.NET:Entity Framework 笔记

有二年没关注EF，今天无意试了下发现跟主流的Hibernate等ORM框架越来越接近了，先看下Entity类的定义：

using System;

using System.Collections.Generic;

using System.ComponentModel.DataAnnotations;

using System.ComponentModel.DataAnnotations.Schema;

namespace EFSample.Model

{



    [Table("T_ORDER")]

    public class Order

    {

        [Key]

        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

        public int ID { set; get; }



        [StringLength(50)]

        [Column("CUSTOMER_NAME")]

        public String CustomerName { set; get; }



        [Column("AMOUNT")]

        public decimal Amount { set; get; }



        public virtual ICollection<OrderItem> OrderItems { set; get; }



    

    }

}

View Code

 1 using System;

 2 using System.ComponentModel.DataAnnotations;

 3 using System.ComponentModel.DataAnnotations.Schema;

 4 

 5 namespace EFSample.Model

 6 {

 7     [Table("T_ORDER_ITEM")]

 8     public class OrderItem

 9     {

10         [Key]

11         [DatabaseGenerated(DatabaseGeneratedOption.Identity)]

12         public int ID { set; get; }

13 

14         [ForeignKey("Order")]

15         [Column("ORDER_ID")]

16         public int OrderID { set; get; }

17 

18         [StringLength(50)]

19         [Column("PRODUCT_NAME")]

20         public String ProductName { set; get; }

21 

22         [Column("PRICE")]

23         public Decimal Price { set; get; }

24 

25         [Column("QUANTITY")]

26         public int Quantity { set; get; }

27 

28         public virtual Order Order { set; get; }

29 

30        

31     }

32 }

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光看Attribute，已经跟Hibernate的Annotation很相似了。

配置文件：

 1 <?xml version="1.0" encoding="utf-8"?>

 2 <configuration>

 3   <configSections>    

 4     <section name="entityFramework"

 5        type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />

 6   </configSections>

 7 

 8   <entityFramework>

 9     <contexts>

10       <context type="EFSample.DAL.OrderContext, EFSample" disableDatabaseInitialization="false">

11         <databaseInitializer type="EFSample.DAL.OrderInitializer, EFSample" />

12       </context>

13     </contexts>

14     <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">

15       <parameters>

16         <parameter value="v11.0" />

17       </parameters>

18     </defaultConnectionFactory>

19     <providers>

20       <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />

21     </providers>

22   </entityFramework>

23 

24   <startup>

25     <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.1" />

26   </startup>

27 

28   <connectionStrings>

29     <!--连接字符串，使用SQLSERVER LocalDb-->

30     <add name="MyConn" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=OrderDatabase;Integrated Security=SSPI;" providerName="System.Data.SqlClient" />

31   </connectionStrings>

32   

33 </configuration>

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注：LocalDb在开发阶段很方便，但是试用中有一个小问题，如果把生成的mdf物理文件删除后，再次运行总是报错(不知道是不是个别现象)，只能把Initial Catalog=OrderDatabase中的文件名改成其它名称（比如：Catalog=OrderDb），才能正常运行。

此外，NuGet Package Manager工具搞得象java的maven一样，可以自动联机下载所需的依赖项，Tools->NuGet Package Manager

输入

Install -Package EntityFramework

就能自动向project添加相关的dll引用

DbContext

 1 using EFSample.Model;

 2 using System.Data.Entity;

 3 using System.Data.Entity.ModelConfiguration.Conventions;

 4 

 5 namespace EFSample.DAL

 6 {

 7     public class OrderContext:DbContext

 8     {

 9         public OrderContext() : base("MyConn") { }

10 

11         public DbSet<Order> Orders { set; get; }

12 

13         public DbSet<OrderItem> OrderItems { set; get; }

14 

15         protected override void OnModelCreating(DbModelBuilder modelBuilder)

16         {

17             modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();

18         }

19     }

20 }

View Code

示例代码：

 1 using EFSample.DAL;

 2 using EFSample.Model;

 3 using System;

 4 using System.Collections.Generic;

 5 using System.Linq;

 6 

 7 namespace EFSample

 8 {

 9     class Program

10     {

11         static void Main(string[] args)

12         {

13             using (var db = new OrderContext())

14             {

15               

16                 //直接执行Sql语句

17                 db.Database.ExecuteSqlCommand("delete from t_order");

18 

19                 var orders = new List<Order>(){            

20                     new Order{ CustomerName="jimmy.yang",Amount=200, OrderItems=new List<OrderItem>(){

21                         new OrderItem(){ Price=10, Quantity=20, ProductName="Mobile"}

22                     }},

23                     new Order{ CustomerName="杨俊明",Amount=300, OrderItems=new List<OrderItem>(){

24                         new OrderItem(){ Price=15, Quantity=20, ProductName="架构之美"}

25                     }}};

26 

27                 //批量添加记录

28                 db.Orders.AddRange(orders);

29 

30                 //提交到db

31                 db.SaveChanges();                

