在Azure移动服务.NET中使用DTO引发目标调用异常

Question

我使用Azure移动服务.NET后端，我们都知道必须使用实体框架类映射到数据库创建/迁移。 所以我需要使用DTO来序列化我想要的属性，计算属性等。我遵循Field Engineer example。但Automapper给了我很多的痛苦，尽管我做了一切应有的事情。

我检查了其他人的博客和网站，有些使用Automapper，其他人不使用，例如this one。我觉得不像使用Automapper那样使用Select（）方法快速创建DTO，就像我之前在实现Web API时所做的那样。

我将TableController类恢复为Post，使用EntityDomainManager，并将GetAllPosts方法留在下面。

public class PostController : TableController<Post> 
{ 
    private MobileServiceContext _context; 

    protected override void Initialize(HttpControllerContext controllerContext) 
    { 
     base.Initialize(controllerContext); 
     _context = new MobileServiceContext(); 
     DomainManager = new EntityDomainManager<Post>(_context, Request, Services); 
    } 

    //[ExpandProperty("User")] 
    // GET tables/Post 
    public IQueryable<PostDto> GetAllPost() 
    { 
     return Query().Include("User").Select(x => new PostDto()); 
    } 
} 

我得到以下错误。

{"message":"An error has occurred.","exceptionMessage":"Exception has been thrown by the target of an invocation.","exceptionType":"System.Reflection.TargetInvocationException","stackTrace":" at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)\r\n at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)\r\n at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)\r\n at System.Reflection.MethodBase.Invoke(Object obj, Object[] parameters)\r\n at System.Web.Http.OData.Query.ODataQueryOptions.LimitResults(IQueryable queryable, Int32 limit, Boolean& resultsLimited)\r\n at System.Web.Http.OData.Query.ODataQueryOptions.ApplyTo(IQueryable query, ODataQuerySettings querySettings)\r\n at System.Web.Http.OData.EnableQueryAttribute.ApplyQuery(IQueryable queryable, ODataQueryOptions queryOptions)\r\n at System.Web.Http.OData.EnableQueryAttribute.ExecuteQuery(Object response, HttpRequestMessage request, HttpActionDescriptor actionDescriptor)\r\n at System.Web.Http.OData.EnableQueryAttribute.OnActionExecuted(HttpActionExecutedContext actionExecutedContext)\r\n at System.Web.Http.Filters.ActionFilterAttribute.OnActionExecutedAsync(HttpActionExecutedContext actionExecutedContext, CancellationToken cancellationToken)\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.TaskAwaiter.GetResult()\r\n at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.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.TaskAwaiter`1.GetResult()\r\n at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>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.TaskAwaiter`1.GetResult()\r\n at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Web.Http.Filters.ActionFilterAttribute.<CallOnActionExecutedAsync>d__5.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.TaskAwaiter`1.GetResult()\r\n at System.Web.Http.Filters.ActionFilterAttribute.<ExecuteActionFilterAsyncCore>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.TaskAwaiter`1.GetResult()\r\n at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__2.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.TaskAwaiter`1.GetResult()\r\n at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__2.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.TaskAwaiter`1.GetResult()\r\n at System.Web.Http.Controllers.AuthenticationFilterResult.<ExecuteAsync>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.TaskAwaiter`1.GetResult()\r\n at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>d__0.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Web.Http.Controllers.ExceptionFilterResult.<ExecuteAsync>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.TaskAwaiter`1.GetResult()\r\n at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext()","innerException":{"message":"An error has occurred.","exceptionMessage":"The specified type member 'DatePosted' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.","exceptionType":"System.NotSupportedException","stackTrace":" at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MemberAccessTranslator.TypedTranslate(ExpressionConverter parent, MemberExpression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input, DbExpressionBinding& binding)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateSet(Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.ThenByTranslatorBase.Translate(ExpressionConverter parent, MethodCallExpression call)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateSet(Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.ThenByTranslatorBase.Translate(ExpressionConverter parent, MethodCallExpression call)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateSet(Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.UnarySequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SequenceMethodTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, SequenceMethod sequenceMethod)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TypedTranslator`1.Translate(ExpressionConverter parent, Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.Convert()\r\n at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)\r\n at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__6()\r\n at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)\r\n at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__5()\r\n at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)\r\n at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)\r\n at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()\r\n at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()\r\n at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)\r\n at System.Web.Http.OData.Query.TruncatedCollection`1..ctor(IQueryable`1 source, Int32 pageSize)\r\n at System.Web.Http.OData.Query.ODataQueryOptions.LimitResults[T](IQueryable`1 queryable, Int32 limit, Boolean& resultsLimited)"}} 

