我看到很多答案使用Newtonsoft.Json 包来更新appsettings。我将提供一些使用System.Text.Json 包的解决方案（内置在.Net Core 3 及更高版本上）。
选项 1
在开始动态更新appsettings.json 文件之前，问自己一个问题，appsettings.json 中需要更新的部分有多复杂。如果需要更新的部分不是很复杂，您可以将appsettings transformation functionality 仅用于需要更新的部分。这是一个例子：
假设我的appsettings.json 文件如下所示：
{
"Username": "Bro300",
"Job": {
"Title": "Programmer",
"Type": "IT"
}
}
假设我只需要更新Job 部分。我可以创建一个较小的文件appsettings.MyOverrides.json，而不是直接更新appsettings.json，它看起来像这样：
{
"Job": {
"Title": "Farmer",
"Type": "Agriculture"
}
}
然后确保将这个新文件添加到我的 .Net Core 应用程序中，.Net Core 将弄清楚如何加载新的更新设置。
现在下一步是创建一个包装类，该类将保存来自appsettings.MyOverrides.json 的值，如下所示：
public class OverridableSettings
{
public JobSettings Job { get; set; }
}
public class JobSettings
{
public string Title { get; set; }
public string Type { get; set; }
}
然后我可以创建如下所示的更新程序类（注意它接受OverridableSettings 并完全覆盖appsettings.MyOverrides.json 文件：
public class AppSettingsUpdater
{
public void UpdateSettings(OverridableSettings settings)
{
// instead of updating appsettings.json file directly I will just write the part I need to update to appsettings.MyOverrides.json
// .Net Core in turn will read my overrides from appsettings.MyOverrides.json file
const string SettinsgOverridesFileName = "appsettings.MyOverrides.json";
var newConfig = JsonSerializer.Serialize(settings, new JsonSerializerOptions { WriteIndented = true });
File.WriteAllText(SettinsgOverridesFileName, newConfig);
}
}
最后，这是演示如何使用它的代码：
public static class Program
{
public static void Main()
{
// Notice that appsettings.MyOverrides.json will contain only the part that we need to update, other settings will live in appsettings.json
// Also appsettings.MyOverrides.json is optional so if it doesn't exist at the program start it's not a problem
var configuration = new ConfigurationBuilder()
.AddJsonFile("appsettings.json")
.AddJsonFile("appsettings.MyOverrides.json", optional: true)
.Build();
// Here we read our current settings
var settings = configuration.Get<OverridableSettings>();
var settingsUpdater = new AppSettingsObjectUpdater();
settings.Job.Title = "Farmer";
settings.Job.Type = "Agriculture";
settingsUpdater.UpdateSettings(settings);
// Here we reload the settings so the new values from appsettings.MyOverrides.json will be read
configuration.Reload();
// and here we retrieve the new updated settings
var newJobSettings = configuration.GetSection("Job").Get<JobSettings>();
}
}
选项 2
如果 appsetting 转换不适合您的情况，并且您必须只更新一级深度的值，您可以使用这个简单的实现：
public void UpdateAppSetting(string key, string value)
{
var configJson = File.ReadAllText("appsettings.json");
var config = JsonSerializer.Deserialize<Dictionary<string, object>>(configJson);
config[key] = value;
var updatedConfigJson = JsonSerializer.Serialize(config, new JsonSerializerOptions { WriteIndented = true });
File.WriteAllText("appsettings.json", updatedConfigJson);
}
选项 3
最后，如果你有一些复杂的情况，你需要更新 appsettings，多层次的深度，这里是另一个实现，它扩展了上一个选项，并使用递归来更新任何级别的设置：
public class AppSettingsUpdater
{
private const string EmptyJson = "{}";
public void UpdateAppSetting(string key, object value)
{
// Empty keys "" are allowed in json by the way
if (key == null)
{
throw new ArgumentException("Json property key cannot be null", nameof(key));
}
const string settinsgFileName = "appsettings.json";
// We will create a new file if appsettings.json doesn't exist or was deleted
if (!File.Exists(settinsgFileName))
{
File.WriteAllText(settinsgFileName, EmptyJson);
}
var config = File.ReadAllText(settinsgFileName);
var updatedConfigDict = UpdateJson(key, value, config);
// After receiving the dictionary with updated key value pair, we serialize it back into json.
var updatedJson = JsonSerializer.Serialize(updatedConfigDict, new JsonSerializerOptions { WriteIndented = true });
File.WriteAllText(settinsgFileName, updatedJson);
}
// This method will recursively read json segments separated by semicolon (firstObject:nestedObject:someProperty)
// until it reaches the desired property that needs to be updated,
// it will update the property and return json document represented by dictonary of dictionaries of dictionaries and so on.
// This dictionary structure can be easily serialized back into json
private Dictionary<string, object> UpdateJson(string key, object value, string jsonSegment)
{
const char keySeparator = ':';
var config = JsonSerializer.Deserialize<Dictionary<string, object>>(jsonSegment);
var keyParts = key.Split(keySeparator);
var isKeyNested = keyParts.Length > 1;
if (isKeyNested)
{
var firstKeyPart = keyParts[0];
var remainingKey = string.Join(keySeparator, keyParts.Skip(1));
// If the key does not exist already, we will create a new key and append it to the json
var newJsonSegment = config.ContainsKey(firstKeyPart) && config[firstKeyPart] != null
? config[firstKeyPart].ToString()
: EmptyJson;
config[firstKeyPart] = UpdateJson(remainingKey, value, newJsonSegment);
}
else
{
config[key] = value;
}
return config;
}
}
你可以这样使用：
var settingsUpdater = new AppSettingsUpdater();
settingsUpdater.UpdateAppSetting("OuterProperty:NestedProperty:PropertyToUpdate", "new value");