DataTable columns in C#

Question

I currently have this code, I'm aware how to print out the rows, but I can't figure out how to get my column headers? I don't want to use the solution I had that I commented out because I want to make the code generic so that I can use it for other lists too.

static DataTable ConvertListToDataTable(List<List<string>> list)
{
    // New table.
    DataTable table = new DataTable();

    /* table.Columns.Add("Employee ID");
       table.Columns.Add("First Name");
       table.Columns.Add("Last Name");
       table.Columns.Add("Job Title");
       table.Columns.Add("Address");
       table.Columns.Add("City"); 
    */

    foreach(List<string> row in list) {
        table.Rows.Add(row.ToArray());
    }

    return table;
}

Answer 1

It's impossible to derive the column headers from the List<List<string>> since the information is simply not available. You could provide them per parameter:

static DataTable ConvertListToDataTable(List<List<string>> list, IList<string> columnNames)
{
    DataTable table = new DataTable();
    foreach (string columnName in columnNames)
        table.Columns.Add(columnName);
    foreach (List<string> row in list)
    {
        if (row.Count != columnNames.Count)
            throw new ArgumentException(string.Format("Invalid data in list, must have the same columns as the columnNames-argument. Line was: '{0}'", string.Join(",", row)), "list");
        DataRow r =  table.Rows.Add();
        for (int i = 0; i < columnNames.Count; i++)
            r[i] = row[i];
    }
    return table;
}

How to use:

string[] columns = { "Employee ID", "First Name", "Last Name", "Job Title", "Address", "City"};
DataTable tblEmployee = ConvertListToDataTable(employees, columns);

But instead of using a List<List<string>> (or a DataTable ) to store your employees you should use a custom class, for example Employee with all those properties. Then you can fill a List<Employee> . On that way your code is much better to read and to maintain.

Answer 2

The following code gives you the facility to convert an IEnumerable type to DataTable with dynamic Headers using System.Reflection.PropertyInfo. try to use this.

    public static DataTable EnumerableToDataTable<T>(IEnumerable<T> varlist)
    {
        DataTable dtReturn = new DataTable();

        // column names  
        PropertyInfo[] oProps = null;

        if (varlist == null) return dtReturn;

        foreach (T rec in varlist)
        {
            // Use reflection to get property names, to create table, Only first time, others will follow  
            if (oProps == null)
            {
                oProps = ((Type)rec.GetType()).GetProperties();
                foreach (PropertyInfo pi in oProps)
                {
                    Type colType = pi.PropertyType;

                    if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition() == typeof(Nullable<>)))
                    {
                        colType = colType.GetGenericArguments()[0];
                    }

                    dtReturn.Columns.Add(new DataColumn(pi.Name, colType));
                }
            }

            DataRow dr = dtReturn.NewRow();

            foreach (PropertyInfo pi in oProps)
            {
                dr[pi.Name] = pi.GetValue(rec, null) == null ? DBNull.Value : pi.GetValue
                (rec, null);
            }

            dtReturn.Rows.Add(dr);
        }
        return dtReturn;
    }