• Entity Framework 学习初级篇--基本操作:增加、更新、删除、事务(转)


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

    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。

    l           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”;

    l           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。”

    l           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);

                    

             }

    l           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。

     
         本文版权归作者所有,欢迎转载,但未经作者同意必须保留此段声明,且在文章页面明显位置给出原文连接,否则保留追究法律责任的权利。
     
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  • 原文地址:https://www.cnblogs.com/KeenLeung/p/3845371.html
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