MyBatis基于注解的使用

╰+攻爆jí腚メ 2022-04-05 04:15 256阅读 0赞

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();