如何：从数据库中删除行 (LINQ to SQL)
更新：November 2007
可以通过将对应的 LINQ to SQL 对象从其与表相关的集合中删除来删除数据库中的行。LINQ to SQL 会将更改转换为相应的 SQL DELETE 命令。
LINQ to SQL 不支持且无法识别级联删除操作。如果要在对行有约束的表中删除行，则必须完成以下任务之一：
在数据库的外键约束中设置 ON DELETE CASCADE 规则。
使用自己的代码首先删除阻止删除父对象的子对象。
否则会引发异常。请参见本主题中后面的第二个代码示例。
.gif "说明") 说明： |
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您可以重写 Insert、Update 和 Delete 数据库操作的 LINQ to SQL 默认方法。有关更多信息，请参见自定义插入、更新和删除操作 (LINQ to SQL)。 使用 Visual Studio 的开发人员可以使用 对象关系设计器 来开发用于实现相同目的的存储过程。对象关系设计器（O/R 设计器） |
以下步骤假定您已通过有效的 DataContext 连接到 Northwind 数据库。有关更多信息，请参见如何：连接到数据库 (LINQ to SQL)。
删除数据库中的行
查询数据库中要删除的行。
调用 DeleteOnSubmit 方法。
将更改提交到数据库。
示例
这第一个代码示例查询数据库中 11000 号订单的详细信息，将这些订单详细信息标记为删除，然后将这些更改提交到数据库。
' Query the database for the rows to be deleted.
Dim deleteOrderDetails = _
From details In db.OrderDetails() _
Where details.OrderID = 11000 _
Select details
For Each detail As OrderDetail In deleteOrderDetails
db.OrderDetails.DeleteOnSubmit(detail)
Next
Try
db.SubmitChanges()
Catch ex As Exception
Console.WriteLine(ex)
' Provide for exceptions
End Try
// Query the database for the rows to be deleted.
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.
}
在第二个示例中，目的是删除订单（10250 号）。代码首先检查 OrderDetails 表以查看要删除的订单是否有子项。如果订单有子项，则首先将子项标为删除，然后将订单标为删除。DataContext 为实际删除设置正确的顺序，以使发送到数据库的删除命令遵守数据库约束。
Dim db As New Northwnd("c:\northwnd.mdf")
db.Log = Console.Out
' Specify order to be removed from database.
Dim reqOrder As Integer = 10252
' Fetch OrderDetails for requested order.
Dim ordDetailQuery = _
From odq In db.OrderDetails _
Where odq.OrderID = reqOrder _
Select odq
For Each selectedDetail As OrderDetail In ordDetailQuery
Console.WriteLine(selectedDetail.Product.ProductID)
db.OrderDetails.DeleteOnSubmit(selectedDetail)
Next
' Display progress.
Console.WriteLine("Detail section finished.")
Console.ReadLine()
' Determine from Detail collection whether parent exists.
If ordDetailQuery.Any Then
Console.WriteLine("The parent is present in the Orders collection.")
' Fetch order.
Try
Dim ordFetch = _
(From ofetch In db.Orders _
Where ofetch.OrderID = reqOrder _
Select ofetch).First()
db.Orders.DeleteOnSubmit(ordFetch)
Console.WriteLine("{0} OrderID is marked for deletion.,", ordFetch.OrderID)
Catch ex As Exception
Console.WriteLine(ex.Message)
Console.ReadLine()
End Try
Else
Console.WriteLine("There was no parent in the Orders collection.")
End If
' Display progress.
Console.WriteLine("Order section finished.")
Console.ReadLine()
Try
db.SubmitChanges()
Catch ex As Exception
Console.WriteLine(ex.Message)
Console.ReadLine()
End Try
' Display progress.
Console.WriteLine("Submit finished.")
Console.ReadLine()
Northwnd db = new Northwnd(@"c:\northwnd.mdf");
db.Log = Console.Out;
// Specify order to be removed from database
int reqOrder = 10250;
// Fetch OrderDetails for requested order.
var ordDetailQuery =
from odq in db.OrderDetails
where odq.OrderID == reqOrder
select odq;
foreach (var selectedDetail in ordDetailQuery)
{
Console.WriteLine(selectedDetail.Product.ProductID);
db.OrderDetails.DeleteOnSubmit(selectedDetail);
}
// Display progress.
Console.WriteLine("detail section finished.");
Console.ReadLine();
// Determine from Detail collection whether parent exists.
if (ordDetailQuery.Any())
{
Console.WriteLine("The parent is presesnt in the Orders collection.");
// Fetch Order.
try
{
var ordFetch =
(from ofetch in db.Orders
where ofetch.OrderID == reqOrder
select ofetch).First();
db.Orders.DeleteOnSubmit(ordFetch);
Console.WriteLine("{0} OrderID is marked for deletion.", ordFetch.OrderID);
}
catch (Exception e)
{
Console.WriteLine(e.Message);
Console.ReadLine();
}
}
else
{
Console.WriteLine("There was no parent in the Orders collection.");
}
// Display progress.
Console.WriteLine("Order section finished.");
Console.ReadLine();
try
{
db.SubmitChanges();
}
catch (Exception e)
{
Console.WriteLine(e.Message);
Console.ReadLine();
}
// Display progress.
Console.WriteLine("Submit finished.");
Console.ReadLine();