Using ConvertAll and Aggregate in LINQ

string strImportResult = this.ImportResult.ToList()
     .ConvertAll<string>(Import => string.Format("<tr><td> 
         {0}</td><td>{1}</td><td>{2}</td><td>
         {3}</td></tr>"
         , Import.CustodianName
         , Import.ImportFile
         , Import.ImportStatus
         , Import.Particular))
    .Aggregate((ImportA, ImportB) => ImportA + ImportB);

Multipal Field Group By IN LINQ

var objOrderList = from OrderList in
        (from OrderDetail in objOrderDetail
      join Item in objItem on OrderDetail.ItemId equals Item.ItemId
      join ItemGroup in objItemGroup on Item.GroupId equals ItemGroup.GroupId
      select new
      {
       GroupName = ItemGroup.GroupName,
       ItemName = Item.ItemName,
       Rate = Item.Rate,
       Qty = OrderDetail.Qty
      }
      )
       group OrderList by new
       {
        OrderList.GroupName,
        OrderList.ItemName
       } into OrderList
       select new
       {
        GroupName = OrderList.Key.GroupName,
        ItemName = OrderList.Key.ItemName,
        OrderTotal = OrderList.Sum(OL => OL.Qty * OL.Rate)
       };

Left Outer Join and Group By In LINQ

List Table1 = new List();
List Table2 = new List();

var objList = from ListData in
                  (from a in Table1
                   join b in Table2 on a.Id equals b.Id into t2
                   from t2Data in t2.DefaultIfEmpty()
                   select new
                   {
                       Product = a.Product,
                       Title = t2Data.Title,
                       Amount = a.Amount
                   }
                )
              group ListData by new
              {
                  ListData.Product,
                  ListData.Title
              } into GroupData
              select new
              {
                  Product = GroupData.Key.Product,
                  Title = GroupData.Key.Title,
                  Amount = GroupData.Sum(OL => OL.Amount)
              };

LINQ Extended method for Update Data

Extended Method

public delegate void Func(TArg0 element);

/// 
/// Executes an Update statement block on all elements in an IEnumerable sequence.
/// 
/// The source element type.
/// The source sequence.
/// The update statement to execute for each element.
/// The numer of records affected.
public static int Update(this IEnumerable source, Func update)
{
    if (source == null) throw new ArgumentNullException("source");
    if (update == null) throw new ArgumentNullException("update");
    if (typeof(TSource).IsValueType)
        throw new NotSupportedException("value type elements are not supported by update.");

    int count = 0;
    foreach (TSource element in source)
    {
        update(element);
        count++;
    }
    return count;
}

Example :

int intUpdate = lstItem
                .Where(a => a.ItemGroupId.Equals(lngItemGroupId))
                .Update(b =>
                            {
                                b.GroupName = strGroupName;
                                b.GroupLocation = strLocation;
                            }
                );