linq"System.NotSupportedException"存在错误； [英] There is an error with linq "System.NotSupportedException"

问题描述

您能否帮助解决此错误问题，或者说一下如何以不同的方式来解决.谢谢！

Could you help to solve the problem with this error or say how it can be done differently. Thank you!

我的任务是输出结果(集合)以及其中每个实体的注释. 如果用户在选举中拥有它.

My task is to output the result (collection) with a note for each entity in it. If the user has it in the elected.

protected Expression < Func < TEntity, TBindingModel > > MapToBindingModel;  
protected ApplicationUserManager UserManager => Request.GetOwinContext().GetUserManager<ApplicationUserManager>();


internal ApplicationUser _applicationUser;

[HttpGet]
[Route]
[EnableQuery]
public virtual async Task<IHttpActionResult> GetAll()
{
    _applicationUser = await UserManager.FindByIdAsync(User.Identity.GetUserId());
    if (_applicationUser == null)
        return BadRequest("User is not found");

    return Ok(Service.GetAll().Select(MapToBindingModel));
}

MapToBindingModel = title => new TitleBindingModel
    {
        Id = title.Id,
       //data..
        Favorite = _applicationUser != null && _applicationUser.Favorite.Titles.Any(i=>i.Id == title.Id)       
    };       

这是错误消息:

{
    "Message": "An error has occurred.",
    "ExceptionMessage": "Could not create constant with type \"Domain.Authorization.ApplicationUser\". In this context only primitive types and enumeration types are supported.",
    "ExceptionType": "System.NotSupportedException",
    "StackTrace": "   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.ConstantTranslator.TypedTranslate(ExpressionConverter parent, ConstantExpression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.EqualsTranslator.CreateIsNullExpression(ExpressionConverter parent, Expression input)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.NotTranslator.TypedTranslate(ExpressionConverter parent, UnaryExpression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.BinaryTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MemberInitTranslator.TypedTranslate(ExpressionConverter parent, MemberInitExpression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, DbExpression& source, DbExpressionBinding& sourceBinding, DbExpression& lambda)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.SelectTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)\r\n   в System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.Convert()\r\n   в System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)\r\n   в System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__6()\r\n   в System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)\r\n   в System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__5()\r\n   в System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)\r\n   в System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)\r\n   в System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()\r\n   в System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()\r\n   в Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n   в Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)\r\n   в Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)\r\n   в System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   в System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding)\r\n   в System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)\r\n--- Конец трассировка стека из предыдущего расположения, где возникло исключение ---\r\n   в System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n   в System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   в System.Web.Http.Owin.HttpMessageHandlerAdapter.<BufferResponseContentAsync>d__27.MoveNext()"
}

推荐答案

在.Select(MapToBindingModel)

由于EF无法将结果投影到TitleBindingModel，因此您应在尝试映射GetAll()的结果之前将其具体化.

Since EF can't project your results to TitleBindingModel you should materialize the result of GetAll() before attempting to map them.

public virtual async Task<IHttpActionResult> GetAll()
{
    ...

    return Ok(Service.GetAll().ToList().Select(MapToBindingModel));
}

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