Entity Framework 学习初级篇7--基本操作：增加、更新、删除、事务

本节，直接写通过代码来学习。这些基本操作都比较简单，与这些基本操作相关的内容在之前的1至6节基本介绍完毕。

·           增加：

方法1：使用AddToXXX(xxx)方法：实例代码如下：            

using (var edm = new NorthwindEntities())
{
  　　Customers c = new Customers { CustomerID = "c#", City = "成都市", Address = "中国四川省", CompanyName = "cnblogs", Country = "中国", 　　　　Fax = "10086", Phone = "1008611", PostalCode = "610000", Region = "天府广场", ContactName = "风车车.Net" };

     edm.AddToCustomers(c);

     int result = edm.SaveChanges();

     Assert.AreEqual(result, 1);

     Customers addc = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c#");

     Console.WriteLine("CustomerId={0},City={1}", addc.CustomerID, addc.City);

}

方法2：使用ObjectContext的AddObject(string entitySetName, object entity)方法。实例代码如下：

using (var edm = new NorthwindEntities())

{

            Customers c = new Customers { CustomerID = "c2", City = "成都市2", Address = "中国四川省2", CompanyName ="cnblogs", Country = "中国", Fax = "10086", Phone = "1008611", PostalCode = "610000", Region = "天府广场", ContactName = "风车车.Net"};

            edm.AddObject("Customers", c);

            int result = edm.SaveChanges();

            Assert.AreEqual(result, 1);

            Customers addc = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c2");

            Console.WriteLine("CustomerId={0},City={1}", addc.CustomerID, addc.City);

}

其中，在代码中，需要注意的是：AddObject方法中参数“entitySetName ”就是指对应实体名称，应该是：“Customers”，而不是“NorthwindEntities.Customers”；

·           更新：

using (var edm = new NorthwindEntities())

{

      Customers addc = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c2");

      addc.City = "CD";

      addc.ContactName = "cnblogs";

      addc.Country = "CN";

      int result = edm.SaveChanges();

      Assert.AreEqual(result, 1);

      Customers updatec = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c2");

      Console.WriteLine("CustomerId={0},City={1}", updatec.CustomerID, updatec.City);

}

其中，需要注意的是：不能去更新主键，否则会报“System.InvalidOperationException : 属性“xxx”是对象的键信息的一部分，不能修改。”

·           删除：

实例代码如下：

using (var edm = new NorthwindEntities())

{

           Customers deletec = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c2");

           edm.DeleteObject(deletec);

           int result = edm.SaveChanges();

           Assert.AreEqual(result, 1);

           Customers c = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c2");

           Assert.AreEqual(c, null);

}

·          事务：

实例代码如下：

NorthwindEntities edm = null;

System.Data.Common.DbTransaction tran = null;

try

{

       edm = new NorthwindEntities();

       edm.Connection.Open();

       tran = edm.Connection.BeginTransaction();

       Customers cst = edm.Customers.FirstOrDefault(cc => cc.CustomerID == "c#");

       cst.Country = "CN";

       cst.City = "CD";

       edm.SaveChanges();

       tran.Commit();

}

catch (Exception ex)

{

       if (tran != null)

            tran.Rollback();

　　 throw ex;

}

finally

{

       if (edm != null && edm.Connection.State != System.Data.ConnectionState.Closed)

             edm.Connection.Close();

}

至此，初级篇基本介绍完毕。后面，打算写点，中级篇的东西。 

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转自：http://www.cnblogs.com/xray2005/archive/2009/05/17/1458568.html