domain-driven-design - DDD 中的工厂、服务、存储库

Question

我对 DDD 中的factories、repositories 和services 有一些疑问。我有以下实体:文件夹、文件、FileData。

在我看来，“文件夹”是一个聚合根，应该负责创建 File 和 FileData 对象。

所以我的第一个问题是我应该使用 factory 来创建这个聚合还是由 repository 决定？此时我有 2 个存储库，一个用于文件夹，另一个用于文件，但在我看来，我应该将它们合并在一起。以下代码片段显示了我的 Folder Repository，它位于我的基础架构层中:

public class FolderRepository : IFolderRepository
{
    #region Fields

    private readonly IFolderContext _context;
    private readonly IUnitOfWork _unitOfWork;

    #endregion

    #region Constructor

    public FolderRepository(IUnitOfWork unitOfWork)
    {
        _unitOfWork = unitOfWork;
        _context = _unitOfWork.Context as IFolderContext;
    }

    #endregion

    public IUnitOfWork UnitOfWork
    {
        get { return _unitOfWork; }
    }

    public IQueryable<Folder> All
    {
        get { return _context.Folders; }
    }

    public Folder Find(Guid id)
    {
        return _context.Folders.Find(id);
    }

    public void InsertGraph(Folder entity)
    {
        _context.Folders.Add(entity);
    }

    public void InsertOrUpdate(Folder entity)
    {
        if (entity.Id == Guid.Empty)
        {
            _context.SetAdd(entity);
        }
        else
        {
            _context.SetModified(entity);
        }
    }

    public bool Delete(Guid id)
    {
        var folder = this.Find(id) ?? _context.Folders.Find(id);
        _context.Folders.Remove(folder);

        return folder == null;
    }

    public int AmountOfFilesIncluded(Folder folder)
    {
        throw new NotImplementedException();
        //return folder.Files.Count();
    }

    public void Dispose()
    {
        _context.Dispose();
    }
}

接下来我在我的应用层中创建了一个服务，称为“IoService”。我对服务的位置有疑问。是否应该移到领域层？

public class IoService : IIoService
{
    #region Fields

    private readonly IFolderRepository _folderRepository;
    private readonly IFileRepository _fileRepository;
    private readonly IUserReferenceRepository _userReferenceRepository;

    #endregion

    #region Constructor

    public IoService(IFolderRepository folderRepository, IFileRepository fileRepository, IUserReferenceRepository userReferenceRepository)
    {
        if(folderRepository == null)
            throw new NullReferenceException("folderRepository");
        if(fileRepository == null)
            throw new NullReferenceException("fileRepository");
        if (userReferenceRepository == null)
            throw new NullReferenceException("userReferenceRepository");

        _folderRepository = folderRepository;
        _fileRepository = fileRepository;
        _userReferenceRepository = userReferenceRepository;
    }

    #endregion

    #region Folder Methods

    /// <summary>
    /// Create a new 'Folder'
    /// </summary>
    /// <param name="userReference"></param>
    /// <param name="name"></param>
    /// <param name="parentFolder"></param>
    /// <param name="userIds">The given users represent who have access to the folder</param>
    /// <param name="keywords"></param>
    /// <param name="share"></param>
    public void AddFolder(UserReference userReference, string name, Folder parentFolder = null, IList<Guid> userIds = null, IEnumerable<string> keywords = null, bool share = false)
    {
        var userReferenceList = new List<UserReference> { userReference };

        if (userIds != null && userIds.Any())
        {
            userReferenceList.AddRange(userIds.Select(id => _userReferenceRepository.Find(id)));
        }

        var folder = new Folder
        {
            Name = name,
            ParentFolder = parentFolder,
            Shared = share,
            Deleted = false,
            CreatedBy = userReference,
            UserReferences = userReferenceList
        };

        if (keywords != null)
        {
            folder.Keywords = keywords.Select(keyword =>
                new Keyword
                {
                    Folder = folder,
                    Type = "web",
                    Value = keyword,
                }).ToList();
        }

        //insert into repository
        _folderRepository.InsertOrUpdate(folder);

        //save
        _folderRepository.UnitOfWork.Save();
    }

    /// <summary>
    /// Get 'Folder' by it's id
    /// </summary>
    /// <param name="id"></param>
    /// <returns></returns>
    public Folder GetFolder(Guid id)
    {
        return _folderRepository.Find(id);
    }

