Entity Framework 学习初级篇Entity SQL

Entity SQL 是 ADO.NET 实体框架 提供的 SQL 类语言，用于支持 实体数据模型 (EDM)。Entity SQL 可用于对象查询和使用 EntityClient 提供程序执行的查询。

l           关键字

Value关键字

 ESQL 提供了 SELECT VALUE 子句以跳过隐式行构造。SELECT VALUE 子句中只能指定一项。在使用这样的子句时，将不会对 SELECT 子句中的项构造行包装器，并且可生成所要形状的集合，例如：SELECT VALUE it FROM NorthwindEntities.Customers as it

it关键字

it 出现在 ESQL 中, 查询对象的别名默认值 "it" 改成其他字符串，例如：

"SELECT VALUE it FROM NorthwindEntities.Customers as it " 。

l           注释：

Entity SQL 查询可以包含注释。注释行以两个短划线 (--) 开头。

"SELECT VALUE it FROM NorthwindEntities.Customers as it  -- this a comment "

l           Select查询

例如：

SELECT VALUE it FROM NorthwindEntities.Customers as it

l           参数

参数是在esql之外定义的变量，每个参数都有名称和类型，参数名称在查询表达式中定义，并以@符号作为前缀。例如：

Select VALUE c from NorthwindEntities.Customers as c where c.CustomerID=@customerID

l           聚合

Enity SQL不支持 * ，所以esql不支持count(*)，而是使用count(0)，例如:

Select count(0) from NorthwindEntities.Customers

l           分页SKIP/LIMIT

可以通过在 ORDER BY 子句中使用 SKIP 和 LIMIT 子子句执行物理分页。若要以确定的方式执行物理分页，应使用 SKIP 和 LIMIT。如果您只是希望以非确定的方式限制结果中的行数，则应使用 TOP。TOP 和 SKIP/LIMIT 是互斥的

使用SKIP/LIMIT分页，esql代码如下：

Select value c from NorthwindEntities.Customers as c order by c.CustomerID skip 0 limit 10

l           TOP

SELECT 子句可以在可选的 ALL/DISTINCT 修饰符之后具有可选的 TOP 子子句。TOP 子子句指定查询结果中将只返回第一组行。esql代码如下：

Select top(10) c.CustomerID from NorthwindEntities.Customers as c order by c.CustomerID

l           NULL处理

Null 文本与 Entity SQL 类型系统中的任何类型都兼容，可以使用cast进行类型转换，例如：

select cast(c.region as string) from NorthwindEntities.Customers as c order by c.CustomerID limit 10

其中， Nvarchar等可以成string，数字类型可以转成int32，其他的类型转换类似。如果无法完成转换，则将报异常。还有可以处理的方法有treat。

l           标识符

Entity SQL 提供两种标识符：简单标识符和带引号的标识符

简单标识符：Entity SQL 中的简单标识符是字母数字和下划线字符的序列。标识符的第一个字符必须是字母字符（a-z 或 A-Z）。

带引号的标识符：带引号的标识符是括在方括号 ([]) 中的任何字符序列。带中文的部分，请使用方括号包括起来，否则会报如下异常信息：“简单标识符“中文”只能包含基本拉丁字符。若要使用UNICODE 字符，请使用转义标识符”

正确的代码如下：

Select c.CustomerID as [中文字符] from NorthwindEntities.Customers as c order by c.CustomerID skip 0 limit 10

l           ROW

Esql可使用row来构建匿名的结构类型的纪录。例如：

SELECT VALUE row(p.ProductID as ProductID,p.ProductName as ProductName) FROM NorthwindEntities.Products as p order by p.ProductID LIMIT 10

l           Key

提取引用或实体表达式的键。如下esql语句，直接返回Customer表的主键：

string esql = "SELECT value key(c) FROM NorthwindEntities.Customers as c order by c.CustomerID LIMIT 10"

