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");或
1: Database.DefaultConnectionFactory = new SqlConnectionFactory("Data Source=.;Database=Test;User=sa;Password=sasa;MultipleActiveResultSets=True");和
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：
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: }
或
1: public TestContext()
2: : base("name=TestContext1") 3: {4:
5: }
或
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 CreateDatabaseIfNotExists<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：
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：
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、MySQL相关
mysql相关工具下载地址：
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