在ASP.NET Core中访问配置选项：选项模式

Question

I have an ASP.NET Core application. I try to use the options pattern but it does not seem to work.

I have the following appsettings.json :

{
    "ConnectionStrings": {
        "MyTablesConnectionString": "Default[...];EndpointSuffix=core.windows.net"
    },

    "Logging": { "IncludeScopes": false, "LogLevel": { "Default": "Warning" }  }
}

The following ConnectionStrings class

public class ConnectionStrings {
    public ConnectionStrings()  {
        MyTablesConnectionString = "default value";
    }

    public string MyTablesConnectionString { get; set; }
}

And here is my Startup.cs

public Startup(IHostingEnvironment env)
{
    var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true)
        .AddEnvironmentVariables();
    Configuration = builder.Build();

    // HERE IS THE GOOD VALUE !!!!!!!!
    Debug.WriteLine($"Connection string is:{Configuration["ConnectionStrings:MyTablesConnectionString"]}");
}

public void ConfigureServices(IServiceCollection services)
{
    // Adds services required for using options.
    services.AddOptions();
    // Register the IConfiguration instance which "ConnectionStrings" binds against.
    services.Configure<ConnectionStrings>(Configuration);

    // Add framework services.
    services.AddMvc();            
}

However, when using it on the dev machine with the following controller

private readonly ConnectionStrings azureConnectionString;
public HelloWorldController(IOptions<ConnectionStrings> optionsAccessor)
{
    // HERE IS THE "DEFAULT" VALUE ?!!!!!!!!
    azureConnectionString = optionsAccessor.Value;            
}

I see that the "default value" instead of the value from the json file (invalid one) is used. Am I missing something?

Answer 1

You need to bind the ConnectionStrings section, like so:

services.Configure<ConnectionStrings>(Configuration.GetSection("ConnectionStrings"));

At the moment it is expecting to find a property "ConnectionStrings" or "Logging" from your class, since you are binding the root.

Answer 2

Alternatively, configure all options automatically

PM> Install-Package Register.Options.Asp.Net.Core

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.ConfigureOptionsFromAssemblies(configuration, new List<Assembly>()
    {
        typeof(ConnectionStrings).Assembly
    });

   ...
}

Disclaimer author of package