Question

我使用Azure Mobile Services .NET后端，我们都知道必须使用Entity Framework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。我正在关注Field Engineer example。但Automapper给了我很大的痛苦，尽管我按照预期做了一切。

我检查过其他几个博客和网站，有些人使用Automapper，有些则没有，例如this one。我感觉更舒服，不使用Automapper并使用Select（）动态创建DTO，就像我在实现Web API之前所做的那样。

我将TableController类恢复为Post，使用EntityDomainManager并将GetAllPosts方法保留为以下内容。

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());
    }
}

我收到以下错误。

{"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Entity Framework类，它就可以了。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; }
    }

搜索互联网找不到任何其他更清晰的教程如何使用Azure移动服务和DTO，但它不应该引入这样的困难。如果您有任何资源，欢迎光临。

我应该提一下，如果我不这样做，测试网站在尝试测试端点时会引发错误。

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

异常快照：

JsonMediaTypeFormatter Error

我真的不需要为这个项目设置DTO，但是如果我现在不解决我不理解的东西，那么从长远来看它会回来追捕我。

Answer 1

我不确定，但认为问题可能来自这行代码

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

如果您不使用AutoMapper，则需要手动解析Select语句中的属性

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
                           }  
               );

Answer 2

似乎Select（）LINQ表达式在元素完全加载或引用仍未设置之前发生冲突。我将方法转换为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，它返回了我在数据库中插入的以下数据。

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

现在应该使用AutoMapper进行测试以涵盖它也可以使用它。

只有未知的一点是我需要将ReferenceLoopHandling属性设置为Ignore，以便服务显示正确的JSON样本数据。

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

在Azure Mobile Service .NET中使用DTO会引发目标调用异常

2 个答案: