[.net]LINQ体验(6)——LINQ语句之Insert/Update/Delete操作 （转）

我们继续讲解LINQ语句，这篇我们来讨论Insert/Update/Delete操作。这个在我们的程序中最为常用了。我们直接看例子。

Insert/Update/Delete操作

Insert

1.简单形式

说明：new一个对象，使用InsertOnSubmit方法将其加入到对应的集合中，使用SubmitChanges()提交到数据库。

NorthwindDataContext db = new NorthwindDataContext();
var newCustomer = new Customer { CustomerID = "MCSFT",CompanyName = "Microsoft",ContactName = "John Doe",
ContactTitle = "Sales Manager",
Address = "1 Microsoft Way",City = "Redmond",Region = "WA",PostalCode = "98052",
Country = "USA",Phone = "(425) 555-1234",Fax = null };
db.Customers.InsertOnSubmit(newCustomer);
db.SubmitChanges();

2.一对多关系

说明：Category与Product是一对多的关系，提交Category(一端)的数据时，LINQ to SQL会自动将Product(多端)的数据一起提交。

var newCategory = new Category { CategoryName = "Widgets", Description = "Widgets are the customer-facing
analogues to sprockets and cogs." };
var newProduct = new Product { ProductName = "Blue Widget", UnitPrice = 34.56M, Category = newCategory };
db.Categories.InsertOnSubmit(newCategory);
db.SubmitChanges();

3.多对多关系

说明：在多对多关系中，我们需要依次提交。

var newEmployee = new Employee { FirstName = "Kira", LastName = "Smith" };
var newTerritory = new Territory { TerritoryID = "12345", TerritoryDescription = "Anytown",
Region = db.Regions.First() };
var newEmployeeTerritory = new EmployeeTerritory { Employee = newEmployee, Territory = newTerritory };
db.Employees.InsertOnSubmit(newEmployee);
db.Territories.InsertOnSubmit(newTerritory);
db.EmployeeTerritories.InsertOnSubmit(newEmployeeTerritory);
db.SubmitChanges();

4.Override using Dynamic CUD

说明：CUD就是Create、Update、Delete的缩写。下面的例子就是新建一个ID(主键)为32的Region，不考虑数据库中有没有ID为32的数据，如果有则替换原来的数据，没有则插入。（不知道这样说对不对。大家指点一下）

Region nwRegion = new Region() { RegionID = 32, RegionDescription = "Rainy" };
db.Regions.InsertOnSubmit(nwRegion);
db.SubmitChanges();

Update

说明：更新操作，先获取对象，进行修改操作之后，直接调用SubmitChanges()方法即可提交。注意，这里是在同一个DataContext中，对于不同的DataContex看下面的讲解。

1.简单形式

Customer cust = db.Customers.First(c => c.CustomerID == "ALFKI");
cust.ContactTitle = "Vice President";
db.SubmitChanges();

2.多个项

var q = from p in db.Products
where p.CategoryID == 1
select p;
foreach (var p in q)
{
p.UnitPrice += 1.00M;
}
db.SubmitChanges();

Delete

1.简单形式

说明：调用DeleteOnSubmit方法即可。

OrderDetail orderDetail = db.OrderDetails.First(c => c.OrderID == 10255 && c.ProductID == 36);
db.OrderDetails.DeleteOnSubmit(orderDetail);
db.SubmitChanges();

2.一对多关系

说明：Order与OrderDetail是一对多关系，首先DeleteOnSubmit其OrderDetail(多端)，其次DeleteOnSubmit其Order(一端)。因为一端是主键。

var orderDetails =
from o in db.OrderDetails
where o.Order.CustomerID == "WARTH" && o.Order.EmployeeID == 3
select o;
var order =
(from o in db.Orders
where o.CustomerID == "WARTH" && o.EmployeeID == 3
select o).First();
foreach (OrderDetail od in orderDetails)
{
db.OrderDetails.DeleteOnSubmit(od);
}
db.Orders.DeleteOnSubmit(order);
db.SubmitChanges();

3.Inferred Delete(推断删除)

说明：Order与OrderDetail是一对多关系，在上面的例子，我们全部删除CustomerID为WARTH和EmployeeID为3 的数据，那么我们不须全部删除呢？例如Order的OrderID为10248的OrderDetail有很多，但是我们只要删除ProductID为11的OrderDetail。这时就用Remove方法。

Order order = db.Orders.First(x => x.OrderID == 10248);
OrderDetail od = order.OrderDetails.First(d => d.ProductID == 11);
order.OrderDetails.Remove(od);
db.SubmitChanges();

Update with Attach

说明：在对于在不同的DataContext之间，使用Attach方法来更新数据。例如在一个名为tempdb的NorthwindDataContext中，查询出Customer和Order，在另一个NorthwindDataContext中，Customer的地址更新为123 First Ave，Order的CustomerID 更新为CHOPS。

Customer c1;
List<Order> deserializedOrders = new List<Order>();
Customer deserializedC1;
using (NorthwindDataContext tempdb = new NorthwindDataContext())
{
c1 = tempdb.Customers.Single(c => c.CustomerID == "ALFKI");
deserializedC1 = new Customer { Address = c1.Address, City = c1.City,CompanyName=c1.CompanyName,
ContactName=c1.ContactName,
ContactTitle=c1.ContactTitle, Country=c1.Country,
CustomerID=c1.CustomerID, Fax=c1.Fax,
Phone=c1.Phone, PostalCode=c1.PostalCode, Region=c1.Region};
Customer tempcust = tempdb.Customers.Single(c => c.CustomerID == "ANTON");
foreach (Order o in tempcust.Orders)
{
deserializedOrders.Add(new Order {CustomerID=o.CustomerID, EmployeeID=o.EmployeeID,
Freight=o.Freight,OrderDate=o.OrderDate,
OrderID=o.OrderID,RequiredDate=o.RequiredDate,
ShipAddress=o.ShipAddress,ShipCity=o.ShipCity,
ShipName=o.ShipName,ShipCountry=o.ShipCountry,
ShippedDate=o.ShippedDate,
ShipPostalCode=o.ShipPostalCode, ShipRegion=o.ShipRegion,
ShipVia=o.ShipVia});
}
}
using (NorthwindDataContext db2 = new NorthwindDataContext())
{
//对Customer更新，不能写错
db2.Customers.Attach(deserializedC1);
deserializedC1.Address = "123 First Ave";
//对Order全部更新
db2.Orders.AttachAll(deserializedOrders);
foreach (Order o in deserializedOrders)
{
o.CustomerID = "CHOPS";
}
db2.SubmitChanges();
}

Update and Delete with Attach

说明：在不同的DataContext中，实现插入、更新、删除。看下面的一个例子：

Customer cust = null;
using (NorthwindDataContext tempdb = new NorthwindDataContext())
{
cust = tempdb.Customers.First(x => x.CustomerID == "ALFKI");
}
Order orderA = cust.Orders.First();
Order orderB = cust.Orders.First(x => x.OrderID > orderA.OrderID);
using (NorthwindDataContext db2 = new NorthwindDataContext())
{
db2.Customers.Attach(cust);
db2.Orders.AttachAll(cust.Orders.ToList());
//更新Customer的Phone.
cust.Phone = "2345 5436";
//更新OrderA的ShipCity.
orderA.ShipCity = "Redmond";
//删除OrderB.
cust.Orders.Remove(orderB);
//添加一个新的Order到Customer中.
Order orderC = new Order() { ShipCity = "New York" };
cust.Orders.Add(orderC);
//提交执行
db2.SubmitChanges();
}

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