C#数据库操作之LINQ to SQL技术详解

// Northwnd inherits from System.Data.Linq.DataContext.
Northwnd nw = new Northwnd(@"northwnd.mdf");
// or, if you are not using SQL Server Express
// Northwnd nw = new Northwnd("Database=Northwind;Server=server_name;Integrated Security=SSPI");

var companyNameQuery =
    from cust in nw.Customers
    where cust.City == "London"
    select cust.CompanyName;

foreach (var customer in companyNameQuery)
{
    Console.WriteLine(customer);
}

//在使用该例展示的方法之前，必须进行以下两个步骤：
//1、添加引用System.Data.Linq；
//2、使用using语句，添加命名空间，否则报错
//   using TableAttribute = System.Data.Linq.Mapping.TableAttribute;
//   using ColumnAttribute = System.Data.Linq.Mapping.ColumnAttribute;

//Table特性，创建了数据库中的名为DVDTable的表与该类之间的映射关系。
[Table(Name = "MyOrders")]
public class Order
{
	//Column特性，创建了DVDTable表中同名列与该类成员属性之间的映射关系。
	[Column(IsPrimaryKey = true)]
	public int id;
	[Column]
	public string name;
	[Column]
	public DateTime date;

	public override string ToString()
	{
		return "Order对象:{" + id + "，" + name + "," + date + "}";
	}
}

//自定义类 ，继承DataContext类。
public class MyOrders : DataContext
{
    public MyOrders(String connection) : base(connection)
    {
    }

    public Table<Order> orders;
}

//创建一个MyOrders 类的对象db，该类继承自DataContext类。
MyOrders myOrders = new MyOrders(@"D:\myFirstOrder.mdf");

public void CreateDatabase()
{
    if (myOrders.DatabaseExists())
    {
        //先判断该路径中，是否存在该数据库文件，如果存在，则删除。
        MessageBox.Show("Deleting old database...");
        myOrders.DeleteDatabase();
    }
    //myOrders对象创建数据库
    myOrders.CreateDatabase();
    //释放DataContext实例，所使用的的所有资源
    //myOrders.Dispose();
}

MyOrders myOrders = new MyOrders(@"D:\myFirstOrder4.mdf");

// Create a new Order object.Order class is user defined class.
Order ord = new Order
{
    id = 12000,
    name = "Harry Potty",
    OrderDate = DateTime.Now
    // …
};

// Add the new object to the Orders collection.
System.Data.Linq.Table<Order> table = myOrders.GetTable<Order>();
table.InsertOnSubmit(ord);

// Submit the change to the database.
try
{
    myOrders.SubmitChanges();
}
catch (Exception e)
{
    MessageBox.Show(e.Message);
    // Make some adjustments.
    // ...
    // Try again.
    myOrders.SubmitChanges();
}
//释放资源
//myOrders.Dispose();

MyOrders myOrders = new MyOrders(@"c:\northwnd.mdf");
System.Data.Linq.Table<Order> table = myOrders.GetTable<Order>();

// Query for customers in London.
IQueryable<Customer> custQuery =
    from order in myOrders.orders
    where order.id == 12000
    select order;

//将查询结果输出
foreach( var o in result)
{
	Console.WriteLine(o.toString());
}

// Query the database for the row to be updated.
var query =
    from ord in myOrders.Orders
    where ord.id== 11000
    select ord;

// Execute the query, and change the column values
// you want to change.
foreach (Order ord in query)
{
    ord.name = "Hong Lou Meng";
    ord.date = DateTime.Now;
    // Insert any additional changes to column values.
}

// Submit the changes to the database.
try
{
    myOrders.SubmitChanges();
}
catch (Exception e)
{
    MessageBox.Show(Console.WriteLine(e));
    // Provide for exceptions.
}
//释放DataContext对象占用的资源。
//myOrders.Dispose();

Table<Order> orders = myOrders.GetTable<Order>();
// Query the database for the rows to be deleted.

var deleteResult =
    from ord in orders
    where ord.id == 11000
    select ord;

foreach (var ord in deleteResult )
{
    orders.DeleteOnSubmit(ord );
}

try
{
    myOrders.SubmitChanges();
}
catch (Exception e)
{
    MessagBox.Show(e.Message);
    // Provide for exceptions.
}

//Northwnd myOrders = new Northwnd(@"c:\northwnd.mdf");

MyOrders myOrders = new MyOrders(@"D:\myFirstOrder.mdf");

myOrders.Log = Console.Out;

// Specify order to be removed from database
int reqOrder = 10250;

// Fetch OrderDetails for requested order.
var ordDetailQuery =
    from odq in myOrders.OrderDetails
    where odq.OrderID == reqOrder
    select odq;

foreach (var selectedDetail in ordDetailQuery)
{
    MessageBox.Show(selectedDetail.toString());
    myOrders.OrderDetails.DeleteOnSubmit(selectedDetail);
}

// Display progress.
MessageBox.Show("detail section finished.");

// Determine from Detail collection whether parent exists.
if (ordDetailQuery.Any())
{
    MessageBox.Show("The parent is present in the Orders collection.");
    // Fetch Order.
    try
    {
        var ordFetch =
            (from ofetch in myOrders.Orders
             where ofetch.OrderID == reqOrder
             select ofetch).First();
        myOrders.Orders.DeleteOnSubmit(ordFetch);
        MessageBox.Show("{0} OrderID is marked for deletion.", ordFetch.OrderID);
    }
    catch (Exception e)
    {
        MessageBox.Show(e.Message);
    }
}
else
{
    MessageBox.Show("There was no parent in the Orders collection.");
}

// Display progress.
MessageBox.Show("Order section finished.");

try
{
    myOrders.SubmitChanges();
}
catch (Exception e)
{
    MessageBox.Show(e.Message);
}

// Display progress.
MessageBox.Show("Submit finished.");