Mybatis—注解开发

Mybatis的注解开发

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。

@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

MyBatis的增删改查

我们完成简单的user表的增删改查的操作
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.itheima.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.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

一对一查询

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

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;}

创建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();
}

测试结果

    @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());}

一对多查询

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

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;
}

创建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);

测试结果

    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());}

多对多查询

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

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;}

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);
}

测试结果

    @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());}