ML.NET 如何从 linq 查询中获取 IDataView？

Question

I want to get the data with a LINQ query that I want to use to create and train a model.

I need the data to be in float to work with the machine learning model, but in the database and my model to get it from the database it isn't all a float.

My code:

        var tempquery = from m in context.Message
                        where m.Unit == 1
                        select new
                        {
                            MessageId = (float)m.MessageId,
                            DateTime = m.DateTime,
                            FillLevel = (float)m.FillLevel,
                            Temperature = (float)m.Temperature,
                            Latitude = (float)m.Latitude,
                            Longitude = (float)m.Longitude,
                            Unit = (float)m.Unit
                        };

The Message model class:

  public class Message
{
    public int MessageId { get; set; }
    public DateTime DateTime { get; set; }
    public double? FillLevel { get; set; }
    public int? Temperature { get; set; }
    public double? Latitude { get; set; }
    public double? Longitude { get; set; }
    public int Unit { get; set; }

}

For my Machine learning model I use:

       public class MessageML
    {
        public int MessageId { get; set; }       
        public DateTime DateTime { get; set; }
        public float FillLevel { get; set; }
        public float Temperature { get; set; }
        public float Latitude { get; set; }
        public float Longitude { get; set; }
        public float Unit { get; set; }
    }

The problem is to convert the var tempQuery to a IDataView object.

I tried:

IDataView data = (IDataView)tempQuery.ToList()

And

   MLContext mlContext = new MLContext();
        DatabaseLoader loader = mlContext.Data.CreateDatabaseLoader<MessageML>();

        IDataView data = loader.Load(tempquery);

When I use this it works (but it isn't what I want, because I want to use LINQ)

  DatabaseLoader loader = mlContext.Data.CreateDatabaseLoader<MessageML>();
        string connectionString = @"ServerTEST;Database=TEST;Trusted_Connection=True";
        string sqlCommand = "SELECT CAST(MessageId as REAL) as MessageId, DateTime, CAST(FillLevel as REAL) as FillLevel, " +
            "CAST(Temperature as REAL) as Temperature, CAST(Latitude as REAL) as Latitude, CAST(Longitude as REAL) as Longitude, " +
            "CAST(Unit as REAL) as Unit from Message";


        DatabaseSource dbSource = new DatabaseSource(SqlClientFactory.Instance, connectionString, sqlCommand);
        IDataView trainingDataView = loader.Load(dbSource);

Answer 1

Use LoadFromEnumerable instead of CreateDatabaseLoader if you want to use LINQ before training

IDataView traindata = mlContext.Data.LoadFromEnumerable(tempquery);