c# - 工作单元的依赖注入(inject)

Question

我有一个问题，我的工作单元在调用时不会创建 AppSettings 实例。 Unitofwork 用于我的存储库数据层。

出现这个错误:

An unhandled exception occurred while processing the request. NullReferenceException: Object reference not set to an instance of an object. Core.UnitOfWork..ctor() in UnitOfWork.cs, line 24

Stack Query Cookies Headers NullReferenceException: Object reference not set to an instance of an object. Core.UnitOfWork..ctor() in UnitOfWork.cs + _connection = new SqlConnection(App.GetConnectionString()); Core.Service.UserService.Login(User entity) in UserService.cs + using (var uow = new UnitOfWork(/connStr/)) SRTManagement.Controllers.LoginController+d__6.MoveNext() in LoginController.cs + var _user = service.Login(user);

启动.cs

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddTransient<IAppSettings,AppSettings>();
        services.AddMvc();
    }

IAppSettings.cs

namespace Core.Etc
{
    public interface IAppSettings
    {
        string GetConnectionString();
    }
}

AppSettings.cs

namespace Core.Etc
{
    public class AppSettings : IAppSettings
    {
        public readonly string _connectionString;

        public AppSettings(IConfiguration configuration)
        {
            _connectionString = configuration.GetConnectionString("DefaultConnection");
        }

        public string GetConnectionString()
        {
            return _connectionString;
        }
    }
}

UnitOfWork.cs

namespace Core
{
    public class UnitOfWork : IUnitOfWork
    {
        private IDbConnection _connection;
        private IDbTransaction _transaction;
        private IUserRepository _user;
        private IRoleRepository _role;
        private IAppSettings App;
        private bool _disposed;
        private bool _token;

        public UnitOfWork()
        {
            _connection = new SqlConnection(App.GetConnectionString());
            _connection.Open();
            _transaction = _connection.BeginTransaction();
            _token = false;
        }

        public IUserRepository UserRepository
        {
            get { return _user ?? (_user = new UserRepository(_transaction)); }
        }

        public IRoleRepository RoleRepository
        {
            get { return _role ?? (_role = new RoleRepository(_transaction)); }
        }

        public bool Success()
        {
            return _token;
        }

        public void Commit()
        {
            try
            {
                _transaction.Commit();
                _token = true;
            }
            catch
            {
                _transaction.Rollback();
                _token = false;
                throw;
            }
            finally
            {
                _transaction.Dispose();
                _transaction = _connection.BeginTransaction();
                ResetRepositories();
            }
        }

        private void ResetRepositories()
        {
            _user = null;
            _role = null;
            App = null;
        }

        public void Dispose()
        {
            DisposeConn(true);
            GC.SuppressFinalize(this);
        }

        private void DisposeConn(bool disposing)
        {
            if (!_disposed)
            {
                if (disposing)
                {
                    if(_transaction != null)
                    {
                        _transaction.Dispose();
                        _transaction = null;
                    }
                    if(_connection != null)
                    {
                        _connection.Dispose();
                        _connection = null;
                    }
                }
                _disposed = true;
            }
        }

        ~UnitOfWork()
        {
            DisposeConn(false);
        }
    }
}

Answer 1

IAppSettings 没有被注入(inject)到您的 UnitOfWork 中，因此当您调用它时它将为 null

public class UnitOfWork : IUnitOfWork {
    private IDbConnection _connection;
    private IDbTransaction _transaction;
    private IUserRepository _user;
    private IRoleRepository _role;
    private IAppSettings App;
    private bool _disposed;
    private bool _token;

    public UnitOfWork(IAppSettings App) {
        this.App = App;
        _connection = new SqlConnection(App.GetConnectionString());
        _connection.Open();
        _transaction = _connection.BeginTransaction();
        _token = false;
    }
    //Remove the rest of the code for brevity
}

假设 UnitOfWork 也已注册到服务集合。

public void ConfigureServices(IServiceCollection services) {
    services.AddTransient<IAppSettings, AppSettings>();
    services.AddTransient<IUnitOfWork, UnitOfWork>();
    services.AddMvc();
}

我还建议重新考虑当前的设计，避免将 UoW 与实现问题紧密耦合，例如 SqlConnection。

如果继续使用 ADO，则考虑使用 IDbConnectionFactory 抽象。

public class MyDbConnectionFactory : IDbConnectionFactory {
    private readonly IAppSettings appSettings;

    public MyDbConnectionFactory(IAppSettings appSettings) {
        this.appSettings = appSettings;
    }

    public IDbConnection CreateConnection() {
        return new SqlConnection(appSettings.GetConnectionString());
    }
}

这将使 UoW 重构为

public class UnitOfWork : IUnitOfWork {
    private IDbConnection _connection;
    private IDbTransaction _transaction;
    private IUserRepository _user;
    private IRoleRepository _role;
    private bool _disposed;
    private bool _token;

    public UnitOfWork(IDbConnectionFactory factory) {
        _connection = factory.CreateConnection();
        _connection.Open();
        _transaction = _connection.BeginTransaction();
        _token = false;
    }

    //Remove the rest of the code for brevity
}

使用常规服务注册

public void ConfigureServices(IServiceCollection services) {
    services.AddTransient<IAppSettings, AppSettings>();
    services.AddTransient<IDbConnectionFactory, MyDbConnectionFactory>();
    services.AddTransient<IUnitOfWork, UnitOfWork>();
    services.AddMvc();
}