如何将复合类型传递给PL/pgsql函数?

我正在尝试(未成功)将PostgreSql复合类型传递给PL/pgsql函数。下面列出了错误消息和示例代码。我还尝试了代码的几种不同变体(例如 this 未成功-每个版本都会生成不同的错误消息)。我是SQL新手,希望我犯了一个简单的错误。如果有人能查看下面的示例代码并解释我犯了什么错误,我将不胜感激。

错误消息

    System.InvalidCastException: When specifying NpgsqlDbType.Enum, SpecificType must be specified as well
       at Npgsql.TypeHandlerRegistry.get_Item(NpgsqlDbType npgsqlDbType, Type specificType)
       at Npgsql.NpgsqlParameter.ResolveHandler(TypeHandlerRegistry registry)
       at Npgsql.NpgsqlParameter.Bind(TypeHandlerRegistry registry)
       at Npgsql.NpgsqlCommand.ValidateParameters()
       at Npgsql.NpgsqlCommand.d__71.MoveNext()
    --- End of stack trace from previous location where exception was thrown ---
       at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
       at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
       at System.Runtime.CompilerServices.ValueTaskAwaiter`1.GetResult()
       at Npgsql.NpgsqlCommand.d__87.MoveNext()
    --- End of stack trace from previous location where exception was thrown ---
       at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
       at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
       at System.Runtime.CompilerServices.ValueTaskAwaiter`1.GetResult()
       at Npgsql.NpgsqlCommand.ExecuteScalar()
       at TestDatabase.TestCompositeType.Test() in F:\Visual Studio 2017\Projects\TestDatabase\TestDatabase\TestCompositeType.cs:line 42
       at TestDatabase.Program.Main(String[] args) in F:\Visual Studio 2017\Projects\TestDatabase\TestDatabase\Program.cs:line 17

系统信息

    Windows 10, 64 bit
    PostgreSQL 10.3, compiled by Visual C++ build 1800, 64-bit
    Npgsql, Version=3.2.6.0

PostgreSql代码

    create schema if not exists MySchema;

    create type MySchema.MyType as(
            X real,
            Y real
        );

    create table if not exists MySchema.MyTable(
        ItemID int primary key generated by default as identity,
        MyType MySchema.MyType
    );

    create or replace function MySchema.SetMyType( 
        ItemID2 int,
        MyType2 MySchema.MyType
    ) 
    returns int
    as $$
    declare
        resultID int;
    begin
        resultID := ItemID2;

        if( exists( select 1 from MySchema.MyTable as mt where mt.ItemID = ItemID2 ) ) then
            insert into MySchema.MyTable( MyType ) 
            values ( MyType2 )
            returning mt.ItemID into resultID;
        else
            update MySchema.MyTable as mt 
            set MyType = MyType2
            where mt.ItemID = ItemID2;
        end if;

        return resultID;
    end;
    $$ language plpgsql;

C#代码

    public void Test()
    {
        NpgsqlConnection.MapCompositeGlobally( "MySchema.MyType" );

        var connection = new NpgsqlConnection( "Host=localhost;Username=postgres;Password=123456;database=testdb" );
        if( null == connection )
            throw new NullReferenceException( "connection" );
        try
        {
            connection.Open();

            var cmd = new NpgsqlCommand( "MySchema.SetMyType", connection );
            cmd.CommandType = System.Data.CommandType.StoredProcedure;

            var par = new NpgsqlParameter( "ItemID2", NpgsqlDbType.Integer );
            par.Value = 1;
            cmd.Parameters.Add( par );

            par = new NpgsqlParameter( "MyType2", NpgsqlDbType.Composite );
            MyType myType = new MyType();
            myType.X = 1;
            myType.Y = 2;
            par.Value = myType;
            cmd.Parameters.Add( par );

            int id = Convert.ToInt32( cmd.ExecuteScalar() );
        }
        finally
        {
            connection.Close();
        }
    }