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理解ASP.NET Core – 选项(Options)

开发技术 开发技术 2天前 6次浏览

注:本文隶属于《理解ASP.NET Core》系列文章,请查看置顶博客或点击此处查看全文目录

Options绑定

上期我们已经聊过了配置(IConfiguration),今天我们来聊一聊Options,中文译为“选项”,该功能用于实现以强类型的方式对程序配置信息进行访问。

既然是强类型的方式,那么就需要定义一个Options类,该类:

  • 推荐命名规则:{Object}Options
  • 特点:
    • 非抽象类
    • 必须包含公共无参的构造函数
    • 类中的所有公共读写属性都会与配置项进行绑定
    • 字段不会被绑定

接下来,为了便于理解,先举个例子:

首先在 appsetting.json 中添加如下配置:

{
  "Book": {
    "Id": 1,
    "Name": "三国演义",
    "Author": "罗贯中"
  }
}

然后定义Options类:

public class BookOptions
{
    public const string Book = "Book";

    public int Id { get; set; }

    public string Name { get; set; }

    public string Author { get; set; }
}

最后进行绑定(有BindGet两种方式):

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        // 方式 1:
        var bookOptions1 = new BookOptions();
        Configuration.GetSection(BookOptions.Book).Bind(bookOptions1);

        // 方式 2:
        var bookOptions2 = Configuration.GetSection(BookOptions.Book).Get<BookOptions>();
    }
}

其中,属性IdTitleAuthor均会与配置进行绑定,但是字段Book并不会被绑定,该字段只是用来让我们避免在程序中使用“魔数”。另外,一定要确保配置项能够转换到其绑定的属性类型(你该不会想把string绑定到int类型上吧)。

如果中文读取出来是乱码,那么你可以按照.L的.net core 读取appsettings.json 文件中文乱码的问题来配置一下。

当然,这样写代码还不够完美,还是要将Options添加到依赖注入服务容器中,例如通过IServiceCollection的扩展方法Configure

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.Configure<BookOptions>(Configuration.GetSection(BookOptions.Book));
    }
}

Options读取

通过Options接口,我们可以读取依赖注入容器中的Options。常用的有三个接口:

  • IOptions<TOptions>
  • IOptionsSnapshot<TOptions>
  • IOptionsMonitor<TOptions>

接下来,我们看看它们的区别。

IOptions

  • 该接口对象实例生命周期为 Singleton,因此能够将该接口注入到任何生命周期的服务中
  • 当该接口被实例化后,其中的选项值将永远保持不变,即使后续修改了与选项进行绑定的配置,也永远读取不到修改后的配置值
  • 不支持命名选项(Named Options),这个下面会说
public class ValuesController : ControllerBase
{
    private readonly BookOptions _bookOptions;

    public ValuesController(IOptions<BookOptions> bookOptions)
    {
        // bookOptions.Value 始终是程序启动时加载的配置,永远不会改变
        _bookOptions = bookOptions.Value;
    }
}

IOptionsSnapshot

  • 该接口被注册为 Scoped,因此该接口无法注入到 Singleton 的服务中,只能注入到 Transient 和 Scoped 的服务中。
  • 在作用域中,创建IOptionsSnapshot<TOptions>对象实例时,会从配置中读取最新选项值作为快照,并在作用域中始终使用该快照。
  • 支持命名选项
public class ValuesController : ControllerBase
{
    private readonly BookOptions _bookOptions;

    public ValuesController(IOptionsSnapshot<BookOptions> bookOptionsSnapshot)
    {
        // bookOptions.Value 是 Options 对象实例创建时读取的配置快照
        _bookOptions = bookOptionsSnapshot.Value;
    }
}

IOptionsMonitor

  • 该接口除了可以查看TOptions的值,还可以监控TOptions配置的更改。
  • 该接口被注册为 Singleton,因此能够将该接口注入到任何生命周期的服务中
  • 每次读取选项值时,都是从配置中读取最新选项值(具体读取逻辑查看下方三种接口对比测试)。
  • 支持:
    • 命名选项
    • 重新加载配置(CurrentValue),并当配置发生更改时,进行通知(OnChange
    • 缓存与缓存失效 (IOptionsMonitorCache<TOptions>)
public class ValuesController : ControllerBase
{
    private readonly IOptionsMonitor<BookOptions> _bookOptionsMonitor;

    public ValuesController(IOptionsMonitor<BookOptions> bookOptionsMonitor)
    {
        // _bookOptionsMonitor.CurrentValue 的值始终是最新配置的值
        _bookOptionsMonitor = bookOptionsMonitor;
    }
}

三种接口对比测试

IOptions<TOptions>就不说了,主要说一下IOptionsSnapshot<TOptions>IOptionsMonitor<TOptions>的不同:

  • IOptionsSnapshot<TOptions> 注册为 Scoped,在创建其实例时,会从配置中读取最新选项值作为快照,并在作用域中使用该快照
  • IOptionsMonitor<TOptions> 注册为 Singleton,每次调用实例的 CurrentValue 时,会先检查缓存(IOptionsMonitorCache<TOptions>)是否有值,如果有值,则直接用,如果没有,则从配置中读取最新选项值,并记入缓存。当配置发生更改时,会将缓存清空。

