使用自定义ValueConverter时Select上的System.InvalidCastException

Question

Problem

I'm trying to introduce a strongly typed ID in one of my entities. To do so, I followed the instructions on https://andrewlock.net/using-strongly-typed-entity-ids-to-avoid-primitive-obsession-part-3/

The only difference to the instructions above is, that I'm trying to persist my ID as a string instead of a Guid.

A short summary of the instructions (a full example can be downloaded here: https://drive.google.com/file/d/1_mtYp1c8W6qJoEAY-8NPNjYvsSAif4mz/view?usp=sharing ):

• Create a struct "OrderId" with a property "Value", which returns the string representation of the ID
• Create the class for the Order entity and add a property "ID" of type "OrderId"
• Create the DbContext with a DbSet
• Create a custom ValueConverter that converts OrderId to string and vice versa
• Apply the value converter to the Id column of the Order entity
• Add an explicit conversion operator from OrderId to string to the OrderId in order to avoid client-side evaluations

With this setup, it's no problem to add entries to the Orders table. BUT: when I try to read them, the following exception is thrown:

System.InvalidCastException
  HResult=0x80004002
  Message=Invalid cast from 'System.String' to 'StronglyTypedIds.OrderId'.
  Source=System.Private.CoreLib
  StackTrace:
   at System.Convert.DefaultToType(IConvertible value, Type targetType, IFormatProvider provider) in E:\A\_work\644\s\src\mscorlib\shared\System\Convert.cs:line 309
   at Microsoft.EntityFrameworkCore.Storage.ValueConversion.ValueConverter`2.Sanitize[T](Object value) in /_/src/EFCore/Storage/ValueConversion/ValueConverter`.cs:line 52
   at Microsoft.EntityFrameworkCore.Storage.ValueConversion.ValueConverter`2.<>c__DisplayClass3_0`2.<SanitizeConverter>b__0(Object v) in /_/src/EFCore/Storage/ValueConversion/ValueConverter`.cs:line 43
   at Microsoft.EntityFrameworkCore.Storage.RelationalTypeMapping.CreateParameter(DbCommand command, String name, Object value, Nullable`1 nullable) in /_/src/EFCore.Relational/Storage/RelationalTypeMapping.cs:line 515
   at Microsoft.EntityFrameworkCore.Storage.Internal.TypeMappedRelationalParameter.AddDbParameter(DbCommand command, Object value) in /_/src/EFCore.Relational/Storage/Internal/TypeMappedRelationalParameter.cs:line 66
   at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalParameterBase.AddDbParameter(DbCommand command, IReadOnlyDictionary`2 parameterValues) in /_/src/EFCore.Relational/Storage/Internal/RelationalParameterBase.cs:line 45
   at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.CreateCommand(IRelationalConnection connection, IReadOnlyDictionary`2 parameterValues) in /_/src/EFCore.Relational/Storage/Internal/RelationalCommand.cs:line 375
   at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.Execute(IRelationalConnection connection, DbCommandMethod executeMethod, IReadOnlyDictionary`2 parameterValues) in /_/src/EFCore.Relational/Storage/Internal/RelationalCommand.cs:line 149
   at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.ExecuteReader(IRelationalConnection connection, IReadOnlyDictionary`2 parameterValues) in /_/src/EFCore.Relational/Storage/Internal/RelationalCommand.cs:line 119
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.BufferlessMoveNext(DbContext _, Boolean buffer) in /_/src/EFCore.Relational/Query/Internal/QueryingEnumerable.cs:line 111
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable`1.Enumerator.MoveNext() in /_/src/EFCore.Relational/Query/Internal/QueryingEnumerable.cs:line 93
   at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable`1 source, Boolean& found) in E:\A\_work\286\s\corefx\src\System.Linq\src\System\Linq\First.cs:line 63
   at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.ResultEnumerable`1.GetEnumerator() in /_/src/EFCore/Query/Internal/LinqOperatorProvider.cs:line 294
   at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.<_TrackEntities>d__17`2.MoveNext() in /_/src/EFCore/Query/Internal/LinqOperatorProvider.cs:line 185
   at Microsoft.EntityFrameworkCore.Query.Internal.LinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext() in /_/src/EFCore/Query/Internal/LinqOperatorProvider.cs:line 143
   at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable`1 source, Boolean& found) in E:\A\_work\286\s\corefx\src\System.Linq\src\System\Linq\First.cs:line 63
   at System.Linq.Enumerable.First[TSource](IEnumerable`1 source) in E:\A\_work\286\s\corefx\src\System.Linq\src\System\Linq\First.cs:line 14
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass15_1`1.<CompileQueryCore>b__0(QueryContext qc) in /_/src/EFCore/Query/Internal/QueryCompiler.cs:line 132
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source, Expression`1 predicate) in E:\A\_work\286\s\corefx\src\System.Linq.Queryable\src\System\Linq\Queryable.cs:line 741
   at StronglyTypedIds.Program.Main() in <path_to_project>\StronglyTypedIds\StronglyTypedIds\Program.cs:line 29

The weird thing is, that it seems to depend on how I build my Where-query:

var order = dbContext.Orders.Where(o => (string)o.Id == "1").ToList();                             // works


const string idAsStringConstant = "1";
order = dbContext.Orders.Where(o => (string)o.Id == idAsStringConstant).ToList();                  // works


var idAsStringVariable = "1";
order = dbContext.Orders.Where(o => (string)o.Id == idAsStringVariable).ToList();                  // doesn't work


order = dbContext.Orders.Where(o => (string)o.Id == OrderId.Parse("1").StringValue).ToList();      // doesn't work

Steps to reproduce

Here is a small VS2019 solution with an example: https://drive.google.com/file/d/1_mtYp1c8W6qJoEAY-8NPNjYvsSAif4mz/view?usp=sharing

Further technical details

EF Core version: 2.2.6 Database Provider: Microsoft.EntityFrameworkCore.SqlServer and Microsoft.EntityFrameworkCore.Sqlite Operating system: Windows 10 1809 IDE: (eg Visual Studio 2019 16.1.6)

Answer 1

Ok, it's a bug in Entity Framework. If I install the preview of version 3.0 of .NET Core and Entity Framework Core it works as expected. Further there seems to be a fix for version 2.2 which just wasn't released yet (see https://github.com/aspnet/EntityFrameworkCore/issues/17610 ).