如何使用控制台应用程序中的通用主机从 appsettings 中获取连接字符串？

Question

Environment:

<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.1.7" />

SQL Server 2016
.NET Core 3.1

I have a working snippet of a console application below that gets connection string out of appsettings but it feels like I have too much code and I should be able to combine some of this but not sure how.

class Program
{
    static void Main(string[] args)
    {
        CreateHostBuilder(args);
    }

    public static void CreateHostBuilder(string[] args)
    {
        IConfiguration config = new ConfigurationBuilder()
            .AddJsonFile(Path.Combine(Directory.GetCurrentDirectory(), "appsettings.json"), true, true)
            .Build();

        var host = Host.CreateDefaultBuilder(args)
            .ConfigureServices((context, services) =>
            {
                services.AddTransient<App>();
                services.AddDbContext<SchoolContext>(options =>
                options.UseSqlServer(config["ConnectionStrings:MyDatabase"]));
            })
            .Build();

        ActivatorUtilities.CreateInstance<Startup>(host.Services);
    }
}

Update
Based on @andy's answer below...

class Program
{
    static void Main(string[] args)
    {
        var host = CreateHostBuilder(args).Build();
        host.RunAsync().GetAwaiter();

        ActivatorUtilities.CreateInstance<Startup>(host.Services);
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args).ConfigureServices((context, services) =>
        {
            var config = context.Configuration; // grab from here
            services.AddTransient<App>();
            services.AddDbContext<SchoolContext>(options =>
            options.UseSqlServer(config["ConnectionStrings:MyDatabase"]));
        });
}

Answer 1

You already created a default builder which includes your appsettings.json file. You can get at it by grabbing it from the context in ConfigureServices

class Program
{
    static Task Main(string[] args)
    {
        var host = CreateHostBuilder(args).Build();
        return host.RunAsync();
    }

    /* or you can use a synchronous main:
    static void Main(string[] args)
    {
        var host = CreateHostBuilder(args).Build();
        host.Run();
    }
    */

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args).ConfigureServices((context, services) =>
        {
            var config = context.Configuration; // grab from here
            services.AddTransient<App>();
            services.AddDbContext<SchoolContext>(options =>
                options.UseSqlServer(config["ConnectionStrings:MyDatabase"]));
        });
}

I also refactored your code a bit to show you a typical create/build/run scenario with a generic host.

ETA

Here is some shameless self-promotion: I came up with a way to move this logic to the good ol' IWebHostBuilder / Startup.cs pattern that we all know and love. If interested, check this out .