collection 一对多和association的多对一关系

学生和班级的一对多的例子

班级类:

package com.glj.pojo;import java.io.Serializable;import java.util.List;public class Clazz implements Serializable{    private Integer id;    private String code;    private String name;        //班级与学生是一对多的关系    private List
     
       students;//省略set/get方法}
     

学生类:

package com.glj.pojo;import java.io.Serializable;public class Student implements Serializable {    private Integer id;    private String name;    private String sex;    private Integer age;        //学生与班级是多对一的关系    private Clazz clazz;//省略set/get方法}

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ClazzMapper使用到了集合-collection 即为一对多，一个班级面对多个学生

package com.glj.mapper;import com.glj.pojo.Clazz;public interface ClazzMapper {    Clazz selectClazzById(Integer id);}

     
         
              select * from tb_clazz where id = #{id}        
              
               
               
               
               
                   
                    
                    
                    
                
           
      
     

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StudentMapper则是与班级为多对一关系，所以使用了关联-association

package com.glj.mapper;import com.glj.pojo.Student;public interface StudentMapper {    Student selectStudentById(Integer id); }

     
         
              select * from tb_clazz c,tb_student s where c.id = s.id and s.id = #{id}        
              select * from tb_student where clazz_id = #{id}