.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()]
        [Column("CUSTOMER_NAME")]
        public String CustomerName { set; get; }
 
        [Column("AMOUNT")]
        public decimal Amount { set; get; }
 
        public virtual ICollection<OrderItem> OrderItems { set; get; }
 
    }
}

 using System;
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
 
 namespace EFSample.Model
 {
     [Table("T_ORDER_ITEM")]
     public class OrderItem
     {
         [Key]
         [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
         public int ID { set; get; }
 
         [ForeignKey("Order")]
         [Column("ORDER_ID")]
         public int OrderID { set; get; }
 
         [StringLength()]
         [Column("PRODUCT_NAME")]
         public String ProductName { set; get; }
 
         [Column("PRICE")]
         public Decimal Price { set; get; }
 
         [Column("QUANTITY")]
         public int Quantity { set; get; }
 
         public virtual Order Order { set; get; }
 
     }
 }

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

配置文件：

 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
   <configSections>
     <section name="entityFramework"
        type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
   </configSections>
 
   <entityFramework>
     <contexts>
       <context type="EFSample.DAL.OrderContext, EFSample" disableDatabaseInitialization="false">
         <databaseInitializer type="EFSample.DAL.OrderInitializer, EFSample" />
       </context>
     </contexts>
     <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory, EntityFramework">
       <parameters>
         <parameter value="v11.0" />
       </parameters>
     </defaultConnectionFactory>
     <providers>
       <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
     </providers>
   </entityFramework>
 
   <startup>
     <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5.1" />
   </startup>
 
   <connectionStrings>
     <!--连接字符串，使用SQLSERVER LocalDb-->
     <add name="MyConn" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=OrderDatabase;Integrated Security=SSPI;" providerName="System.Data.SqlClient" />
   </connectionStrings>
 
 </configuration>

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

 using EFSample.Model;
 using System.Data.Entity;
 using System.Data.Entity.ModelConfiguration.Conventions;
 
 namespace EFSample.DAL
 {
     public class OrderContext:DbContext
     {
         public OrderContext() : base("MyConn") { }
 
         public DbSet<Order> Orders { set; get; }
 
         public DbSet<OrderItem> OrderItems { set; get; }
 
         protected override void OnModelCreating(DbModelBuilder modelBuilder)
         {
             modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
         }
     }
 }

示例代码：

 using EFSample.DAL;
 using EFSample.Model;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 
 namespace EFSample
 {
     class Program
     {
         static void Main(string[] args)
         {
             using (var db = new OrderContext())
             {
 
                 //直接执行Sql语句
                 db.Database.ExecuteSqlCommand("delete from t_order");
 
                 var orders = new List<Order>(){
                     new Order{ CustomerName="jimmy.yang",Amount=, OrderItems=new List<OrderItem>(){
                         new OrderItem(){ Price=, Quantity=, ProductName="Mobile"}
                     }},
                     new Order{ CustomerName="杨俊明",Amount=, OrderItems=new List<OrderItem>(){
                         new OrderItem(){ Price=, Quantity=, ProductName="架构之美"}
                     }}};
 
                 //批量添加记录
                 db.Orders.AddRange(orders);
 
                 //提交到db
                 db.SaveChanges();                
 
                 //查询
                 var query = db.Orders.Where(c => c.CustomerName == "Jimmy.yang").AsQueryable();
 
                 //输出Sql语句
                 Console.WriteLine(query.ToString());
 
                 List<Order> orderEntities = query.ToList();
 
                 foreach (var order in orderEntities)
                 {
                     Console.WriteLine(String.Format("ID:{0}/CustomerName:{1}/Amount:{2}/ItemCount:{3}", order.ID, order.CustomerName, order.Amount,order.OrderItems.Count));
                 }
             }
 
             Console.WriteLine("ok!");
             Console.Read();
         }
     }
 }

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：

 XE =
   (DESCRIPTION =
     (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.187.128)(PORT = 1521))
     (CONNECT_DATA =
       (SERVER = DEDICATED)
       (SERVICE_NAME = XE)
     )
   )

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：

 create sequence S_CD_TIPO minvalue 1 maxvalue 9999999 start with 1 increment by 1;
 
 create or replace trigger tp_procedimento_trigger
 before insert on tp_procedimento for each row
 begin
   if :new.cd_tipo is null then select s_cd_tipo.nextval into :new.cd_tipo from dual;
   endif;
 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：

 using System;
 using System.Data;
 using System.Data.Entity;
 
 namespace EntityFrameworkTest
 {
     public static class SequenceHelper
     {
         public static int GetNextVal(this DbContext db,String sequenceName) {
             if (db.Database.Connection.State != ConnectionState.Open) {
                 db.Database.Connection.Open();
             }
             var cmd = db.Database.Connection.CreateCommand();
             cmd.CommandText = String.Format("select {0}.nextval from dual", sequenceName);
             cmd.CommandType = CommandType.Text;
 
             int result = ;
             int.TryParse(cmd.ExecuteScalar().ToString(),out result);
 
             return result;
         }
     }
 }

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：

 using System;
 using System.Linq;
 
 namespace EntityFrameworkTest
 {
     class Program
     {
         static void Main(string[] args)
         {
             using (MyDbContext db = new MyDbContext())
             {
                 //insert
                 T_BAS_AGENT newAgent = new T_BAS_AGENT();
                 newAgent.AGENT = "XYZ";
                 newAgent.CYEAR = ;
                 newAgent.RECID = db.GetNextVal("SEQ_T_BAS_CARRIER");
                 db.T_BAS_AGENT.Add(newAgent);
                 db.SaveChanges();
 
                 //query
                 var findAgent = db.T_BAS_AGENT.SingleOrDefault(c => c.RECID == newAgent.RECID);
                 Console.WriteLine(string.Format("{0}/{1}/{2}", findAgent.RECID, findAgent.AGENT, findAgent.CYEAR));
 
             }
 
             Console.Read();
         }
     }
 }