将Env Conn字符串注入.NET Core 2.0 w / EF Core DbContext中的不同类lib比启动prj并实现IDesignTimeDbContextFactory

Question

老实说，我不敢相信这有多难......首先是我要求的要求：

• 实现实体框架Core IDesignTimeDbContextFactory ， IDbContextFactory被重命名为开发人员不会混淆它的作用
• 我不想不止一次加载appsettings.json 。 一个原因是因为我的迁移在MyClassLibrary.Data域中运行，并且该类库中没有appsettings.js文件，我将不得不Copy to Output Directory appsettings.js 。 另一个原因是它不是很优雅。

所以这就是我目前的工作方式：

using System;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;
using Microsoft.Extensions.Configuration;
using AppContext = Tsl.Example.Data.AppContext;

namespace Tsl.Example
{
    public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<AppContext>
    {
        public AppContext CreateDbContext(string[] args)
        {
            string basePath = AppDomain.CurrentDomain.BaseDirectory;

            string envName = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");

            IConfigurationRoot configuration = new ConfigurationBuilder()
                .SetBasePath(basePath)
                .AddJsonFile("appsettings.json")
                .AddJsonFile($"appsettings.{envName}.json", true)
                .Build();

            var builder = new DbContextOptionsBuilder<AppContext>();

            var connectionString = configuration.GetConnectionString("DefaultConnection");

            builder.UseMySql(connectionString);

            return new AppContext(builder.Options);
        }
    }
}

这是我的Program.cs：

using System.IO;
using System.Reflection;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Logging;

namespace Tsl.Example
{
    public class Program
    {
        public static void Main(string[] args)
        {
            BuildWebHost(args).Run();
        }

        //public static IWebHost BuildWebHost(string[] args) =>
        //    WebHost.CreateDefaultBuilder(args)
        //        .UseStartup<Startup>()
        //        .Build();

        /// <summary>
        /// This the magical WebHost.CreateDefaultBuilder method "unboxed", mostly, ConfigureServices uses an internal class so there is one piece of CreateDefaultBuilder that cannot be used here
        /// https://andrewlock.net/exploring-program-and-startup-in-asp-net-core-2-preview1-2/
        /// </summary>
        /// <param name="args"></param>
        /// <returns></returns>
        public static IWebHost BuildWebHost(string[] args)
        {
            return new WebHostBuilder()
                .UseKestrel()
                .UseContentRoot(Directory.GetCurrentDirectory())
                .ConfigureAppConfiguration((hostingContext, config) =>
                {
                    IHostingEnvironment env = hostingContext.HostingEnvironment;

                    config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);

                    if (env.IsDevelopment())
                    {
                        var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
                        if (appAssembly != null)
                        {
                            config.AddUserSecrets(appAssembly, optional: true);
                        }
                    }

                    config.AddEnvironmentVariables();

                    if (args != null)
                    {
                        config.AddCommandLine(args);
                    }
                })
                .ConfigureLogging((hostingContext, logging) =>
                {
                    logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
                    logging.AddConsole();
                    logging.AddDebug();
                })
                //.UseIISIntegration()
                .UseDefaultServiceProvider((context, options) =>
                {
                    options.ValidateScopes = context.HostingEnvironment.IsDevelopment();
                })
                .UseStartup<Startup>()
                .Build();
        }
    }
}

这是我的Startup.cs：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using ServiceStack;
using Tsl.Example.Interfaces;
using Tsl.Example.Provider;
using AppContext = Tsl.Example.Data.AppContext;

namespace Tsl.Example
{
    public class Startup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddTransient<IAppContext, AppContext>();
            services.AddTransient<IExampleDataProvider, ExampleDataProvider>();
        }

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        { 
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseServiceStack(new AppHost());
        }
    }
}

我想要做的是使用IOptions模式 ，所以我创建了这个类：

namespace Tsl.Example
{
    /// <summary>
    /// Strongly typed settings to share in app using the .NET Core IOptions pattern
    /// https://andrewlock.net/how-to-use-the-ioptions-pattern-for-configuration-in-asp-net-core-rc2/
    /// </summary>
    public class AppSettings
    {
        public string DefaultConnection { get; set; }
    }
}

将此行添加到Startup.ConfigureServices ：

  services.Configure<AppSettings>(options => Configuration.GetSection("AppSettings").Bind(options));

然后尝试将IDesignTimeDbContextFactory<AppContext>实现更改为：

public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<AppContext>
{
    private readonly AppSettings _appSettings;

    public DesignTimeDbContextFactory(IOptions<AppSettings> appSettings)
    {
        this._appSettings = appSettings.Value;
    }

    public AppContext CreateDbContext(string[] args)
    {
        var builder = new DbContextOptionsBuilder<AppContext>();
        builder.UseMySql(_appSettings.DefaultConnection);
        return new AppContext(builder.Options);
    }
}

