AutoMapper投影误差

Question

我在web中获得了以下方法：

public async Task<IHttpActionResult> Get()
{
   var categories = await _context.Categories.Include(x => x.SubCategories)
                                  .Where(c => c.IsActive)
                                  .ToListAsync();
   var outPut = AutoMapper.Mapper.Map<List<CategoryDto>>(categories);
   return Ok(outPut);
}

此方法正在按预期工作。但是我不想从数据库中检索所有的记录，然后映射到DTO并返回结果，我想使用AutoMapper.QueryableExtensions，只选择所需的字段。

var categories = await _context.Categories.Include(x => x.SubCategories)
                                          .Where(c => c.IsActive)
                                          .ProjectTo<List<CategoryDto>>()
                                          .ToListAsync();

在映射配置中，我定义了映射如下：

public static void Config()
{
    AutoMapper.Mapper.Initialize(config =>
    {
        config.CreateMap<SubCategory, SubCategoryDto>();
        config.CreateMap<Category, CategoryDto>().ForMember(
                    des=>des.SubCategoriesCount,
                    opt=>opt.MapFrom(src=>src.SubCategories.Count));
    });

}

在运行时，我会得到以下异常

“System.Collections.Generic.List1[CategoriesAndBrandsServices.Dtos.CategoryDto]. Create using Mapper.CreateMap<Category, List1>."，”：“从CategoriesAndBrandsServices.Models.Category到CategoriesAndBrandsServices.Models.Category的缺失地图”exceptionType："System.InvalidOperationException"，"stackTrace"：“应AutoMapper.QueryableExtensions.ExpressionBuilder.CreateMapExpression(ExpressionRequest请求，表达式instanceParameter，\r\n在AutoMapper.QueryableExtensions.ExpressionBuilder.CreateMapExpression(ExpressionRequest请求下)\r\n在AutoMapper.LockingConcurrentDictionary2.<>c__DisplayClass2_1.<.ctor>b__1()\r\n at System.Lazy1.CreateValue()\r\n at System.Lazy1.LazyInitValue()\r\n at System.Lazy1.get_Value()\r\n在AutoMapper.LockingConcurrentDictionary2.GetOrAdd(TKey key)\r\n at AutoMapper.QueryableExtensions.ExpressionBuilder.CreateMapExpression(Type sourceType, Type destinationType, IDictionary2参数，\r\n在AutoMapper.QueryableExtensions.ProjectionExpression.ToTResult\r\n at AutoMapper.QueryableExtensions.ProjectionExpression.ToTResult\r\n at AutoMapper.QueryableExtensions.Extensions.ProjectToTDestination\r\n at AutoMapper.QueryableExtensions.Extensions.ProjectToTDestination\r\n at CategoriesAndBrandsServices.Controllers.CategoriesController.d0.MoveNext() in c:\OnlineShoppingWebsite\Services\CategoriesAndBrandsServices\CategoriesAndBrandsServices\Controllers\CategoriesController.cs:line 24\r\n--从以前的异常位置开始的堆栈跟踪被抛出)\r\n在堆栈跟踪的System.Runtime.CompilerServices.TaskAwaiter1.GetResult()\r\n at System.Web.Http.Controllers.ApiControllerActionInvoker.d\_\_0.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Runtime.CompilerServices.TaskAwaiter1.GetResult()\r\n的System.Web.Http.Controllers.ActionFilterResult.d2.MoveNext()\r\n---末端，从以前抛出异常的位置开始r\n在System.Web.Http.Dispatcher.HttpControllerDispatcher.d__1.MoveNext()“

Answer 1

我假设这个项目是一对一的，并且您尝试从一个类别转换到一个类别dtos列表，所以尝试用这个来恢复项目。

.ProjectTo<CategoryDto>()

PS。从异常“从System.Collections.Generic.List1CategoriesAndBrandsServices.Dtos.CategoryDto.到CategoriesAndBrandsServices.Models.Category的缺少映射使用Mapper.CreateMap创建”。