1.SQL语句建表

1 CREATE TABLE teacher( 2 t_id INT PRIMARY KEY AUTO_INCREMENT, t_name VARCHAR(20) 3 ); 4 CREATE TABLE class( 5 c_id INT PRIMARY KEY AUTO_INCREMENT, c_name VARCHAR(20), 6 teacher_id INT 7 ); 8 ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id); 9 INSERT INTO teacher(t_name) VALUES('LS1'); INSERT INTO teacher(t_name) VALUES('LS2');10 INSERT INTO class(c_name, teacher_id) VALUES('bj_a', 1); INSERT INTO class(c_name, teacher_id) VALUES('bj_b', 2);

2.实体类

1 package com.zhengbin.entity; 2  3 public class Teacher { 4     private int id; 5     private String name; 6     public int getId() { 7         return id; 8     } 9     public void setId(int id) {10         this.id = id;11     }12     public String getName() {13         return name;14     }15     public void setName(String name) {16         this.name = name;17     }18     @Override19     public String toString() {20         return "Teacher [id=" + id + ", name=" + name + "]";21     }22     public Teacher(int id, String name) {23         super();24         this.id = id;25         this.name = name;26     }27     public Teacher() {28         super();29         // TODO Auto-generated constructor stub30     }31 }

1 package com.zhengbin.entity; 2  3 public class Classes { 4     private int id; 5     private String name; 6     private Teacher teacher; 7     @Override 8     public String toString() { 9         return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + "]";10     }11     public Classes() {12         super();13     }14     public int getId() {15         return id;16     }17     public void setId(int id) {18         this.id = id;19     }20     public String getName() {21         return name;22     }23     public void setName(String name) {24         this.name = name;25     }26     public Teacher getTeacher() {27         return teacher;28     }29     public void setTeacher(Teacher teacher) {30         this.teacher = teacher;31     }32 }

3.实体类映射文件

　　两种方式：

　　　　1. 联表查询

　　　　　　关键是返回值的设置

　　　　2. 执行两次查询

　　　　　　关键是返回值的设置，和第二次查询所需参数的传递

1 
       2  3 
       4 
      
        5     
        6     
        7      8     
       12     
       13         select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id};14     15     
       
        16         
        17         
        18         
        
         19             
         20             
         21         
        22     
       23     
       29      
       30          select * from class where c_id=#{id}31      32      
       33          select t_id id,t_name name from teacher where t_id=#{id}34      35      
       
        36          
        37          
        38          
        39      
       40 
      

4.测试类

1 package com.zhengbin.test; 2  3 import org.apache.ibatis.session.SqlSession; 4 import org.apache.ibatis.session.SqlSessionFactory; 5  6 import com.zhengbin.entity.Classes; 7 import com.zhengbin.util.MyBatisUtils; 8  9 public class Test3 {10     @org.junit.Test11     public void getTeacher(){12         SqlSessionFactory sessionFactory = MyBatisUtils.getFactory();13         // 参数为TRUE，相当于session.commit();14         SqlSession session = sessionFactory.openSession(true);15         // 读取映射文件16         String statement = "com.zhengbin.entity.classMapper" + ".getClass";17 //        String statement = "com.zhengbin.entity.classMapper" + ".getClass2";18         Classes c = session.selectOne(statement,1);19         System.out.println(c);20         session.close();21     }22 }

5.几个关键的属性

association : 用于一对一的关联查询property : 对象属性的名称javaType : 对象属性的类型column : 所对应的外键字段名称select : 使用另一个查询封装的结果