CoreFrist多个上下文
出现这个怎么解决：No DbContext was found in assembly' ShopCore'. Ensure that you' re using the correct assembly and that the type is neither abstract nor generic.
add-migration migrationname -c AppDbContext
如果出现：Unable to create an object of type 'AppDbContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728
就是说明：缺少无参构造函数
例如：
public AppDbContext()
{
}