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
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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
using (var data = new Formula1Entities())
{
string country = "Brazil";
ObjectQuery
"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
Console.WriteLine(racers.CommandText);
Console.WriteLine(racers.ToTraceString());
}
3. Linq to Entities
因为实体对象都继承于ObjectQuery
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