    #endregion

    #region File Methods

    /// <summary>
    /// Add a new 'File'
    /// </summary>
    /// <param name="userReference"></param>
    /// <param name="folder"></param>
    /// <param name="data"></param>
    /// <param name="name"></param>
    /// <param name="title"></param>
    /// <param name="keywords"></param>
    /// <param name="shared"></param>
    public void AddFile(UserReference userReference, Folder folder, FileData data, string name, string title = "", IEnumerable<string> keywords = null, bool shared = false)
    {
        var file = new File
        {
            Name = name,
            Folder = folder,
            FileData = data,
            CreatedBy = userReference,
            Type = data.Type
        };

        if (keywords != null)
        {
            file.Keywords = keywords.Select(keyword =>
                new Keyword
                {
                    File = file,
                    Type = "web",
                    Value = keyword,
                }).ToList();
        }

        folder.Files.Add(file);
        folder.Updated = DateTime.UtcNow;

        _folderRepository.InsertOrUpdate(folder);

        //save
        _folderRepository.UnitOfWork.Save();
    }

    /// <summary>
    /// Get 'File' by it's id
    /// </summary>
    /// <param name="id"></param>
    /// <returns></returns>
    public File GetFile(Guid id)
    {
        return _fileRepository.Find(id);
    }

    #endregion
}

总结一下:我是否应该使用该服务来创建文件夹对象。或者服务应该只使用一个工厂，它负责创建对象并将创建的对象发送到存储库？服务中的依赖注入(inject)怎么样，我应该使用 Unity 等 IOC 容器从 UI 层注入(inject)我的服务，还是应该只对服务中的依赖项进行硬编码？

谢谢

Answer 1

So my first question is should I use a factory to create this aggregate or is it up to the repository?

工厂负责创建，而存储库负责持久性。重构后，存储库将有效地创建实例。然而，这个创建过程通常是通过反射完成的，并且不会通过工厂来防止应该只在创建时发生的初始化。

At this time I have 2 repositories, one for Folder and another for File, but it seems to me I should merge them together.

在 DDD 中，每个聚合都有一个存储库。该存储库将负责持久化作为聚合一部分的所有实体和值对象。

I have my doubts about the location of the service. Should it be moved to the domain layer?

IMO，一个应用服务可以被放置到领域层，因为它已经作为一个门面，将它们放在一起会带来凝聚力的好处。关于 IoService 的一种想法是，诸如 AddFile 之类的方法通常会通过聚合标识而不是实例来参数化。由于应用程序服务已经引用了一个存储库，它可以根据需要加载适当的聚合。否则，调用代码将负责调用存储库。

Should I use the service for creating the folder object. Or should the service just use a factory, which have the responsibility of creating the object and send the created object to the repository?

IoService 看起来不错，除了前面的评论是通过身份而不是实例来参数化。

What about dependency injection in the service, should I inject my services from the UI layer with IOC containers like Unity or should I just hardcode the dependencies in the service?

这是一个偏好问题。如果您可以从使用 IoC 容器中受益，请使用它。但是，不要仅仅为了使用它而使用它。您已经在进行依赖注入(inject)，只是没有花哨的 IoC 容器。

示例

class File
{
    public File(string name, Folder folder, FileData data,  UserReference createdBy, IEnumerable<string> keywords = null)
    {
        //...
    }
}

...

class Folder
{
    public File AddFile(string name, FileData data, UserReference createdBy, IEnumerable<string> keywords = null)
    {
        var file = new File(name, this, data, createdBy, keywords)
        this.Files.Add(file);
        this.Updated = DateTime.UtcNow;
        return file;
    }
}

...

public void AddFile(UserReference userReference, Guid folderId, FileData data, string name, string title = "", IEnumerable<string> keywords = null, bool shared = false)
{
    var folder = _folderRepository.Find(folderId);
    if (folder == null)
        throw new Exception();

    folder.AddFile(name, data, keywords);

    _folderRepository.InsertOrUpdate(folder);
    _folderRepository.UnitOfWork.Save();
}

在此示例中，更多的行为被委托(delegate)给文件夹聚合和文件实体。应用程序服务简单地调用聚合上的适当方法。