.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; }

    
    }
}

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(50)]
        [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=200, OrderItems=new List<OrderItem>(){
                        new OrderItem(){ Price=10, Quantity=20, ProductName="Mobile"}
                    }},
                    new Order{ CustomerName="杨俊明",Amount=300, OrderItems=new List<OrderItem>(){
                        new OrderItem(){ Price=15, Quantity=20, 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 = 0;
            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 = 2014;
                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();
        }
    }
}