c# - .NET Core 配置管理器，读取一个键里面有一个冒号的字典，给出一个关于值的奇怪的错误消息，这是预期的吗？

Question

以下程序:

using System;
using System.Collections.Generic;
using Microsoft.Extensions.Configuration;

namespace ConsoleApp3
{
    class Program
    {
        static void Main()
        {
            var builder = new ConfigurationBuilder();
            builder.AddJsonFile("appsettings.json");

            var configuration = builder.Build();
            var options = configuration.Get<Options>();
            foreach (var kvp in options.Values)
                Console.WriteLine($"{kvp.Key}: {kvp.Value}");
        }
    }

    internal class Options
    {
        public Dictionary<string, bool> Values { get; } = new Dictionary<string, bool>();
    }
}

当给出这个 appsettings.json文件，完美运行:

{
    "Values": {
        "a": true,
        "b": false
    }
}

但更改 appsettings.json内容:

{
    "Values": {
        "a:b": true,
        "b": false
    }
}

我得到这个异常(exception):

Unhandled Exception: System.InvalidOperationException: Cannot create instance of type 'System.Boolean' because it is missing a public parameterless constructor.

堆栈跟踪:

   at Microsoft.Extensions.Configuration.ConfigurationBinder.CreateInstance(Type type)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.BindInstance(Type type, Object instance, IConfiguration config, BinderOptions options)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.BindDictionary(Object dictionary, Type dictionaryType, IConfiguration config, BinderOptions options)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.BindInstance(Type type, Object instance, IConfiguration config, BinderOptions options)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.BindProperty(PropertyInfo property, Object instance, IConfiguration config, BinderOptions options)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.BindNonScalar(IConfiguration configuration, Object instance, BinderOptions options)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.BindInstance(Type type, Object instance, IConfiguration config, BinderOptions options)
   at Microsoft.Extensions.Configuration.ConfigurationBinder.Get[T](IConfiguration configuration, Action`1 configureOptions)
   at ConsoleApp3.Program.Main() in D:\Dev\ConsoleApp3\ConsoleApp3\Program.cs:line 15

我究竟做错了什么？请注意，键中有一个冒号是完全合法的 json，但也许不支持在 appsettings.json 文件中存储任何奇怪的字典？

Answer 1

引用 Configuration in ASP.NET Core: Hierarchical configuration data

The Configuration API is capable of maintaining hierarchical configuration data by flattening the hierarchical data with the use of a delimiter in the configuration keys.

When the file is read into configuration, unique keys are created to maintain the original hierarchical data structure of the configuration source. The sections and keys are flattened with the use of a colon (:) to maintain the original structure

这意味着在以下 appsettings.json 文件中

{
    "Values": {
        "a:b": true,
        "b": false
    }
}

键将被展平为

值:a:b

值:b

当 ConfigurationBinder.BindDictionary 时，这将破坏设置文件的结构尝试绑定(bind) Dictionary<string, bool>属性(property)在 Options
还引用此 GitHub Issue

Colons are reserved for special meaning in the keys, so they shouldn't be used as part of normal key values.