异步不适用于 EF + 工作单元 + Repo

Question

我尝试与 Entity Framework 和 ASP.net API 项目一起实施工作单元和回购模式。

首先，我想指出我知道 DbContext 和 DbSets 是 UoW 和 Repo 模式的实现，但我正在尝试看看什么适合我的项目。

问题

我注意到，如果我从我的服务中调用异步回购方法，没有任何反应，该方法被调用，但似乎从未触发等待。如果我同步调用该方法，一切都很好。（方法示例是 Count / CountAsync）。

更奇怪的是（我不知道为什么）这个相同的方法调用出于某种原因在一个服务方法中有效，但在另一个服务方法中无效。

我会在展示我的代码后进行更详细的解释。

项目结构

我的项目结构是这样的：

我有一个API，其中注入了服务层
In-Service 注入 UoW 和 Repos
在 Repo 中注入 UoW
最后，UoW 调用数据库上下文工厂，其职责是创建我的 DbContex 的新实例

--- 代码 ---

这里是目前的实现，当然，为简洁起见省略了部分代码。

数据库上下文工厂

/// <summary>
///     Interface for factory which is in charge of creating new DbContexts
/// </summary>
/// <autogeneratedoc />
public interface IDatabaseContextFactory
{
    /// <summary>
    /// Creates new Master Database Context.
    /// </summary>
    /// <returns>newly created MasterDatabaseContext</returns>
    /// <autogeneratedoc />
    DbContext MasterDbContext();
}


/// <inheritdoc />
/// <summary>
/// This is factory which is in charge of creating new DbContexts
/// It is implemented as Singleton as factory should be implemented (according to Gang of four) 
/// </summary>
/// <seealso cref="T:Master.Domain.DataAccessLayer.IDatabaseContextFactory" />
/// <autogeneratedoc />
public class DatabaseContextFactory : IDatabaseContextFactory
{
    /// <summary>
    /// This is implementation of singleton
    /// </summary>
    /// <remarks>
    /// To read more, visit: http://csharpindepth.com/Articles/General/Singleton.aspx (Jon skeet)
    /// </remarks>
    /// <autogeneratedoc />
    private static readonly DatabaseContextFactory instance = new DatabaseContextFactory();

    // Explicit static constructor to tell C# compiler
    // not to mark type as beforefieldinit (more about this: http://csharpindepth.com/Articles/General/Beforefieldinit.aspx)
    static DatabaseContextFactory()
    {
        
    }

    //so that class cannot be initiated 
    private DatabaseContextFactory()
    {
    }


    /// <summary>
    /// Instance of DatabaseContextFactory
    /// </summary>
    public static DatabaseContextFactory Instance => instance;

    /// <inheritdoc />
    /// <summary>
    /// Creates new MasterDatabaseContext
    /// </summary>
    /// <returns></returns>
    public DbContext MasterDbContext()
    {
        return new MasterDatabaseContext();
    }
}

工作单元

 /// <inheritdoc />
/// <summary>
/// Unit of work interface
/// Maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems.
/// </summary>
/// <seealso cref="T:System.IDisposable" />
/// <autogeneratedoc />
public interface IUnitOfWork : IDisposable
{
    /// <summary>
    /// Gets the database context. DatabaseContext is part of EF and itself is implementation of UoW (and repo) patterns
    /// </summary>
    /// <value>
    /// The database context.
    /// </value>
    /// <remarks> 
    /// If true  UoW was implemented this wouldn't be here, but we are exposing this for simplicity sake. 
    /// For example so that repository  could use benefits of DbContext and DbSet <see cref="DbSet"/>. One of those benefits are Find and FindAsnyc methods
    /// </remarks>
    /// <autogeneratedoc />
    DbContext DatabaseContext { get; }
    /// <summary>
    /// Commits the changes to database
    /// </summary>
    /// <returns></returns>
    /// <autogeneratedoc />
    void Commit();
    
    /// <summary>
    /// Asynchronously commits changes to database.
    /// </summary>
    /// <returns></returns>
    /// <autogeneratedoc />
    Task CommitAsync();
 
}

 /// <inheritdoc />
/// <summary>
/// This is implementation of UoW pattern
/// </summary>
/// <remarks>
/// Martin Fowler: "Maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems."
/// According to P of EEA, Unit of work should have following methods: commit(), registerNew((object), registerDirty(object), registerClean(object), registerDeleted(object)
/// The thing is DbContext is already implementation of UoW so there is no need to implement all this
/// In case that we were not using ORM all these methods would have been implemented
/// </remarks>
/// <seealso cref="T:Master.Domain.DataAccessLayer.UnitOfWork.IUnitOfWork" />
/// <autogeneratedoc />
public class UnitOfWork : IUnitOfWork
{
    /// <summary>
    /// Is instance already disposed
    /// </summary>
    /// <remarks>
    /// Default value of bool is false
    /// </remarks>
    /// <autogeneratedoc />
    private bool _disposed;