l           CreateRef/ref/deref

CreateRef创建对实体集中的实体的引用。

ref返回对实体实例的引用，之后就可以当作实体来访问其属性，esql语句如下：

SELECT ref(c).CustomerID FROM NorthwindEntities.Customers as c order by c.CustomerID LIMIT 10

deref运算符取消引用一个引用值，并生成该取消引用的结果。

l           CASE语句：

 string esql = "using SqlServer;select case when len(trim(c.CustomerID))==0 then true else false end  from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

l           运算符

Esql支持的运算符有：加+、减-、乘*、除/、取模%、-负号。Esql语句如下：

select 100/2 as OP from NorthwindEntities.Customers as c order by c.CustomerID limit 10

l           比较运算符

Esql支持的比较运算符有:=,>,>=,IS [NOT] NULL,<,[NOT] BETWEEN,!=,<>,[NOT] LIKE。Esql语句如下：

select value p from NorthwindEntities.Products as p where p.UnitPrice > 20 order by p.ProductID limit 10

l           逻辑运算符

Esql支持的逻辑运算符有：and(&&),not(!),or(||)。Esql语句如下：

select value p from NorthwindEntities.Products as p where p.UnitPrice > 20 and p.UnitPrice<100 order by p.ProductID limit 10

或

select value p from NorthwindEntities.Products as p where p.UnitPrice > 20 && p.UnitPrice<100 order by p.ProductID limit 10

l           字符串连接运算符。

加号 (+) 是 Entity SQL 中可将字符串串联起来的唯一运算符。Esql语句如下：

select c.CustomerID + c.ContactName from NorthwindEntities.Customers as c  order by c.CustomerID limit 10

l           嵌套查询

在 Entity SQL 中，嵌套查询必须括在括号中，将不保留嵌套查询的顺序

select c1.CustomerID from( select value c from NorthwindEntities.Customers as c  order by c.CustomerID limit 10) as c1

l           日期时间函数

Esql提供的日期时间函数有：CurrentDateTime()获取当前服务器的日期时间，还有month,day，year，second, Minute ，Hour等。例如:

select CurrentDateTime()  from NorthwindEntities.Customers as c  order by c.CustomerID limit 10

l           字符串函数

Esql提供的字符串函数有：Concat,IndexOf,Left,Length,Ltrim,Replace,Reverse,Rtrim,SubString,Trim,ToLower,ToUpper.例如：

select Reverse(p.ProductName) as ProductName from NorthwindEntities.Products as p  order by p.ProductID limit 10

l           GUID

Esql提供newguid()函数，产生一个新的Guid。例如：

select newguid()  from NorthwindEntities.Customers as c  order by c.CustomerID limit 10

l           数学函数：

Abs,Ceiling,Floor,Round

l           统计函数：

Avg，BigCount,Count,Max,Min,StDev,Sum

l           位计算函数

如果提供 Null 输入，则这些函数返回 Null。这些函数的返回类型与参数类型相同。如果函数采用多个参数，则这些参数必须具有相同的类型。若要对不同类型执行位运算，则需要显式强制转换为相同类型.

BitWiseAnd,BitWiseNot,BitWiseOr,BitWiseXor

l           命名空间

Entity SQL 引入命名空间以避免全局标识符（如类型名称、实体集、函数等）出现名称冲突。Entity SQL 中的命名空间支持与 .NET Framework 中的命名空间支持类似。

Entity SQL 提供两种形式的 USING 子句：限定命名空间（其中，提供较短的别名以表示命名空间）和非限定命名空间，如下例所示：

USING System.Data;

USING tsql = System.Data;

例如：

string esql = "using System; select cast(p.UnitPrice as Int32)  from NorthwindEntities.Products as p  order by p.ProductID limit 10 ";

string esql = "using System;using SqlServer; select (cast(p.UnitPrice as Int32)),SqlServer.ltrim(p.ProductName) as nameLen from NorthwindEntities.Products as p  order by p.ProductID limit 10 ";

