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

       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。