关于NHibernate、LINQ、Entity Framework

NHibernate采用非侵入式的方式进行对象-关系映射，从而成就了其轻量级ORM技术的美名，这一点相信成为很多架构师钟爱他的重要理由。NHibernate技术架构如下图所示：

NHibernate的使用大致可以分为配置信息、编写映射文件和持久化数据几个步骤：

一、配置信息

NHibernate需要对配置文件作以下配置方可使用：

<?xml version="1.0" encoding="utf-8" ?>
 <configuration>
   <configSections>
     <section name="hibernate-configuration" type="NHibernate.Cfg.ConfigurationSectionHandler, NHibernate" />
   </configSections>
 
   <hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
     <session-factory>
       <property name="dialect">NHibernate.Dialect.MsSql2008Dialect</property>
       <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
       <property name="connection.connection_string">Data Source=localhost;User Id=sa;Password=11111111;Initial Catalog=Apollo;MultipleActiveResultSets=True;</property>
       <mapping assembly="Apollo.Blog.EF.Chapter1.Domain" />
     </session-factory>
   </hibernate-configuration>
 </configuration>

二、映射文件

<?xml version="1.0" encoding="utf-8" ?>
 <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Apollo.Blog.EF.Chapter1.Domain" namespace="Apollo.Blog.EF.Chapter1.Domain">
   <class name="User" table="`User`" lazy="false">
     <id name="ID">
       <generator class="guid" />
     </id>
     <property name="Name" type="string" not-null="true" />
   </class>
 </hibernate-mapping>

三、数据持久化

1 var sessionFactory = new Configuration().Configure().BuildSessionFactory();
2 using (var session = sessionFactory.OpenSession())
3 {
4     session.Save(user);
5     session.Flush();
6 }

---

LINQ（Language Integrated Query，语言集成查询）是一组用于C#和VB.NET语言的扩展，它允许编写C#或者VB.NET代码以查询数据库相同的方式操作内存数据。LINQ提供提供了丰富的类似SQL的查询语法，功能强大且容易上手。

LINQ技术通过提供程序扩展，可以实现对任何数据源的访问。常用的提供程序有LINQ to SQL、LINQ to XML、LINQ to Objects、LINQ to Entities、LINQ to Datasets、LINQ to ADO.NET。LINQ技术架构如下图所示：

LINQ的使用大致包括连接配置、关系映射、上下文环境定义和数据持久化四步：

一、连接配置

LINQ的数据库连接配置与ADO.NET一样：

<?xml version="1.0" encoding="utf-8" ?>
 <configuration>
   <connectionStrings>
     <add name="AdoNet" connectionString="Data Source=localhost;User Id=sa;Password=11111111;Initial Catalog=Apollo;MultipleActiveResultSets=True;" providerName="System.Data.SqlClient"/>
   </connectionStrings>
 </configuration>

二、侵入式关系映射

[Table(Name = "User")]
 public class LinqUser : User
 {
     [Column(IsPrimaryKey = true)]
     public override Guid ID { get; set; }
 
     [Column]
     public override string Name { get; set; }
 }

三、上下文环境

internal class LinqContext : DataContext
 {
     public LinqContext(string connection)
         : base(connection)
     {
     }
 
     public LinqContext(IDbConnection connection)
         : base(connection)
     {
     }
 
     public Table<LinqUser> Users
     {
         get { return this.GetTable<LinqUser>(); }
     }
 }

四、数据持久化

1 using (var db = new LinqContext(CONNECTION_STRING))
2 {
3     db.Users.InsertOnSubmit(user);
4     db.SubmitChanges();
5 }

