.net postgres EF core Cannot write DateTime with Kind=Local to PostgreSQL type 'timestamp with time zone'

Question

I have a.Net6 console app that uses nuget packages:

• "Microsoft.EntityFrameworkCore, Version 6.0.8"
• "Npgsql.EntityFrameworkCore.PostgreSQL, Version 6.0.6"
• "Npgsql, Version 6.0.6"

I am using postgres 14.4 as thats installed and used for running scripts, etc.
I run a.sql script called "createTables.sql" that looks like this

create table if not exists "Messages" (
    "Id" uuid primary key,
    "Time" timestamp without time zone,
    "MessageType" text,
    "Message" text
);

My EF core context looks like this

namespace Database;

public class MessageContext : DbContext
{
  protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
  {
    var dbConfig = Configurer.Config.MessageDbConfig;
    optionsBuilder.UseNpgsql(new NpgsqlConnectionStringBuilder
      {
        Database = dbConfig.DbName,
        Username = dbConfig.Username,
        Password = dbConfig.Password,
        Host = dbConfig.Host,
        Port = dbConfig.Port,
        Pooling = dbConfig.Pooling
      }.ConnectionString,
     optionsBuilder => optionsBuilder.SetPostgresVersion(Version.Parse("14.4")));

    base.OnConfiguring(optionsBuilder);
  }

  public DbSet<Msg> Messages { get; set; }
}

public class Msg
{
  public Guid Id { get; set; } = Guid.NewGuid();
  public DateTime Time { get; set; } = DateTime.Now;
  public string MessageType { get; set; }
  public string Message { get; set; }
}

after running the.sql file using the psql command from the command line. I check on pgAdmin 4 and see
confirming that the column type is timestamp without timezone. Yet when i create a new Message via

    using var context = new MessageContext();
    context.Messages.Add(new Msg
    {
      MessageType = message.GetType()
        .FullName,
      Message = message.ToString()
    });
    context.SaveChanges();

when saving the changes, i get the exception

Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while saving the entity changes. See the inner exception for details.
 ---> System.InvalidCastException: Cannot write DateTime with Kind=Local to PostgreSQL type 'timestamp with time zone', only UTC is supported. Note that it's not possible to mix DateTimes with different Kinds in an array/range. See the Npgsql.EnableLegacyTimestampBehavior AppContext switch to enable legacy behavior.
   at Npgsql.Internal.TypeHandlers.DateTimeHandlers.TimestampTzHandler.ValidateAndGetLength(DateTime value, NpgsqlParameter parameter)
   at Npgsql.Internal.TypeHandlers.DateTimeHandlers.TimestampTzHandler.ValidateObjectAndGetLength(Object value, NpgsqlLengthCache& lengthCache, NpgsqlParameter parameter)
   at Npgsql.NpgsqlParameter.ValidateAndGetLength()
   at Npgsql.NpgsqlParameterCollection.ValidateAndBind(ConnectorTypeMapper typeMapper)
   at Npgsql.NpgsqlCommand.ExecuteReader(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlCommand.ExecuteReader(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlCommand.ExecuteReader(CommandBehavior behavior)
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReader(RelationalCommandParameterObject parameterObject)
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.Execute(IRelationalConnection connection)
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.Execute(IRelationalConnection connection)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.Execute(IEnumerable`1 commandBatches, IRelationalConnection connection)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(IList`1 entriesToSave)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(StateManager stateManager, Boolean acceptAllChangesOnSuccess)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(Boolean acceptAllChangesOnSuccess)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)

Looks very contradicting because it is set without timezone and when the Msg is created is instantiates the "Time" property with the local time zone kind. If i switch it to "DateTime.UtcNow" instead of "DateTime.Now", it works. I don't get why it throws exception when i set it to "timestamp without time zone". obviously an easy solution is to just use utc time but regardless, why is the exception being thrown knowing the details?

Answer 1

npgsql 6.0 breaking changes

UTC timestamps have been cleanly separated from non-UTC timestamps, aligning with the PostgreSQL types. The former are represented by timestamp with time zone and DateTime with Kind UTC, the latter by timestamp without time zone and DateTime with Kind Local or Unspecified. It is recommended to use UTC timestamps where possible.

Solution 1: enable to the pre-6.0 behavior

MessageContext.SetSwitch("Npgsql.EnableLegacyTimestampBehavior", true);

Solution 2: use DateTimeOffset

public DateTime Time { get; set; } = DateTimeOffset.Now;

Excellent article for DateTimeOffset vs DateTime