初期的 MyBatis 是一个 XML 驱动的框架。配置信息是基于 XML 的，映射语句也是定义在 XML 中的。而在 MyBatis 3 中，提供了其它的配置方式。MyBatis 3 构建在全面且强大的基于 Java 语言的配置 API 之上。它是 XML 和注解配置的基础。注解提供了一种简单且低成本的方式来实现简单的映射语句。
public interface UserMapper {
// 新增
@Insert(value = "insert into user(id, username, `password`, birthday) values (#{id}, #{username}, #{password}, #{birthday})")
void addUser(User user);
// 更新
@Update(value = "update user set username = #{username}, `password` = #{password}, birthday = #{birthday} where id = #{id}")
void updateUser(User user);
// 查询
@Select(value = "select * from user")
List selectAll();
// 删除
@Delete(value = "delete from user where id = #{id}")
void deleteUser(Integer id);
}
4.1.2 一对一查询
执行过程：
1）执行@Select标签的sql语句。
2）执行@Results标签的语句封装@Select的查询结果。
3）封装结果的时候有一个属性是user ，内部的one属性关联到了另外一个查询结果。所以就会去UserMapper中执行selectById 根据 column=uid 将 order 的uid作为参数去查询结果。
// 订单一对一查询
public interface OrdersMapper {
// select * from orders o left join user u on o.uid = u.id
@Results({
@Result(property = "id", column = "id"),
@Result(property = "ordertime", column = "ordertime"),
@Result(property = "total", column = "total"),
@Result(
javaType = User.class,
property = "user",
column = "uid",
one = @One(select = "com.zyj.mapper.UserMapper.selectById"))
})
@Select(value = "select * from orders")
List findAllOrderAndUser();
}
// 用户查询
public interface UserMapper {
@Select(value = "select * from user where id = #{id}")
User selectById(Integer id);
}
注解和标签对应关系总结：
注解
标签
@Select
select
@Results
resultMap
@Result
id和
@One
association
4.1.3 一对多查询
执行过程：
1）执行@Select标签的sql语句。
2）执行@Results标签的语句封装@Select的查询结果。
3）封装结果的时候有一个属性是orderList ，内部的Many属性关联到了另外一个查询结果。所以就会去OrderMapper中执行selectByUId 根据 column=id 将 User 的id作为参数去查询结果。
// 用户查询一对多
public interface UserMapper {
// select * from user u left join orders o on u.id = o.uid;
@Results({
@Result(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.zyj.mapper.OrdersMapper.selectByUId")
)
})
@Select(value = "select * from user")
List findAllUserAndOrder();
}
// 根据用户id查询用户订单
public interface OrdersMapper {
// 根据用户id返回查询结果
@Select(value = "select * from orders where uid = #{uid}")
List selectByUId(Integer uid);
}
注解和标签对应关系总结：
注解
标签
@Select
@Results
@Result
和
@Many
4.1.4多对多查询
执行过程：
1）执行@Select标签的sql语句。
2）执行@Results标签的语句封装@Select的查询结果。
3）封装结果的时候有一个属性是roleList ，内部的Many属性关联到了另外一个查询结果。所以就会去RoleMapper中执行selectByUserId 根据 column=id 将 User 的id作为参数去查询结果。
public interface UserMapper {
// select * from user u left join sys_user_role ur on u.id = ur.userid left join sys_role r on ur.roleid = r.id;
@Results({
@Result(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.zyj.mapper.RoleMapper.selectByUserId")
)
})
@Select(value = "select * from user")
List findAllUserAndRole();
}
// 根据用户id查询角色
public interface RoleMapper {
@Select(value = "select r.* from sys_role r inner join sys_user_role ur on r.id = ur.roleid where userid = #{uid}")
List selectByUserId(Integer uid);
}
