C# 抽象工廠模式實戰：從三層架構到依賴倒置的完整範例

抽象工廠模式在 ASP.NET MVC 三層架構中的落地實踐：介面隔離、工廠封裝、配置驅動、依賴倒置，附完整專案結構與代碼。

架構分層與依賴關係

AXCModel (實體) ← IAXCDAL (DAL介面) ← AXCDAL (DAL實作)
                    ↑                    ↑
              IAXCBLL (BLL介面) ← AXCBLL (BLL實作)
                    ↑                    ↑
              AXCFactoryDAL (DAL工廠) ← AXCFactoryBLL (BLL工廠)
                    ↑
              AXCWeb (表現層) → 依賴介面與工廠

**核心原則**：高層模組 (BLL/Web) 不依賴低層實作 (DAL)，雙方依賴抽象 (介面)；工廠負責具體類別實例化。

程式碼實作

1. 實體層

namespace AXCModel
{
    public class PeopleModel
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
        public bool Sex { get; set; }
    }
}

2. DAL 介面與實作

// IAXCDAL
public interface IPeopleDAL
{
    List<PeopleModel> GetPeopleList();
}

// AXCDAL
public class PeopleDAL : IPeopleDAL
{
    public List<PeopleModel> GetPeopleList()
    {
        // 模擬資料，實際連接資料庫
        return new List<PeopleModel>
        {
            new PeopleModel { Id=1, Name="艾新草", Age=25, Sex=false },
            new PeopleModel { Id=2, Name="艾新草1", Age=23, Sex=true },
            new PeopleModel { Id=3, Name="艾新草2", Age=22, Sex=false }
        };
    }
}

3. DAL 抽象工廠

// AXCFactoryDAL
public abstract class AbsFactoryDAL
{
    public static AbsFactoryDAL GetFactory()
    {
        string type = ConfigurationManager.AppSettings["dalType"]; // "dal"
        switch (type)
        {
            case "dal": return new DALFactory();
            default: throw new NotSupportedException($"Unknown DAL type: {type}");
        }
    }
    public abstract IPeopleDAL GetPeople();
}

public class DALFactory : AbsFactoryDAL
{
    public override IPeopleDAL GetPeople() => new PeopleDAL();
}

4. BLL 介面與實作

// IAXCBLL
public interface IPeopleBLL
{
    List<PeopleModel> GetPeopleList();
}

// AXCBLL
public class PeopleBLL : IPeopleBLL
{
    private readonly AbsFactoryDAL _dalFactory = AbsFactoryDAL.GetFactory();

    public List<PeopleModel> GetPeopleList()
    {
        IPeopleDAL dal = _dalFactory.GetPeople();
        return dal.GetPeopleList(); // 可加入業務邏輯、快取、驗證
    }
}

5. BLL 抽象工廠

// AXCFactory
public abstract class AbsFactoryBLL
{
    public static AbsFactoryBLL GetFactory()
    {
        string type = ConfigurationManager.AppSettings["bllType"]; // "bll"
        switch (type)
        {
            case "bll": return new BLLFactory();
            default: throw new NotSupportedException($"Unknown BLL type: {type}");
        }
    }
    public abstract IPeopleBLL GetPeople();
}

public class BLLFactory : AbsFactoryBLL
{
    public override IPeopleBLL GetPeople() => new PeopleBLL();
}

6. Web.config 設定

<appSettings>
  <add key="dalType" value="dal" />
  <add key="bllType" value="bll" />
</appSettings>

7. 表現層調用

public ActionResult Index()
{
    AbsFactoryBLL bllFactory = AbsFactoryBLL.GetFactory();
    IPeopleBLL peopleBll = bllFactory.GetPeople();
    List<PeopleModel> list = peopleBll.GetPeopleList();
    return View(list);
}

進階：遷移至依賴注入容器

抽象工廠是「手動 DI」過渡形態。現代 ASP.NET Core 內建 DI 容器可直接註冊：

// Program.cs / Startup.cs
services.AddScoped<IPeopleDAL, PeopleDAL>();
services.AddScoped<IPeopleBLL, PeopleBLL>();

// Controller 建構函數注入
public class HomeController : Controller
{
    private readonly IPeopleBLL _peopleBll;
    public HomeController(IPeopleBLL peopleBll) => _peopleBll = peopleBll;
    
    public IActionResult Index() => View(_peopleBll.GetPeopleList());
}

模式比較

抽象工廠是理解「依賴倒置」的最佳切入點。掌握其精髓——**介面隔離變化、工廠封裝創建**——再遷移至 DI 容器將水到渠成。