依赖注入 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：

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。services.AddScoped<IDbConnection>我改成的代码services.AddTransient<IDbConnection>解决了这个问题。但现在我又犯了这个错误。

编辑

请查找发生异常时的代码：

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)

这不好。您为同一个连接创建一个新变量，因此在使用块完成后，您的连接将被处理。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变量被释放，任何从容器获取连接的类（在 Scoped 的情况下）或任何已经具有此变量并由于它是实例字段而第二次使用它的类将使用已经处理的连接。