml
│ ├─mapper
│ │ ├─ClazzMapper.java
│ │ └─StudentMapper.java
│ ├─mybatis-config.xml
│ ├─tb_clazz_tb_student.sql
│ └─test
│   ├─SelectClazzByIdTest.java
│   └─SelectStudentByIdTest.java
└─WebContent
  ├─META-INF
  │ └─MANIFEST.MF
  └─WEB-INF
    └─lib
      ├─ant-1.9.6.jar
      ├─ant-launcher-1.9.6.jar
      ├─asm-5.2.jar
      ├─cglib-3.2.5.jar
      ├─commons-logging-1.2.jar
      ├─javassist-3.22.0-CR2.jar
      ├─log4j-1.2.17.jar
      ├─log4j-api-2.3.jar
      ├─log4j-core-2.3.jar
      ├─mybatis-3.4.5.jar
      ├─mysql-connector-java-5.1.44-bin.jar
      ├─ognl-3.1.15.jar
      ├─slf4j-api-1.7.25.jar
      └─slf4j-log4j12-1.7.25.jar

数据库脚本

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# 创建tb_clazz表
DROP TABLE IF EXISTS `tb_clazz`;
CREATE TABLE `tb_clazz` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `code` varchar(18) NOT NULL,
  `name` varchar(18) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
# 插入数据到tb_clazz表
INSERT INTO `tb_clazz` VALUES ('1', 'B151516', 'Java基础班');
DROP TABLE IF EXISTS `tb_student`;
CREATE TABLE `tb_student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(18) DEFAULT NULL,
  `sex` varchar(18) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `clazz_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `clazz_id` (`clazz_id`),
  CONSTRAINT `tb_student_ibfk_1` FOREIGN KEY (`clazz_id`)
  REFERENCES `tb_clazz` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
INSERT INTO `tb_student` VALUES ('1', '小明', '男', '24', '1');
INSERT INTO `tb_student` VALUES ('2', '小王', '男', '23', '1');
INSERT INTO `tb_student` VALUES ('3', '小芳', '女', '22', '1');
INSERT INTO `tb_student` VALUES ('4', '小丽', '女', '22', '1');

db.properties

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# 保存为db.properties文件,然后在mybatis-config.xml中通过下面标签引入:
# <properties resource="db.properties"/>
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis
username=root
password=root

log4j.xml

/MyAOneToManyTest/src/log4j.xml
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration 
    PUBLIC "-//LOG4J//DTD LOG4J//EN" 
    "https://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/xml/doc-files/log4j.dtd" >
<!-- 请在mybatis-config.xml中配置如下设置 -->
<!-- <settings> -->
<!--     <setting -->
<!--         name="logImpl" -->
<!--         value="log4j"/> -->
<!-- </settings> -->
<log4j:configuration>
    <appender
        name="STDOUT"
        class="org.apache.log4j.ConsoleAppender">
        <layout class="org.apache.log4j.PatternLayout">
            <param
                name="ConversionPattern"
                value="%5p [%t] %m%n"/>
        </layout>
    </appender>
    <logger name="mapper">
        <level value="DEBUG"/>
    </logger>
    <root>
        <level value="ERROR"/>
        <appender-ref ref="STDOUT"/>
    </root>
</log4j:configuration>

mybatis-config.xml

/MyAOneToManyTest/src/mybatis-config.xml
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<?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">
<!-- 该配置文件包含对 MyBatis 系统的核心设置 -->
<configuration>
    <properties resource="db.properties"/>
    <settings>
        <setting
            name="logImpl"
            value="log4j"/>
        <!-- 要使延迟加载生效必须配置下面两个属性 -->
        <setting
            name="lazyLoadingEnabled"
            value="true"/>
        <setting
            name="aggressiveLazyLoading"
            value="false"/>
    </settings>
    <environments default="mysql">
        <environment id="mysql">
            <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 class="mapper.ClazzMapper"/>
        <mapper class="mapper.StudentMapper"/>
    </mappers>
</configuration>

持久化对象

Clazz.java

/MyAOneToManyTest/src/domain/Clazz.java
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package domain;

import java.io.Serializable;
import java.util.List;

public class Clazz implements Serializable {
    private static final long serialVersionUID = -1924365559257770561L;
    private Integer id;
    private String code;
    private String name;
    List<Student> students;

    public Clazz() {
    }

    public Clazz(String code, String name) {
        super();
        this.code = code;
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }

    @Override
    public String toString() {
        return "Clazz [id=" + id + ", code=" + code + ", name=" + name + "]";
    }
}

Student.java

/MyAOneToManyTest/src/domain/Student.java
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package domain;

import java.io.Serializable;

public class Student implements Serializable {
    private static final long serialVersionUID = 2713166808172094576L;
    private Integer id;
    private String name;
    private String sex;
    private Integer age;
    private Clazz clazz;

    public Student() {
    }

    public Student(String name, String sex, Integer age) {
        super();
        this.name = name;
        this.sex = sex;
        this.age = age;
    }

    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 String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Clazz getClazz() {
        return clazz;
    }

    public void setClazz(Clazz clazz) {
        this.clazz = clazz;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", sex=" + sex + ", age=" + age + "]";
    }
}

会话工具类

/MyAOneToManyTest/src/fractory/SqlSessionFactoryTools.java
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package fractory;
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 SqlSessionFactoryTools {
    private static SqlSessionFactory sqlSessionFactory = null;
    static
    {
        try
        {
            InputStream mybatisConfigXML = Resources.getResourceAsStream("mybatis-config.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(mybatisConfigXML);
        } catch (IOException e)
        {
            e.printStackTrace();
        }
    }
    public static SqlSession getSqlSession()
    {
        return sqlSessionFactory.openSession();
    }
}

mapper接口

ClazzMapper.java

/MyAOneToManyTest/src/mapper/ClazzMapper.java
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package mapper;

