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2.Mybatis的注解开发

2.1 MyBatis的常用注解

这几年来注解开发越来越流行，Mybatis也可以使用注解开发方式，这样我们就可以减少编写Mapper

映射文件了。我们先围绕一些基本的CRUD来学习，再学习复杂映射多表操作。

@Insert：实现新增

@Update：实现更新

@Delete：实现删除

@Select：实现查询

@Result：实现结果集封装

@Results：可以与@Result 一起使用，封装多个结果集

@One：实现一对一结果集封装

@Many：实现一对多结果集封装

2.2 MyBatis的增删改查

我们完成简单的user表的增删改查的操作

private UserMapper userMapper;@Before
public void before() throws IOException {InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession(true);userMapper = sqlSession.getMapper(UserMapper.class);
}@Test
public void testAdd() {User user = new User();user.setUsername("测试数据");user.setPassword("123");user.setBirthday(new Date());userMapper.add(user);
}
@Test
public void testUpdate() throws IOException {User user = new User();user.setId(16);user.setUsername("测试数据修改");user.setPassword("abc");user.setBirthday(new Date());userMapper.update(user);
}@Test
public void testDelete() throws IOException {userMapper.delete(16);
}
@Test
public void testFindById() throws IOException {User user = userMapper.findById(1);System.out.println(user);
}
@Test
public void testFindAll() throws IOException {List<User> all = userMapper.findAll();for(User user : all){System.out.println(user);}
}

修改MyBatis的核心配置文件，我们使用了注解替代的映射文件，所以我们只需要加载使用了注解的Mapper接口即可

<mappers><!--扫描使用注解的类--><mapper class="com.learn.mapper.UserMapper"></mapper>
</mappers>

或者指定扫描包含映射关系的接口所在的包也可以

<mappers><!--扫描使用注解的类所在的包--><package name="com.learn.mapper"></package>
</mappers>

2.3 MyBatis的注解实现复杂映射开发

实现复杂关系映射之前我们可以在映射文件中通过配置来实现，使用注解开发后，我们可以使用@Results注解，@Result注解，@One注解，@Many注解组合完成复杂关系的配置

2.4 一对一查询

2.4.1 一对一查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户

一对一查询的需求：查询一个订单，与此同时查询出该订单所属的用户

2.4.2 一对一查询的语句

对应的sql语句：

select * from orders;select * from user where id=查询出订单的uid;

查询的结果如下：

2.4.3 创建Order和User实体

public class Order {private int id;private Date ordertime;private double total;//代表当前订单从属于哪一个客户private User user;
}public class User {private int id;private String username;private String password;private Date birthday;}

2.4.4 创建OrderMapper接口

public interface OrderMapper {List<Order> findAll();
}

2.4.5 使用注解配置Mapper

public interface OrderMapper {@Select("select * from orders")@Results({@Result(id=true,property = "id",column = "id"),@Result(property = "ordertime",column = "ordertime"),@Result(property = "total",column = "total"),@Result(property = "user",column = "uid",javaType = User.class,one = @One(select = "com.learn.mapper.UserMapper.findById"))})List<Order> findAll();
}

public interface UserMapper {@Select("select * from user where id=#{id}")User findById(int id);}

2.4.6 测试结果

@Test
public void testSelectOrderAndUser() {List<Order> all = orderMapper.findAll();for(Order order : all){System.out.println(order);}
}

2.5 一对多查询

2.5.1 一对多查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户

一对多查询的需求：查询一个用户，与此同时查询出该用户具有的订单

2.5.2 一对多查询的语句

对应的sql语句：

select * from user;select * from orders where uid=查询出用户的id;

查询的结果如下：

2.5.3 修改User实体

public class Order {private int id;private Date ordertime;private double total;//代表当前订单从属于哪一个客户private User user;
}public class User {private int id;private String username;private String password;private Date birthday;//代表当前用户具备哪些订单private List<Order> orderList;
}

2.5.4 创建UserMapper接口

List<User> findAllUserAndOrder();

2.5.5 使用注解配置Mapper

public interface UserMapper {@Select("select * from user")@Results({@Result(id = true,property = "id",column = "id"),@Result(property = "username",column = "username"),@Result(property = "password",column = "password"),@Result(property = "birthday",column = "birthday"),@Result(property = "orderList",column = "id",javaType = List.class,many = @Many(select = "com.learn.mapper.OrderMapper.findByUid"))})List<User> findAllUserAndOrder();
}public interface OrderMapper {@Select("select * from orders where uid=#{uid}")List<Order> findByUid(int uid);}

2.5.6 测试结果

List<User> all = userMapper.findAllUserAndOrder();
for(User user : all){System.out.println(user.getUsername());List<Order> orderList = user.getOrderList();for(Order order : orderList){System.out.println(order);}System.out.println("-----------------------------");
}

2.6 多对多查询

2.6.1 多对多查询的模型

用户表和角色表的关系为，一个用户有多个角色，一个角色被多个用户使用

多对多查询的需求：查询用户同时查询出该用户的所有角色

2.6.2 多对多查询的语句

对应的sql语句：

select * from user;select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=用户的id

查询的结果如下：

2.6.3 创建Role实体，修改User实体

public class User {private int id;private String username;private String password;private Date birthday;//代表当前用户具备哪些订单private List<Order> orderList;//代表当前用户具备哪些角色private List<Role> roleList;
}public class Role {private int id;private String rolename;}

2.6.4 添加UserMapper接口方法

List<User> findAllUserAndRole();

2.6.5 使用注解配置Mapper

public interface UserMapper {@Select("select * from user")@Results({@Result(id = true,property = "id",column = "id"),@Result(property = "username",column = "username"),@Result(property = "password",column = "password"),@Result(property = "birthday",column = "birthday"),@Result(property = "roleList",column = "id",javaType = List.class,many = @Many(select = "com.learn.mapper.RoleMapper.findByUid"))
})
List<User> findAllUserAndRole();}public interface RoleMapper {@Select("select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=#{uid}")List<Role> findByUid(int uid);
}

2.6.6 测试结果

UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAllUserAndRole();
for(User user : all){System.out.println(user.getUsername());List<Role> roleList = user.getRoleList();for(Role role : roleList){System.out.println(role);}System.out.println("----------------------------------");
}

在这里共享一下例子代码，需要的请去下载https://gitee.com/LCreator/spring_learning