Visual Studio 2008開發新特性系列課程(3)：VS2008新特性之LINQ入門

1.Today’s Problem: Data != Objects
問題：在業務邏輯中，我們需要的是對象，而在數據庫中存儲的是數據，在以前的技術中，通常需要寫很多的代碼來編寫數據訪問層。

public class Customer
{
 public int CustomerId;
 public string Name;
 public string City;
 public void Validate() // Todo: Add Business Validation
 }
}

GridView1.DataSource = from customer in db.Customers
   where customer.City == "London" 
   select customer;
GridView1 DataBind();

可以採用Sql server 2005的跟蹤器，跟蹤批處理和存儲過程，可以很好的跟蹤到這些執行情況。

 

2.Searching/Sorting an Array

string [] cities = { “Auckland”, “Oslo”, “Sydney”,“Seattle”, “Paris”, “Los Angeles” };
IEnumerable<string> places = from city in cities
        where city.Length > 5
        orderby city descending
        select city;
GridView1.DataSource = places;
GridView1.DataBind();

 

3.Searching/Sorting City Collection[強類型集合的查詢]

public class City
{
public string Name;
public string Country;
public int DistanceFromSeattle;
}
List<City> locations = GetLocations();

IEnumerable<City> places = from city in locations
      where city.DistanceFromSeattle > 1000
      orderby city.Country, city.Name
      select city;
GridView1.DataSource = places;
GridView1.DataBind();

 

4.LINQ需求和特性
利用編譯器對”匿名類型”的支持可以放心的使用LINQ
List<City> cities = CityUtilityHelper.GetCities();
var places = from city in cities
  where city.DistanceFromSeattle > 1000
  select new {
  City = city.Name,
  Country = city.Country,
  DistanceInKm = city.DistanceFromSeattle * 1.61
  };
GridView1.DataSource = places;
GridView1.DataBind();

 

5.總結
LINQ 的查詢結果序列可以被綁定到任何ASP NET 中的數據綁定控件