dotnet Core - Need to create a generic extension method that has two generics and one being the extension

Question

I am trying to create a generic CSV conversion static method. It has the entity - the extension.. let that be "T" however I also need to include a different context based on the entity. There are two databases each have a suburb entity and the DBs context.

How do I have two generic vars so to speak with one being the extension.. This is what I started with:

    public static Suburb FromCsv(string csvLine, CATALOGContext context)
    {
        if (csvLine == null) throw new ArgumentNullException(nameof(csvLine));
        if (context == null) throw new ArgumentNullException(nameof(context));

        var values = csvLine.Split(',');
        if (context.States == null) return null;
        if (values.Length <= 3) return null;
        var suburb = new Suburb
        {
            PostCode = values[0],
            SuburbName = values[1],
            State = context.States.FirstOrDefault(s => s.StateShortName == values[2]),
            Latitude = Convert.ToDouble(values[3], CultureInfo.CurrentCulture),
            Longitude = Convert.ToDouble(values[4], CultureInfo.CurrentCulture)
        };

        return suburb;
    }

This is what I had but its clearly not right.

        public static T FromCsv<T, I>(this T source, string csvLine, I context)
        {
            if (csvLine == null) throw new ArgumentNullException(nameof(csvLine));
            if (context == null) throw new ArgumentNullException(nameof(context));

            var values = csvLine.Split(',');
            if (context.States == null) return null;
            if (values.Length <= 3) return null;
            var suburb = new Suburb
            {
                PostCode = values[0],
                SuburbName = values[1],
                State = context.States.FirstOrDefault(s => s.StateShortName == values[2]),
                Latitude = Convert.ToDouble(values[3], CultureInfo.CurrentCulture),
                Longitude = Convert.ToDouble(values[4], CultureInfo.CurrentCulture)
            };

            return suburb;
        }

It does not know that this is a dbContext (context) so I need to use a where clause and I am unsure how to do that. Further, each dbContext has a "State" but this is error-ing for the above reason -doesnt know its a context.

How can I have multiple generics with one being the extension - the entity and the other being the context (not even sure I can have this) where you can use it with different database contexts etc?

Answer 1

You cannot use specific entity to return T. You have to use T to return T. Why not using this simple one?

public enum DBcon
{
      DB1, DB2
}
public static Suburb FromCsv(string csvLine, DBcon con)
{
    var context = con == DBcon.DB1 ? new CATALOGContext() : new DB2Context();

    if (csvLine == null) throw new ArgumentNullException(nameof(csvLine));
    if (context == null) throw new ArgumentNullException(nameof(context));

    var values = csvLine.Split(',');
    if (context.States == null) return null;
    if (values.Length <= 3) return null;
    var suburb = new Suburb
    {
        PostCode = values[0],
        SuburbName = values[1],
        State = context.States.FirstOrDefault(s => s.StateShortName == values[2]),
        Latitude = Convert.ToDouble(values[3], CultureInfo.CurrentCulture),
        Longitude = Convert.ToDouble(values[4], CultureInfo.CurrentCulture)
    };

    return suburb;
}