【SSM直击大厂】第十五章：Mybatis 注解开发

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📋📋 精彩摘要：注解开发是在企业中较为常见的一种开发技术，Mybatis注解开发方式可以减少编写Mapper 映射文件，使程序结构更加简洁，便于维护和更新。本章将通过基础CRUD操作介绍Mybatis注解开发。

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📚目录

📖Mybatis 注解开发

📝1️⃣MyBatis的常用注解

📝2️⃣MyBatis的增删改查

📝3️⃣复杂映射开发

📝4️⃣一对一查询

📝5️⃣一对多查询

📝6️⃣多对多查询

📝7️⃣本章小结

📖Mybatis 注解开发

📝1️⃣MyBatis的常用注解

   Mybatis中的注解基本上都在org.apache.ibatis.annotations目录下，这里简单介绍几种常用注解：

📝2️⃣MyBatis的增删改查

user表的增删改查的原始操作

测试类：Test：

    private UserMapper userMapper;@Beforepublic 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);}@Testpublic void testAdd() {User user = new User();user.setUsername("测试数据");user.setPassword("123");user.setBirthday(new Date());userMapper.add(user);}@Testpublic 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);}@Testpublic void testDelete() throws IOException {userMapper.delete(16);}@Testpublic void testFindById() throws IOException {User user = userMapper.findById(1);System.out.println(user);}@Testpublic void testFindAll() throws IOException {List all = userMapper.findAll();for (User user : all) {System.out.println(user);}}

使用注解开发：

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。

除此之外，也可以 指定扫描包含映射关系的接口所在的包

📝3️⃣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，@Result，@One，@Many注解组合完成复杂关系的配置。

📝4️⃣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

一对一查询的语句

select * from orders; select * from user where id=查询出订单的uid; 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 findAll();}

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.projtct.mapper.UserMapper.findById")) })List findAll();}//对应@onepublic interface UserMapper {   @Select("select * from user where id=#{id}")   User findById(int id);}

测试结果

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

📝5️⃣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

一对多查询的语句

select * from user;

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

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 orderList;}

创建UserMapper接口

List findAllUserAndOrder();

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.project.mapper.OrderMapper.findByUid")) })List findAllUserAndOrder();}//对应@Manypublic interface OrderMapper {    @Select("select * from orders where uid=#{uid}")List findByUid(int uid);}

测试结果

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

📝6️⃣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

多对多查询的语句

select * from user;

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

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 orderList;// 代表当前用户具备哪些角色private List roleList;}public class Role {private int id;private String rolename;}

添加UserMapper接口方法

List findAllUserAndRole();

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.project.mapper.RoleMapper.findByUid")) })List findAllUserAndRole();}//对应@Manypublic interface RoleMapper {@Select("select * from role r,user_role urwhere r.id=ur.role_id and ur.user_id=#{uid}")List findByUid(int uid);}

测试结果

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

📝7️⃣本章小结

Mybatis常用注解

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