Select of string value bombs out

My Data Model

public class FrameworkUserConfiguration
    {
        //used to store object in sqlite database


    public Guid FrameworkUserUid { get; set; }
    public byte[] Picture { get; set; }
    public DateTime LastUpdate { get; set; }
    public FrameworkUserDataType Type { get; set; }
    public string Description { get; set; }
    public string AudioFile { get; set; }
    public bool? RepeatAudio { get; set; }
    public bool ContainsPicture { get; set; }

    [SQLite.PrimaryKey]
    public string Identifier
    {
        get
        {
            return FrameworkUserUid.ToString() + "-" + Type;
        }
        set
        {

        }
    }
}    

  public enum FrameworkUserDataType
    {
        ActualUser,
        Admin,
        User
    }

A simple select bombs out telling me there’s no parameterless constructor (after filling the table with some random data entries)

List<string> guids = conn.Table<FrameworkUserConfiguration>().Select(x => x.Identifier).ToList();

At first glance this appears to be an issue because public IEnumerator<T> GetEnumerator () is called for T being System.String - so it then creates a dummy table mapping and once we get to var obj = Activator.CreateInstance(map.MappedType); things go wrong because System.String has no parameterless constructor.

[kinderry]

I had added some mthods in SQLite.cs in SQLiteCommand:

public IEnumerable<T> ExcuteSingleQuery<T>()
        {
            if (_conn.Trace)
            {
                _conn.Tracer?.Invoke("Executing Query: " + this);
            }
            var stmt = Prepare();
            try
            {
                if (SQLite3.ColumnCount(stmt) != 1)
                {
                    throw new NotSupportedException("Column count error");
                }
                while (SQLite3.Step(stmt) == SQLite3.Result.Row)
                {
                        var colType = SQLite3.ColumnType(stmt, 0);
                        var val = ReadCol(stmt, 0, colType, typeof(T));
                        yield return (T)val;
                }
            }
            finally
            {
                Finalize(stmt);
            }
        }

in SQLiteConnection:

   public List<T> SingleQuery<T>(string query, params object[] args)
        {
            var cmd = CreateCommand(query, args);
            return cmd.ExcuteSingleQuery<T>().ToList();
        }

so you can use it like this: var singlequery = conn.SingleQuery<string>("select ColumnName from TableName"); Hope for help.

[tipa]

@praeclarum is there any reason the code above is not being merged? Are you waiting for a PR? It appears that many people encounter this little problem and there are also a lot of duplicate issues on this, which could also be closed with a small code addition that seems to have no negative side-effects from what I can tell.