C# Starter L05-LINQ

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  • 1. Mohammad Shaker mohammadshaker.com C# Programming Course @ZGTRShaker 2011, 2012, 2013, 2014 C# Starter L05 – LINQ and Lambda Expressions
  • 2. LINQ
  • 3. LINQ One of the most awesome things ever done!
  • 4. LINQ Where’s Java?
  • 5. LINQ Where’s Java? 2013 with some tool (not as good as .NET)
  • 6. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); }
  • 7. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); }
  • 8. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } List<string> queryResults = new List<string>(); foreach (var item in names) { if (n.StartsWith(“S”)) { queryResults.Add(item); } } var queryResults = from n in names where n.StartsWith("S") select n;
  • 9. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } List<string> queryResults = new List<string>(); foreach (var item in names) { if (n.StartsWith(“S”)) { queryResults.Add(item); } } var queryResults = from n in names where n.StartsWith("S") select n;
  • 10. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } List<string> queryResults = new List<string>(); foreach (var item in names) { if (n.StartsWith(“S”)) { queryResults.Add(item); } } var queryResults = from n in names where n.StartsWith("S") select n; The SAME!
  • 11. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } List<string> queryResults = new List<string>(); foreach (var item in names) { if (n.StartsWith(“S”)) { queryResults.Add(item); } } var queryResults = from n in names where n.StartsWith("S") select n; The SAME!
  • 12. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); }
  • 13. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } Names beginning with S: Smith Smythe Small Singh Samba Program finished, press Enter/Return to continue:
  • 14. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); }
  • 15. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } Names beginning with S: Alonso Zheng Smith Jones Smythe Small Ruiz Hsieh Jorgenson Ilyich Singh Samba Program finished, press Enter/Return to continue:
  • 16. LINQ static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } Names beginning with S: Alonso Zheng Smith Jones Smythe Small Ruiz Hsieh Jorgenson Ilyich Singh Samba Program finished, press Enter/Return to continue:
  • 17. Lambda Expressions
  • 18. Tons of code in a line
  • 19. Lambda Expressions • The operator => is called the lambda operator. n => n < 1000 “ Lambda ” comes from the lambda calculus, the mathematical formalism underlying functional programming languages, which are the kind of programming on which LINQ is based. If you are interested, check out sources such as the Wikipedia article on lambda calculus. You don ’ t need to understand the mathematics to use lambda functions, although understanding functional programming is helpful for advanced LINQ programming.
  • 20. Lambda Expressions var queryResults = from n in names where n.StartsWith("S") select n;
  • 21. Lambda Expressions n => n.StartsWith(“S”) var queryResults = from n in names where n.StartsWith("S") select n;
  • 22. Lambda Expressions n => n.StartsWith(“S”) var queryResults = from n in names where n.StartsWith("S") select n;
  • 23. Lambda Expressions static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = names.Where(n => n.StartsWith("S")); Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); }
  • 24. Lambda Expressions static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = names.Where(n => n.StartsWith("S")); Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); }
  • 25. Lambda Expressions static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = names.Where(n => n.StartsWith("S")); Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } Names beginning with S: Smith Smythe Small Singh Samba Program finished, press Enter/Return to continue:
  • 26. Query Techniques
  • 27. Ordering Query Results static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") orderby n select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); }
  • 28. Ordering Query Results static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = from n in names where n.StartsWith("S") orderby n select n; Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } Names beginning with S: Samba Singh Small Smith Smythe Program finished, press Enter/Return to continue:
  • 29. Ordering Query Results • Descending order • This orders the example results as follows: orderby n descending Smythe Smith Small Singh Samba
  • 30. Ordering Query Results • Ordering Using Method Syntax var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith(“S”)); static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith("S")); Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); }
  • 31. Ordering Query Results • Ordering Using Method Syntax var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith(“S”)); static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith("S")); Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } Names beginning with S: Samba Singh Small Smith Smythe Program finished, press Enter/Return to continue:
