Question

I’m working on a system in which the DB call returns a Strongly Typed list. I need to intercept the list, make changes to the data and then send it on. This is time sensitive, high volume and through put app; so I need a very efficent way to do this conversion. Because of the nature of the data manipulations I’m converting the list to a datatable. The conversion to a DT is no problem as is the manipulation; the conversion back to a Strongly Typed List is the problem. I must convert it back as the down stream code expects a List. I’ve looked and most pages talk about converting a List to DataTable, a couple do conversion of a Datatable to GENERIC List not Typed List.

I have tried AsEnumerable() and ToList(), the problem is assigning it back to the typed list.

Logic:

List<< TypedlistDef>> Lst = new List<< TypedlistDef>>();
DataTable dt = new DataTable();

dt = Helper.ListToDataTable(Lst)

manipulate dt

Lst = List<< TypedlistDef>>dt.????????        <---- Problem

I’m working in VS2010 Framework 3.5.

Thank You in advance for any and all help.

Answer 1

You can use Linq to DataSets if you like

  List<SomeType> Lst  = (from r in dataTable.AsEnumerable()
                        select new YourType()
            {
                SomeProperty = r.Field<string>("SomeField"),
                SomeOtherProperty = r.Field<string>("SomeOtherField")
            }).ToList();

Here’s a full example

class Program
    {
        static void Main(string[] args)
        {

            DataSet ds = new DataSet();
            DataTable dt = new DataTable();
            dt.TableName = "source";
            dt.Columns.Add(new DataColumn ("First",typeof (string)));
            dt.Columns.Add(new DataColumn ("Last",typeof (string)));

            ds.Tables.Add(dt);
            dt.Rows.Add("Charles", "Babbage ");
            dt.Rows.Add("Ada", "Lovelace");

            List<YourType>  YourTypeList = (from r in ds.Tables[0].AsEnumerable()
                        select new YourType()
            {
                First = r.Field<string>("First"),
                Last = r.Field<string>("Last")
            }).ToList();

            foreach(YourType yt in YourTypeList)
            {
                Console.WriteLine("{0}, {1}", yt.First, yt.Last);
            }

        }

    }

    class YourType
    { 
        public string First {get;set;}
        public string Last { get; set; }



    }

using foreach over the DataTable.Rows and adding them to the list will also work

         List<YourType> YourTypeList = new List<YourType>();
        foreach(DataRow r in dt.Rows )
        {
            YourTypeList.Add(new YourType() { 
                First = r.Field<string>("First"), 
                Last = r.Field<string>("Last") });

        }