    /// <summary>
    /// Initializes a new instance of the <see cref="UnitOfWork"/> class.
    /// </summary>
    /// <param name="dbContextfactory">The database context factory.</param>
    /// <exception cref="ArgumentNullException">
    /// dbContextfactory
    /// or
    /// MasterDbContext - Master database context cannot be null
    /// </exception>
    /// <autogeneratedoc />
    public UnitOfWork(IDatabaseContextFactory dbContextfactory)
    {
        if (dbContextfactory == null)
        {
            throw new ArgumentNullException(nameof(dbContextfactory));
        }

        var MasterDbContext = dbContextfactory.MasterDbContext();

        if (MasterDbContext == null)
        {
            throw new ArgumentNullException(nameof(MasterDbContext), @"Master database context cannot be null");
        }

        DatabaseContext = MasterDbContext;
    }

    /// <summary>
    /// Gets the database context. DatabaseContext is part of EF and itself is implementation of UoW (and repo) patterns
    /// </summary>
    /// <value>
    /// The database context.
    /// </value>
    /// <remarks>
    /// If true  UoW was implemented this wouldn't be here, but we are exposing this for simplicity sake.
    /// For example so that repository  could use benefits of DbContext and DbSet <see cref="DbSet" />. One of those benefits are Find and FindAsnyc methods
    /// </remarks>
    /// <autogeneratedoc />
    public DbContext DatabaseContext { get; }

    /// <inheritdoc />
    /// <summary>
    /// Commits the changes to database
    /// </summary>
    /// <autogeneratedoc />
    public void Commit()
    {
         DatabaseContext.SaveChanges();
    }

    /// <inheritdoc />
    /// <summary>
    /// Asynchronously commits changes to database.
    /// </summary>
    /// <returns></returns>
    /// <autogeneratedoc />
    public async Task CommitAsync()
    {
        await DatabaseContext.SaveChangesAsync();
    }


    /// <inheritdoc />
    /// <summary>
    /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
    /// </summary>
    /// <autogeneratedoc />
    public void Dispose()
    {
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    /// <summary>
    /// Releases unmanaged and - optionally - managed resources.
    /// </summary>
    /// <param name="disposning"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged resources.</param>
    /// <autogeneratedoc />
    protected virtual void Dispose(bool disposning)
    {
        if (_disposed)
            return;


        if (disposning)
        {
            DatabaseContext.Dispose();
        }


        _disposed = true;
    }

    /// <summary>
    /// Finalizes an instance of the <see cref="UnitOfWork"/> class.
    /// </summary>
    /// <autogeneratedoc />
    ~UnitOfWork()
    {
        Dispose(false);
    }
}

通用存储库

/// <summary>
/// Generic repository pattern implementation
/// Repository  Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects.
/// </summary>
/// <remarks>
/// More info: https://martinfowler.com/eaaCatalog/repository.html
/// </remarks>
/// <typeparam name="TEntity">The type of the entity.</typeparam>
/// <typeparam name="TKey">The type of the key.</typeparam>
/// <autogeneratedoc />
public interface IMasterRepository<TEntity, in TKey> where TEntity : class
{
    /// <summary>
    ///     Gets entity (of type) from repository based on given ID
    /// </summary>
    /// <param name="id">The identifier.</param>
    /// <returns>Entity</returns>
    /// <autogeneratedoc />
    TEntity Get(TKey id);

    /// <summary>
    /// Asynchronously gets entity (of type) from repository based on given ID
    /// </summary>
    /// <param name="id">The identifier.</param>
    /// <returns></returns>
    /// <autogeneratedoc />
    Task<TEntity> GetAsnyc(TKey id);
    
    /// <summary>
    ///     Gets all entities of type from repository
    /// </summary>
    /// <returns></returns>
    /// <autogeneratedoc />
    IEnumerable<TEntity> GetAll();

    /// <summary>
    ///  Asynchronously gets all entities of type from repository
    /// </summary>
    /// <returns></returns>
    /// <autogeneratedoc />
    Task<IEnumerable<TEntity>> GetAllAsync();

    /// <summary>
    ///     Finds all entities of type which match given predicate
    /// </summary>
    /// <param name="predicate">The predicate.</param>
    /// <returns>Entities which satisfy conditions</returns>
    /// <autogeneratedoc />
    IEnumerable<TEntity> Find(Expression<Func<TEntity, bool>> predicate);
}


//Note to self: according to P of EAA Repo plays nicely with QueryObject, Data mapper and Metadata mapper - Learn about those !!!



