ADO.NET Entity FrameWork

缺點：Entity FrameWork 沒有提供獲取不同層上的對象的方式，無助于創建多層上的解決方案,可以結合WCF實現分層

核心概念：

邏輯層，SSDL store schema definition language描述數據庫表及其關系

概念層，CSDL conceptual schema definition L  描述 實體及關系

映射層 MSL  mapping Specification L  把CSDL實體類型定義映射到SSDL

查詢對象的三種方法

1. Entity SQL

using (var data = new Formula1Entities())

            {

                string country = "Brazil";

                ObjectQuery<Racer> racers = data.CreateQuery<Racer>(

                   "SELECT VALUE it FROM ([Formula1Entities].[Racers]) AS it WHERE it.Country = @Country",

                   new ObjectParameter("Country", country));

                foreach (var r in racers)

                {

                    Console.WriteLine("{0} {1}", r.Firstname, r.Lastname);

                }

            }

2.QueryBuilder

類似于LINQ,但Linq的參數是委托，而QueryBuilder的參數是字符串

可以用Find(),GroupBy(),OrderBy()等方法，

  using (var data = new Formula1Entities())

            {

                string country = "Brazil";

                ObjectQuery<Racer> racers = data.Racers.Where("it.Country = @Country", new ObjectParameter("Country", country));

                Console.WriteLine(racers.CommandText);

                Console.WriteLine(racers.ToTraceString());

            }

3. Linq to Entities

因為實體對象都繼承于ObjectQuery<T>，而該類實現了IQueryable接口

using (var data = new Formula1Entities())

            {

                var racers = from r in data.Racers

                             where r.Wins > 40

                             orderby r.Wins descending

                             select r;

                foreach (Racer r in racers)

                {

                    Console.WriteLine("{0} {1}", r.Firstname, r.Lastname);

                }

            }

增刪改查CRUD的實現

  using (var data = new Formula1Entities())

            {

                var jaime = new Racer

                {

                    Firstname = "Jaime",

                    Lastname = "Alguersuari",

                    Country = "Spain",

                    Starts = 0

                };

                data.Racers.AddObject(jaime);

           //添加

Racer niki1 = data.Racers.Where("it.Country='Austria' && it.Lastname='Berger'").First();

   data.Racers.DeleteObject( niki1 );

//刪除

  Racer niki2 = data.Racers.Where("it.Country='Austria'").OrderBy("it.Wins DESC").First();

niki2.Stars++;//修改

                int changes = 0;

                try

                {

                    changes += data.SaveChanges();

//提交到數據源

                }

   catch (OptimisticConcurrencyException ex)

                {

                    data.Refresh(RefreshMode.ClientWins, ex.StateEntries);

                    changes += data.SaveChanges();

                }

}

//懶惰加載

using (var data = new NorthwindEntities())

            {

                data.ContextOptions.LazyLoadingEnabled = false;

                int a = data.Customers.Count();

                foreach (Customer customer in data.Customers.Include("Orders"))

                {

                    Console.WriteLine("{0}", customer.CompanyName);

                    bool a2 = customer.Orders.IsLoaded;

              //   if (!customer.Orders.IsLoaded)

              //      {

              //          customer.Orders.Load();

                    }

                    foreach (Order order in customer.Orders)

                    {

                        Console.WriteLine("\t{0} {1:d}", order.OrderID, order.OrderDate);

                    }

                }

            }

data.ContextOptions.LazyLoadingEnabled = false;

LazyLoadingEnabled  懶惰加載，意思是在訪問對象時，會自動加載對象的相關屬性   

foreach (Customer customer in data.Customers)

LazyLoadingEnabled  默認為true,若設為false,則需要使用

Include("Orders")) 稱為預先加載

     customer.Orders.Load();（延遲加載