How to check if a section in MVC Core configuration file exist?

问题

How can I check if a specific section in loaded ASP.NET Core configuration file exist?

I have a JSON configuration file that I load it in Startup class via ConfigurationBuilder.AddJsonFile method.

This JSON file is an array with this layout:

{
   "Url": "",
   "Regex": [ "", "" ],
   "Keys": {
     "Title": "",
     "Description": "",
     "Keywords": [ "" ]
   }
}

But some of them doesn't have Keys. I tried to check return type of section.GetSection("Keys") against null, But it doesn't return null even if Keys section isn't present.

回答1:

Use GetChildren method:

var keysExists = Configuration.GetChildren().Any(x => x.Key == "Keys"));

回答2:

Also it is possible to use use Exists extension method from Microsoft.Extensions.Configuration.Abstractions. Exapmle:

var section = Configuration.GetSection("Keys")
var sectionExists = section.Exists();

or

public bool IsExistsConfigurationSection(string sectionKey)
{
    return Configuration.GetSection(sectionKey).Exists();
}

回答3:

I would use ConfigurationExtensions.Exists(IConfigurationSection) method as Алексей Сидоров suggested because this method as it's said in the official documentation

determines whether the section has a Value or has children

Not only children.

Here are my extension methods with checking section existence which might be helpful for someone.

Usage:

_configRoot.GetSectionChecked(nameof(Site));
// instead of 
// IConfigurationSection section = _configRoot.GetSection(nameof(Site));
// if (!section.Exists())
//     throw new ArgumentException(nameof(Site));

services.ConfigureSection<Site>(_configRoot);
// instead of 
// services.Configure<Site>("Site", _config);

services.ConfigureSection<PostsConfig>(_configRoot.GetSection(nameof(Site)), nameof(Site.Posts));
// instead of 
// services.Configure<PostsConfig>(_configRoot.GetSection(nameof(Site)).GetSection(nameof(Site.Posts)));

Extension methods:

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using System;

public static class ConfigurationExtensions
{
    public static IConfigurationSection GetSectionChecked(this IConfiguration config, string sectionName)
    {
        var section = config.GetSection(sectionName);
        CheckSection(section);
        return section;
    }

    public static IServiceCollection ConfigureSection<TOptions>(this IServiceCollection services, IConfiguration config, string sectionName = null) 
        where TOptions : class
    {
        string typeName = sectionName ?? typeof(TOptions).Name;
        IConfigurationSection section = config.GetSectionChecked(typeName);
        return services.Configure<TOptions>(section);
    }

    public static IServiceCollection ConfigureSection<TOptions>(this IServiceCollection services, IConfigurationSection section, string sectionName = null)
        where TOptions : class
    {
        CheckSection(section);
        return services.ConfigureSection<TOptions>((IConfiguration)section, sectionName);
    }

    private static void CheckSection(IConfigurationSection section)
    {
        if (!section.Exists())
            throw new ArgumentException($"Configuration section '{section.Path}' doesn't exist.");
    }
}

来源：https://stackoverflow.com/questions/61779244/how-to-know-if-a-key-exists-on-iconfiguration