/// <summary>
/// Generic repository pattern implementation
/// Repository  Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects.
/// </summary>
/// <typeparam name="TEntity">The type of the entity.</typeparam>
/// <typeparam name="TKey">The type of the key.</typeparam>
/// <seealso cref="Master.Domain.DataAccessLayer.Repository.Generic.IMasterRepository{TEntity, TKey}" />
/// <inheritdoc cref="IMasterRepository{TEntity,TKey}" />
public class MasterRepository<TEntity, TKey> : IMasterRepository<TEntity, TKey>
    where TEntity : class 
{

    /// <summary>
    /// DbSet is part of EF, it holds entities of the context in memory, per EF guidelines DbSet was used instead of IDbSet 
    /// </summary>
    /// <remarks>
    /// <para>
    /// Even though we are not 100% happy about this, 
    /// We decided to go with this instead of (for example) IEnumerable so that we can use benefits of <see cref="DbSet"/>
    /// Those benefits for example are Find and FindAsync methods which are much faster in fetching entities by their key than for example Single of First methods
    /// </para>
    /// </remarks>
    /// <autogeneratedoc />
    private readonly DbSet<TEntity> _dbSet;


    /// <summary>
    /// Initializes a new instance of the <see cref="MasterRepository{TEntity, TKey}"/> class.
    /// </summary>
    /// <param name="unitOfWork">The unit of work.</param>
    /// <exception cref="ArgumentNullException">unitOfWork - Unit of work cannot be null</exception>
    /// <autogeneratedoc />
    public MasterRepository(IUnitOfWork unitOfWork)
    {
        if (unitOfWork == null)
        {
            throw new ArgumentNullException(nameof(unitOfWork), @"Unit of work cannot be null");
        }

        _dbSet = unitOfWork.DatabaseContext.Set<TEntity>();
    }

    /// <inheritdoc />
    /// <summary>
    /// Gets entity with given key
    /// </summary>
    /// <param name="id">The key of the entity</param>
    /// <returns>Entity with key id</returns>
    public TEntity Get(TKey id)
    {
        return _dbSet.Find(id);
    }

    /// <inheritdoc />
    /// <summary>
    /// Asynchronously gets entity with given key
    /// </summary>
    /// <param name="id">The key of the entity</param>
    /// <returns>Entity with key id</returns>
    public async Task<TEntity> GetAsnyc(TKey id)
    {
         return await _dbSet.FindAsync(id);
    }

    /// <inheritdoc />
    /// <summary>
    /// Gets all entities
    /// </summary>
    /// <returns>List of entities of type TEntiy</returns>
    public IEnumerable<TEntity> GetAll()
    {
        return _dbSet.ToList();
    }

    public async Task<IEnumerable<TEntity>> GetAllAsync()
    {
        return await _dbSet.ToListAsync();

    }

    public IEnumerable<TEntity> Find(Expression<Func<TEntity, bool>> predicate)
    {
        return _dbSet.Where(predicate).ToList();
    }

}

保存的电影存储库

 /// <inheritdoc />
/// <summary>
/// Repository for dealing with <see cref="T:Master.Domain.Model.MovieAggregate.SavedMovie" /> entity
/// </summary>
/// <seealso cref="!:Master.Domain.DataAccessLayer.Repository.Generic.IMasterRepository{Master.Domain.Model.MovieAggregate.SavedMovie,System.Guid}" />
/// <autogeneratedoc />
public interface ISavedMoviesRepository : IMasterRepository<SavedMovie, Guid>
{
    /// <summary>
    /// Asynchronously Gets number of saved Movies for the user
    /// </summary>
    /// <param name="user">The user.</param>
    /// <returns>Number of saved Movies</returns>
    /// <autogeneratedoc />
    Task<int> CountForUser(Model.UserAggregate.User user);
}


