缺点：Entity FrameWork 没有提供获取不同层上的对象的方式，无助于创建多层上的解决方案,可以结合WCF实现分层

核心概念：

逻辑层，SSDL store schema definition language描述数据库表及其关系

概念层，CSDL conceptual schema definition L 描述 实体及关系

映射层 MSL mapping Specification L 把CSDL实体类型定义映射到SSDL

查询对象的三种方法

1. Entity SQL

Technorati 标签: ADO.NET Entity FrameWork

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

类似于LINQ,但Linq的参数是委托，而QueryBuilder的参数是字符串

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

因为实体对象都继承于ObjectQuery<T>，而该类实现了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);

}

}

增删改查CRUD的实现

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 );

//删除

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

niki2.Stars++;//修改

int changes = 0;

try

{

changes += data.SaveChanges();

//提交到数据源

}

catch (OptimisticConcurrencyException ex)

{

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

changes += data.SaveChanges();

}

}

//懒惰加载

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 懒惰加载，意思是在访问对象时，会自动加载对象的相关属性

foreach (Customer customer in data.Customers)

LazyLoadingEnabled 默认为true,若设为false,则需要使用

Include("Orders")) 称为预先加载

customer.Orders.Load();（延迟加载