ML.NET loading data from enumerable returns empty IDataView

Question

I am trying to put data from a database into a list and then loading it into an IDataView, but the IDataView is empty every time. Here is the problem code:

(IDataView training, IDataView test) LoadData(MLContext mlContext)
{
    var trainData = new List<ModelInput>();


    try
    {
        using var conn = new MySqlConnection(connection);

        conn.Open();

        var selectCmd = "SELECT user_id, movie_id, review_value FROM review";

        var command = new MySqlCommand(selectCmd, conn);

        var reader = command.ExecuteReader();

        while (reader.Read())
        {
            trainData.Add(new ModelInput
            {
                user_id = reader.GetInt32(0),
                movie_id = reader.GetInt32(1),
                review_value = reader.GetFloat(2),
            });
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }

    var testDataPath = "recommendation-ratings-test.csv";

    IDataView trainingDataView = mlContext.Data.LoadFromEnumerable<ModelInput>(trainData);
    IDataView testDataView = mlContext.Data.LoadFromTextFile<ModelInput>(testDataPath, hasHeader: true, separatorChar: ',');

    return (trainingDataView, testDataView);
}

I cannot find anything only about this problem and about how to solve it. Please help.