控制台应用程序 - DbContext 实例不能在 OnConfiguring 中使用

Question

我正在使用 Asp.Net Core 控制台应用程序和 Entiy Framework Core 以及工作单元存储库模式。当我使用多线程函数时，出现此错误：

DbContext instance cannot be used inside OnConfiguring since it is still being configured at this point. This can happen if a second operation is started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.

UnitOfwork.cs

public interface IUnitOfWork : IDisposable
{
    void Commit();
    ApplicationDbContext GetContext();
}

public class UnitOfWork : IUnitOfWork
{
    private readonly ApplicationDbContext _applicationDbContext;

    public UnitOfWork(ApplicationDbContext applicationDbContext)
    {
        _applicationDbContext = applicationDbContext;
    }

    public void Commit()
    {
        try
        {
            _applicationDbContext.SaveChanges();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex);
        }
    }

    public ApplicationDbContext GetContext()
    {
        return _applicationDbContext;
    }

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

IRepository.cs

public interface IGenericRepository<T>
    where T : class, IEntity
{
    List<T> GetAll(Expression<Func<T, bool>> filter = null,
        Func<IQueryable<T>, IOrderedEnumerable<T>> orderBy = null,
        string includeProperties = "");

    T FindSingle(int id);

    T FindBy(Expression<Func<T, bool>> predicate, string includeProperties = "");

    void Add(T toAdd);

    void Update(T toUpdate);

    void Delete(int id);

    void Delete(T entity);
}

Repository.cs

public class GenericRepository<T> : IGenericRepository<T>
    where T : class, IEntity
{
    private readonly IUnitOfWork _unitOfWork;

    public GenericRepository(IUnitOfWork unitOfWork)
    {
        _unitOfWork = unitOfWork;
    }

    public virtual List<T> GetAll(Expression<Func<T, bool>> filter = null,
        Func<IQueryable<T>, IOrderedEnumerable<T>> orderBy = null,
        string includeProperties = "")
    {
        IQueryable<T> query = _unitOfWork.GetContext().Set<T>();

        if (filter != null)
        {
            query = query.Where(filter);
        }

        foreach (string includeProperty in includeProperties.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
        {
            query = query.Include(includeProperty);
        }

        if (orderBy != null)
        {
            return orderBy(query).ToList();
        }

        return query.ToList();
    }

    public virtual T FindSingle(int id)
    {
        return _unitOfWork.GetContext().Set<T>().Find(id);
    }

    public virtual T FindBy(Expression<Func<T, bool>> predicate, string includeProperties = "")
    {
        IQueryable<T> query = _unitOfWork.GetContext().Set<T>();
        foreach (string includeProperty in includeProperties.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
        {
            query = query.Include(includeProperty);
        }
        return query.Where(predicate).FirstOrDefault();
    }

    public virtual void Add(T toAdd)
    {
        _unitOfWork.GetContext().Set<T>().Add(toAdd);
    }

    public virtual void Update(T toUpdate)
    {
        _unitOfWork.GetContext().Entry(toUpdate).State = EntityState.Modified;
    }

    public virtual void Delete(int id)
    {
        T entity = FindSingle(id);
        _unitOfWork.GetContext().Set<T>().Remove(entity);
    }

    public virtual void Delete(T entity)
    {
        _unitOfWork.GetContext().Set<T>().Remove(entity);
    }
}

商业服务；

public interface IUserService
{
    void CreateUser(UserEntity userEntity, bool commit = false);
}
public class UserService : IUserService
{
    private readonly IGenericRepository<UserEntity> _userRepository;
    private readonly IUnitOfWork _unitOfWork;

    public UserService(IUnitOfWork unitOfWork, IGenericRepository<UserEntity> userRepository)
    {
        _unitOfWork = unitOfWork;
        _userRepository = userRepository;
    }

    public void CreateUser(UserEntity userEntity, bool commit = false)
    {
        try
        {
            _userRepository.Add(userEntity);

            if (commit)
                _unitOfWork.Commit();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
    }
}

控制台Main.cs；

class Program
{
    public static ServiceProvider ServiceProvider;

    static void Main(string[] args)
    {
        InitializeIoc();

        Task.Run(() => { FuncA(); });

        Task.Run(() => { FuncB(); });

        Console.ReadLine();
    }

    private static void InitializeIoc()
    {
        ServiceProvider = new ServiceCollection()
            .AddDbContext<ApplicationDbContext>()
            .AddTransient<IUnitOfWork, UnitOfWork>()
            .AddTransient(typeof(IGenericRepository<>), typeof(GenericRepository<>))
            .AddTransient<IUserService, UserService>()
            .BuildServiceProvider();
    }

    private static void FuncA()
    {
        var userService = ServiceProvider.GetService<IUserService>();
        for (int i = 0; i < 100; i++)
        {
            userService.CreateUser(new UserEntity { FirstName = "FuncA_" + Guid.NewGuid(), LastName = "Last", CreatedDate = DateTime.Now }, false);
        }
    }
    private static void FuncB()
    {
        var userService = ServiceProvider.GetService<IUserService>();
        for (int i = 0; i < 100; i++)
        {
            userService.CreateUser(new UserEntity { FirstName = "FuncB_" + Guid.NewGuid(), LastName = "Last", CreatedDate = DateTime.Now }, false);
        }
    }
}

我该如何解决这个问题？

感谢您的帮助。

Answer 1

问题是使用过的 AddDbContext 将你的 ApplicationDbContext 注册到 ServiceLifetime.Scoped，但你没有创建范围因此它有效地作为单例工作，因此被共享和同时访问导致相关异常的多个线程（可能还有许多其他线程，因为 DbContext 不是线程安全的）。

解决方案是使用范围，例如调用 CreateScope 并使用返回的对象 ServiceProvider 属性来解析服务：

private static void FuncA()
{
    using (var scope = ServicePropvider.CreateScope())
    {
        var userService = scope.ServiceProvider.GetService<IUserService>();
        // Do something ...
    }
}

private static void FuncB()
{
    using (var scope = ServicePropvider.CreateScope())
    {
        var userService = scope.ServiceProvider.GetService<IUserService>();
        // Do something ...
    }
}

控制台应用程序 - DbContext 实例不能在 OnConfiguring 中使用

Console Application - DbContext instance cannot be used inside OnConfiguring

multithreading

dependency-injection

console-application

.net-core

ef-core-2.0