Read AppSettings in ASP.NET Core 2.x

Today, I was rewriting an old ASP.NET MVC5 Demo project to ASP.NET Core, and found that the way we used to read Web.config by ConfigurationManager.AppSettings[] is no longer working. .NET Core has many new ways to achieve this. I picked one that suitable for my project. Here is how I do it.

The Classic ASP.NET Code

web.config

<appSettings>
  <add key="StorageConnectionString" value="DefaultEndpointsProtocol=https;AccountName=YOURACCOUNT;AccountKey=YOURKEY" />
  <add key="AzureStorageAccountContainer" value="YOURCONTAINER" />
</appSettings>

Controller

private static CloudBlobContainer GetBlobContainer()
{
    string connectionString = WebConfigurationManager.AppSettings["StorageConnectionString"];
    blobClient.GetContainerReference(WebConfigurationManager.AppSettings["AzureStorageAccountContainer"]);
    return container;
}

This is how we used to read web.config in ASP.NET. If you want to know more, please refer to my post《如何高逼格读取Web.config中的AppSettings》, which shows how to use a strong type configuration item. Now, in ASP.NET Core, we can do the same.

ASP.NET Core Settings Model

First, ASP.NET Core settings file is called appsettings.json, instead of web.config. In an ASP.NET Core application, web.config is only used by IIS when deployed to a Windows Server. It has nothing to do with ASP.NET Core itself.

The definition of appsettings.json is like:

{
    "Logging": {
        "IncludeScopes": false,
        "LogLevel": {
            "Default": "Debug",
            "System": "Information",
            "Microsoft": "Information"
        }
    }
}

To add our own configuration:

{
    "Logging": {
        "IncludeScopes": false,
        "LogLevel": {
            "Default": "Debug",
            "System": "Information",
            "Microsoft": "Information"
        }
    },
    "AppSettings": {
        "StorageConnectionString": "DefaultEndpointsProtocol=https;AccountName=YOURACCOUNTNAME;AccountKey=YOURKEY",
        "AzureStorageAccountContainer": "YOURCONTAINERNAME"
    }
}

Next, create a new C# Class, and add the properties that match your configuration file:

public class AppSettings
{
    public string StorageConnectionString { get; set; }
    public string AzureStorageAccountContainer { get; set; }
}

Open Startup.cs, add the code for Configure AppSettings.

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<AppSettings>(Configuration.GetSection("AppSettings"));
}

What this line of code does is whenever you use the type AppSettings in your code, it will return an instance of Configuration.GetSection("AppSettings"). .NET Core will do the type converting and mapping, which is the same as I did in my 《如何高逼格读取Web.config中的AppSettings》

Finally, in your Controller, modify the constructor like this:

private AppSettings AppSettings { get; set; }

public HomeController(IOptions<AppSettings> settings)
{
    AppSettings = settings.Value;
}

Then, we can use the strong type configuration values like this:

private CloudBlobContainer GetBlobContainer()
{
    string connectionString = AppSettings.StorageConnectionString;
    CloudStorageAccount storageAccount = CloudStorageAccount.Parse(connectionString);
    CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();
    CloudBlobContainer container =
        blobClient.GetContainerReference(AppSettings.AzureStorageAccountContainer);
    return container;
}

If you like to use the AppSettings on Razor Views (.cshtml), you can DI into the view itself:

@using Microsoft.Extensions.Options;
@inject IOptions<AppSettings> Settings

And use it like this:

@Settings.Value.Copyright

For more advanced scenarios, refer to Microsoft docs here.