我正在使用IOptions描述的in the official documentation模式。
当我从appsetting.json读取值时，这工作正常，但如何更新值并将更改保存回appsetting.json？
在我的例子中，我有几个字段可以从用户界面编辑（由管理员用户在应用程序中）。因此，我正在寻找通过选项访问器更新这些值的理想方法。
在撰写此答案时，似乎没有Microsoft.Extensions.Options包提供的组件具有将配置值写回appsettings.json的功能。
在我的一个ASP.NET Core项目中，我想让用户更改一些应用程序设置 - 这些设置值应该存储在appsettings.json中，更精确地存储在可选的appsettings.custom.json文件中，如果存在则会添加到配置中。
像这样...
public Startup(IHostingEnvironment env)
{
IConfigurationBuilder builder = new ConfigurationBuilder()
.SetBasePath(env.ContentRootPath)
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
.AddJsonFile("appsettings.custom.json", optional: true, reloadOnChange: true)
.AddEnvironmentVariables();
this.Configuration = builder.Build();
}
我宣布扩展IWritableOptions<T>的IOptions<T>接口;因此，只要我想读写设置，我就可以用IOptions<T>替换IWritableOptions<T>。
public interface IWritableOptions<out T> : IOptions<T> where T : class, new()
{
void Update(Action<T> applyChanges);
}
另外，我想出了IOptionsWriter，它是IWritableOptions<T>用来更新配置部分的组件。这是我对前面提到的接口的实现......
class OptionsWriter : IOptionsWriter
{
private readonly IHostingEnvironment environment;
private readonly IConfigurationRoot configuration;
private readonly string file;
public OptionsWriter(
IHostingEnvironment environment,
IConfigurationRoot configuration,
string file)
{
this.environment = environment;
this.configuration = configuration;
this.file = file;
}
public void UpdateOptions(Action<JObject> callback, bool reload = true)
{
IFileProvider fileProvider = this.environment.ContentRootFileProvider;
IFileInfo fi = fileProvider.GetFileInfo(this.file);
JObject config = fileProvider.ReadJsonFileAsObject(fi);
callback(config);
using (var stream = File.OpenWrite(fi.PhysicalPath))
{
stream.SetLength(0);
config.WriteTo(stream);
}
this.configuration.Reload();
}
}
由于编写器不知道文件结构，我决定将部分处理为JObject对象。访问者尝试查找请求的部分并将其反序列化为T的实例，使用当前值（如果未找到），或者仅创建T的新实例（如果当前值为null）。然后将此持有者对象传递给调用者，调用者将对其应用更改。比已更改的对象转换回JToken实例，该实例将替换该部分...
class WritableOptions<T> : IWritableOptions<T> where T : class, new()
{
private readonly string sectionName;
private readonly IOptionsWriter writer;
private readonly IOptionsMonitor<T> options;
public WritableOptions(
string sectionName,
IOptionsWriter writer,
IOptionsMonitor<T> options)
{
this.sectionName = sectionName;
this.writer = writer;
this.options = options;
}
public T Value => this.options.CurrentValue;
public void Update(Action<T> applyChanges)
{
this.writer.UpdateOptions(opt =>
{
JToken section;
T sectionObject = opt.TryGetValue(this.sectionName, out section) ?
JsonConvert.DeserializeObject<T>(section.ToString()) :
this.options.CurrentValue ?? new T();
applyChanges(sectionObject);
string json = JsonConvert.SerializeObject(sectionObject);
opt[this.sectionName] = JObject.Parse(json);
});
}
}
最后，我实现了IServicesCollection的扩展方法，允许我轻松配置可写选项访问器...
static class ServicesCollectionExtensions
{
public static void ConfigureWritable<T>(
this IServiceCollection services,
IConfigurationRoot configuration,
string sectionName,
string file) where T : class, new()
{
services.Configure<T>(configuration.GetSection(sectionName));
services.AddTransient<IWritableOptions<T>>(provider =>
{
var environment = provider.GetService<IHostingEnvironment>();
var options = provider.GetService<IOptionsMonitor<T>>();
IOptionsWriter writer = new OptionsWriter(environment, configuration, file);
return new WritableOptions<T>(sectionName, writer, options);
});
}
}
哪个可以在ConfigureServices中使用...
