LINQ CHEAT SHEET, Lecture notes of Advanced Computer Programming

Download LINQ CHEAT SHEET and more Lecture notes Advanced Computer Programming in PDF only on Docsity! LINQ CHEAT SHEET Query Syntax Lambda Syntax Filtering var col = from o in Orders where o.CustomerID == 84 select o; var col2 = Orders.Where(o => o.CustomerID == 84); Return Anonymous Type var col = from o in orders select new { OrderID = o.OrderID, Cost = o.Cost }; var col2 = orders.Select(o => new { OrderID = o.OrderID, Cost = o.Cost } ); Ordering var col = from o in orders orderby o.Cost ascending select o; var col2 = orders.OrderBy(o => o.Cost); var col3 = from o in orders orderby o.Cost descending select o; var col4 = orders.OrderByDescending(o => o.Cost); var col9 = from o in orders orderby o.CustomerID, o.Cost descending select o; var col6 = orders.OrderBy(o => o.CustomerID). ThenByDescending(o => o.Cost); //returns same results as above var col5 = from o in orders orderby o.Cost descending orderby o.CustomerID select o; //NOTE the ordering of the orderby’s Joining var col = from c in customers join o in orders on c.CustomerID equals o.CustomerID select new { c.CustomerID, c.Name, o.OrderID, o.Cost }; var col2 = customers.Join(orders, c => c.CustomerID,o => o.CustomerID, (c, o) => new { c.CustomerID, c.Name, o.OrderID, o.Cost } ); Grouping var OrderCounts = from o in orders group o by o.CustomerID into g select new { CustomerID = g.Key, TotalOrders = g.Count() }; var OrderCounts1 = orders.GroupBy( o => o.CustomerID). Select(g => new { CustomerID = g.Key, TotalOrders = g.Count() }); NOTE: the grouping’s key is the same type as the grouping value. E.g. in above example grouping key is an int because o.CustomerID is an int. LINQ CHEAT SHEET Query Syntax Lambda Syntax Paging (using Skip & Take) //select top 3 var col = (from o in orders where o.CustomerID == 84 select o).Take(3); var col2 = orders.Where( o => o.CustomerID == 84 ).Take(3); //skip first 2 and return the 2 after var col3 = (from o in orders where o.CustomerID == 84 orderby o.Cost select o).Skip(2).Take(2); var col3 = (from o in orders where o.CustomerID == 84 orderby o.Cost select o).Skip(2).Take(2); Element Operators (Single, Last, First, ElementAt, Defaults) //throws exception if no elements var cust = (from c in customers where c.CustomerID == 84 select c).Single(); var cust1 = customers.Single( c => c.CustomerID == 84); //returns null if no elements var cust = (from c in customers where c.CustomerID == 84 select c).SingleOrDefault(); var cust1 = customers.SingleOrDefault( c => c.CustomerID == 84); //returns a new customer instance if no elements var cust = (from c in customers where c.CustomerID == 85 select c).DefaultIfEmpty( new Customer()).Single(); var cust1 = customers.Where( c => c.CustomerID == 85 ).DefaultIfEmpty(new Customer()).Single(); //First, Last and ElementAt used in same way var cust4 = (from o in orders where o.CustomerID == 84 orderby o.Cost select o).Last(); var cust5 = orders.Where( o => o.CustomerID == 84). OrderBy(o => o.Cost).Last(); //returns 0 if no elements var i = (from c in customers where c.CustomerID == 85 select c.CustomerID).SingleOrDefault(); var j = customers.Where( c => c.CustomerID == 85). Select(o => o.CustomerID).SingleOrDefault(); NOTE: Single, Last, First, ElementAt all throw exceptions if source sequence is empty. SingleOrDefault, LastOrDefault, FirstOrDefault, ElementAtOrDefault all return default(T) if source sequence is empty. i.e. NULL will be returned if T is a reference type or nullable value type; default(T) will be returned if T is a non-nullable value type (int, bool etc). This can be seen in the last example above.