一周一话题之一（EF-CodeFirst、MEF、T4框架搭建学习）

本话题是根据郭明峰博客《MVC实用架构系列》的搭建学习总结。

-->目录导航

一、数据仓储访问的构建

    1.UnitOfWork的构建

    2.Repository的构建

    3.使用MEF应用IOC

        (1)优势

        (2)使用

        (3)MVC项目的应用

        (4)MEF排错

    4.DBContext

        (1)实体映射配置

        (2)EFDbContext

        (3)EFCachingDbContext

        (4)根据配置来获得当前数据库访问上下文对象

二、T4模板的运用

    1.两个VS插件

    2.T4模型类

    3.同时生成多个文件

一、数据仓储访问的构建

充分采用面向对象思想，针对接口、针对抽象进行设计；

1.UnitOfWork的构建



最终使得所有的数据操作最终都提交到一个与IUnitOfWork接口的实现类中进行操作，以保证各个实体的Repository与IUnitOfWork使用的是同一个DbContext上下文

2.Repository的构建





注：EF的操作提交 context.SaveChanged() 默认就是事务性的，只要保证了当前的所有实体的操作都是在一个共同的上下文中进行的，就实现了事务操作了

3.使用MEF应用IOC

(1)优势

(2)使用

-->在接口和类上加上特定的Attribute，

例如：使用[Export(typeof(IUnitOfWork))]将EFUnitOfWorkContext进行导出

[Export(typeof(IUnitOfWork))]
internal class EFUnitOfWorkContext : UnitOfWorkContextBase

使用[Import]，在需要EFUnitOfWorkContext时直接将其导入

 

[Import]
protected IUnitOfWork UnitOfWork { get; set; }

(3)MVC项目的应用

IOC组件是通过 DependencyResolver类中的 SetResolver(IDependencyResolver resolver) 方法来向MVC提供注册点的，所以我们只需要实现一个 IDependencyResolver 接口的MEF实现类，即可完成MEF在MVC中的注册工作。

/// <summary>
/// MEF依赖关系解析类
/// </summary>
public class MefDependencySolver : IDependencyResolver
{
private readonly ComposablePartCatalog _catalog;
private const string HttpContextKey = "MefContainerKey";

public MefDependencySolver(ComposablePartCatalog catalog)
{
_catalog = catalog;
}

public CompositionContainer Container
{
get
{
if (!HttpContext.Current.Items.Contains(HttpContextKey))
{
HttpContext.Current.Items.Add(HttpContextKey, new CompositionContainer(_catalog));
}
CompositionContainer container = (CompositionContainer)HttpContext.Current.Items[HttpContextKey];
HttpContext.Current.Application["Container"] = container;
return container;
}
}

#region IDependencyResolver Members

public object GetService(Type serviceType)
{
string contractName = AttributedModelServices.GetContractName(serviceType);
return Container.GetExportedValueOrDefault<object>(contractName);
}

public IEnumerable<object> GetServices(Type serviceType)
{
return Container.GetExportedValues<object>(serviceType.FullName);
}

#endregion
}

(4)MEF排错

-->MEF的导出导入是整体关联的，只要树中某一个部件匹配失败，整个树将无法实例化，也就是会出现Import的属性值为Null

使用MEF开发团队提供的调试工具MEFX来进行调试

-->常用命令



4.DBContext

(1)实体映射配置

-->映射配置通用接口

/// <summary>
///     实体映射接口
/// </summary>
[InheritedExport]
public interface IEntityMapper
{
/// <summary>
///     将当前实体映射对象注册到当前数据访问上下文实体映射配置注册器中
/// </summary>
/// <param name="configurations"></param>
void RegistTo(ConfigurationRegistrar configurations);
}

IEntityMapper接口添加了MEF的InheritedExport特性，该特性可以沿着继承链传递所施加的特性。在需要的时候，就可以通过ImportManyAttribute一次性导出所有实现了IEntityMapper接口的实现类对象。

-->实体映射类

internal partial class RoleConfiguration : EntityTypeConfiguration<Role>,IEntityMapper
{
/// <summary>
/// 实体类-数据表映射构造函数——角色信息
/// </summary>
public RoleConfiguration()
{
RoleConfigurationAppend();
}

/// <summary>
/// 额外的数据映射
/// </summary>
partial void RoleConfigurationAppend();