---

Entity Framework的全称为ADO.NET Entity Framework，是在ADO.NET上层实现的ORM封装，其技术架构如下图所示：

Entity Framework的使用与LINQ一样，分为连接配置、关系映射、上下文环境定义和数据持久化四步：

一、连接配置

<?xml version="1.0" encoding="utf-8" ?>
 <configuration>
   <connectionStrings>
     <add name="EntityFramework" providerName="System.Data.EntityClient"
          connectionString="provider=System.Data.SqlClient;
                       provider connection string=&quot;
                       Data Source=localhost;
                       User Id=sa;
                       Password=11111111;
                       Initial Catalog=Apollo;
                       Integrated Security=False;
                       MultipleActiveResultSets=True;&quot;;
                       metadata=..\..\..\Apollo.Blog.EF.Chapter1.Domain\Edmx\Chapter1.ssdl|
                                 ..\..\..\Apollo.Blog.EF.Chapter1.Domain\Edmx\Chapter1.csdl|
                                 ..\..\..\Apollo.Blog.EF.Chapter1.Domain\Edmx\Chapter1.msl"/>
   </connectionStrings>
 </configuration>

二、关系映射

Entity Framework是通过定义概念模型（CSDL）、物理模型（SSDL）及两者的映射关系（MSL），实现对象与关系映射的。

SSDL映射文件内容如下：

<?xml version="1.0" encoding="utf-8"?>
 <Schema Namespace="Chapter1.Store" Alias="Self" Provider="System.Data.SqlClient" ProviderManifestToken="2005"
         xmlns="http://schemas.microsoft.com/ado/2009/02/edm/ssdl"
         xmlns:store="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator">
   <EntityContainer Name="Chapter1StoreContainer">
     <EntitySet Name="User" EntityType="Chapter1.Store.User" store:Type="Tables" Schema="dbo" />
   </EntityContainer>
 
   <EntityType Name="User">
     <Key>
       <PropertyRef Name="ID" />
     </Key>
     <Property Name="ID" Type="uniqueidentifier" Nullable="false" />
     <Property Name="Name" Type="nvarchar" Nullable="false" MaxLength="40" />
   </EntityType>
 </Schema>

CSDL映射文件内容如下：

<?xml version="1.0" encoding="utf-8"?>
 <Schema Namespace="Chapter1" Alias="Self"
         xmlns="http://schemas.microsoft.com/ado/2008/09/edm"
         xmlns:cg="http://schemas.microsoft.com/ado/2006/04/codegeneration"
         xmlns:store="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator"
         xmlns:annotation="http://schemas.microsoft.com/ado/2009/02/edm/annotation">
   <EntityContainer Name="Chapter1" annotation:LazyLoadingEnabled="true">
     <EntitySet Name="User" EntityType="Chapter1.User" />
   </EntityContainer>
 
   <EntityType Name="User">
     <Key>
       <PropertyRef Name="ID" />
     </Key>
     <Property Name="ID" Type="Guid" Nullable="false" />
     <Property Name="Name" Type="String" Nullable="false" />
   </EntityType>
 </Schema>

MSL映射文件内容如下：

<?xml version="1.0" encoding="utf-8"?>
 <Mapping Space="C-S" xmlns="http://schemas.microsoft.com/ado/2008/09/mapping/cs">
   <Alias Key="Cdm" Value="Chapter1" />
   <Alias Key="Storage" Value="Chapter1.Store" />
   <EntityContainerMapping CdmEntityContainer="Chapter1" StorageEntityContainer="Chapter1StoreContainer">
     <EntitySetMapping Name="User">
       <EntityTypeMapping TypeName="Cdm.User">
         <MappingFragment StoreEntitySet="User">
           <ScalarProperty Name="ID" ColumnName="ID" />
           <ScalarProperty Name="Name" ColumnName="Name" />
         </MappingFragment>
       </EntityTypeMapping>
     </EntitySetMapping>
   </EntityContainerMapping>
 </Mapping>

三、上下文环境

Entity Framework提供了ObjectContext上下文环境，以对数据对象进行持久化操作。通过继承它，可以方便的实现自定义数据对象的访问。

internal class EntityContext : ObjectContext
 {
     public EntityContext()
         : this("name=EntityFramework")
     {
     }
 
     public EntityContext(string connectionString)
         : base(connectionString, "Chapter1")
     {
         this.Users = CreateObjectSet<User>();
     }
 
     public ObjectSet<User> Users { get; set; }
 }

四、数据持久化

1 using (var db = new EntityContext())
2 {
3     db.Users.AddObject(user);
4     db.SaveChanges();
5 }