32 

33                 //查询

34                 var query = db.Orders.Where(c => c.CustomerName == "Jimmy.yang").AsQueryable();

35 

36                 //输出Sql语句

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

38 

39                 List<Order> orderEntities = query.ToList();

40 

41                 foreach (var order in orderEntities)

42                 {

43                     Console.WriteLine(String.Format("ID:{0}/CustomerName:{1}/Amount:{2}/ItemCount:{3}", order.ID, order.CustomerName, order.Amount,order.OrderItems.Count));

44                 }

45             }

46 

47             Console.WriteLine("ok!");

48             Console.Read();

49         }

50     }

51 }

View Code

输出：

SELECT
[Extent1].[ID] AS [ID],
[Extent1].[CUSTOMER_NAME] AS [CUSTOMER_NAME],
[Extent1].[AMOUNT] AS [AMOUNT]
FROM [dbo].[T_ORDER] AS [Extent1]
WHERE N'Jimmy.yang' = [Extent1].[CUSTOMER_NAME]

ID:9/CustomerName:jimmy.yang/Amount:200/ItemCount:1
ok!

对Oracle的支持

MS默认并没有提供EF对Oracle的支持，需要到Oracle官网下载 http://www.oracle.com/technetwork/topics/dotnet/downloads/index.html

下载比较慢，耐心等待，完成后，一路Next即可。

注意：tnsnames.ora文件的配置，一般在x:\app\client\Administrator\product\12.1.0\client_1\Network\Admin 目录下，参考内容如下：

1 XE =

2   (DESCRIPTION =

3     (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.187.128)(PORT = 1521))

4     (CONNECT_DATA =

5       (SERVER = DEDICATED)

6       (SERVICE_NAME = XE)

7     )

8   )

然后在vs中创建ADO.NET Entity Data Model时就能连接到Oracle db了，目前尚不支持Code-First，只能使用EF5，估计EF6要等明年才会正式发布
使用细节，可参考官网教程：http://www.oracle.com/webfolder/technetwork/tutorials/obe/db/dotnet/EntityFrameworkOBE/EntityFrameworkOBE.htm#t10

Sequence的处理：

Oracle中没有自增主键，msdn和oracle建议用trigger+sequence来处理自增主键的问题，即：insert前写个触发器，检测主键是否为空，如果为空，则将sequece.nextval赋值给它，参见：https://social.msdn.microsoft.com/Forums/th-TH/73453344-bbb9-4904-b77a-a9ba807dcfd2/oracle-e-entityframework?forum=mvcpt

示例代码：

1 create sequence S_CD_TIPO minvalue 1 maxvalue 9999999 start with 1 increment by 1;

2 

3 create or replace trigger tp_procedimento_trigger  

4 before insert on tp_procedimento for each row 

5 begin 

6   if :new.cd_tipo is null then select s_cd_tipo.nextval into :new.cd_tipo from dual; 

7   endif; 

8 end;

但我个人并不喜欢这种做法，感觉对db有点“侵入”，我比较喜欢在c#代码层掌控一切的感觉，如果大家跟我有一样的癖好，可以这么干：

 1 using System;

 2 using System.Data;

 3 using System.Data.Entity;

 4 

 5 namespace EntityFrameworkTest

 6 {

 7     public static class SequenceHelper

 8     {

 9         public static int GetNextVal(this DbContext db,String sequenceName) {

10             if (db.Database.Connection.State != ConnectionState.Open) {

11                 db.Database.Connection.Open();

12             }

13             var cmd = db.Database.Connection.CreateCommand();

14             cmd.CommandText = String.Format("select {0}.nextval from dual", sequenceName);

15             cmd.CommandType = CommandType.Text;

16 

17             int result = 0;

18             int.TryParse(cmd.ExecuteScalar().ToString(),out result);

19 

20             return result;

21         }

22     }

23 }

对DbContext写一个扩展方法，手动传入Sequence名称，然后在添加记录时，这样用：

 1 using System;

 2 using System.Linq;

 3 

 4 namespace EntityFrameworkTest

 5 {

 6     class Program

 7     {

 8         static void Main(string[] args)

 9         {

10             using (MyDbContext db = new MyDbContext())

11             {

12                 //insert

13                 T_BAS_AGENT newAgent = new T_BAS_AGENT();

14                 newAgent.AGENT = "XYZ";

15                 newAgent.CYEAR = 2014;

16                 newAgent.RECID = db.GetNextVal("SEQ_T_BAS_CARRIER");

17                 db.T_BAS_AGENT.Add(newAgent);

18                 db.SaveChanges();

19 

20                 //query

21                 var findAgent = db.T_BAS_AGENT.SingleOrDefault(c => c.RECID == newAgent.RECID);

22                 Console.WriteLine(string.Format("{0}/{1}/{2}", findAgent.RECID, findAgent.AGENT, findAgent.CYEAR));

23 

24             }

25 

26             Console.Read();

27         }

28     }

29 }