/// <summary>
/// 将当前实体映射对象注册到当前数据访问上下文实体映射配置注册器中
/// </summary>
/// <param name="configurations">实体映射配置注册器</param>
public void RegistTo(ConfigurationRegistrar configurations)
{
configurations.Add(this);
}
}

 

(2)EFDbContext

namespace Xwb.Component.Data
{
[Export("EF",typeof(DbContext))]
public class EFDbContext : DbContext
{
#region 构造函数

/// <summary>
///     初始化一个 使用连接名为“default”的数据访问上下文类 的新实例
/// </summary>
public EFDbContext()
: base("default"){}

public EFDbContext(string nameOrConnectionString)
: base(nameOrConnectionString){}

public EFDbContext(DbConnection existingConnection)
: base(existingConnection, true) { }

#endregion

[ImportMany(typeof(IEntityMapper))]
public IEnumerable<IEntityMapper> EntityMappers { get; set; }

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
if (EntityMappers == null)
{
return;
}
foreach (var entityMapper in EntityMappers)
{
entityMapper.RegistTo(modelBuilder.Configurations);
}
}
}
}

至此我们有了依托于EF的DBContext上下文对象了。

(3)EFCachingDbContext

接下来我们利用Community Entity Framework Provider Wrappers来完成EF4、5的缓存扩展，构建一个带缓存的EFDbContext

/// <summary>
///     启用缓存的自定义EntityFramework数据访问上下文
/// </summary>
[Export("EFCaching", typeof(DbContext))]
public class EFCachingDbContext:EFDbContext
{
private static readonly InMemoryCache InMemoryCache= new InMemoryCache();

public EFCachingDbContext()
: base(CreateConnectionWrapper("default")){}

public EFCachingDbContext(string connectionStringName)
: base(CreateConnectionWrapper(connectionStringName)) { }

/// <summary>
/// 由数据库连接字符串创建连接对象
/// </summary>
/// <param name="connectionStringName">连接字符串名称</param>
/// <returns></returns>
private static DbConnection CreateConnectionWrapper(string connectionStringName)
{
PublicHelper.CheckArgument(connectionStringName, "connectionStringName");
string providerInvariantName = "System.Data.SqlClient";
string connectionString = null;
ConnectionStringSettings connectionStringSetting = ConfigurationManager.ConnectionStrings[connectionStringName];
if (connectionStringSetting != null)
{
providerInvariantName = connectionStringSetting.ProviderName;
connectionString = connectionStringSetting.ConnectionString;
}
if (connectionString == null)
{
throw PublicHelper.ThrowComponentException("名称为“" + connectionStringName + "”数据库连接串的ConnectionString值为空。");
}
string wrappedConnectionString = "wrappedProvider=" + providerInvariantName + ";" + connectionString;
EFCachingConnection connection = new EFCachingConnection
{
ConnectionString = wrappedConnectionString,
//这里缓存策略使用了缓存所有数据（CacheAllPolicy）的策略，在实际项目中，最好自定义缓存策略，而不要使用这个策略，以免服务器内存被撑爆。
CachingPolicy = CachingPolicy.CacheAll,
Cache = InMemoryCache
};
return connection;
}
}

(4)根据配置来获得当前数据库访问上下文对象

[Export(typeof(IUnitOfWork))]
internal class EFUnitOfWorkContext : UnitOfWorkContextBase
{
[Import("EF", typeof(DbContext))]
private Lazy<EFDbContext> EFDbContext { get; set; }

[Import("EFCaching", typeof(DbContext))]
private Lazy<EFCachingDbContext> EFCachingDbContext { get; set; }

/// <summary>
///     获得 当前使用的数据库访问上下文对象
/// </summary>
protected override DbContext Context
{
get
{
bool secondCachingEnabled = ConfigurationManager.AppSettings["EntityFrameworkCachingEnabled"].CastTo(false);
return secondCachingEnabled ? EFCachingDbContext.Value : EFDbContext.Value;
}
}
}

二、T4模板的运用

1.两个VS插件

Devart T4 Editor：为VS提供智能提示功能。

T4 Toolbox：生成多文件

2.T4模型类

/// <summary>
///     T4实体模型信息类
/// </summary>
public class T4ModelInfo
{
/// <summary>
/// 获取 是否使用模块文件夹
/// </summary>
public bool UseModuleDir { get; private set; }