/// <inheritdoc cref="ISavedMoviesRepository" />
/// />
/// <summary>
///     Repository for dealing with <see cref="T:Master.Domain.Model.MovieAggregate.SavedMovie" /> entity
/// </summary>
/// <seealso cref="!:Master.Domain.DataAccessLayer.Repository.Generic.MasterRepository{Master.Domain.Model.MovieAggregate.SavedMovie, System.Guid}" />
/// <seealso cref="T:Master.Domain.DataAccessLayer.Repository.SavedMovies.ISavedMoviesRepository" />
/// <autogeneratedoc />
public class SavedMovieRepository : MasterRepository<SavedMovie, Guid>, ISavedMoviesRepository
{
    /// <summary>
    ///     Ef's DbSet - in-memory collection for dealing with entities
    /// </summary>
    /// <autogeneratedoc />
    private readonly DbSet<SavedMovie> _dbSet;
    private readonly IUnitOfWork _unitOfWork;



    /// <inheritdoc />
    /// <summary>
    ///     Initializes a new instance of the
    ///     <see cref="T:Master.Domain.DataAccessLayer.Repository.SavedMovies.SavedMovieRepository" /> class.
    /// </summary>
    /// <param name="unitOfWork">The unit of work.</param>
    /// <exception cref="T:System.ArgumentNullException"></exception>
    /// <autogeneratedoc />
    public SavedMovieRepository(UnitOfWork.UnitOfWork unitOfWork) : base(unitOfWork)
    {
        if (unitOfWork == null)
            throw new ArgumentNullException();
        _dbSet = unitOfWork.DatabaseContext.Set<SavedMovie>();
        _unitOfWork = unitOfWork;

    }

    /// <inheritdoc />
    /// <summary>
    ///     Asynchronously Gets number of saved Movies for the user
    /// </summary>
    /// <param name="user">The user.</param>
    /// <returns>
    ///     Number of saved Movies
    /// </returns>
    /// <exception cref="T:System.ArgumentNullException">user - User cannot be null</exception>
    /// <autogeneratedoc />
    public async Task<int> CountForUser(Model.UserAggregate.User user)
    {
        if (user == null)
            throw new ArgumentNullException(nameof(user), @"User cannot be null");

        return await _dbSet.CountAsync(r => r.UserWhoSavedId == user.Id);
    }
}

保存的电影服务

/// <inheritdoc />
/// <summary>
///     This is service for handling saved Movies!
/// </summary>
/// <seealso cref="T:Master.Infrastructure.Services.SavedMovieService.Interfaces.ISavedMovieService" />
/// <autogeneratedoc />
public class SavedMovieService : ISavedMovieService
{
    /// <summary>
    /// The saved Movies repository <see cref="ISavedMoviesRepository"/>
    /// </summary>
    /// <autogeneratedoc />
    private readonly ISavedMoviesRepository _savedMoviesRepository;
   
    /// <summary>
    /// The unit of work <see cref="IUnitOfWork"/>
    /// </summary>
    /// <autogeneratedoc />
    private readonly IUnitOfWork _unitOfWork;

    /// <summary>
    /// The user repository <see cref="IUserRepository"/>
    /// </summary>
    /// <autogeneratedoc />
    private readonly IUserRepository _userRepository;

    /// <summary>
    /// Initializes a new instance of the <see cref="SavedMovieService"/> class.
    /// </summary>
    /// <param name="savedMoviesRepository">The saved Movies repository.</param>
    /// <param name="userRepository">The user repository.</param>
    /// <param name="unitOfWork">The unit of work.</param>
    /// <autogeneratedoc />
    public SavedMovieService(ISavedMoviesRepository savedMoviesRepository, IUserRepository userRepository,
        IUnitOfWork unitOfWork)
    {
        _savedMoviesRepository = savedMoviesRepository;
        _userRepository = userRepository;
        _unitOfWork = unitOfWork;
    }

    public Task<int> CountNumberOfSavedMoviesForUser(string userId)
    {
        if (string.IsNullOrEmpty(userId))
            throw new ArgumentNullException(nameof(userId), @"User id must not be empty");


        var user = _userRepository.Get(userId);
        return _savedMoviesRepository.CountForUser(user);
    }
    
      public async Task<Guid> SaveWorkoutFromLibraryAsync(string userWhoIsSavingId, Guid galleryId,
        bool isUserPro)
    {
        if (string.IsNullOrEmpty(userWhoIsSavingId))
            throw new ArgumentNullException(nameof(userWhoIsSavingId), @"User id cannot be empty");

        if (galleryId == Guid.Empty)
            throw new ArgumentException(@"Id of gallery cannot be empty", nameof(galleryId));

            //get user who is saving from DB
            var userWhoIsSaving = _userRepository.Get(userWhoIsSavingId);
           

            if (userWhoIsSaving == null)
                throw new ObjectNotFoundException($"User with provided id not found - id: {userWhoIsSavingId}");

