# mybatis注解开发


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## 一、常用注解
- @Insert
- @Update
- @Delete
- @Select
- @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

## 二、简单增删改查
```java
    @Insert("insert into user (username) values (#{username})")
    public void add(User user);

    @Update("update user set username = #{username} where id = #{id}")
    public void update(User user);

    @Delete("delete from user where id = #{id}")
    public void delete(Integer id);

    @Select("select * from user")
    public List<User> select();

    @Select("select * from user where id = #{id}")
    public User findById(Integer id);
```

## 三、实现复杂映射
- @Results 代替的标签是 `<resultMap>`,可以使用单个`@Result`,或@Result集合：`@Results({@Result(), @Result(), ...})` 或 `@Results({@Result()})`
- @Result 代替了`<id>`和`<result>`标签
  - column: 数据库列名
  - property: 装配的属性名
  - one: 需要使用@One注解`(@Result(one=@One)())`
  - many: 需要使用@Many注解`(@Result(many=@Many)())`
- @One 代替了`<assocation>`标签
- @Many 代替了`<collection>`标签
### 1.一对一
```java
    /**
     * @One里可以写sql，也可以引用方法
     */
    @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.example.demo.mapper.AnnoUserMapper.findById"))
    })
    @Select("select * from orders")
    public List<Order> findOrderAndUser();
```

### 2.一对多
```java
    @Select("select * from user")
    @Results({
        @Result(property = "id", column = "id"),
        @Result(property = "username", column = "username"),
        @Result(property = "orderList", column = "id", javaType = List.class,
            many = @Many(select = "com.example.demo.mapper.AnnoOrderMapper.findOrderByUid"))
    })
    public List<User> findAll();
```

### 3.多对多
类似一对多

> 示例代码见：https://gitee.com/ixinglan/mybatis-tec.git