1.linq 框架
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C# VB
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.Net Language INtegrated Query(LINQ)
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Linq enabled data sources
1.linq to objects
2.Linq enabled ADO.NET
----linq to DataSet
----linq to SQL
----linq to Entities
3.linq to XML
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Data
Objects,Relations,XML
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2.LINQ for SQL
? 把.NET 類和SQL 數據通過關係進行映射(對象<--->關係的相互映射)
? 把LINQ 查詢轉化爲SQL 語言進行執行
? 支持對插入,更新,刪除操作進行跟蹤.
? 支持實體級別的驗證規則
? 構建於ADO.NET之上並且集成連接池和事ADO.務處理(ADO.NET之上)
舉例1：（查詢實例）
NorthWindDataContext dc = new NorthWindDataContext();
var query = from P in dc.Products
where P.CategoryID.Value>6
select P;
this.GridView1.DataSource = query;
this.GridView1.DataBind();
舉例2：（修改單個記錄實例）
NorthWindDataContext dc = new NorthWindDataContext();
Product product = dc.Products.Single(p => p.ProductName == "Tofu");
product.UnitPrice = 1111111111;
product.UnitsInStock = 55;
dc.SubmitChanges();
3.數據表映射
? 映射數據表和實體類之間的關係
? 使用數據庫中典型的主/外鍵進行表示
? 支持靈活的關係查詢並且不用寫任務的SQL
? 代碼就可以執行處理過程
舉例3：
-----產品類型 Categories<1>-----> <n>產品Products <n>
-----產品Products <n> <----<1>提供商 Suppliers
Table Suplier
-------------------------------------------------------
SuplierID
CompanyName
.....
Table Category
-------------------------------------------------------
CategoryID
CanegoryName
....
Table Product
-------------------------------------------------------
ProductID
ProductName
....
SuplierID
CategoryID
模型中的代碼關聯如下：
public partial class Product {
public int ProductID;
public string ProductName;
public Nullable<int> SupplierID;
public Nullable<int> CategoryID;
public Supplier Supplier; //兩者組合以來，一對一
public Category Category; //兩者組合以來，一對一
}
public partial class Supplier {
public int SupplierID;
public string CompanyName;
public EntitySet<Product> Products; //一對多
}
public partial class Category {
public int CategoryID;
public EntitySet<Product> Products; //一對多
}
我們可以這樣理解：在對Product進行數據訪問的時候，可以直接訪問Supplier和Category的的單個對象；在對Supplier訪問時，可以訪問對於的一組Products對象；在對Category訪問時，可以訪問對於的一組Products對象；
舉例查詢1：（在Supplier裏面直接訪問Product）
NorthWindDataContext db = new NorthWindDataContext();
GridView1.DataSource = from s in db.Suppliers
select new
{
Name = s.CompanyName,
Country = s.Country,
Products = from p in s.Products //在Supplier裏面直接訪問Products
select new
{
ProductName = p.ProductName
}
};
GridView1.DataBind();
}
舉例2：（在Supplier裏面訪問Product）
NorthwindDataContext db = new NorthwindDataContext();
var suppliers = from s in db.Suppliers
where s.Products.Count > 2
select s;
foreach (Supplier supplier in suppliers) {
Response.Write("<h3>" + supplier.CompanyName + "</h3>");
foreach (Product product in supplier.Products) {
Response.Write("-- ");
Response.Write(product.ProductName);
Response.Write("<br/>");
}
}
舉例3：（使用一些函數）
NorthwindDataContext db = new NorthwindDataContext();
SupplierList.DataSource = from s in db.Suppliers
where s.Products.Count > 2
select s;
SupplierList.DataBind();
NorthwindDataContext db = new NorthwindDataContext();
GridView1.DataSource = (from s in db.Suppliers
where s.Products.Count > 4
select s).Including(s => s.Products)
GridView1.DataBind();
4.聯合查詢
舉例1：兩個表的join操作。
NorthWindDataContext db = new NorthWindDataContext();
var custTotalOrders = from c in db.Customers
join o in db.Orders
on c.CustomerID equals o.CustomerID into custOrders //存放早custOrders的臨時結果集中
from o in custOrders //從這個結果集中繼續查詢
select new
{
Customer = c.CompanyName,
OrderDate = o.OrderDate,
OrderTotal = o.Order_Details.Sum(d => d.UnitPrice * d.Quantity)
};
GridView1.DataSource = custTotalOrders;
GridView1.DataBind();
舉例2：（直接查詢）
var innerJoinQuery =
from category in categories
join prod in products on category.ID equals prod.CategoryID
select new { ProductName = prod.Name, Category = category.Name };
5.數據分頁
相對於以前的TSQL語句而言，不是一次把所有的數據都取出來，而是根據需要從數據庫中讀取數據。
int startRow = Convert.ToInt32(Request.QueryString["startRow"]);
NorthwindDataContext db = new NorthwindDataContext();
var results = from c in db.Customers join o in db.Orders
on c.CustomerID equals o.CustomerID into custOrders
from o in custOrders
select new {
Customer = c.CompanyName,
OrderDate = o.OrderDate,
OrderTotal = o.OrderDetails.Sum(d=>d.UnitPrice)
};
GridView1.DataSource = results.Skip(startRow).Take(10);//分頁
GridView1.DataBind();
5.更新一個特定的產品
NorthwindDataContext db = new NorthwindDataContext();
Product product = db.Products.Single(p => p.ProductName== "Chai");
product.UnitsInStock = 11;
product.ReorderLevel = 10;
product.UnitsOnOrder = 2;
db.SubmitChanges();
6.插入記錄
Order ord = new Order
{
OrderID = 12000,
ShipCity = "Seattle",
OrderDate = DateTime.Now
// …
};
// Add the new object to the Orders collection.
db.Orders.InsertOnSubmit(ord);
// Submit the change to the database.
try
{
db.SubmitChanges();
}
catch (Exception e)
{
Console.WriteLine(e);
// Make some adjustments.
// ...
// Try again.
db.SubmitChanges();
}
7.刪除記錄
var deleteOrderDetails =
from details in db.OrderDetails
where details.OrderID == 11000
select details;
foreach (var detail in deleteOrderDetails)
{
db.OrderDetails.DeleteOnSubmit(detail);
}
try
{
db.SubmitChanges();
}
catch (Exception e)
{
Console.WriteLine(e);
// Provide for exceptions.
}
8.其它的LINQ for SQL 功能
? 能夠執行實體/屬性驗證
? 可以使用存儲過程和視圖
? 可以清晰地定義和參與內部的TransactionScope()操作(簡單分佈式事務的寫法，可以指定事務是否包含在上一層事務中，通過DataContex制定)
? 實體類型的保存可以使用同一個DataContext進行多種數據查詢
9.LINQ to XML
以前的操作方式：流的方式、結點的方式
? XML 文檔的更好的操作
? 支持language integrated queries
? 更方便,更快速更智能更簡單的XML API
NorthwindDataContext db = new NorthwindDataContext();
XElement rssRoot = new XElement("rss",
new XAttribute("version", "2.0"),
new XElement("channel"
new XElement("title", "My RSS Feed"),
new XElement("link", "http://weblogs.asp.net"),
new XElement("description", "Northwind Products Feed"),
from product in db.Products
orderby product.ProductName descending
select new XElement("item",
new XElement("title", product.ProductName),
new XElement("link", “p.aspx?id="+product.ProductID),
new XElement("description", "Supplier: " +
product.Supplier.CompanyName)
)
)
);
Response.Write(rssRoot.ToString());