            //how many movies has this user saved so far
            var numberOfAlreadySavedMoviesForUser = await _savedWorkoutsRepository.CountForUserAsync(userWhoIsSaving);

            // more code here
    }

}

Web Api 控制器

[Authorize]
[RoutePrefix("api/Saved")]
[ApiVersion("2.0")]
public class SavedController : ApiController
{
    private readonly ISavedMovieService _savedMovieService;



    /// <inheritdoc />
    /// <summary>
    ///     Initializes a new instance of the <see cref="T:Master.Infrastructure.Api.V2.Controllers.SavedController" /> class.
    /// </summary>
    /// <param name="savedMovieService">The saved Movie service.</param>
    /// <autogeneratedoc />
    public SavedController(ISavedMovieService savedMovieService)
    {        
        _savedMovieService = savedMovieService;
    }

    public async Task<IHttpActionResult> GetNumberOfSavedForUser()
    {
        var cnt = await _savedMovieService.CountNumberOfSavedMoviesForUser(User.Identity.GetUserId());

        return Ok(cnt);
    }
    
    public async Task<IHttpActionResult> SaveFromGalery(SaveModel model)
    {
        await _savedMovieService.SaveWorkoutFromGalleryAsync(User.Identity.GetUserId(), model.Id, model.IsPro);

        return Ok();
    }
}

Ninject配置

（仅重要部分）

        kernel.Bind<MasterDatabaseContext>().ToSelf().InRequestScope();
        kernel.Bind<IDatabaseContextFactory>().ToMethod(c => DatabaseContextFactory.Instance).InSingletonScope();
        kernel.Bind<IUnitOfWork>().To<UnitOfWork>().InRequestScope();

        kernel.Bind(typeof(IMasterRepository<,>)).To(typeof(MasterRepository<,>));

        kernel.Bind<ISavedMoviesRepository>().To<SavedMovieRepository>();
        kernel.Bind<IUserRepository>().To<UserRepository>();
        kernel.Bind<ISavedMovieService>().To<SavedMovieService>();

我想指出的是，我在 SavedService 中注入了更多的存储库（总共 4 个，包括 Saved 和 User），但我不认为它们相关，因为它们与 SavedRepo 几乎相同，但如果需要，我也可以添加它们。此外，这是目前唯一实现此模式和方法的服务。

所以这是我调用 SaveFromGalery 时发生的事情：

UoW 构造函数被调用
DatabaseContextFactory MasterDbContext() 被调用
MasterRepository 构造函数被调用
调用了 SavedMoviesRepository 构造函数
UoW 构造函数被调用（第二次）
DatabaseContextFactory MasterDbContext() 被调用（第二次）
MasterRepository 构造函数被调用（第二次）
UserRepository 被调用
MasterRepository 构造函数被调用（再次第 3 次）
MasterRepository 构造函数被调用（又是第 4 次）
调用了 SavedService 构造函数
调用了 HTTP GET SaveFromGalery
成功从用户仓库中获取用户
_savedWorkoutsRepository.CountForUserAsync被称为
程序进入方法命中等待但从未returns结果

另一方面，当调用 GetNumberOfSavedForUser 时，会发生以下情况：

1 - 11 步相同
调用 HTTP GET GetNumberOfSavedForUser
成功从用户仓库中获取用户
_savedWorkoutsRepository.CountForUserAsync 调用成功
UoW Dispose 被调用
调用UoW处理

同样如前所述，如果 _savedWorkoutsRepository.CountForUserAsync 是同步的，一切都会顺利进行。

有人可以帮我弄清楚到底发生了什么吗？

Answer 1

您可能在实际代码中使用了 Wait 或 Result（不是此处发布的代码，它不完整）。这将 cause a deadlock 上 ASP.NET 经典。

具体来说，当您将任务传递给 await 时，默认情况下它会捕获 "current context" 并在该任务完成时使用它来恢复异步方法。然后代码块在任务上（即 Wait 或 Result）。问题是 ASP.NET classic 上的上下文一次只允许一个线程。因此，只要该线程在任务上被阻塞，它就是 "taking up" 该上下文，这实际上阻止了任务完成。因此，僵局。

请注意 ConfigureAwait(false) 不是解决方法；这充其量是一种解决方法。正确的解决方法是将 Wait / Result 替换为 await.

异步不适用于 EF + 工作单元 + Repo

Async not working with EF + Unit of Work + Repo

c#

entity-framework

repository

unit-of-work

async-await