最后，简单说一下Esql与T-Sql的某些差异:

l           Entity SQL 中的所有列引用都必须用表别名限定.

l           Esql不支持Any，all限定运算符以及*运算

l           Entity SQL 当前未提供对 DML 语句（insert、update、delete）的支持。

l           Entity SQL 的当前版本未提供对 DDL 的支持。

ObjectQuery 类支持对 实体数据模型 (EDM) 执行 LINQ to Entities 和 Entity SQL 查询。ObjectQuery 还实现了一组查询生成器方法，这些方法可用于按顺序构造等效于 Entity SQL 的查询命令。下面是 ObjectQuery 的查询生成器方法以及等效的 Entity SQL 语句：

Distinct,Except,GroupBy,Intersect,OfType,OrderBy,Select,SelectValue,Skip,Top,Union,UnionAll,Where

每个查询生成器方法返回 ObjectQuery 的一个新实例。使用这些方法可以构造查询，而查询的结果集基于前面 ObjectQuery 实例序列的操作。下面来看具体的代码片断：

l           Execute方法:

using (var edm = new NorthwindEntities())

        {

                string esql = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<Customers> query = edm.CreateQuery<Customers>(esql);

                ObjectResult<Customers> results = query.Execute(MergeOption.NoTracking);

                Assert.AreEqual(results.Count(), 10);

                foreach (Customers c in query)

                    Console.WriteLine(c.CustomerID);

            }

其中需要说明的是: MergeOption这个枚举类型的参数项,MergeOption有四种值分别是：

l           AppendOnly： 只追加新实体，不修改以前获取的现有实体。这是默认行为。

l           OverwriteChanges： 将 ObjectStateEntry 中的当前值替换为存储区中的值。这将使用服务器上的数据重写在本地所做的更改。

l           PreserveChanges： 将替换原始值，而不修改当前值。这对于在发生开放式并发异常之后强制成功保存本地值非常有用。

l           NoTracking： 将不修改 ObjectStateManager，不会获取与其他对象相关联的关系，可以改善性能。

l           GetResultType方法：返回查询结果的类型信息.例如：

using (var edm = new NorthwindEntities())

            {

                string esql = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<Customers> query = edm.CreateQuery<Customers>(esql);

                Console.WriteLine(query.GetResultType().ToString());

                //输出结果为：

                //NorthWindModel.Customers

            }

l           ToTraceString方法：获取当前执行的SQL语句。

l           Where

实例代码如下：

using (var edm = new NorthwindEntities())

     {

                string esql = "select value c from NorthwindEntities.Customers as c ";

                ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql);

                //使用ObjectParameter的写法               

                query1 = query1.Where("it.CustomerId=@customerid");

                query1.Parameters.Add(new ObjectParameter("customerid", "ALFKI"));

                //也可以这样写

                //ObjectQuery<Customers> query2 = edm.Customers.Where("it.CustomerID='ALFKI'");

                foreach (var c in query1)

                    Console.WriteLine(c.CustomerID);

                //显示查询执行的SQL语句

                Console.WriteLine(query1.ToTraceString());

              

            }

l           First/ FirstOrDefault

实例代码如下：

using (var edm = new NorthwindEntities())

     {

                string esql = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<Customers> query = edm.CreateQuery<Customers>(esql);

                Customers c1 = query.First();

                Customers c2 = query.FirstOrDefault();

                Console.WriteLine(c1.CustomerID);

                Assert.IsNotNull(c2);

                Console.WriteLine(c2.CustomerID);

      }

l           Distinct

实例代码如下：

using (var edm = new NorthwindEntities())

    {

                string esql = "select value c.City from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<string> query = edm.CreateQuery<string>(esql);

                query = query.Distinct();

                foreach (string c in query)

                {

                    Console.WriteLine("City {0}", c);

