名为“ Item”的列已属于此DataTable

扩展方式

public static class list2Dt
    {
        public static DataTable ToDataTable<T>(List<T> items)
        {
            DataTable dataTable = new DataTable(typeof(T).Name);

            //Get all the properties
            PropertyInfo[] Props = typeof(T).GetProperties(BindingFlags.Public | BindingFlags.Instance);
            foreach (PropertyInfo prop in Props)
            {
                //Setting column names as Property names
                dataTable.Columns.Add(prop.Name);
            }
            foreach (T item in items)
            {
                var values = new object[Props.Length];
                for (int i = 0; i < Props.Length; i++)
                {
                    //inserting property values to datatable rows
                    values[i] = Props[i].GetValue(item, null);
                }
                dataTable.Rows.Add(values);
            }
            //put a breakpoint here and check datatable
            return dataTable;
        }
    }

控制者

var noDups = firstTable.AsEnumerable()
                            .GroupBy(d => new
                            {
                                name = d.Field<string>("name"),
                                date = d.Field<string>("date")
                            })
                            .Where(d => d.Count() > 1) 
                            .Select(d => d.First())
                             .ToList();

                        DataTable secondTable = new DataTable();
                        secondTable.Columns.Add("name", typeof(string));
                        secondTable.Columns.Add("date", typeof(string));
                        secondTable.Columns.Add("clockIn", typeof(string));
                        secondTable.Columns.Add("clockOut", typeof(string));

                        secondTable = list2Dt.ToDataTable(noDups);

我收到以下错误消息：

An exception of type 'System.Data.DuplicateNameException' occurred in System.Data.dll but was not handled in user code

Additional information: A column named 'Item' already belongs to this DataTable.

上面的错误在线上引发：

dataTable.Columns.Add(prop.Name);

有人可以找到问题所在吗？

您要向其传递一个DataRow实例列表,该实例的类具有多个overloads of property Item,这意味着当您尝试构建新的DataTable时,它将尝试添加名称为Item的多个列,该列在DataTable中无效.

解决方法是将noDups投影到新对象,而不是保留DataRow：

public class MyClass
{
    public string Name{get;set;}
    public string Date{get;set;}
}

var noDups = firstTable.AsEnumerable()
                        .GroupBy(d => new
                        {
                            name = d.Field<string>("name"),
                            date = d.Field<string>("date")
                        })
                        .Where(d => d.Count() > 1) 
                        .Select(d => {
                              var first = d.First();
                              return new MyClass()
                                 {
                                     Name = (string)first["name"],
                                     Date = (string)first["date"]
                                 }
                         })

                         .ToList();