不幸的是，这不起作用，因为未注入public DesignTimeDbContextFactory(IOptions<AppSettings> appSettings)构造函数的Ioptions<AppSettings>参数。 我假设这是因为IDesignTimeDbContextFactory<AppContext>是在设计时调用的，并且依赖注入在.NET Core应用程序设计时并没有“准备就绪”？

我认为使用实现IDesignTimeDbContextFactory的Entity Framework Core 2.0模式注入特定于环境的连接字符串是如此困难，并且不必IDesignTimeDbContextFactory复制和加载appsettings.json等设置文件。

Answer 1

如果您正在寻找从appsettings.json文件初始化的自定义设置类中获取数据库连接字符串的解决方案 - 这就是您可以执行此操作的方法。 不幸的是，您无法通过DI将IOptions注入IDesignTimeDbContextFactory实现构造函数。

public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<AppContext>
{
   public AppContext CreateDbContext(string[] args)
   {
       // IDesignTimeDbContextFactory is used usually when you execute EF Core commands like Add-Migration, Update-Database, and so on
       // So it is usually your local development machine environment
       var envName = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");

       // Prepare configuration builder
       var configuration = new ConfigurationBuilder()
           .SetBasePath(Path.Combine(Directory.GetCurrentDirectory()))
           .AddJsonFile("appsettings.json", optional: false)
           .AddJsonFile($"appsettings.{envName}.json", optional: false)
           .Build();

       // Bind your custom settings class instance to values from appsettings.json
       var settingsSection = configuration.GetSection("Settings");
       var appSettings = new AppSettings();
       settingsSection.Bind(appSettings);

       // Create DB context with connection from your AppSettings 
       var optionsBuilder = new DbContextOptionsBuilder<AppContext>()
           .UseMySql(appSettings.DefaultConnection);

       return new AppContext(optionsBuilder.Options);
   }
}

当然，在AppSettings类和appsettings.json您可以拥有构建连接字符串的更复杂的逻辑。 例如，像这样：

public class AppSettings
{
   public bool UseInMemory { get; set; }

   public string Server { get; set; }
   public string Port { get; set; }
   public string Database { get; set; }
   public string User { get; set; }
   public string Password { get; set; }

   public string BuildConnectionString()
   {
       if(UseInMemory) return null;

       // You can set environment variable name which stores your real value, or use as value if not configured as environment variable
       var server = Environment.GetEnvironmentVariable(Host) ?? Host;
       var port = Environment.GetEnvironmentVariable(Port) ?? Port;
       var database = Environment.GetEnvironmentVariable(Database) ?? Database;
       var user = Environment.GetEnvironmentVariable(User) ?? User;
       var password = Environment.GetEnvironmentVariable(Password) ?? Password;

       var connectionString = $"Server={server};Port={port};Database={database};Uid={user};Pwd={password}";

       return connectionString;
   }
}

只有存储在appsettings.json值：

{
  "Settings": {
    "UseInMemory": false,
    "Server": "myserver",
    "Port": "1234",
    "Database": "mydatabase",
    "User": "dbuser",
    "Password": "dbpassw0rd"
  }
}

密码和用户存储在环境变量中：

{
  "Settings": {
    "UseInMemory": false,
    "Server": "myserver",
    "Port": "1234",
    "Database": "mydatabase",
    "User": "MY-DB-UID-ENV-VAR",
    "Password": "MY-DB-PWD-ENV-VAR"
  }
}

在这种情况下，您应该这样使用它：

// Create DB context with connection from your AppSettings 
var optionsBuilder = new DbContextOptionsBuilder<AppContext>();
if(appSettings.UseInMemory) {
optionsBuilder = appSettings.UseInMemory
   ? optionsBuilder.UseInMemoryDatabase("MyInMemoryDB")
   : optionsBuilder.UseMySql(appSettings.BuildConnectionString());

return new AppContext(optionsBuilder.Options);

Answer 2

我对你的问题有点困惑。 您是否正在为DbContext使用依赖注入，或者您是否尝试初始化并构建特定的上下文？

我正在做我在我的一个解决方案中描述的内容。 这是我的解决方案结构：

• Corp.ApplicationName.Data
• Corp.ApplicationName.Web

Startup.cs

public Startup(IHostingEnvironment env)
{
    IConfigurationBuilder builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", false, true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json")
        .AddEnvironmentVariables();
    // ...
}

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddDbContext<MyDbContext>(
        options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"),
        sqlOptions => sqlOptions.EnableRetryOnFailure()));

    // SQL configuration for non-injected dbcontext
    DbContextOptionsBuilder<MyDbContext> builder = new DbContextOptionsBuilder<MyDbContext>();
    builder.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"));
    services.AddSingleton(builder.Options);

    // ...
}

MyDbContext.cs

public class MyDbContext : IdentityDbContext<ApplicationUser>
{
    public MyDbContext(DbContextOptions options) : base(options) { }
}

如果您没有使用依赖项注入来传递DbContext，则可以通过注入DbContextOptions<MyDbContext>来访问SQL属性。

在这个例子中，appsettings文件只是每次读取一次，一切正常。