services.ConfigureWritable<CustomizableOptions>(this.Configuration,
"MySection", "appsettings.custom.json");
在我的Controller类中，我可以要求一个IWritableOptions<CustomizableOptions>实例，它具有与IOptions<T>相同的特性，但也允许更改和存储配置值。
private IWritableOptions<CustomizableOptions> options;
...
this.options.Update((opt) => {
opt.SampleOption = "...";
});
简化版Matze的答案：
public interface IWritableOptions<out T> : IOptionsSnapshot<T> where T : class, new()
{
void Update(Action<T> applyChanges);
}
public class WritableOptions<T> : IWritableOptions<T> where T : class, new()
{
private readonly IHostingEnvironment _environment;
private readonly IOptionsMonitor<T> _options;
private readonly string _section;
private readonly string _file;
public WritableOptions(
IHostingEnvironment environment,
IOptionsMonitor<T> options,
string section,
string file)
{
_environment = environment;
_options = options;
_section = section;
_file = file;
}
public T Value => _options.CurrentValue;
public T Get(string name) => _options.Get(name);
public void Update(Action<T> applyChanges)
{
var fileProvider = _environment.ContentRootFileProvider;
var fileInfo = fileProvider.GetFileInfo(_file);
var physicalPath = fileInfo.PhysicalPath;
var jObject = JsonConvert.DeserializeObject<JObject>(File.ReadAllText(physicalPath));
var sectionObject = jObject.TryGetValue(_section, out JToken section) ?
JsonConvert.DeserializeObject<T>(section.ToString()) : (Value ?? new T());
applyChanges(sectionObject);
jObject[_section] = JObject.Parse(JsonConvert.SerializeObject(sectionObject));
File.WriteAllText(physicalPath, JsonConvert.SerializeObject(jObject, Formatting.Indented));
}
}
public static class ServiceCollectionExtensions
{
public static void ConfigureWritable<T>(
this IServiceCollection services,
IConfigurationSection section,
string file = "appsettings.json") where T : class, new()
{
services.Configure<T>(section);
services.AddTransient<IWritableOptions<T>>(provider =>
{
var environment = provider.GetService<IHostingEnvironment>();
var options = provider.GetService<IOptionsMonitor<T>>();
return new WritableOptions<T>(environment, options, section.Key, file);
});
}
}
用法：
services.ConfigureWritable<MyOptions>(Configuration.GetSection("MySection"));
然后：
private readonly IWritableOptions<MyOptions> _options;
public MyClass(IWritableOptions<MyOptions> options)
{
_options = options;
}
要将更改保存到文件：
_options.Update(opt => {
opt.Field1 = "value1";
opt.Field2 = "value2";
});
并且您可以将自定义json文件作为可选参数传递（默认情况下它将使用appsettings.json）：
services.ConfigureWritable<MyOptions>(Configuration.GetSection("MySection"), "appsettings.custom.json");
我希望我的场景涵盖您的意图，如果在启动时传递给应用程序的环境变量，我想覆盖appsettings.json值。
我使用了dotnet core 2.1中提供的ConfigureOptions方法。
以下是用于appsettings.json的JSON的Model
public class Integration
{
public string FOO_API {get;set;}
}
对于startup.cs中的服务：
var section = Configuration.GetSection ("integration");
services.Configure<Integration> (section);
services.ConfigureOptions<ConfigureIntegrationSettings>();
这是实施：
public class ConfigureIntegrationSettings : IConfigureOptions<Integration>
{
public void Configure(Integration options)
{
if (!string.IsNullOrEmpty(Environment.GetEnvironmentVariable("FOO")))
options.FOO_API = Environment.GetEnvironmentVariable("FOO_API");
}
}
因此，如果没有设置值，则会回退到appsettings.json