c# - linq "System.NotSupportedException"有错误

Question

您能否帮助解决此错误的问题或说明如何以不同的方式完成此操作。谢谢!

我的任务是输出结果(集合)，其中包含每个实体的注释。如果用户在选中它。

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)       
    };       

这是错误信息:

{
    "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()"
}

Answer 1

在 .Select(MapToBindingModel) 之前需要一个 ToList()

由于 EF 无法将您的结果投影到 TitleBindingModel，您应该在尝试映射它们之前具体化 GetAll() 的结果。

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

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