Filtering
//1、Simple Local Filter
string[] names = { "Tom", "Dick", "Harry", "Mary", "Jay" }; IEnumerable< string> query = names.Where (name => name.EndsWith ( "y")); query.Dump ( "In lambda syntax"); query = from n in names where n.EndsWith ( "y") select n; query.Dump ( "In query comprehension syntax");
//2、Multiple Where Clauses
var names = new[] { "Tom", "Dick", "Harry", "Mary", "Jay" }.AsQueryable(); var query = from n in names where n.Length > 3 let u = n.ToUpper() where u.EndsWith ( "Y") select u; query.Dump(); //3、Indexed Filtering
string[] names = { "Tom", "Dick", "Harry", "Mary", "Jay" }; names.Where ((n, i) => i % 2 == 0).Dump ( "Skipping every second element");
//4、Contains and LIKE with LINQ to SQL
Customers.Where (c => c.Name.Contains ( "a")) .Dump ( "Notice the SQL translation uses LIKE"); Customers.Where (c => c.Name.StartsWith ( "J")) .Dump ( "StartsWith and EndsWith also translate to LIKE"); Customers.Where (c => SqlMethods.Like (c.Name, "_ar%y")) .Dump ( "A more complex use of LIKE"); // The following string functions all have translations to SQL:// StartsWith, EndsWith, Contains, Length, IndexOf,// Trim, Substring, Insert, Remove, Replace,// ToUpper, ToLower
//5、IN and NOT IN with LINQ to SQL
string[] chosenOnes = { "Tom", "Jay" }; Customers.Where (c => chosenOnes.Contains (c.Name)) .Dump ( "This translates to SQL WHERE ... IN"); Customers.Where (c => !chosenOnes.Contains (c.Name)) .Dump ( "This translates to SQL WHERE NOT ... IN");
//6、Extra - Where-based Subqueries
var names = new[] { "Tom", "Dick", "Harry", "Mary", "Jay" }.AsQueryable(); ( from n in names where n.Length == names.Min (n2 => n2.Length) select n ) .Dump ( "Basic subquery"); // The same principle works well in LINQ to SQL:( from c in Customers where c.Name.Length == Customers.Min (c2 => c2.Name.Length) select c ) .Dump ( "Basic subquery, LINQ to SQL"); // We can construct similar subqueries across association properties:( from c in Customers where c.Purchases.Any (p => p.Price > 1000) select c ) .Dump ( "Customers who have purchased at least one item > $1000");
//6、Extra - Where-based Subqueries with let
// The let keyword in comprehension queries comes in useful with subqueries: it lets// you re-use the subquery in the projection:
from c in Customers let highValuePurchases = c.Purchases.Where (p => p.Price > 1000) where highValuePurchases.Any() select new { c.Name, highValuePurchases }
//7、Take and Skip
// reflection (using LINQ, of course!) The following query extracts all type // names in the mscorlib assembly:
string[] typeNames = ( from t in typeof ( int).Assembly.GetTypes() select t.Name).ToArray(); typeNames .Where (t => t.Contains ( "Exception")) .OrderBy (t => t) .Take (20) .Dump ( "The first 20 matches"); typeNames .Where (t => t.Contains ( "Exception")) .OrderBy (t => t) .Skip (20) .Take (20) .Dump ( "Matches 21 through 40");
//8、TakeWhile and SkipWhile
int[] numbers = { 3, 5, 2, 234, 4, 1 }; numbers.TakeWhile (n => n < 100).Dump ( "TakeWhile"); numbers.SkipWhile (n => n < 100).Dump ( "SkipWhile"); 
//9、Distinct
"HelloWorld".Distinct()
Purchases.Select (p => p.Description).Distinct()
