Question

我试图使用带有实体框架6的Effort数据提供程序来使用一些测试代码。我尝试做的事情似乎应该是绝对最简单的用例，但我＆＃39 ;我只是无法让事情发挥作用。

这是我的DbContext类：

public class CcdReductionFrameCatalogue : DbContext
    {
    public CcdReductionFrameCatalogue()
        : this("name=CcdReductionFrameCatalogue") {}

    public CcdReductionFrameCatalogue(string connectionString) : base(connectionString) {}

    public CcdReductionFrameCatalogue(DbConnection connection) : base(connection, true) {}

    public virtual DbSet<CcdFrame> CcdFrames { get; set; }
    }

POCO实体定义为：

public class CcdFrame : IEquatable<CcdFrame>
    {
    public CcdFrame()
        {
        AcquisitionTimeUtc = DateTime.UtcNow;
        }

    public int Id { get; set; }
    public string Location { get; set; }
    [FitsKeyword("INSTRUME")] public string CameraName { get; set; }

    [FitsKeyword("EXPTIME")] public double ExposureTimeSeconds { get; set; }

    [FitsKeyword("SET-TEMP"), FitsKeyword("CCD-TEMP")] public double TemperatureSetpoint { get; set; }

    [FitsKeyword("NAXIS1")] public int SizeX { get; set; }

    [FitsKeyword("NAXIS2")] public int SizeY { get; set; }

    [FitsKeyword("XBINNING")] public int BinningX { get; set; }

    [FitsKeyword("YBINNING")] public int BinningY { get; set; }

    [FitsKeyword("IMAGETYP")] public string FrameType { get; set; }

    [FitsKeyword("DATE-OBS")] public DateTime AcquisitionTimeUtc { get; set; }
    [FitsKeyword("XORGSUBF")] public int SubframeOriginX { get; set; }
    [FitsKeyword("YORGSUBF")] public int SubframeOriginY { get; set; }

    // IEquatable implementation elided for clarity
    }

[FitsKeyword]属性是我定义的自定义属性，不应对实体框架产生任何影响。

在我的单元测试中，我设置了这样的数据连接，如Effort快速入门指南中所示：

        Connection = DbConnectionFactory.CreateTransient();
        Repository = new CcdReductionFrameCatalogue(Connection);

一旦我在DbSet上使用任何LINQ，我就会得到愚蠢无意义的错误消息。例如，当我将我的存储库传递给这个简单的代码时：

    static void AddOrUpdate(CcdFrame newFrame, CcdReductionFrameCatalogue repository)
        {
        var existingFrames = from frame in repository.CcdFrames
                             where frame.Equals(newFrame)
                             select frame;
        Console.WriteLine(existingFrames.Count());
        // ...never gets past here

当我运行此代码时，我得到：

System.NotSupportedExceptionUnable to create a constant value of type 'TA.ReductionManager.DomainObjects.CcdFrame'. Only primitive types or enumeration types are supported in this context.
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.ConstantTranslator.TypedTranslate(ExpressionConverter parent, ConstantExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.EqualsTranslator.TypedTranslate(ExpressionConverter parent, BinaryExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateLambda(LambdaExpression lambda, DbExpression input)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call, ref DbExpression source, ref DbExpressionBinding sourceBinding, ref DbExpression lambda)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.OneLambdaTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.AggregateTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
   at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.Convert()
   at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.c__DisplayClass7.b__6()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction(Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectQuery`1.c__DisplayClass7.b__5()
   at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
   at System.Data.Entity.Core.Objects.ObjectQuery`1..GetEnumerator>b__0()
   at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
   at System.Linq.Enumerable.Single(IEnumerable`1 source)
   at System.Linq.Queryable.Count(IQueryable`1 source)
   at TA.ReductionManager.Specifications.FitsImporter.AddOrUpdate(CcdFrame newFrame, CcdReductionFrameCatalogue repository) in FitsImporter.cs: line 38
   at TA.ReductionManager.Specifications.FitsImporter.ImportCollection(IEnumerable`1 collection, CcdReductionFrameCatalogue repository) in FitsImporter.cs: line 29
   at TA.ReductionManager.Specifications.when_importing_fits_files_into_the_catalogue_and_there_are_no_subdirectories.b__5() in FileEnumeratorSpecs.cs: line 27

现在这是一个令人难以置信的简单LINQ代码，我在这里缺少什么？

Answer 1

您无法比较LINQ查询中的自定义对象。您应该只比较基本类型（int，string等）。

var existingFrames = from frame in repository.CcdFrames
                     where frame.Id == newFrame.Id
                     select frame;

您可以在此处获取一些信息：Only primitive types or enumeration types are supported in this context

使用Effort with Entity Framework 6的正确方法是什么？

1 个答案: