转:工欲善其事必先利其器—Entity Framework实例详解

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开始本篇文章之前,先说一下Entity Framework 6 Alpha1在NuGet中已可用,原文链接http://blogs.msdn.com/b/adonet/archive/2012/10/30/ef6-alpha-1-available-on-nuget.aspx

俗话说:“工欲善其事必先利其器”,在深入讲解Entity Framework之前,先准备一下开发工具以及前期的配置。

一、开发工具

开发工具基本略过,这里说一下,我使用的是Visual Studio 2012,Entity Framework版本为4.3.1,获取这个版本的办法:在Package Manager Console中输入Install-Package EntityFramework -Version 4.3.1。至于数据库,主要是LocalDb。

二、连接数据库

当使用NuGet安装完Entity Framework后,在配置文件中会自动加入entityFramework节,里面有defaultConnectionFactory元素,如下:

   1: <?xml version="1.0" encoding="utf-8"?>
   2: <configuration>
   3:   <configSections>
   4:     <!-- For more information on Entity Framework configuration, visit http://go.microsoft.com/fwlink/?LinkID=237468 -->
   5:     <section name="entityFramework" type="System.Data.Entity.Internal.ConfigFile.EntityFrameworkSection, EntityFramework, Version=4.3.1.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
   6:   </configSections>
   7:   <entityFramework>
   8:     <defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework">
   9:       <parameters>
  10:         <parameter value="Data Source=(localdb)\\v11.0; Integrated Security=True; MultipleActiveResultSets=True" />
  11:       </parameters>
  12:     </defaultConnectionFactory>
  13:   </entityFramework>
  14: </configuration>

在没有提供具体数据库连接的情况下,EF默认使用这一配置。如上面代码中,默认会连接到LocalDb,数据库的名称为上下文完全限定名(命名空间+类名)。以前经常提到默认连接到.\\SQLEXPRESS,因为安装的版本不同。

EF中提供了两个连接工厂:SqlConnectionFactory和SqlCeConnectionFactory。使用方式分别如下:

   1: Database.DefaultConnectionFactory = new SqlConnectionFactory("Data Source=.;Database=Test;UId=sa;Pwd=sasa;MultipleActiveResultSets=True");

   1: Database.DefaultConnectionFactory = new SqlConnectionFactory("Data Source=.;Database=Test;User=sa;Password=sasa;MultipleActiveResultSets=True");

   1: Database.DefaultConnectionFactory = new SqlCeConnectionFactory("System.Data.SqlServerCe.4.0");

在配置文件和代码中同时有DefaultConnectionFactory的情况下,代码中的优先。

下面,写一个简单的控制台程序。代码如下:

   1: namespace ConnectDatabase
   2: {
   3:     class Program
   4:     {
   5:         static void Main(string[] args)
   6:         {
   7:             using (TestContext ctx = new TestContext())
   8:             {
   9:                 var blog = new Blog()
  10:                 {
  11:                     Name = "EF"
  12:                 };
  13:                 blog.Posts.Add(new Post()
  14:                 {
  15:                     Title = "连接数据库",
  16:                     Content = "这是连接数据库的测试",
  17:                     Creationdate = DateTime.Now,
  18:                     Blog = blog
  19:                 });
  20:                 ctx.Blogs.Add(blog);
  21:                 ctx.SaveChanges();
  22:  
  23:                 foreach (var item in ctx.Blogs)
  24:                 {
  25:                     Console.WriteLine(item.Name);
  26:                 }
  27:             }
  28:         }
  29:     }
  30:  
  31:     public class TestContext : DbContext
  32:     {
  33:         protected override void OnModelCreating(DbModelBuilder modelBuilder)
  34:         {
  35:             base.OnModelCreating(modelBuilder);
  36:         }
  37:  
  38:         public DbSet<Blog> Blogs { get; set; }
  39:         public DbSet<Post> Posts { get; set; }
  40:     }
  41:  
  42:     public class Blog
  43:     {
  44:         public Blog()
  45:         {
  46:             Posts = new List<Post>();
  47:         }
  48:  
  49:         public int Id { get; set; }
  50:         public string Name { get; set; }
  51:         public virtual List<Post> Posts { get; set; }
  52:     }
  53:  
  54:     public class Post
  55:     {
  56:         public int Id { get; set; }
  57:         public string Title { get; set; }
  58:         public string Content { get; set; }
  59:         public DateTime Creationdate { get; set; }
  60:         public virtual Blog Blog { get; set; }
  61:     }
  62: }

使用默认连接配置,生成的数据库名称为:ConnectDatabase.TestContext,如下图所示:

技术分享

重写上面配置有以下方法:

1.在配置文件中添加connectionStrings,name和上下文类名一致。

   1: <connectionStrings>
   2:   <add name="TestContext1" connectionString="Data Source=(localdb)\\v11.0;Database=Test;Integrated Security=True;MultipleActiveResultSets=True" providerName="System.Data.SqlClient"/>
   3: </connectionStrings>

2.同1,但是name和上下文类名不一致。这就需要修改TextContext代码,如下:

   1: public TestContext() : this("TestContext1") { }
   2:  
   3: public TestContext(string nameOrConnectionString)
   4:     : base(nameOrConnectionString)
   5: {
   6:  
   7: }

   1: public TestContext()
   2:     : base("name=TestContext1")
   3: {
   4:  
   5: }

  1: public TestContext():base("TestContext1"){}

下面给出连接具体数据库的配置:

1.连接Sql Server数据库

   1: <connectionStrings>
   2:   <add name="TestContext" connectionString="Data Source=.;Database=Test;User=sa;Password=sasa;MultipleActiveResultSets=True" providerName="System.Data.SqlClient"/>
   3: </connectionStrings>

2.连接Sql Server Compact 4.0

   1: <connectionStrings>
   2:   <add name="TestContext" connectionString="Data Source=|DataDirectory|\\Test.sdf" providerName="System.Data.SqlServerCe.4.0"/>
   3: </connectionStrings>

3.连接mysql 5.5

连接MySql数据库需要安装mysql提供程序mysql-connector-net-6.6.4,本文最后提供这些工具的下载地址。

   1: <connectionStrings>
   2:   <add name="TestContext"
   3:     connectionString="User Id=root;server=localhost;password=sasa;database=test1"
   4:     providerName="MySql.Data.MySqlClient" />
   5: </connectionStrings>

三、数据库初始化

1.关闭初始化

   1: Database.SetInitializer<TestContext>(null);

2.CreateDatabaseIfNotExists

这是Entity Framework的默认初始化策略,没有必要设置它,如果真的需要设置,如下:

   1: Database.SetInitializer(new CreateDatabaseIfNotExists<TestContext>());

3.DropCreateDatabaseWhenModelChanges

如果模型发生了改变,则删除并重建数据库。

   1: Database.SetInitializer(new DropCreateDatabaseWhenModelChanges<TestContext>());

4.DropCreateDatabaseAlways

无论模型和数据库匹配与否,都删除并重建数据库。

   1: Database.SetInitializer(new DropCreateDatabaseAlways<TestContext>());

5.Database.Initialize可以强制初始化,即使在当前AppDomain中已经发生了。下面我写个单元测试程序,来演示这一点:

