MyBatis注解之一对多关联实战

雨点打透心脏的1/2处 2021-07-24 15:19 311阅读 0赞

**一 领域模型**

1 Clazz

package org.fkit.domain;
    
    import java.io.Serializable;
    import java.util.List;
    
    public class Clazz implements Serializable {
        
        private static final long serialVersionUID = 1L;
        
        private Integer id; // 班级id，主键
        private String code; // 班级编号
        private String name; // 班级名称
        
        // 班级和学生是一对多的关系，即一个班级可以有多个学生
        private List<Student> students;
        
        public Clazz() {
            super();
            // TODO Auto-generated constructor stub
        }
        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 + "]";
        }
    }

2 Student

package org.fkit.domain;
    import java.io.Serializable;
    /**
    *
    CREATE TABLE tb_clazz(
    id INT PRIMARY KEY AUTO_INCREMENT,
    CODE VARCHAR(18),
    NAME VARCHAR(18)
    );
    INSERT INTO tb_clazz(CODE,NAME) VALUES('j1601','Java就业班');
    CREATE TABLE tb_student(
    id INT PRIMARY KEY AUTO_INCREMENT,
    NAME VARCHAR(18),
    sex VARCHAR(18),
    age INT,
    clazz_id INT,
    FOREIGN KEY (clazz_id) REFERENCES tb_clazz(id)
    );
    INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('jack','男',23,1);
    INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('rose','女',18,1);
    INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('tom','男',21,1);
    INSERT INTO tb_student(NAME,sex,age,clazz_id) VALUES('alice','女',20,1);
    * */
    public class Student implements Serializable {
         private static final long serialVersionUID = 1L;
         
         private Integer id; // 学生id，主键
         private String name; // 姓名
         private String sex;  // 性别
         private Integer age; // 年龄
         
         // 学生和班级是多对一的关系，即一个学生只属于一个班级
         private Clazz clazz;
         public Student() {
               super();
               // TODO Auto-generated constructor stub
         }
         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 + "]";
         }
         
    }

**二 会话工厂**

package org.fkit.factory;
    
    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 FKSqlSessionFactory {
        
        private static SqlSessionFactory sqlSessionFactory = null;
        
        // 初始化创建SqlSessionFactory对象
        static{
            try (// 读取mybatis-config.xml文件
                    InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
                ){
                sqlSessionFactory = new SqlSessionFactoryBuilder()
                        .build(is);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        
        // 获取SqlSession对象的静态方法
        public static SqlSession getSqlSession(){
            return sqlSessionFactory.openSession();
        }
    
        // 获取SqlSessionFactory的静态方法
        public static SqlSessionFactory getSqlSessionFactory() {
            return sqlSessionFactory;
        }
    }

**三 mapper**

1 ClazzMapper

package org.fkit.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 org.fkit.domain.Clazz;
    
    public interface ClazzMapper {
    
        // 根据id查询班级信息
        @Select("SELECT * FROM TB_CLAZZ  WHERE ID = #{id}")
        @Results({
            @Result(id=true,column="id",property="id"),
            @Result(column="code",property="code"),
            @Result(column="name",property="name"),
            @Result(column="id",property="students",
            many=@Many(
                    select="org.fkit.mapper.StudentMapper.selectByClazzId",
                    fetchType=FetchType.LAZY))
        })
        Clazz selectById(Integer id);
    
            
    }

2 StudentMapper

package org.fkit.mapper;
    
    import java.util.List;
    import org.apache.ibatis.annotations.Result;
    import org.apache.ibatis.annotations.Results;
    import org.apache.ibatis.annotations.Select;
    import org.fkit.domain.Student;
    
    public interface StudentMapper {
        
        // 根据班级id查询班级所有学生
        @Select("SELECT * FROM TB_STUDENT WHERE CLAZZ_ID = #{id}")
        @Results({
            @Result(id=true,column="id",property="id"),
            @Result(column="name",property="name"),
            @Result(column="sex",property="sex"),
            @Result(column="age",property="age")
        })
        List<Student> selectByClazzId(Integer clazz_id);
            
    }

**四 配置文件**

1 db.properties

driver=com.mysql.jdbc.Driver
    url=jdbc:mysql://127.0.0.1:3306/mybatis
    username=root
    password=123456

2 log4j.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">  
    <log4j:configuration  xmlns:log4j="http://jakarta.apache.org/log4j/">  
        <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="org.fkit.mapper">  
            <level value="DEBUG" />  
        </logger>
        <root>  
            <level value="ERROR" />  
            <appender-ref ref="STDOUT" />  
        </root>  
    </log4j:configuration>

3 mybatis-config.xml

<?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="db.properties"/>
         
         <settings>
               <setting name="logImpl" value="LOG4J"/>
               
               <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="org.fkit.mapper.ClazzMapper"/>
          <mapper class="org.fkit.mapper.StudentMapper"/>
      </mappers>
    </configuration>

**五 测试**

package org.fkit.test;
    
    import org.apache.ibatis.session.SqlSession;
    import org.fkit.domain.Clazz;
    import org.fkit.factory.FKSqlSessionFactory;
    import org.fkit.mapper.ClazzMapper;
    public class OneToManyTest {
    
        public static void main(String[] args) {
            // 定义SqlSession变量
            SqlSession sqlSession = null;
            try {
                // 创建SqlSession实例
                sqlSession = FKSqlSessionFactory.getSqlSession();
                // 获取ClazzMapper实例
                ClazzMapper cm = sqlSession.getMapper(ClazzMapper.class);
                // 根据id查询Clazz对象
                Clazz clazz = cm.selectById(1);
                // 查看查询到的Clazz对象
                System.out.println(clazz.getId() + " "+ clazz.getCode() + " "+clazz.getName());
                // 查看关联的学生集合，因为配置使用的是LAZY懒加载，所以当使用时才执行SQL语句
                clazz.getStudents().forEach(student->System.out.println(student));
                // 提交事务
                sqlSession.commit();
            } catch (Exception e) {
                // 回滚事务
                sqlSession.rollback();
                e.printStackTrace();
            }finally {
                // 关闭SqlSession
                if(sqlSession != null)
                    sqlSession.close();
            }
        }
    }

测试结果

DEBUG [main] ==>  Preparing: SELECT * FROM TB_CLAZZ WHERE ID = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 1
    1 j1601 Java就业班
    DEBUG [main] ==>  Preparing: SELECT * FROM TB_STUDENT WHERE  CLAZZ_ID = ?
    DEBUG [main] ==> Parameters: 1(Integer)
    DEBUG [main] <==      Total: 4
    Student [id=1, name=jack, sex=男, age=23]
    Student [id=2, name=rose, sex=女, age=18]
    Student [id=3, name=tom, sex=男, age=21]
    Student [id=4, name=alice, sex=女, age=20]