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c# - 依赖注入 IDbConnection SqlConnection

问题描述

我有时会提出这个异常：

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。services.AddScoped<IDbConnection>我改成的代码services.AddTransient<IDbConnection>解决了这个问题。但现在我又遇到了错误。

编辑

发生异常时请查找代码：

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);
        }
    }
 }

另请查找完整的堆栈跟踪：

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()

标签： c#asp.net-coredependency-injection

解决方案

using (var db = _connection)

这是不好的。您为同一连接创建一个新变量，因此在 using 块完成后，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。

最有可能发生的事情是您的_connection变量已被释放，并且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第二次使用它的类，因为它是一个实例字段，将使用已经部署的连接。

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