                }

     }

l           Except:返回两个查询的差集。实例代码如下：

using (var edm = new NorthwindEntities())

     {

                string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1);

                string esql2 = "select value c from NorthwindEntities.Customers as c where c.Country='UK' order by c.CustomerID limit 10";

                ObjectQuery<Customers> query2 = edm.CreateQuery<Customers>(esql2);

                query1 = query1.Except(query2);

                foreach (Customers c in query1)

                {

                    Console.WriteLine(c.Country);

                    //输出:UK

                }

        }

l           Intersect：返回两个查询的交集。实例代码如下：

using (var edm = new NorthwindEntities())

     {

                string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1);

                string esql2 = "select value c from NorthwindEntities.Customers as c where c.Country='UK' order by c.CustomerID limit 10";

                ObjectQuery<Customers> query2 = edm.CreateQuery<Customers>(esql2);

                query1 = query1.Intersect(query2);

                foreach (Customers c in query1)

                {

                    Console.WriteLine(c.Country);

                }

      }

l           Union/UnionAll:返回两个查询的合集，包括重复项。其中UnionAll必须是相同类型或者是可以相互转换的。

l           Include:可通过此方法查询出与相关的实体对象。实例代码如下：

using (var edm = new NorthwindEntities())

     {

                string esql1 = "select value c from NorthwindEntities.Customers as c WHERE c.CustomerID ='HANAR'";

                ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1);

                query1 = query1.Include("Orders");

                foreach (Customers c in query1)

                {

                    Console.WriteLine("{0},{1}", c.CustomerID, c.Orders.Count);

                    //输出：HANAR,14

                }

 

     }

l           OfType： 根据制定类筛选元素创建一个新的类型。此类型是要在实体模型中已定义过的。

l           OrderBy

实例代码如下：

using (var edm = new NorthwindEntities())

    {

                string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1);

                query1.OrderBy("it.country asc,it.city asc");

//也可以这样写               

//query1.OrderBy("it.country asc");

                //query1.OrderBy("it.city asc");

                foreach (Customers c in query1)

                {

                    Console.WriteLine("{0},{1}", c.Country, c.City);

                }

      }

l           Select

实例代码如下：

using (var edm = new NorthwindEntities())

    {

                string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1);

                ObjectQuery<DbDataRecord> records = query1.Select("it.customerid,it.country");

                foreach (DbDataRecord c in records)

                {

                    Console.WriteLine("{0},{1}", c[0], c[1]);

                }

                Console.WriteLine(records.ToTraceString());

                //SQL输出：

                //SELECT TOP (10)

                //1 AS [C1],

                //[Extent1].[CustomerID] AS [CustomerID],

                //[Extent1].[Country] AS [Country]

                //FROM [dbo].[Customers] AS [Extent1]

                //ORDER BY [Extent1].[CustomerID] ASC

      }

l           SelectValue

实例代码如下：

using (var edm = new NorthwindEntities())

    {

                string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10";

                ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1);

                ObjectQuery<string> records = query1.SelectValue<string>("it.customerid");

                foreach (string c in records)

                {

                    Console.WriteLine("{0}", c);

                }

                Console.WriteLine(records.ToTraceString());

                //SQL输出：

                //SELECT TOP (10)

                //[Extent1].[CustomerID] AS [CustomerID]

                //FROM [dbo].[Customers] AS [Extent1]

                //ORDER BY [Extent1].[CustomerID] ASC

       }

l           Skip/Top

实例代码如下：

using (var edm = new NorthwindEntities())

    {

                string esql1 = "select value c from NorthwindEntities.Customers as c order by c.CustomerID ";

                ObjectQuery<Customers> query1 = edm.CreateQuery<Customers>(esql1);

                query1 = query1.Skip("it.customerid asc", "10");

                query1 = query1.Top("10");

                foreach (Customers c in query1)

                {

                    Console.WriteLine("{0}", c.CustomerID);