   1: [TestClass]
   2: public class UnitTest1
   3: {
   4:     [TestMethod]
   5:     public void TestForceInitialize()
   6:     {
   7:         //说明一点:我Demo中的TestContext和Microsoft.VisualStudio.TestTools.UnitTesting.TestContext冲突了,所以写成了ConnectDatabase.TestContext
   8:         //Arrage
   9:         Database.SetInitializer(new DropCreateDatabaseAlways<ConnectDatabase.TestContext>());
  10:         //Act
  11:         using (ConnectDatabase.TestContext ctx = new ConnectDatabase.TestContext())
  12:         {
  13:             ctx.Database.Initialize(force: true);
  14:             ctx.Blogs.Add(new ConnectDatabase.Blog()
  15:             {
  16:                 Name = "强制初始化1"
  17:             });
  18:             ctx.SaveChanges();
  19:         }
  20:         using (ConnectDatabase.TestContext ctx = new ConnectDatabase.TestContext())
  21:         {
  22:             ctx.Database.Initialize(force: true);
  23:             ctx.Blogs.Add(new ConnectDatabase.Blog()
  24:             {
  25:                 Name = "强制初始化2"
  26:             });
  27:             ctx.SaveChanges();
  28:         }
  29:         ConnectDatabase.Blog blog = null;
  30:         using (ConnectDatabase.TestContext ctx = new ConnectDatabase.TestContext())
  31:         {
  32:             blog = ctx.Blogs.FirstOrDefault();
  33:         }
  34:  
  35:         //Assert
  36:         Assert.IsNotNull(blog);
  37:         Assert.AreEqual("强制初始化2", blog.Name);
  38:  
  39:     }
  40: }

测试结果:

技术分享

因为设置的初始化策略为DropCreateDatabaseAlways,每一次调用Database.Initialize,参数为true,都会重新删除并创建数据库。

四、Seed数据

创建数据库时初始化一些数据,首先自定义初始化策略,重写Seed方法,代码如下:

   1: public class DropCreateDatabaseWithSeedData : DropCreateDatabaseAlways<TestContext>
   2: {
   3:     protected override void Seed(TestContext context)
   4:     {
   5:         context.Blogs.Add(new Blog()
   6:         {
   7:             Name = "种子数据1"
   8:         });
   9:         context.Blogs.Add(new Blog()
  10:         {
  11:             Name = "种子数据2"
  12:         });
  13:         //注意没有调用context.SaveChanges(),base.Seed(context)会调用
  14:         base.Seed(context);
  15:     }
  16: }

下面是测试程序:

   1: [TestMethod]
   2: public void SeedData()
   3: {
   4:     Database.SetInitializer(new DropCreateDatabaseWithSeedData());
   5:     List<ConnectDatabase.Blog> blogList = null;
   6:     using (ConnectDatabase.TestContext ctx = new ConnectDatabase.TestContext())
   7:     {
   8:         blogList = ctx.Blogs.OrderBy(t => t.Id).ToList();
   9:     }
  10:     Assert.AreEqual(2, blogList.Count);
  11:     Assert.AreEqual("种子数据1", blogList[0].Name);
  12:     Assert.AreEqual("种子数据2", blogList[1].Name);
  13: }

测试结果:

技术分享

五、创建索引

在Seed方法中,使用ExecuteSqlCommand创建索引,代码如下:

   1: protected override void Seed(TestContext context)
   2: {
   3:     context.Database.ExecuteSqlCommand("CREATE INDEX IX_Test_Name ON Blogs (Name)");
   4:     context.Blogs.Add(new Blog()
   5:     {
   6:         Name = "种子数据1"
   7:     });
   8:     context.Blogs.Add(new Blog()
   9:     {
  10:         Name = "种子数据2"
  11:     });
  12:     //注意没有调用context.SaveChanges(),base.Seed(context)会调用
  13:     base.Seed(context);
  14: }

六、结束语

mysql相关工具下载地址:

1.mysql-5.5.28-winx64.msi

2.mysql-connector-net-6.6.4.msi

3.mysql-workbench-gpl-5.2.44-win32.msi

本篇中主要讲了Entity Framework连接数据库、初始化的一些知识,跟题目”工欲善其事必先利其器“有点不符,但仔细想想也相差不了多远,解决了最基本的,后面的才能更顺利。

系列的其他文章。

如果遇到问题,可以访问Entity Framework社区,网址是www.ef-community.com

转:http://www.cnblogs.com/nianming/archive/2012/11/04/2753183.html

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