準備工作：1.使用微軟的例子資料庫-Northwind,沒有的可以到微軟掛官網去下,附件到sql server2005資料庫中

               2.使用微軟O/R設計器，將Northwind對映到專案中，以下例項在此環境下進行,使用vs2008

以下為程式碼:

using System; using System.Collections.Generic; using System.Linq; using System.Text; using DBClass;//此處為O/R對映Northwind using System.Data.Linq; using System.Data.Linq.SqlClient; namespace Linq_to_Sql_Demo1 { class Program { static void Main(string[] args) { LinqForLike(); } #region linq中select語句的使用 public static void SqlFroSelectOne() { NorthwindDataContext db = new NorthwindDataContext(); var q = from c in db.Customers where c.City == "London" select new { c.CompanyName, c.City }; //上下兩句表達意思是一樣的，上面為標準查詢語句，下面為級連表示式 // var q = db.Customers.Where(c => c.City == "London").Select(c => c.ContactName); /* 手動填寫資料庫物件後的方法 DataContext dc = new DataContext("server=.//sql2005;database=Northwind;uid=sa;pwd=king_860119"); var q = from c in dc.GetTable<Customers>() where c.City == "London" select c.CompanyName; */ foreach (var c in q) { Console.WriteLine(c); } Console.ReadLine(); } #endregion #region linq中select語句的使用2 public static void SqlFroSelectTwo() { NorthwindDataContext dc = new NorthwindDataContext(); var q=from s in dc.Customers select new{城市名稱=s.City}; //在這裡相當於宣告一個匿名類q,q中存在屬性“城市名稱”,而其中S為一條條的dc.Customers物件 //其中“城市名稱”這個屬性噹噹與對S.city的重新命名一樣 foreach(var a in q) { Console.WriteLine(a); } Console.Read(); } #endregion #region linq中select語句的使用3 public static void SqlFroSelectThree() { NorthwindDataContext dc = new NorthwindDataContext(); var q=from s in dc.Products select new {s.ProductName,我的條件=s.UnitsInStock-s.UnitsOnOrder<0?"out":"in"}; foreach(var a in q) { Console.WriteLine(a); } Console.Read(); } #endregion #region linq中where語句的使用1 public static void SqlFroWhereOne() { NorthwindDataContext db = new NorthwindDataContext(); var q = from p in db.Products where p.UnitPrice > 10m || p.Discontinued select p; foreach (var a in q) { Console.WriteLine(a.Categories.CategoryID); } Console.Read(); } #endregion #region linq中order語句的使用1 public static void SqlFroOrderOne() { NorthwindDataContext db = new NorthwindDataContext(); var q = from s in db.Employees orderby s.EmployeeID descending select new { s.EmployeeID,s.FirstName,s.LastName}; //orderby子句在select子句前面，與where等子句位置無要求 foreach (var s in q) { Console.WriteLine(s.ToString()); } Console.Read(); } #endregion #region Linq中GroupBy語句的使用1 public static void SqlFroGroupByOne() { NorthwindDataContext db = new NorthwindDataContext(); var q = from p in db.Products group p by p.CategoryID into g select g; foreach (var gp in q) { if (gp.Key == 7) { foreach (var p in gp) { //do something } } } Console.ReadKey(); } #endregion #region Linq中GroupBy語句的使用2 public static void SqlForGroupByTwo() { NorthwindDataContext db = new NorthwindDataContext(); var q = from p in db.Products group p by p.CategoryID into g select new { CategoryID = g.Key, g }; foreach (var gp in q) { //do something } } #endregion #region Linq中GroupBy語句的使用30-聚合函式的使用 public static void SqlForGroupByThree() { NorthwindDataContext db = new NorthwindDataContext(); var q = from p in db.Products group p by p.CategoryID into g select new { g.Key, TotalPrice = g.Sum(p => p.UnitPrice) }; foreach (var a in q) { Console.WriteLine(a); } Console.Read(); } #endregion #region Linq中Join語句的使用1 public static void LinqForJoinOne() { NorthwindDataContext db = new NorthwindDataContext(); var q = from p in db.Customers join o in db.Orders on p.CustomerID equals o.CustomerID select new { p.CustomerID, o.EmployeeID }; //下面註釋的語句為此句的lambda的寫法 // var q = db.Customers.Join(db.Orders, p => p.CustomerID, o => o.CustomerID, (p, o) => new { p.CustomerID, o.EmployeeID }); foreach (var s in q) { Console.WriteLine(s); } Console.Read(); } #endregion #region Linq中In語句的使用 public static void LinqForInOne() { NorthwindDataContext db = new NorthwindDataContext(); string[] customerID_Set = new string[] { "AROUT", "BOLID", "FISSA" }; var q = from s in db.Orders where customerID_Set.Contains(s.CustomerID) select s.EmployeeID; //相當於sql中的in，意思就是從這個in的集合中取出，如果not in 就在集合的前面加上！ foreach (var a in q) { Console.WriteLine(a); } Console.Read(); } #endregion #region Linq中Like語句的使用 public static void LinqForLike() { NorthwindDataContext db = new NorthwindDataContext(); //中間部分包含And的 var q = from s in db.Customers where s.ContactName.Contains("And") select s.ContactName; //開頭部分包含A的 var p = from s in db.Customers where s.ContactName.StartsWith("A") select s.ContactName; //結束部分包含g的 var a = from s in db.Customers where s.ContactName.EndsWith("g") select s.ContactName; //另外的一種寫法，需要名稱空間System.Data.Linq.SqlClient var c = from s in db.Customers where SqlMethods.Like(s.ContactName, "%g") select s.ContactName; foreach (var b in c) { Console.WriteLine(b); } Console.Read(); } #endregion } }

使用O/R對映的資料庫例項程式碼（均為系統自動生成）,連線字元在app.config中

附加上增刪改的使用

#region linq中insert語句的使用 public static void LinqForInsert() { NorthwindDataContext db = new NorthwindDataContext(); var rgdata = new Region { RegionID = 5, RegionDescription = "test" }; try { db.Region.InsertOnSubmit(rgdata);//插入資料 db.SubmitChanges();//提交更改 } catch (Exception err) { Console.WriteLine(err.Message); } Console.Read(); } #endregion #region Linq中update語句的使用 public static void LinqForUpdata() { NorthwindDataContext db = new NorthwindDataContext(); var o = from c in db.Region where c.RegionID == 5 select c; foreach (var item in o) { if(item.RegionID==5) item.RegionDescription = "test改過了"; } db.SubmitChanges(); } #endregion #region Linq中del語句的使用 public static void LinqForDel() { NorthwindDataContext db = new NorthwindDataContext(); var q = from c in db.Region where c.RegionID == 5 select c; foreach (var item in q) { db.Region.DeleteOnSubmit(item); } db.SubmitChanges(); } #endregion