一、返回集合

1.返回JavaBean集合

public List
     
       selectMyUserByNameLike(String name);
     

       select * from myuser where name like #{name}

测试方法

public static void main(String[] args) {    SqlSession session = null;    try {        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);        session = sqlSessionFactory.openSession();        MyUserMapper mapper = session.getMapper(MyUserMapper.class);        List
     
       myUsers = mapper.selectMyUserByNameLike("%a%");        System.out.println(myUsers);    } catch (IOException e) {        e.printStackTrace();    } finally {        if (session != null) {            session.close();        }    }}
     

2.返回 Map 集合

       select * from myuser

 

二、返回 Map

1.一条记录

public Map
     
       selectMyUserById(Integer id);
     

  select * from myuser where id = #{id}

2.多条记录，需要指定 Map 的 Key 和 Value 的类型

// 指定 Map 的 Key 从记录中的 id 列获取@MapKey("id")public Map
     
       selectMyUserByGtId(Integer id);
     

       select * from myuser where id > #{id}

 

三、返回 resultMap 自定义结果集封装

关于自动映射封装的配置

默认数据库字段与 JavaBean 对应不上时可开启驼峰命名或查询时使用别名

 

1.自定义 JavaBean 的封装

确认是否成功可以关掉 MyBatis 的自动映射

public MyUser selectMyUserById(Integer id);

     
         
          
          
          
          
          
      
     
       select * from myuser where id = #{id}

 

2.关联查询的封装，一对一，JavaBean 属性包含 JavaBean

public MyUser selectMyUserById(Integer id);

直接调用属性赋值

         
          
          
          
          
          
      
       SELECT m.id, m.name, m.age, m.did, d.name AS dname FROM myuser m,dept d WHERE m.did = d.id AND m.id = #{id}

使用 association

         
          
          
          
          
              
               
           
      
       SELECT m.id, m.name, m.age, m.did, d.name AS dname FROM myuser m,dept d WHERE m.did = d.id AND m.id = #{id}

使用 association 二次查询，即有两条 SQL

         
          
          
          
          
      
       SELECT * FROM myuser WHERE id = #{id}

     
     
         
            select * from dept where id = #{id}    
      

开启懒加载：在没有使用 Dept 的属性时，则只会加载 MyUser 的属性。即只会发送一条 SQL 语句，要使用 Dept 属性时才会发送第二条 SQL。不会一次性发送两条 SQL

 

3.关联查询的封装，一对多，JavaBean 属性包含 JavaBean 的集合

使用 association

public Dept getDeptById(Integer id);

         
          
          
          
              
               
               
               
           
      
         SELECT m.id,m.name,m.age,m.did,d.name AS dname FROM myuser m,dept d WHERE m.did = d.id AND d.id = #{id}

关闭懒加载，使用二次查询

public Dept getDeptByIdStep(Integer did);

     
         
          
          
          
      
         select * from dept where id = #{id}

public List
     
       selectMyUserByDid(Integer dId);
     

  select * from myuser where dId = #{did}

 

4.鉴别器 discriminator

       SELECT * FROM myuser WHERE id = #{id}
         
          
          
          
          
              
               
                   
                
               
               
                   
                
           
      
     

       select * from dept where id = #{id}

 

 

 

上面测试中使用的实体类与数据

public class Dept {    private Integer id;    private String name;    private List
     
       myUsers;
     

public class MyUser {    private Integer id;    private String name;    private Integer age;    private Dept dept;

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