异常:Batch update returned unexpected row count from update [0]; actual row count: 0;

使用了hibernate的主键生成策略，而在程序中又主动去设置了主键值。<class name="ProductRegion" table="PRODUCT_REGION" lazy="false">
        <id name="id" column="PRODUCT_REGION_ID">
            <generator class="native" />
        </id>    
        <many-to-one class = "gira.domain.place.Region" name="region" column="PRODUCT_REGION_REGION_ID" />
        <many-to-one class = "Product" name="product" column="PRODUCT_REGION_PRODUCT_ID" ></many-to-one>
        <property name="index" column="PRODUCT_REGION_INDEX" />
</class>

程序中：
for(Long l:regionIds){
                Region region=regionDao.findById(l);
                ProductRegion productRegion=new ProductRegion();
                productRegion.setProduct(product);
                productRegion.setRegion(region);
                productRegion.setId(i);
                i++;
                productRegions.add(productRegion);
}
从而出现异常了