MyBatis基于注解的使用

Mybtis注解

增加接口CategoryMapper ，并在接口中声明的方法上，加上注解
增加对CategoryMapper 的映射：
<mappers>
//com.shop.mapper包下的CategoryMapper接口
        <mapper class="com.shop.mapper.CategoryMapper"/> 
</mappers>
以后mapper内每增加一个接口，需要在mappers标签内增加对应的映射

或者直接映射包：(只要接口在该包下，就不用再写映射了)
<mappers>
//com.shop.mapper包
        <package name="com.shop.mapper"/>
</mappers>

基于注解的简单增删改查：
public interface CategoryMapper {
  
    @Insert(" insert into category ( name ) values (#{name}) ") 
    public int add(Category category); 
        
    @Delete(" delete from category where id= #{id} ") 
    public void delete(int id); 
      
    @Update("update category set name=#{name} where id=#{id} ") 
    public int update(Category category);  
        
    @Select(" select * from category ") 
    public List<Category> list(); 
}

多个参数：例如分页
需要在参数前加上注释@Param("参数名")
@Select("select * from comment where cbid=#{cbid} limit #{begin},#{pageSize}")
public List<Comment> Listpage(@Param("pageSize") int pageSize,@Param("begin") int begin,@Param("cbid") int cbid);

注解方式:一对多
查询所有Category，及Category下的Product
新增接口ProductMapper
注解@Select用于根据分类id获取产品集合
public interface ProductMapper {
    @Select(" select * from product where cid = #{cid}")
    public List<Product> listByCategory(int cid);
}
@Select注解获取Category类本身,@Results 通过@Result和@Many中调用ProductMapper.listByCategory()方法相结合，来获取一对多关系
public interface CategoryMapper {
    @Select(" select * from category ")
    @Results({ 
//下句可以省略
                @Result(property = "id", column = "id"),
//column = "id"对应Category的id的字段，select = "com.shop.mapper.ProductMapper.listByCategory")写全包名+接口名+方法名
//一对多用many=@Many()，一对多需要添加属性：javaType = List.class
                @Result(property = "products", javaType = List.class, column = "id", many = @Many(select = "com.shop.mapper.ProductMapper.listByCategory") )
            })
    public List<Category> list();
}

注解方式:多对一
CategoryMapper接口，提供get方法
public interface CategoryMapper {
    @Select(" select * from category where id = #{id}")
    public Category get(int id);
}
ProductMapper接口，提供list方法
public interface ProductMapper {
    @Select(" select * from product ")
    @Results({ 
//column="cid"对应product表中的cid，多对一用one=@One（）
        @Result(property="category",column="cid",one=@One(select="com.how2java.mapper.CategoryMapper.get")) 
    })
    public List<Product> list();
}

注解方式:多对多
订单项与商品是多对一关系，订单与订单项是一对多关系
ProductMapper接口，提供 get方法：
public interface ProductMapper {
    @Select("select * from product_ where id = #{id}")
    public Product get(int id);
}
OrderItemMapper，提供listByOrder方法：
public interface OrderItemMapper {
    @Select(" select * from order_item_ where oid = #{oid}")
    @Results({ 
        @Result(property="product",column="pid",one=@One(select="com.how2java.mapper.ProductMapper.get")) 
    }) 
    public List<OrderItem> listByOrder(int oid);
}
OrderMapper，提供list方法
public interface OrderMapper {
    @Select("select * from order_")
     @Results({
            @Result(property = "id", column = "id"),
            @Result(property = "orderItems", javaType = List.class, column = "id", 
                    many = @Many(select = "com.how2java.mapper.OrderItemMapper.listByOrder"))
            })      
    public List<Order> list();
}

注解方式:动态SQL
用script标签包围，然后像xml语法一样书写
例子：
@Select("<script>select * from comment <where>"
            + "<if test='cbid!=0'> and cbid=#{cbid}</if>"
            + "<if test='cuid!=0'> and cuid=#{cuid}</if>"
            + "</where></script>")

注解方式：返回insert语句的自增长id
例如：
@Insert("insert into discuss values(null,now(),#{dresult},#{event.eveid},1)")
@Options(useGeneratedKeys=true,keyProperty="did",keyColumn="did")
public int addDiscuss(Discuss dis);
返回的自增长id被储存到参数Discuss对象中
int did = dis.getDid();