我們繼續講解LINQ to SQL語句,這篇我們來討論Insert/Update/Delete操作。這個在我們的程序中最爲常用了。我們直接看例子。
Insert/Update/Delete操作
插入(Insert)
1.簡單形式
說明:new一個對象,使用InsertOnSubmit方法將其加入到對應的集合中,使用SubmitChanges()提交到數據庫。
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();
語句描述:使用InsertOnSubmit方法將新客戶添加到Customers 表對象。調用SubmitChanges 將此新Customer保存到數據庫。
2.一對多關係
說明:Category與Product是一對多的關係,提交Category(一端)的數據時,LINQ to SQL會自動將Product(多端)的數據一起提交。
var newCategory = new Category { CategoryName = "Widgets", Description = "Widgets are the ……" }; var newProduct = new Product { ProductName = "Blue Widget", UnitPrice = 34.56M, Category = newCategory }; db.Categories.InsertOnSubmit(newCategory); db.SubmitChanges();
語句描述:使用InsertOnSubmit方法將新類別添加到Categories表中,並將新Product對象添加到與此新Category有外鍵關係的Products表中。調用SubmitChanges將這些新對象及其關係保存到數據庫。
3.多對多關係
說明:在多對多關係中,我們需要依次提交。
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();
語句描述:使用InsertOnSubmit方法將新僱員添加到Employees 表中,將新Territory添加到Territories表中,並將新EmployeeTerritory對象添加到與此新Employee對象和新Territory對象有外鍵關係的EmployeeTerritories表中。調用SubmitChanges將這些新對象及其關係保持到數據庫。
4.使用動態CUD重寫(Override using Dynamic CUD)
說明:CUD就是Create、Update、Delete的縮寫。下面的例子就是新建一個ID(主鍵)爲32的Region,不考慮數據庫中有沒有ID爲32的數據,如果有則替換原來的數據,沒有則插入。
Region nwRegion = new Region() { RegionID = 32, RegionDescription = "Rainy" }; db.Regions.InsertOnSubmit(nwRegion); db.SubmitChanges();
語句描述:使用DataContext提供的分部方法InsertRegion插入一個區域。對SubmitChanges 的調用調用InsertRegion 重寫,後者使用動態CUD運行Linq To SQL生成的默認SQL查詢。
更新(Update)
說明:更新操作,先獲取對象,進行修改操作之後,直接調用SubmitChanges()方法即可提交。注意,這裏是在同一個DataContext中,對於不同的DataContex看下面的講解。
1.簡單形式
Customer cust = db.Customers.First(c => c.CustomerID == "ALFKI"); cust.ContactTitle = "Vice President"; db.SubmitChanges();
語句描述:使用SubmitChanges將對檢索到的一個Customer對象做出的更新保持回數據庫。
2.多項更改
var q = from p in db.Products where p.CategoryID == 1 select p; foreach (var p in q) { p.UnitPrice += 1.00M; } db.SubmitChanges();
語句描述:使用SubmitChanges將對檢索到的進行的更新保持回數據庫。
刪除(Delete)
1.簡單形式
說明:調用DeleteOnSubmit方法即可。
OrderDetail orderDetail =
db.OrderDetails.First
(c => c.OrderID == 10255 && c.ProductID == 36);
db.OrderDetails.DeleteOnSubmit(orderDetail);
db.SubmitChanges();
語句描述:使用DeleteOnSubmit方法從OrderDetail 表中刪除OrderDetail對象。調用SubmitChanges 將此刪除保持到數據庫。
2.一對多關係
說明:Order與OrderDetail是一對多關係,首先DeleteOnSubmit其OrderDetail(多端),其次DeleteOnSubmit其Order(一端)。因爲一端是主鍵。
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();
語句描述語句描述:使用DeleteOnSubmit方法從Order 和Order Details表中刪除Order和Order Detail對象。首先從Order Details刪除,然後從Orders刪除。調用SubmitChanges將此刪除保持到數據庫。
3.推理刪除(Inferred Delete)
說明:Order與OrderDetail是一對多關係,在上面的例子,我們全部刪除CustomerID爲WARTH和EmployeeID爲3 的數據,那麼我們不須全部刪除呢?例如Order的OrderID爲10248的OrderDetail有很多,但是我們只要刪除ProductID爲11的OrderDetail。這時就用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();
語句描述語句描述:這個例子說明在實體對象的引用實體將該對象從其EntitySet 中移除時,推理刪除如何導致在該對象上發生實際的刪除操作。僅當實體的關聯映射將DeleteOnNull設置爲true且CanBeNull 爲false 時,纔會發生推理刪除行爲。
使用Attach更新(Update with Attach)
說明:在對於在不同的DataContext之間,使用Attach方法來更新數據。例如在一個名爲tempdb的NorthwindDataContext中,查詢出Customer和Order,在另一個NorthwindDataContext中,Customer的地址更新爲123 First Ave,Order的CustomerID 更新爲CHOPS。
//通常,通過從其他層反序列化 XML 來獲取要附加的實體 //不支持將實體從一個DataContext附加到另一個DataContext //因此若要複製反序列化實體的操作,將在此處重新創建這些實體 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()) { //將第一個實體附加到當前數據上下文,以跟蹤更改 //對Customer更新,不能寫錯 db2.Customers.Attach(deserializedC1); //更改所跟蹤的實體 deserializedC1.Address = "123 First Ave"; //附加訂單列表中的所有實體 db2.Orders.AttachAll(deserializedOrders); //將訂單更新爲屬於其他客戶 foreach (Order o in deserializedOrders) { o.CustomerID = "CHOPS"; } //在當前數據上下文中提交更改 db2.SubmitChanges(); }
語句描述:從另一個層中獲取實體,使用Attach和AttachAll將反序列化後的實體附加到數據上下文,然後更新實體。更改被提交到數據庫。
使用Attach更新和刪除(Update and Delete with Attach)
說明:在不同的DataContext中,實現插入、更新、刪除。看下面的一個例子:
//通常,通過從其他層反序列化XML獲取要附加的實體 //此示例使用 LoadWith 在一個查詢中預先加載客戶和訂單, //並禁用延遲加載 Customer cust = null; using (NorthwindDataContext tempdb = new NorthwindDataContext()) { DataLoadOptions shape = new DataLoadOptions(); shape.LoadWith<Customer>(c => c.Orders); //加載第一個客戶實體及其訂單 tempdb.LoadOptions = shape; tempdb.DeferredLoadingEnabled = false; 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()) { //將第一個實體附加到當前數據上下文,以跟蹤更改 db2.Customers.Attach(cust); //附加相關訂單以進行跟蹤; 否則將在提交時插入它們 db2.Orders.AttachAll(cust.Orders.ToList()); //更新客戶的Phone. cust.Phone = "2345 5436"; //更新第一個訂單OrderA的ShipCity. orderA.ShipCity = "Redmond"; //移除第二個訂單OrderB. cust.Orders.Remove(orderB); //添加一個新的訂單Order到客戶Customer中. Order orderC = new Order() { ShipCity = "New York" }; cust.Orders.Add(orderC); //提交執行 db2.SubmitChanges(); }
語句描述:從一個上下文提取實體,並使用 Attach 和 AttachAll 附加來自其他上下文的實體,然後更新這兩個實體,刪除一個實體,添加另一個實體。更改被提交到數據庫。
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