Let keyword learning and linqlet keyword learning in linq
In linq, The let keyword is an alias for subqueries. The let clause is used to add a new local variable to the query to make it visible in subsequent queries.
Examples of let keywords in linq
1. Differences between traditional subqueries and LET keywords
C # code Replication
Static void Main (string [] args) {int [] numbers = new [] {1, 2, 3, 4, 5, 6, 7, 8, 9 }; // The traditional subquery method var query = from num in numbers select num * (from n in numbers where n % 2 = 0 select n ). count (); // using the LET keyword var query = from num in numbers let evenNumbers = from n in numbers where n % 2 = 0 select n select num * evenNumbers. count (); foreach (var item in query) {Console. writeLine (item);} Console. read ();}
2. Find out the characters whose names start with a or e.
C # code Replication
Using System; using System. linq; public class Test {static void Main (string [] args) {string [] strings = {"A penny saved is a penny earned. "," The aaxly sdj "," the pa is no "}; var query = from sentence in strings let words = sentence. split ('') // use spaces to Split the string into arrays from word in words let w = word. toLower () // lowercase where w [0] = 'A' | w [0] = 'E' select word; foreach (var s in query) {Console. writeLine (s);} Console. readLine ();}}
3. linq instance 3
C # code Replication
Var query = from p in persons let friendlyName = p. Gender = "male "? "Mr": "Ms" + p. name select new {UserID = p. ID, FriendName = friendlyName}; foreach (var item in query) {Console. writeLine ("No: {0}, Friendly Name: {1}", item. userID, item. friendName );}
4. linq instance 4
C # code Replication
Public class Singer {public string Name {set; get;} public int Age {set; get ;}list <Singer> List = new list <Singer> () {new Singer {Name = "zhangs", Age = 21}, new Singer {Name = "zhangs", Age = 25}, new Singer {Name = "margy ", age = 21 }}; var query = from a in list let B =. name let c =. age where B = "zhangs" & c> 21 select a; foreach (var item in query) {Response. write ("name:" + item. name + "Age:" + item. age);} // result name: zhangs Age: 25 // use let to create a range variable. This range variable is used in subsequent where clauses. If the let clause is not used, the expression of the where clause will be written as follows: // where. name = "zhangs" &. age> 21 </span>
In C #, how can I use Linq to retrieve multiple keywords in multiple columns in SQL Server tables?
Var result = from p in Wuzi
Where keyword. Contains (p. Column1)
| Keyword. Contains (p. Column2)
| Keyword. Contains (p. Column3)
Selelct p;
Well, this is probably the case.
What are the tutorials for beginners of LINQ?
Of course it's MSDN.
Msdn.microsoft.com/zh-cn/library/bb1_676.aspx
Reference: msdn.microsoft.com/zh-cn/library/bb1_676.aspx