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 domain.Clazz;

public interface ClazzMapper {
    @Select("select * from tb_clazz where id=#{id}")
    @Results({
        @Result(column = "id",property = "id", id = true),
        @Result(column = "code",property = "code"),
        @Result(column = "name",property = "name"),
        @Result(column = "id",property = "students", 
            many = @Many(select = "mapper.StudentMapper.selectStudentsByClassId", fetchType = FetchType.LAZY)
        )
    })
    Clazz selectClazzById(Integer id);

    @Select("select * from tb_clazz where id=#{id}")
    @Results({
        @Result(column = "id",property = "id", id = true),
        @Result(column = "code",property = "code"),
        @Result(column = "name",property = "name") 
    })
    Clazz selectClazzByUserClazzId(Integer id);
}

StudentMapper.java

/MyAOneToManyTest/src/mapper/StudentMapper.java
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package mapper;

import java.util.List;
import org.apache.ibatis.annotations.One;
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 domain.Student;

public interface StudentMapper {
    @Select("select * from tb_student where id=#{id}")
    @Results({
        @Result(column = "id",property = "id", id = true),
        @Result(column = "name",property = "name"),
        @Result(column = "sex",property = "sex"),
        @Result(column = "age",property = "age"),
        @Result(column = "clazz_id",property = "clazz", 
            one = @One(select = "mapper.ClazzMapper.selectClazzByUserClazzId", fetchType = FetchType.EAGER)
        ) 
    })
    Student selectStudentById(Integer id);

    @Select("select * from tb_student where clazz_id=#{clazzId}")
    @Results({
        @Result(column = "id",property = "id", id = true),
        @Result(column = "name",property = "name"),
        @Result(column = "sex",property = "sex"),
        @Result(column = "age",property = "age") 
    }) 
    List<Student> selectStudentsByClassId(Integer clazzId);
}

fetchType = FetchType.EAGER表示理解加载

测试类

SelectClazzByIdTest.java

/MyAOneToManyTest/src/test/SelectClazzByIdTest.java
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package test;

import java.util.List;
import org.apache.ibatis.session.SqlSession;
import domain.Clazz;
import domain.Student;
import fractory.SqlSessionFactoryTools;
import mapper.ClazzMapper;

public class SelectClazzByIdTest {
    public static void main(String[] args) {
        SqlSession sqlSession = null;
        try {
            // 加载mybatis-config.xml,获取SqlSession实例
            sqlSession = SqlSessionFactoryTools.getSqlSession();
            // 获取mapper接口代理对象
            ClazzMapper clazzMapper = sqlSession.getMapper(ClazzMapper.class);
            Clazz clazz = clazzMapper.selectClazzById(1);
            System.out.println(clazz.toStringSimple());
            // System.out.println(clazz.toString());
            System.out.println("--------------------------------------------------------------");
            List<Student> students = clazz.getStudents();
            students.forEach(student -> System.out.println(student));
            // 提交事务
            sqlSession.commit();
        } catch (Exception e) {
            // 出错回滚事务
            sqlSession.rollback();
            e.printStackTrace();
        } finally {
            // 关闭会话
            if (sqlSession != null)
                sqlSession.close();
        }

    }
}

运行效果:

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DEBUG [main] ==>  Preparing: select * from tb_clazz where id=? 
DEBUG [main] ==> Parameters: 1(Integer)
DEBUG [main] <==      Total: 1
Clazz [id=1, code=B100, name=Java基础班]
--------------------------------------------------------------
DEBUG [main] ==>  Preparing: select * from tb_student where clazz_id=? 
DEBUG [main] ==> Parameters: 1(Integer)
DEBUG [main] <==      Total: 2
Student [id=2, name=小王, sex=男, age=23]
Student [id=4, name=小丽, sex=女, age=22]

SelectStudentByIdTest.java

/MyAOneToManyTest/src/test/SelectStudentByIdTest.java
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package test;

import org.apache.ibatis.session.SqlSession;
import domain.Student;
import fractory.SqlSessionFactoryTools;
import mapper.StudentMapper;

public class SelectStudentByIdTest {
    public static void main(String[] args) {
        SqlSession sqlSession = null;
        try {
            // 加载mybatis-config.xml,获取SqlSession实例
            sqlSession = SqlSessionFactoryTools.getSqlSession();
            // 获取mapper接口代理对象
            StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
            // 执行mapper接口方法
            Student student = studentMapper.selectStudentById(1);
            // System.out.println(student.toString());
            System.out.println(student.toStringSimple());
            System.out.println("===========================================");
            System.out.println(student.getClazz().toString());
            // 提交事务
            sqlSession.commit();
        } catch (Exception e) {
            // 出错回滚事务
            sqlSession.rollback();
            e.printStackTrace();
        } finally {
            // 关闭会话
            if (sqlSession != null)
                sqlSession.close();
        }

    }
}

运行效果:

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DEBUG [main] ==>  Preparing: select * from tb_student where id=? 
DEBUG [main] ==> Parameters: 1(Integer)
DEBUG [main] ====>  Preparing: select * from tb_clazz where id=? 
DEBUG [main] ====> Parameters: 2(Integer)
DEBUG [main] <====      Total: 1
DEBUG [main] <==      Total: 1
Student [id=1, name=小明, sex=男, age=24]
===========================================
Clazz [id=2, code=B101, name=JSP]