.NET 6 DateOnly and TimeOnly mapping support

[arnederuwe]

.NET 6 will introduce the DateOnly and TimeOnly structs, these are good mapping candidates for SQL Server's Date and Time types.

There is an open issue in the .NET SqlClient repo here

Am I correct to assume that once SqlClient supports it, Dapper will implicitly support it as well? Or is there some work required in this repo as well in order for this to work?

[roji]

I gave this a try with an Npgsql 6.0 RC, which does already support DateOnly/TimeOnly, and it seems this doesn't work:

await conn.ExecuteScalarAsync("SELECT @Foo", new { Foo = new DateOnly(2020, 1, 1) })

Throws:

Unhandled exception. System.NotSupportedException: The member Foo of type System.DateOnly cannot be used as a parameter value
 at Dapper.SqlMapper.LookupDbType(Type type, String name, Boolean demand, ITypeHandler& handler) in /_/Dapper/SqlMapper.cs:line 417
 at Dapper.SqlMapper.CreateParamInfoGenerator(Identity identity, Boolean checkForDuplicates, Boolean removeUnused, IList`1 literals) in /_/Dapper/SqlMapper.cs:line 2504
 at Dapper.SqlMapper.GetCacheInfo(Identity identity, Object exampleParameters, Boolean addToCache) in /_/Dapper/SqlMapper.cs:line 1727
 at Dapper.SqlMapper.ExecuteScalarImplAsync[T](IDbConnection cnn, CommandDefinition command) in /_/Dapper/SqlMapper.Async.cs:line 1200
 at Program.<Main>$(String[] args) in /home/roji/projects/test/Program.cs:line 12
 at Program.<Main>$(String[] args) in /home/roji/projects/test/Program.cs:line 12
 at Program.<Main>(String[] args)

Somewhat related to #1716... I know nothing about Dapper internals, but ideally it would be possible to use any arbitrary .NET type as a parameter, and Dapper would simply pass that along to the DbParameter.Value, without anything else (that would obviate needing any special type handlers or something). But there may be some good reason why things don't work this way currently.

[FatTigerWang]

I tracked the source code and found that the TimeOnly and DateOnly types are not supported here. I am not sure if adding these two types to the collection and specifying them as DbType.Date and DbType.Time will work. I will try if it works.

Dapper does not support .NET 6, so DateOnly and TimeOnly types cannot be used

Reference: System.Data.DbType

[kevingates]

Any timeline when this may be fixed?

[mgravell]

@kevingates see also #1728; there is an open branch, but we need to first be sure how this is intended to interact with the various providers

[szalapski]

Very much would like to see this. It is weird that SQL Server's DATE type should map to anything but DateOnly in C#.

[h181422]

For those who are looking for a workaround: make your own type handler.

Add the following to your configuration:

SqlMapper.AddTypeHandler(new SqlTimeOnlyTypeHandler());

public class SqlTimeOnlyTypeHandler : SqlMapper.TypeHandler<TimeOnly>
{
 public override void SetValue(IDbDataParameter parameter, TimeOnly time)
 {
 parameter.Value = time.ToString();
 }

 public override TimeOnly Parse(object value)
 {
 return TimeOnly.FromTimeSpan((TimeSpan)value);
 }
}

[danielearwicker]

And similarly for DateOnly:

public class DapperSqlDateOnlyTypeHandler : SqlMapper.TypeHandler<DateOnly>
{
 public override void SetValue(IDbDataParameter parameter, DateOnly date)
 => parameter.Value = date.ToDateTime(new TimeOnly(0, 0));
 
 public override DateOnly Parse(object value)
 => DateOnly.FromDateTime((DateTime)value);
}

[K0rhak]

I had problems with database conversion so I had to specify the type. Like this

public override void SetValue(IDbDataParameter parameter, DateOnly date)
{
 parameter.DbType = DbType.DateTime;
 parameter.Value = date.ToDateTime(new TimeOnly(0, 0));
}

[PedroC88]

How exactly is the TypeHandler used? I have the following line in the constructor of my DB class

SqlMapper.AddTypeHandler(new DateOnlyTypeHandler());
SqlMapper.AddTypeHandler(new TimeOnlyTypeHandler());

and the following TypeHandlers

public class DateOnlyTypeHandler : SqlMapper.TypeHandler<DateOnly>
{
 public override DateOnly Parse(object value) => DateOnly.FromDateTime((DateTime)value);

 public override void SetValue(IDbDataParameter parameter, DateOnly value)
 {
 parameter.DbType = DbType.Date;
 parameter.Value = value;
 }
}

public class TimeOnlyTypeHandler : SqlMapper.TypeHandler<TimeOnly>
{
 public override TimeOnly Parse(object value) => TimeOnly.FromDateTime((DateTime)value);

 public override void SetValue(IDbDataParameter parameter, TimeOnly value)
 {
 parameter.DbType = DbType.Time;
 parameter.Value = value;
 }
}

But I'm still getting a an exception that the Date field in my object is NULL and the breakpoints on the convertion methods aren't being hit.

[h181422]

SqlMapper.AddTypeHandler(new DateOnlyTypeHandler());
SqlMapper.AddTypeHandler(new TimeOnlyTypeHandler());

I've got them in my container config, where they are registered at startup.

[PedroC88]

That makes more sense indeed. And I also realized that z.dapper.pluss doesn't use the TypeHandlers for bulk inserts, which is why the breakpoints weren't hitting the methods in the first place.

[ScottRFrost]

Found this issue in a search and was able to get the type handlers working (The SqlMapper.AddTypeHandler lines go in Startup.cs \ ConfigureServices if you're working on an API by they way, that took me a few minutes to figure out).

However, to make them work in converting either a MS SQL DateTime OR a MS SQL Time to TimeOnly, I needed this modification (MS SQL Date to DateOnly seemed to work without change):

 public class DateOnlyTypeHandler : SqlMapper.TypeHandler<DateOnly> // Dapper handler for DateOnly
 {
 public override DateOnly Parse(object value) => DateOnly.FromDateTime((DateTime)value);

 public override void SetValue(IDbDataParameter parameter, DateOnly value)
 {
 parameter.DbType = DbType.Date;
 parameter.Value = value;
 }
 }

 public class TimeOnlyTypeHandler : SqlMapper.TypeHandler<TimeOnly> // Dapper handler for TimeOnly
 {
 public override TimeOnly Parse(object value)
 {
 if (value.GetType() == typeof(DateTime))
 {
 return TimeOnly.FromDateTime((DateTime)value);
 }
 else if (value.GetType() == typeof(TimeSpan))
 {
 return TimeOnly.FromTimeSpan((TimeSpan)value);
 }
 return default;
 }

 public override void SetValue(IDbDataParameter parameter, TimeOnly value)
 {
 parameter.DbType = DbType.Time;
 parameter.Value = value;
 }
 }

Hopefully these mappings can be added to default dapper one day