SelectMany - Multiple from

Query

public void Linq18()
{
    List customers = GetCustomerList();
  
    DateTime cutoffDate = new DateTime(1997, 1, 1);
  
    var orders =
        from c in customers
        where c.Region == "WA"
        from o in c.Orders
        where o.OrderDate >= cutoffDate
        select new { c.CustomerID, o.OrderID };
  
    ObjectDumper.Write(orders);
}

Lambda Expression

public void DataSetLinq18()
{
    var customers = testDS.Tables["Customers"].AsEnumerable();
    var orders = testDS.Tables["Orders"].AsEnumerable();
    DateTime cutoffDate = new DateTime(1997, 1, 1);
 
    var myOrders =
        customers.Where(c => c.Field("Region") == "WA").SelectMany(c => orders, (c, o) => new {c, o})
        .Where(@t => @t.c.Field("CustomerID") == @t.o.Field("CustomerID") && (DateTime) @t.o["OrderDate"] >= cutoffDate)
        .Select(@t => new {
            CustomerID = @t.c.Field("CustomerID"),
            OrderID = @t.o.Field("OrderID")
        });
 
    ObjectDumper.Write(myOrders);
}

Output

CustomerID=LAZYK OrderID=10482
CustomerID=LAZYK OrderID=10545
CustomerID=TRAIH OrderID=10574
CustomerID=TRAIH OrderID=10577
CustomerID=TRAIH OrderID=10822
CustomerID=WHITC OrderID=10469
CustomerID=WHITC OrderID=10483
CustomerID=WHITC OrderID=10504
CustomerID=WHITC OrderID=10596
CustomerID=WHITC OrderID=10693
CustomerID=WHITC OrderID=10696
CustomerID=WHITC OrderID=10723
CustomerID=WHITC OrderID=10740
CustomerID=WHITC OrderID=10861
CustomerID=WHITC OrderID=10904
CustomerID=WHITC OrderID=11032
CustomerID=WHITC OrderID=11066