/// <summary>
///     获取 模型所在模块名称
/// </summary>
public string ModuleName { get; private set; }

/// <summary>
///     获取 模型名称
/// </summary>
public string Name { get; private set; }

/// <summary>
///     获取 模型描述
/// </summary>
public string Description { get; private set; }

/// <summary>
/// 主键类型
/// </summary>
public Type KeyType { get; set; }

/// <summary>
/// 主键类型名称
/// </summary>
public string KeyTypeName { get; set; }

/// <summary>
///     获取 属性
/// </summary>
public IEnumerable<PropertyInfo> Properties { get; private set; }

/// <summary>
/// 构造函数
/// </summary>
/// <param name="modelType"></param>
/// <param name="useModuleDir"></param>
public T4ModelInfo(Type modelType, bool useModuleDir = false)
{
var @namespace = modelType.Namespace;
if (@namespace == null)
{
return;
}
UseModuleDir = useModuleDir;
if (UseModuleDir)
{
var index = @namespace.LastIndexOf('.') + 1;
ModuleName = @namespace.Substring(index, @namespace.Length - index);
}

Name = modelType.Name;
PropertyInfo keyProp = modelType.GetProperty("Id");
KeyType = keyProp.PropertyType;
KeyTypeName = KeyType.Name;

var descAttributes = modelType.GetCustomAttributes(typeof(DescriptionAttribute), true);
Description = descAttributes.Length == 1 ? ((DescriptionAttribute)descAttributes[0]).Description : Name;
Properties = modelType.GetProperties();
}
}

3.同时生成多个文件

(1)通过反射的方式拿到定义的所有实体类型信息

//当前文件所在目录的绝对路径
string currentPath= Path.GetDirectoryName(Host.TemplateFile);
//项目的绝对路径
string projectPath= currentPath.Substring(0,currentPath.IndexOf(@"\T4"));
//解决方案的绝对路径
string solutionPath= currentPath.Substring(0,currentPath.IndexOf(@"Xwb.Core.Data"));
//加载模型实体
string modelFile= Path.Combine(solutionPath,@"Xwb.Core.Models\bin\Debug\Xwb.Core.Models.dll");
byte[] fileData= File.ReadAllBytes(modelFile);
Assembly assembly = Assembly.Load(fileData);
//调用方通过反射从业务实体程序集中获取所有基类为 EntityBase<int>或EntityBase<Guid> 的并且不是抽象类的实体类型信息
IEnumerable<Type> modelTypes = assembly.GetTypes().Where(m => (typeof(EntityBase<int>).IsAssignableFrom(m) || typeof(EntityBase<Guid>).IsAssignableFrom(m)) && !m.IsAbstract);

 

(2)定义每一个T4 ToolBox模板

public class EntityRepositoryTemplate : CSharpTemplate
{
private T4ModelInfo _model;

public EntityRepositoryTemplate(T4ModelInfo model)
{
_model = model;
}

public string FileName
{
get
{
return string.Format("{0}Repository.generated.cs",_model.Name);
}
}
public override string TransformText()
{
#>
using System;
using System.ComponentModel.Composition;
using Xwb.Component.Data;
using Xwb.Core.Models<#= _model.UseModuleDir ? "." + _model.ModuleName : null #>;

namespace Xwb.Core.Data.Repositories<#= _model.UseModuleDir ? "." + _model.ModuleName : null #>.Impl
{
/// <summary>
/// 仓储操作实现--<#= _model.Description #>
/// </summary>
[Export(typeof(I<#= _model.Name #>Repository))]
public partial class <#= _model.Name #>Repository : EFRepositoryBase<<#= _model.Name #>, <#= _model.KeyTypeName #>>, I<#= _model.Name #>Repository
{ }
}
<#+
return this.GenerationEnvironment.ToString();
}
}
#>

 

(3)循环调用每个模板，一次性在不同目录下生成多个文件

foreach(Type modelType in modelTypes)
{
T4ModelInfo model = new T4ModelInfo(modelType, true);

//实体映射类
EntityConfigurationTemplate config = new EntityConfigurationTemplate(model);
string path = model.UseModuleDir
? string.Format(@"{0}\Configurations\{1}", projectPath, model.ModuleName)
: string.Format(@"{0}\Configurations", projectPath);
config.Output.Encoding = Encoding.UTF8;
config.RenderToFile(Path.Combine(path, config.FileName));
}
#>