如何通过System.Data.SQLite检索f#查询表达式的SQL查询字符串

我正在使用System.Data.SQLite，我正在尝试检索由下面的查询表达式生成的SQL字符串。查询执行正确，但是SQL字符串是SELECT NULL AS [EMPTY]。

似乎不支持GetCommand().CommandText，但如果是这样，如何才能访问生成的SQL字符串?

[<Test>]
member this.showSQL() =
    let connectionString = sprintf @"Data Source=%s;UTF8Encoding=True;Version=3" dbFilename
    let connection = new SQLiteConnection(connectionString)
    use dc = new DataContext(connection)
    let channelMap = dc.GetTable<ChannelData>()
    let map = query {
        for row in channelMap do
        where (row.ChannelId = 1)
        select (row.ChannelId, row.Data0, row.State) }
    let cmd = dc.GetCommand(map).CommandText;
    printf "SQL: %s" cmd

    static void Main(string[] args)
    {
        string sql = "select * from foo";
        SQLiteCommand command = new SQLiteCommand(sql, null);
        Console.WriteLine(command.CommandText);
        Console.ReadLine();
    }