Mybatis的注解開發

MyBatis的常用注解

這幾年來注解開發越來越流行，Mybatis也可以使用注解開發方式，這樣我們就可以減少編寫Mapper映射文件了。

@Insert：實現新增

@Update：實現更新

@Delete：實現刪除

@Select：實現查詢

@Result：實現結果集封裝

@Results：可以與@Result 一起使用，封裝多個結果集

@One：實現一對一結果集封裝

@Many：實現一對多結果集封裝

MyBatis的增刪改查

我們完成簡單的user表的增刪改查的操作
修改MyBatis的核心配置文件，我們使用了注解替代的映射文件，所以我們只需要加載使用了注解的Mapper接口即可

<mappers><!--掃描使用注解的類--><mapper class="com.itheima.mapper.UserMapper"></mapper>
</mappers>

或者指定掃描包含映射關系的接口所在的包也可以

<mappers><!--掃描使用注解的類所在的包--><package name="com.itheima.mapper"></package>
</mappers>

    userMapper mapper;@Beforepublic void before(){InputStream resourceAsStream = null;try {resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");} catch (IOException ioException) {ioException.printStackTrace();}SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession(true);mapper = sqlSession.getMapper(userMapper.class);}@Testpublic void tset4() {User user = new User();user.setUsername("cx");user.setPassword("159");mapper.add(user);}@Testpublic void tset5() {mapper.delete(5);}@Testpublic void tset6() {User user = new User();user.setId(4);user.setPassword("159");mapper.update(user);}@Testpublic void tset7() {System.out.println(mapper.findById(1));}

public interface userMapper {@Select(" select * from  user")public List<User> findAll();@Select("select * from  user where id=#{id}")public User findById(int i);@Insert(" insert into user values (#{id},#{username},#{password},#{birthday})")public void add(User user);@Update(" update user set password=#{password} where id=#{id}")public void update(User user);@Delete("delete from user where id=#{id}")public void delete(int i);}

MyBatis的注解實現復雜映射開發

實現復雜關系映射之前我們可以在映射文件中通過配置來實現，使用注解開發后，我們可以使用@Results注解，@Result注解，@One注解，@Many注解組合完成復雜關系的配置

一對一查詢

一對一查詢的模型

用戶表和訂單表的關系為，一個用戶有多個訂單，一個訂單只從屬于一個用戶

一對一查詢的需求：查詢一個訂單，與此同時查詢出該訂單所屬的用戶

創建Order和User實體

public class Order {private int id;private Date ordertime;private double total;//代表當前訂單從屬于哪一個客戶private User user;
}public class User {private int id;private String username;private String password;private Date birthday;}

創建OrderMapper接口

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

使用注解配置Mapper

public interface OrderMapper {@Select("select * from orders")@Results({@Result(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.controller.userMapper.findById"))})List<Order> findAll();
}

測試結果

    @Testpublic void tset3() {InputStream resourceAsStream = null;try {resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");} catch (IOException ioException) {ioException.printStackTrace();}SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession(true);OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);System.out.println(mapper.findAll());}

一對多查詢

一對多查詢的模型

用戶表和訂單表的關系為，一個用戶有多個訂單，一個訂單只從屬于一個用戶

一對多查詢的需求：查詢一個用戶，與此同時查詢出該用戶具有的訂單

修改User實體

public class Order {private int id;private Date ordertime;private double total;//代表當前訂單從屬于哪一個客戶private User user;
}public class User {private int id;private String username;private String password;private Date birthday;//代表當前用戶具備哪些訂單private List<Order> orderList;
}

創建UserMapper接口

List<User> findAllUserAndOrder();

使用注解配置Mapper

    @Select( "select * from user")@Results({@Result(property = "username" ,column = "username"),@Result(property = "password",column = "password"),@Result(property = "birthday" ,column = "birthday"),@Result(id=true,property = "id",column = "id"),@Result(property = "orderList",column = "id",javaType = List.class,many = @Many(select = "com.controller.OrderMapper.findByUid"))})public  List<User> findAllUserAndOrder();

    @Select("select * from  orders where uid=#{uid}")Order findByUid(int i);

測試結果

    userMapper mapper;@Beforepublic void before(){InputStream resourceAsStream = null;try {resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");} catch (IOException ioException) {ioException.printStackTrace();}SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession(true);mapper = sqlSession.getMapper(userMapper.class);}  @Testpublic void tset7() {System.out.println(mapper.findAllUserAndOrder());}

多對多查詢

多對多查詢的模型

用戶表和角色表的關系為，一個用戶有多個角色，一個角色被多個用戶使用

多對多查詢的需求：查詢用戶同時查詢出該用戶的所有角色

public class User {private int id;private String username;private String password;private Date birthday;//代表當前用戶具備哪些訂單private List<Order> orderList;//代表當前用戶具備哪些角色private List<Role> roleList;
}public class Role {private int id;private String rolename;}

添加UserMapper接口方法

List<User> findAllUserAndRole();

使用注解配置Mapper

    @Select( "select * from user")@Results({@Result(property = "username" ,column = "username"),@Result(property = "password",column = "password"),@Result(property = "birthday" ,column = "birthday"),@Result(id=true,property = "id",column = "id"),@Result(property = "roleList",column = "id",javaType = List.class,many = @Many(select = "com.controller.RoleMapper.findById"))})public  List<User> findAllUserAndRole();

public interface RoleMapper {@Select("select r.* from sys_user_role ur,sys_role r where ur.roleid=r.id and #{id}=ur.userid")List<Role> findById(int i);
}

測試結果

    @Beforepublic void before(){InputStream resourceAsStream = null;try {resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");} catch (IOException ioException) {ioException.printStackTrace();}SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession(true);mapper = sqlSession.getMapper(userMapper.class);}@Testpublic void tset7() {System.out.println(mapper.findAllUserAndRole());}