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假設我在 ASP.NET Core 有個服務 CopyService，建構式接收 IConfiguration 從中讀取設定值，appsettings.json 格式如下：

{
    "Logging": {
        "LogLevel": {
            "Default": "Information",
            "Microsoft.AspNetCore": "Warning"
        }
    },
    "AllowedHosts": "*",
    "CodeName": "Test",
    "Folders": [
        {
            "Name": "Folder1",
            "Path": "D:\\Folder1",
            "ExcludePaths": [
                "File1",
                "File2"
            ]
        },
        {
            "Name": "Folder2",
            "Path": "D:\\Folder2"
        }
    ]
}

CopyService 使用 _config["CodeName"] 讀取 CodeName，並使用 GetSection("Folders").Get<List<FolderSetting>>() 對映成 FolderSetting 物件集合：

public class CopyService 
{
    IConfiguration _config;
    public CopyService(IConfiguration config)
    {
        _config = config;
    }
    public string DebugInfo =>
             _config["CodeName"] + "\n" +
             string.Join("\n", 
                _config.GetSection("Folders").Get<List<FolderSetting>>()
                    .Select(x => $"{x.Name}/{x.Path}/{x.ExcludePaths}").ToArray());       
}

public class FolderSetting {
    public string Name {get; set;}
    public string Path {get; set;}
    public string ExcludePaths {get; set;}
}

這段程式配合 appsettings.json 可以順利運作，但有沒有可能不產生 appsettings.json，在程式裡捏造一組設定值做測試呢？

.NET 設想周到，什麼怪兵器都有，Memory Configuration Provider 支援用 Dictionary<string, string> 存放設定值，可以滿足我們的需求。

var config = new ConfigurationBuilder()
    .AddInMemoryCollection(new Dictionary<string, string> {
        ["CodeName"] = "TEST",
        ["Folders:0:Name"] = "Folder1",
        ["Folders:0:Path"] = "X:\\Folder1",
        ["Folders:0:ExcludePaths"] = "data.json",
        ["Folders:1:Name"] = "Folder2",
        ["Folders:1:Path"] = "X:\\Folder2"
    }).Build();
var copyService = new CopyService(config);
Console.WriteLine(copyService.DebugInfo);

使用 "Folder:0:Name" 表示法，連 List<FolderSetting> 都能模擬，讚!

Example of using Dictionary as IConfiguration provider ASP.NET Core.


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