c# - .Net Core 3 控制台无法从 appsettings 获取连接字符串

Question

我已经创建了一个 .Net Core 3.1 控制台应用程序，并且正在尝试使用 EntityFramework 来处理我的 Oracle 数据库。我发现了一些关于这个主题的视频和文章，但它们都涉及 HTTP 应用程序而不是控制台应用程序。

我使用 powershell 命令构建表并创建一个名为 ModelContext 的 DbContext。在我的 Program.cs 中，我有一个 Host.CreateDefaultBuilder 并添加了 services.AddDbContext 并将连接字符串放入我的 appsettings.json 文件中。

我的问题是，当它试图将上下文添加到主机中的服务时，我无法让它从应用程序设置中提取连接字符串。我在 Configuration.GetConnectionString 上收到设计时错误，提示 “Configuration does not contain a definition for ‘GetConnectionString’”。

我通过 NuGet 安装了 System.Configuration.ConfigurationManager 并在我的 Program.cs 文件中添加了 using System.Configuration。如何从我的主机构建器中的应用程序设置中获取连接字符串？

程序.cs

var host = Host.CreateDefaultBuilder().ConfigureServices((context, services) =>
                {
                    services.AddTransient<IAppHost, AppHost>();
                    services.AddTransient<IFileManager, FileManager>();
                    services.AddTransient<IDataManager, DataManager>();

                    var connstring = Configuration.GetConnectionString("DbConnection");
                    services.AddDbContext<ModelContext>(options =>
                    {
                        options.UseOracle(connstring);
                    });

                    services.AddLogging(builder =>
                    {
                        builder.AddNLog("nlog.config");
                    });
                }).Build();

更新代码

这是我的 Program.cs 文件中的所有代码。不幸的是，我不确定我做了什么导致这种情况，但现在我的 FileManger 类出现错误。

Unable to resolve service for type 'Microsoft.Extensions.Logging.Logger`1[EmailUpdateExport.FileManager]' while attempting to activate 'EmailUpdateExport.FileManager'.

我什至取消了从我刚刚添加的应用程序设置中获取 DbConnection 的代码，但仍然出现错误。

class Program
        {
            static void Main(string[] args)
            {
                //Calls the Builder so that you can get to the appsettings.
                var builder = new ConfigurationBuilder();
                BuildConfig(builder);
    
                var logger = NLog.Web.NLogBuilder.ConfigureNLog("nlog.config").GetCurrentClassLogger();
    
                try
                {
                    logger.Debug("Initializing Program.Main");
                    
                    var host = Host.CreateDefaultBuilder()
                        .ConfigureAppConfiguration((hostingContext, config) =>
                        {
                            config.SetBasePath(Path.Combine(AppContext.BaseDirectory));
                            config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
                        })
                        .ConfigureServices((context, services) =>
                        {
                            services.AddTransient<IAppHost, AppHost>();
                            services.AddTransient<IFileManager, FileManager>();
                            services.AddTransient<IDataManager, DataManager>();
    
                            var connstring = context.Configuration["ConnectionStrings:DbConnection"];
                            services.AddDbContext<ModelContext>(options =>
                            {
                                options.UseOracle(connstring);
                            });
    
                            services.AddLogging(builder =>
                            {
                                builder.AddNLog("nlog.config");
                            });
                        }).Build();
    
    
                    //Create instance of AppHost and call the Run() function to run the business logic.
                    var svc = ActivatorUtilities.CreateInstance<AppHost>(host.Services);
                    svc.Run();
                }
                catch (Exception ex)
                {
                    //NLog: catch setup errors
                    logger.Error("Stopped program setup with Error. {0} | {1} | {2}", ex.Message, ex.StackTrace, ex.InnerException);
                    throw;
                }
                finally
                {
                    // Ensure to flush and stop internal timers/threads before application-exit
                    NLog.LogManager.Shutdown();
                }
            }
    
            static void BuildConfig(IConfigurationBuilder builder)
            {
                //Sets up the ability to talk to the appsettings.json 
                builder.SetBasePath(Directory.GetCurrentDirectory())
                    .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
                    .AddJsonFile($"appsettings.{Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production"}.json", optional: true)
                    .AddEnvironmentVariables();
            }
    
        }

这是我的 FileManger，以防有人对此提出建议。

public class FileManager : IFileManager
    {
        private readonly ILogger<FileManager> _log;
        private readonly IConfiguration _configuration;

        public FileManager(Logger<FileManager> log, IConfiguration config)
        {
            _log = log;
            _configuration = config;
        }

        public void CreateFileDirectory(string FilePath)
        {
            try
            {
                //create the target location if it doesn't exist
                if (!Directory.Exists(FilePath))
                {
                    _log.LogInformation("Create directory: " + FilePath);
                    Directory.CreateDirectory(FilePath);
                }
            }
            catch (Exception ex)
            {
                _log.LogError("Error creating Export directory. {0} | {1} | {2} ", ex.Message, ex.StackTrace, ex.InnerException);
            }
        }


        public void CopyFile(string sourceLocation, string destinationLocation, string fileName)
        {
            _log.LogInformation("Source location: {0} | Destination location: {1} | File Name: {2}", sourceLocation, destinationLocation, fileName);

            var sourceFile = Path.Combine(sourceLocation, fileName);
            var destinationFile = Path.Combine(destinationLocation, fileName);

            _log.LogInformation("SourceFilePath: {0}", sourceFile);
            _log.LogInformation("DestinationFilePath: {0}", destinationFile);

            try
            {
                //check to make sure source exists first
                if (File.Exists(sourceFile))
                {
                    //get rid of the file if it already exists. Shouldn't be an issue most to the time.
                    if (File.Exists(destinationFile))
                    {
                        File.Delete(destinationFile);
                    }
                    File.Copy(sourceFile, destinationFile);
                }
                else
                    _log.LogInformation("Source file does not exist. File: {0}", sourceFile);

            }
            catch (Exception ex)
            {
                _log.LogError("Error copying file. Source: {0} | Destination: {1}. {2} | {3} | {4}", sourceFile, destinationFile, ex.Message, ex.StackTrace, ex.InnerException);
                throw;
            }
                
    }

Answer 1

这是您可以做到的一种方式。此示例根据键名访问配置值。将此配置映射到一个类是个好主意，这样检索设置就不容易出错。您可以查看我在评论中发布的链接，了解有关如何操作的详细信息。

var host = Host.CreateDefaultBuilder()
                .ConfigureAppConfiguration((hostingContext, config) =>
                {
                    config.SetBasePath(Path.Combine(AppContext.BaseDirectory));
                    config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
                })
                .ConfigureServices((hostContext, services) =>
                {
                    services.AddDbContext<ModelContext>(options =>
                            {
                                options.UseSqlServer(hostContext.Configuration["ConnectionStrings:DefaultConnection"]);
                            }, ServiceLifetime.Transient)
                    // add other services
                })
                .UseConsoleLifetime()
                .Build();

应用设置.json:

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=localhost;Database=myDB;Trusted_Connection=True;"
  },
  .....
}