c# - 依赖注入(inject) IDbConnection SqlConnection

Question

我有时会引发此异常:

System.InvalidOperationException: 'The ConnectionString property has not been initialized.'

我使用内置的依赖注入(inject):

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IDbConnection>(db => new SqlConnection(
                    Configuration.GetConnectionString("AppConnectionString")));

    services.AddScoped<IAppConfigurationRepository, AppConfigurationRepository>();
    services.AddScoped<IHomeworkingRequestRepository, HomeworkingRequestRepository>();
    services.AddScoped<IEmployeeRepository, EmployeeRepository>();
    services.AddScoped<IEmployeeService, EmployeeService>();
    services.AddScoped<IHomeworkingRequestService, HomeworkingRequestService>();
    services.AddMvc();
}

之前，我已经有这个错误了。代码services.AddScoped<IDbConnection>我改为services.AddTransient<IDbConnection>并解决了这个问题。但是现在我又遇到了错误。

编辑

请查找异常发生时的代码:

public class EmployeeRepository : IEmployeeRepository
{
    private readonly IDbConnection _connection;

    public EmployeeRepository(IDbConnection connection)
    {
        _connection = connection;
    }

    public IEnumerable<Employee> GetAllActiveEmployees()
    {
        string query = @"
           SELECT
               FirstName
              ,LastName
              ,BusinessUnit
          FROM Employees";

        using (var db = _connection)
        {
            _connection.Open(); // <-- The exception is thrown here
            return db.Query<Employee>(query);
        }
    }
 }

还请找到完整的堆栈跟踪:

at System.Data.SqlClient.SqlConnection.PermissionDemand()
   at System.Data.SqlClient.SqlConnectionFactory.PermissionDemand(DbConnection outerConnection)
   at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
   at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
   at System.Data.SqlClient.SqlConnection.Open()
   at Homeworking.Dal.EmployeeRepository.GetAllActiveEmployees() in C:\Users\florian.nouri\source\repos\Homeworking\Homeworking.Repository\EmployeeRepository.cs:line 42
   at Homeworking.Service.EmployeeService.GetAllEmployees() in C:\Users\florian.nouri\source\repos\Homeworking\Homeworking.Service\EmployeeService.cs:line 22
   at Homeworking.Service.HomeworkingRequestService.GetAllEmployees() in C:\Users\florian.nouri\source\repos\Homeworking\Homeworking.Service\HomeworkingRequestService.cs:line 23
   at Homeworking.Web.Controllers.AppController.Index() in C:\Users\florian.nouri\source\repos\Homeworking\Homeworking.Web\Controllers\AppController.cs:line 22
   at lambda_method(Closure , Object , Object[] )
   at Microsoft.Extensions.Internal.ObjectMethodExecutor.Execute(Object target, Object[] parameters)
   at Microsoft.AspNetCore.Mvc.Internal.ActionMethodExecutor.SyncActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeActionMethodAsync()

Answer 1

using (var db = _connection)

这很糟糕。您为同一连接创建了一个新变量，因此在使用 block 完成后，您的连接将被释放。你不应该这样做。如果你使用容器来创建东西，容器应该处理那些它不再需要的实例。

最有可能发生的情况是您的 _connection 变量被处理掉，并且任何从容器获取连接的类(在 Scoped 的情况下)或任何已经拥有此变量并使用它的类第二次因为它是一个实例字段，将使用已经处理好的连接。