                }

                Console.WriteLine(query1.ToTraceString());

                //SQL输出：

                //SELECT TOP (10)

                //[Extent1].[CustomerID] AS [CustomerID]

                //FROM [dbo].[Customers] AS [Extent1]

                //ORDER BY [Extent1].[CustomerID] ASC

}

    本节，简单的介绍一下与ObjectQuery查询相关的语法，我个人觉得查询写法比较多，需要在日常的编程中去发现，在这里就不一一复述了。下节，将介绍EntityClient相关的内容。

System.Data.EntityClient 命名空间是 实体框架的 .NET Framework 数据提供程序。EntityClient 提供程序使用存储特定的 ADO.NET 数据提供程序类和映射元数据与实体数据模型进行交互。EntityClient 首先将对概念性实体执行的操作转换为对物理数据源执行的操作。然后再将物理数据源返回的结果集转换为概念性实体。

EntityClient下的类有以下几个：

l           EntityConnection

l           EntityCommand

l           EntityConnectionStringBuilder

l           EntityParameter

l           EntityDataReader 

l           EntityParameterCollection

l           EntityProviderFactory

l           EntityTransaction

从类的名字上看，我们就知道它们的作用是什么了。在此，就不再一一解释了。直接通过实例代码来学习它们。

l         EntityConnection:

实例代码1：

string con = "name = NorthwindEntities";

            using (EntityConnection econn = new EntityConnection(con))

            {

                string esql = "Select VALUE c from NorthwindEntities.Customers as c where c.CustomerID='ALFKI'";

                econn.Open();

                EntityCommand ecmd = new EntityCommand(esql, econn);

                EntityDataReader ereader = ecmd.ExecuteReader(CommandBehavior.SequentialAccess);

                if (ereader.Read())

                {

                    Console.WriteLine(ereader["CustomerID"]);

                }

                Console.WriteLine(ecmd.ToTraceString());

            }

上述代码中，需要注意的是EntityConnection的构造方法。其中，连接字符串写法有多很，如下：

写法1：

string con ="name = NorthwindEntities" ;其中的”NorthwindEntities”是配置文件中的连接字符串名称

写法2:

string con = System.Configuration.ConfigurationManager.ConnectionStrings["NorthwindEntities"].ConnectionString; 其中的”NorthwindEntities”是配置文件中的连接字符串名称

写法3:

string con = @" metadata=res://*/NorthWind.csdl|res://*/NorthWind.ssdl|res://*/NorthWind.msl;provider=System.Data.SqlClient;provider connection string='Data Source=.\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=True;MultipleActiveResultSets=True'";其中的这些字符串是配置文件中的连接字符串的值

写法4:

NorthwindEntities edm = new NorthwindEntities();

string con = edm.Connection.ConnectionString;

上述写法中,基于写法简单、方便我比较推荐使用第1种或者第2种写法。

l         EntityCommand

它具有的方法有：ExecuteDbDataReader、 ExecuteNonQuery 、 ExecuteReader 、 ExecuteScalar等。

实例代码2：

string con = "name = NorthwindEntities";

            using (EntityConnection econn = new EntityConnection(con))

            {

                string esql = "Select VALUE c from NorthwindEntities.Customers as c where c.CustomerID='ALFKI'";

                econn.Open();

                EntityCommand ecmd = econn.CreateCommand();

                ecmd.CommandText = esql;

                EntityDataReader ereader = ecmd.ExecuteReader(CommandBehavior.SequentialAccess);

                if (ereader.Read())

                {

                    Console.WriteLine(ereader["CustomerID"]);

                }

                Console.WriteLine(ecmd.ToTraceString());