  • 32. Ordering Query Results • Ordering Using Method Syntax var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith(“S”)); static void Main(string[] args) { string[] names = { "Alonso", "Zheng", "Smith", "Jones", "Smythe", "Small", "Ruiz", "Hsieh", "Jorgenson", "Ilyich", "Singh", "Samba"}; var queryResults = names.OrderBy(n => n).Where(n => n.StartsWith("S")); Console.WriteLine("Names beginning with S:"); foreach (var item in queryResults) { Console.WriteLine(item); } Console.Write("Program finished, press Enter/Return to continue:"); Console.ReadLine(); } Names beginning with S: Samba Singh Small Smith Smythe Program finished, press Enter/Return to continue: IOrderedEnumerable < string > and IEnumerable < string >
  • 33. Ordering Query Results • Descending order var queryResults = names.OrderByDescending(n => n).Where(n => n.StartsWith(“S”));
  • 34. Ordering Query Results • What does this do? var queryResults = names.OrderBy(n => n.Substring(n.Length-1)).Where(n => n.StartsWith(“S”));
  • 35. Ordering Query Results • What does this do? var queryResults = names.OrderBy(n => n.Substring(n.Length-1)).Where(n => n.StartsWith(“S”));
  • 36. Ordering Query Results • What does this do? var queryResults = names.OrderBy(n => n.Substring(n.Length-1)).Where(n => n.StartsWith(“S”));
  • 37. Querying Complex Objects
  • 38. Querying Complex Objects class Customer { public string ID { get; set; } public string City { get; set; } public string Country { get; set; } public string Region { get; set; } public decimal Sales { get; set; } }
  • 39. Querying Complex Objects static void Main(string[] args) { List < Customer > customers = new List < Customer > { new Customer { ID=”A”, City=”New York”, Country=”USA”,Region=”North America”, Sales=9999}, new Customer { ID=”B”, City=”Mumbai”, Country=”India”,Region=”Asia”, Sales=8888 }, new Customer { ID=”C”, City=”Karachi”, Country=”Pakistan”,Region=”Asia”, Sales=7777 }, new Customer { ID=”D”, City=”Delhi”, Country=”India”,Region=”Asia”, Sales=6666 }, new Customer { ID=”E”, City=”S ã o Paulo”, Country=”Brazil”,Region=”South America”, Sales=5555 }, new Customer { ID=”F”, City=”Moscow”, Country=”Russia”,Region=”Europe”, Sales=4444 }, … }; var queryResults = from c in customers where c.Region == “Asia” select c; Console.WriteLine(“Customers in Asia:”); foreach (Customer c in queryResults) { Console.WriteLine(c); } Console.Write(“Program finished, press Enter/Return to continue:”); Console.ReadLine(); }
  • 40. Querying Complex Objects • The output: • Why?! – Because ToString() is called for each Customer object. ToString() Is inherited directly from the object class. • Solution: Override the ToString() method. Customers in Asia: CSharpCourse2011.Customer CSharpCourse2011.Customer CSharpCourse2011.Customer CSharpCourse2011.Customer CSharpCourse2011.Customer CSharpCourse2011.Customer CSharpCourse2011.Customer CSharpCourse2011.Customer CSharpCourse2011.Customer CSharpCourse2011.Customer Program finished, press Enter/Return to continue:
  • 41. Querying Complex Objects • From this: • To this: class Customer { public string ID { get; set; } public string City { get; set; } public string Country { get; set; } public string Region { get; set; } public decimal Sales { get; set; } public override string ToString() { return “ID: “ + ID + “ City: “ + City + “ Country: “ + Country + “ Region: “ + Region + “ Sales: “ + Sales; } } class Customer { public string ID { get; set; } public string City { get; set; } public string Country { get; set; } public string Region { get; set; } public decimal Sales { get; set; } }
  • 42. Querying Complex Objects • The output now is: Customers in Asia: ID: B City: Mumbai Country: India Region: Asia Sales: 8888 ID: C City: Karachi Country: Pakistan Region: Asia Sales: 7777 ID: D City: Delhi Country: India Region: Asia Sales: 6666 ID: G City: Seoul Country: Korea Region: Asia Sales: 3333 ID: H City: Istanbul Country: Turkey Region: Asia Sales: 2222 ID: I City: Shanghai Country: China Region: Asia Sales: 1111 ID: L City: Jakarta Country: Indonesia Region: Asia Sales: 3000 ID: M City: Tokyo Country: Japan Region: Asia Sales: 4000 ID: P City: Tehran Country: Iran Region: Asia Sales: 7000 ID: R City: Beijing Country: China Region: Asia Sales: 9000 Program finished, press Enter/Return to continue:
  • 43. Querying Complex Objects var queryResults = from c in customers where c.Region == “Asia” select c.City; Mumbai Karachi Delhi Seoul Istanbul Shanghai Jakarta Tokyo Tehran Beijing
  • 44. Selecting Multiple Properties
  • 45. Querying Complex Objects • Let’s see this: select c.City, c.Country, c.Sales
  • 46. Querying Complex Objects • Let’s see this: • It’s an error. Unlike in SQL, LINQ does not allow multiple fields in a select clause! – So, what’s the solution? • Just creating a new object on-the-fly in the select clause to hold the results you want for your query! select c.City, c.Country, c.Sales
