Matze..  32

在编写此答案时,似乎没有Microsoft.Extensions.Options包提供的组件具有将配置值写回的功能appsettings.json.

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appsettings.json更准确地存储在可选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IWritableOptions<T>扩展的接口IOptions<T>; 这样我就可以替代IOptions<T>由IWritableOptions<T>每当我想读写设置.

public interface IWritableOptions<out T> : IOptions<T> where T : class, new()
{
    void Update(Action<T> applyChanges);
}

此外,我想出了IOptionsWriter一个组件,旨在用于IWritableOptions<T>更新配置部分.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,我决定将段处理为JObject对象.访问者尝试查找请求的部分并将其反序列化为实例T,使用当前值(如果未找到),或者仅创建新实例(T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.比更改的对象转换回JToken将要替换该部分的实例…

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,我实现了一个扩展方法,IServicesCollection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);
        });
    }
}

哪个可以用在ConfigureServices……

services.ConfigureWritable<CustomizableOptions>(this.Configuration, 
    "MySection", "appsettings.custom.json");

在我的Controller课程中,我可以要求一个IWritableOptions<CustomizableOptions>具有相同特征的实例IOptions<T>,但也允许更改和存储配置值.

private IWritableOptions<CustomizableOptions> options;

...

this.options.Update((opt) => {
    opt.SampleOption = "...";
});

ceferrari..  30

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");

• 我不太确定“ MyOptions”，但是阅读此内容有助于我弄清楚。https://codingblast.com/asp-net-core-configuration-reloading-binding-injecting/ (2认同)