MyBatis框架基于Annotation注解的一对多关联映射

素颜马尾好姑娘i 2022-06-18 08:28 214阅读 0赞

代码：

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="com.mapper.ClazzMapper"/> 
      	<mapper class="com.mapper.StudentMapper"/> 
      </mappers>
    </configuration>

Clazz.java

package com.bean;
    
    import java.io.Serializable;
    import java.util.List;
    
    public class Clazz implements Serializable {
    	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() {
    		// TODO Auto-generated method stub
    		return "Clazz [id=" + id + ", code=" + code + ", name=" + name + "]";
    	}
    	
    }

Student.java

package com.bean;
    
    import java.io.Serializable;
    
    public class Student implements Serializable {
    	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() {
    		// TODO Auto-generated method stub
    		return "Student [id=" + id + ", name=" + name + ", sex=" + sex + ", age=" + age + "]";
    	}
    	
    }

FKSqlSessionFactory.java

package com.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 inputStream = Resources.getResourceAsStream("mybatis-config.xml");
    			sqlSessionFactory = new SqlSessionFactoryBuilder()
    					.build(inputStream);
    		} 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;
    	}
    
    }

ClazzMapper.xml

package com.mapper;
    
    import java.util.List;
    
    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 com.bean.Clazz;
    import com.bean.Student;
    
    public interface ClazzMapper {
    	@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="com.mapper.StudentMapper.selectByClazzId",
    				fetchType=FetchType.LAZY))
    	})
    	Clazz selectById(Integer id);
    }

StudentMapper.xml

package com.mapper;
    
    import java.util.List;
    
    import org.apache.ibatis.annotations.Result;
    import org.apache.ibatis.annotations.Results;
    import org.apache.ibatis.annotations.Select;
    
    import com.bean.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);
    }

OneToManyTest.java

package com.test;
    
    import org.apache.ibatis.session.SqlSession;
    
    import com.bean.Clazz;
    import com.factory.FKSqlSessionFactory;
    import com.mapper.ClazzMapper;
    
    public class OneToManyTest {
    
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
          SqlSession session = FKSqlSessionFactory.getSqlSession();
          ClazzMapper cm =session.getMapper(ClazzMapper.class);
          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));
          session.commit();
          session.close();
    	}
    
    }

截图：

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[Center]: /images/20220618/da0fda67876c408e9bdd9cd2d0e78535.png