如果我只是将它转换为实体框架类，它的工作原理。您会注意到我没有填写任何财产，仅用于测试目的。

我使用IIS Express进行本地测试。

数据对象和模型。

public class Post : EntityData 
    { 
     public DateTimeOffset DatePosted { get; set; } 
     public string StatusText { get; set; } 
     public PostType TypeOfPost { get; set; } 

     [ForeignKey("Id")] 
     public virtual User User { get; set; } 

     [ForeignKey("Id")] 
     public virtual ICollection<PostPhotoUrl> PhotoUrls { get; set; } 
    } 

    public class PostDto 
    { 
     public PostDto() 
     { 
      PhotoUrls = new HashSet<PostPhotoUrlDto>();  
     } 

     public DateTimeOffset DatePosted { get; set; } 
     public string StatusText { get; set; } 
     public int TypeOfPost { get; set; } 

     public UserDto User { get; set; } 
     public ICollection<PostPhotoUrlDto> PhotoUrls { get; set; } 
    } 

搜索互联网无法找到任何其他更明确的教程如何使用Azure的移动服务和DTO的，但它不应该引入这样的困难。如果你有任何资源，欢迎。

我应该提到，如果我不做以下测试网站在尝试测试端点时产生错误。

config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore; 

例外快照：

我并不真的需要为这个项目的DTO，但如果我不解决什么，我现在不知道它会从这项服务的长期来看，我会回来追捕我。

Answer 1

看来，Select（）LINQ表达式在元素被完全加载或引用仍未被设置之前发生冲突。 我将该方法转换为IEnumerable返回类型，并在转换为DTO之前急切地加载数据。

 public IEnumerable<PostDto> GetAllPost() 
     { 
      return Query().Include("User").ToList().Select(x => new PostDto 
      { 
       DatePosted = x.DatePosted, 
       StatusText = x.StatusText, 
       TypeOfPost = (int)x.TypeOfPost, 
       User = new UserDto 
       { 
        Id = x.User.Id 
       } 
      }); 
     } 

测试我的服务后，它返回了我插入到我的数据库中的以下数据。

[ 
    { 
     "datePosted": "2015-04-27T04:05:38.843Z", 
     "statusText": "Post Text", 
     "typeOfPost": 1, 
     "user": { 
      "id": "a59d0f12-8bb1-448e-9c08-56f862b77ee4" 
     }, 
     "photoUrls": [] 
    } 
] 

现在应该用AutoMapper进行测试，以覆盖它与它一起工作。

只有未知点是为什么我需要将ReferenceLoopHandling属性设置为Ignore以使服务正确显示JSON示例数据。

config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore; 

Answer 2

我不知道，但认为这个问题可能是这行代码

return Query().Include("User").Select(x => new PostDto()); 

如果你不会使用AutoMapper那么你需要在你的SELECT语句是这样的

手动解析特性

return Query().Include("User") 
       .Select(x => new PostDto() 
       { 
        DatePosted = x.DatePosted, 
        StatusText = x.StatusText, 
        TypeOfPost = x.TypeOfPost, 
        User = new UserDto 
          { 
           //Your propertoes here 
           //eg Id = x.User.Id etc 
          } 
       );