  • 47. Querying Complex Objects • Let’s see this: • It’s an error. Unlike in SQL, LINQ does not allow multiple fields in a select clause! – So, what’s the solution? • Just creating a new object on-the-fly in the select clause to hold the results you want for your query! select c.City, c.Country, c.Sales var queryResults = from c in customers where c.Region == “North America” select new { c.City, c.Country, c.Sales }; foreach (var item in queryResults) { Console.WriteLine(item); }
  • 48. Querying Complex Objects • Let’s see this: • It’s an error. Unlike in SQL, LINQ does not allow multiple fields in a select clause! – So, what’s the solution? • Just creating a new object on-the-fly in the select clause to hold the results you want for your query! select c.City, c.Country, c.Sales var queryResults = from c in customers where c.Region == “North America” select new { c.City, c.Country, c.Sales }; foreach (var item in queryResults) { Console.WriteLine(item); } { City = New York, Country = USA, Sales = 9999 } { City = Mexico City, Country = Mexico, Sales = 2000 } { City = Los Angeles, Country = USA, Sales = 5000 } Program finished, press Enter/Return to continue:
  • 49. Querying Complex Objects • Now, instead of all this: • Let’s try this: var queryResults = customers.Where(c => c.Region == “North America”) .Select(c => new { c.City, c.Country, c.Sales }); var queryResults = from c in customers where c.Region == “North America” select new { c.City, c.Country, c.Sales }; foreach (var item in queryResults) { Console.WriteLine(item); }
  • 50. Querying Complex Objects • Now, instead of all this: • Let’s try this: var queryResults = customers.Where(c => c.Region == “North America”) .Select(c => new { c.City, c.Country, c.Sales }); { City = New York, Country = USA, Sales = 9999 } { City = Mexico City, Country = Mexico, Sales = 2000 } { City = Los Angeles, Country = USA, Sales = 5000 } Program finished, press Enter/Return to continue: var queryResults = from c in customers where c.Region == “North America” select new { c.City, c.Country, c.Sales }; foreach (var item in queryResults) { Console.WriteLine(item); }
  • 51. Querying Complex Objects • Now, instead of this: • Let’s try this: var queryResults = customers.Select(c => new { c.City, c.Country, c.Sales }) .Where(c => c.Region == “North America”); var queryResults = customers.Where(c => c.Region == “North America”) .Select(c => new { c.City, c.Country, c.Sales });
  • 52. Querying Complex Objects • Now, instead of this: • Let’s try this: • It’s a Compiler Error! Because: The Region property is not included in the anonymous type. {c.City, c.Country, c.Sales } created by the Select() projection. The compiler doesn’t know it yet! var queryResults = customers.Select(c => new { c.City, c.Country, c.Sales }) .Where(c => c.Region == “North America”); var queryResults = customers.Where(c => c.Region == “North America”) .Select(c => new { c.City, c.Country, c.Sales });
  • 53. Querying Complex Objects • OK, now, instead of this: • Let’s try this: var queryResults = customers.Select(c => new { c.City, c.Country, c.Sales }) .Where(c => c.City == “New York”); var queryResults = customers.Where(c => c.Region == “North America”) .Select(c => new { c.City, c.Country, c.Sales });
  • 54. Querying Complex Objects • OK, now, instead of this: • Let’s try this: • Works beautifully! var queryResults = customers.Select(c => new { c.City, c.Country, c.Sales }) .Where(c => c.City == “New York”); var queryResults = customers.Where(c => c.Region == “North America”) .Select(c => new { c.City, c.Country, c.Sales });
  • 55. Querying Complex Objects • Distinct var queryResults = customers.Select(c => c.Region).Distinct(); var queryResults = (from c in customers select c.Region).Distinct();
  • 56. Ordering By Multiple Levels
  • 57. Ordering By Multiple Levels var queryResults = from c in customers orderby c.Region, c.Country, c.City select new { c.ID, c.Region, c.Country, c.City };
  • 58. Ordering By Multiple Levels var queryResults = from c in customers orderby c.Region, c.Country, c.City select new { c.ID, c.Region, c.Country, c.City }; { ID = O, Region = Africa, Country = Egypt, City = Cairo } { ID = J, Region = Africa, Country = Nigeria, City = Lagos } { ID = R, Region = Asia, Country = China, City = Beijing } { ID = I, Region = Asia, Country = China, City = Shanghai } { ID = D, Region = Asia, Country = India, City = Delhi } { ID = B, Region = Asia, Country = India, City = Mumbai } { ID = L, Region = Asia, Country = Indonesia, City = Jakarta } { ID = P, Region = Asia, Country = Iran, City = Tehran } { ID = M, Region = Asia, Country = Japan, City = Tokyo } { ID = G, Region = Asia, Country = Korea, City = Seoul } ….
  • 59. Drilling further • Many other techniques • Grouping • Joining • Take • Skip • ….