[Npgsql.EntityFrameworkCore.PostgreSQL.NodaTime] saving CLR DateTime field throws exception

Hello, it seems that using of Npgsql.EntityFrameworkCore.PostgreSQL.NodaTime somehow blocks/corrupts working with CLR DateTime/DateTimeOffset types of properties. When trying to save DateTime field, an exception is being thrown: System.InvalidCastException : Can't write CLR type System.DateTime with handler type TimestampHandler

Steps to reproduce

.csproj references:

<PackageReference Include="Npgsql" Version="4.0.2" />
<PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="2.1.1.1" />
<PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL.NodaTime" Version="2.1.1" />
<PackageReference Include="Microsoft.EntityFrameworkCore" Version="2.1.1" />

Code:

public class NpgsqlNodaTimeTests
{
    public const string ConnectionString = "connection-string";

    [Fact]
    public async Task SavingDateTime_ShouldNotThrow()
    {
        var context = new BlogContext();

        context.Database.EnsureDeleted();
        context.Database.EnsureCreated();

        var blog = new Blog { Id = 1, Created = DateTime.Now };

        context.Blogs.Add(blog);

        await context.SaveChangesAsync();
    }
}

public class Blog
{
    public int Id { get; set; }
    public DateTime Created { get; set; }
}

public class BlogContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder builder)
        => builder.UseNpgsql(NpgsqlNodaTimeTests.ConnectionString, o => o.UseNodaTime());

    protected override void OnModelCreating(ModelBuilder builder)
        => builder.Entity<Blog>().HasKey(p => p.Id);
}

Exception

Microsoft.EntityFrameworkCore.DbUpdateException : An error occurred while updating the entries. See the inner exception for details.
---- System.InvalidCastException : Can't write CLR type System.DateTime with handler type TimestampHandler
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(DbContext _, ValueTuple`2 parameters, CancellationToken cancellationToken)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func`4 operation, Func`4 verifySucceeded, CancellationToken cancellationToken) in C:\projects\EFCore.PG\src\EFCore.PG\Storage\Internal\NpgsqlExecutionStrategy.cs:line 72
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IReadOnlyList`1 entriesToSave, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at NpgsqlNodaTimeTests.SavingDateTime_ShouldNotThrow() in -CUT--
--- End of stack trace from previous location where exception was thrown ---
----- Inner Stack Trace -----
   at lambda_method(Closure , NpgsqlTypeHandler , Object , NpgsqlLengthCache& , NpgsqlParameter )
   at Npgsql.TypeHandling.NpgsqlSimpleTypeHandler`1.ValidateObjectAndGetLength(Object value, NpgsqlLengthCache& lengthCache, NpgsqlParameter parameter) in C:\projects\npgsql\src\Npgsql\TypeHandling\NpgsqlSimpleTypeHandler.cs:line 236
   at Npgsql.NpgsqlParameter.ValidateAndGetLength() in C:\projects\npgsql\src\Npgsql\NpgsqlParameter.cs:line 553
   at Npgsql.NpgsqlCommand.ValidateParameters() in C:\projects\npgsql\src\Npgsql\NpgsqlCommand.cs:line 793
   at Npgsql.NpgsqlCommand.ExecuteDbDataReader(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken) in C:\projects\npgsql\src\Npgsql\NpgsqlCommand.cs:line 1141
   at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.ExecuteAsync(IRelationalConnection connection, DbCommandMethod executeMethod, IReadOnlyDictionary`2 parameterValues, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)

[roji]

First, https://github.com/npgsql/npgsql/pull/3124 was recently merged, which means it will soon be fine to use both NodaTime and BCL date/time types on the same connection etc. (this should happen in the upcoming 5.0 release).

As of today, you can’t natively use NodaTime types - including Duration - and BCL date/time types together; by natively I mean “without a value converter”. If you want to use a value converter and convert from NodaTime to BCL types yourself, it will work (and you don’t need to install the NodaTime plugin), but query translation won’t work - you can’t access properties on value-converted values inside a LINQ query.

Hope that clarifies things.

[krisztiankocsis]

I have the same issue. We use IdentityFramework with approx. 20 additional entities. Unfortunately, it has must-have properties on User that are DateTimeOffset types. On the other hand, we use NodaTime types due to their advantages in our own entities. Since we derive our context from IdentityDbContext to share the database. It is not the best to have separate DbContexts just to separate identity and other data - not to mention if you have foreign keys.

I normally expected that Noda plugins just “adds” support for these types, not replaces support for DateTime. In my opinion, this should be supported in parallel.

Value converters are not options for us due to missing SQL translation in the current EF Core version (2.2).

What are your opinions?