            }

代码中，EntityCommand创建方式和实例代码1中的稍有不同，相信大家都明白，就不多说了。

l         EntityConnectionStringBuilder

实例代码3：

            EntityConnectionStringBuilder esb = new EntityConnectionStringBuilder();

            esb.Provider = "System.Data.SqlClient";

            esb.Metadata = @"res://*/NorthWind.csdl|res://*/NorthWind.ssdl|res://*/NorthWind.msl";

            esb.ProviderConnectionString = @"Data Source=.\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=True;MultipleActiveResultSets=True";

           EntityConnection econn = new EntityConnection(esb.ConnectionString)//创建连接

l         EntityParameter

代码实例4：

string con = "name = NorthwindEntities";

            using (EntityConnection econn = new EntityConnection(con))

            {

                string esql = "Select value c from NorthwindEntities.Customers as c order by c.CustomerID skip @start limit @end";

                econn.Open();

                EntityCommand ecmd = new EntityCommand(esql, econn);

                EntityParameter p1 = new EntityParameter("start", DbType.Int32);

                p1.Value = 0;

                EntityParameter p2 = new EntityParameter("end", DbType.Int32);

                p2.Value = 10;

                ecmd.Parameters.Add(p1);

                ecmd.Parameters.Add(p2);

                 EntityDataReader ereader = ecmd.ExecuteReader(CommandBehavior.SequentialAccess);

                while (ereader.Read())

                {

                    Console.WriteLine(ereader["CustomerID"]);

                }

                Console.WriteLine(ecmd.ToTraceString());

            }

其中，参数是以@符号前缀的，EntityParameter实体参数类，除了可以直接构造出实例来。为实体命令对象添加参数，我们还可以直接调用Parameters.AddWithValue方法。如下代码：

     ecmd.Parameters.AddWithValue("start", 0);

     ecmd.Parameters.AddWithValue("end", 10);

    我比较喜欢用上面的代码，简单、方便。

l         EntityDataReader

string con = "name = NorthwindEntities";

            using (EntityConnection econn = new EntityConnection(con))

            {

                string esql = "Select value c from NorthwindEntities.Customers as c order by c.CustomerID limit 10 ";

                econn.Open();

                EntityCommand ecmd = new EntityCommand(esql, econn);

                EntityDataReader ereader = ecmd.ExecuteReader(CommandBehavior.SequentialAccess);

                while (ereader.Read())

                {

                    Console.WriteLine("{0},{1},{2},{3},{4}", ereader[0], ereader[1], ereader[2], ereader[3], ereader[4]);               

                }

                Console.WriteLine(ecmd.ToTraceString());

            }

需要注意的是：CommandBehavior.SequentialAccess;这个地方。不同的枚举项，对查询会有不同影响。枚举如下：

l           Default 此查询可能返回多个结果集。在功能上等效于调用 ExecuteReader()。 

l           SingleResult 查询返回一个结果集。 

l           SchemaOnly 查询仅返回列信息。

l           KeyInfo 此查询返回列和主键信息。 

l           SingleRow 查询应返回一行。

l           SequentialAccess 提供一种方法，以便 DataReader 处理包含带有大二进制值的列的行。

l           CloseConnection 在执行该命令时，如果关闭关联的 DataReader 对象，则关联的 Connection 对象也将关闭。

需要说明的是，如果使用SequentialAccess则需按顺序访问列，否则将抛异常。如下代码，将会抛异常：

while (ereader.Read())

    {

          //异常信息：从列序列号“1”开始读取的尝试无效。通过CommandBehavior.SequentialAccess，只能从列序列号“5”或更大值处开始读取

          Console.WriteLine("{0},{1},{2},{3},{4}", ereader[4], ereader[1], ereader[2], ereader[3], ereader[0]);    

}

l         EntityTransaction：

事务类。目前由于ESQL仅提供查询的命令，没有提供对Insert、Update、Delete等的支持。所以，我觉得目前这个类基本没有用，（不可能我做查询还使用事务吧！）。

从上述简单的介绍，我们可以看到，EntityClient和SqlClient下的类基本上是一致的。所以很容易掌握。其他就不多说了。

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。