搞个测试小程序:

[ApiController]
[Route("[controller]")]
public class ValuesController : ControllerBase
{
    private readonly IOptions<BookOptions> _bookOptions;
    private readonly IOptionsSnapshot<BookOptions> _bookOptionsSnapshot;
    private readonly IOptionsMonitor<BookOptions> _bookOptionsMonitor;

    public ValuesController(
        IOptions<BookOptions> bookOptions,
        IOptionsSnapshot<BookOptions> bookOptionsSnapshot,
        IOptionsMonitor<BookOptions> bookOptionsMonitor)
    {
        _bookOptions = bookOptions;
        _bookOptionsSnapshot = bookOptionsSnapshot;
        _bookOptionsMonitor = bookOptionsMonitor;

    }

    [HttpGet]
    public dynamic Get()
    {
        var bookOptionsValue1 = _bookOptions.Value;
        var bookOptionsSnapshotValue1 = _bookOptionsSnapshot.Value;
        var bookOptionsMonitorValue1 = _bookOptionsMonitor.CurrentValue;

        Console.WriteLine("请修改配置文件 appsettings.json");
        Task.Delay(TimeSpan.FromSeconds(10)).Wait();

        var bookOptionsValue2 = _bookOptions.Value;
        var bookOptionsSnapshotValue2 = _bookOptionsSnapshot.Value;
        var bookOptionsMonitorValue2 = _bookOptionsMonitor.CurrentValue;


        return new
        {
            bookOptionsValue1,
            bookOptionsSnapshotValue1,
            bookOptionsMonitorValue1,
            bookOptionsValue2,
            bookOptionsSnapshotValue2,
            bookOptionsMonitorValue2
        };
    }
}

运行2次,并按照指示修改两次配置文件(初始是“三国演义”,第一次修改为“水浒传”,第二次修改为“红楼梦”)

  • 第1次输出:
{
  "bookOptionsValue1": {
    "id": 1,
    "name": "三国演义",
    "author": "罗贯中"
  },
  "bookOptionsSnapshotValue1": {
    "id": 1,
    "name": "三国演义",
    "author": "罗贯中"
  },
  "bookOptionsMonitorValue1": {
    "id": 1,
    "name": "三国演义",
    "author": "罗贯中"
  },
  "bookOptionsValue2": {
    "id": 1,
    "name": "三国演义",
    "author": "罗贯中"
  },
  // 注意 OptionsSnapshot 的值在当前作用域内没有进行更新
  "bookOptionsSnapshotValue2": {
    "id": 1,
    "name": "三国演义",
    "author": "罗贯中"
  },
  
  // 注意 OptionsMonitor 的值变成最新的
  "bookOptionsMonitorValue2": {
    "id": 1,
    "name": "水浒传",
    "author": "施耐庵"
  }
}
  • 第2次输出:
{
  // Options 的值始终没有变化
  "bookOptionsValue1": {
    "id": 1,
    "name": "三国演义",
    "author": "罗贯中"
  },
  
  // 注意 OptionsSnapshot 的值变成当前最新值了
  "bookOptionsSnapshotValue1": {
    "id": 1,
    "name": "水浒传",
    "author": "施耐庵"
  },
  // 注意 OptionsMonitor 的值始终是最新的
  "bookOptionsMonitorValue1": {
    "id": 1,
    "name": "水浒传",
    "author": "施耐庵"
  },
  
  // Options 的值始终没有变化
  "bookOptionsValue2": {
    "id": 1,
    "name": "三国演义",
    "author": "罗贯中"
  },
  // 注意 OptionsSnapshot 的值在当前作用域内没有进行更新
  "bookOptionsSnapshotValue2": {
    "id": 1,
    "name": "水浒传",
    "author": "施耐庵"
  },
  
  // 注意 OptionsMonitor 的值始终是最新的
  "bookOptionsMonitorValue2": {
    "id": 1,
    "name": "红楼梦",
    "author": "曹雪芹"
  }
}

通过测试我相信你应该能深刻理解它们之间的区别了。

命名选项(Named Options)

上面我们提到了命名选项,命名选项常用于多个配置节点绑定同一属性的情况,举个例子你就明白了:

在 appsettings.json 中添加如下配置

{
  "DateTime": {
    "Beijing": {
      "Year": 2021,
      "Month": 1,
      "Day":1,
      "Hour":12,
      "Minute":0,
      "Second":0
    },
    "Tokyo": {
      "Year": 2021,
      "Month": 1,
      "Day":1,
      "Hour":13,
      "Minute":0,
      "Second":0
    },
  }
}

很显然,虽然“Beijing”和“Tokyo”是两个配置项,但是属性都是一样的,我们没必要创建两个Options类,只需要创建一个就好了:

public class DateTimeOptions
{
    public const string Beijing = "Beijing";
    public const string Tokyo = "Tokyo";

    public int Year { get; set; }
    public int Month { get; set; }
    public int Day { get; set; }
    public int Hour { get; set; }
    public int Minute { get; set; }
    public int Second { get; set; }
}

然后,通过对选项进行指定命名的方式,一个叫做“Beijing”,一个叫做“Tokyo”,将选项添加到DI容器中:

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        services.Configure<BookOptions>(Configuration.GetSection(BookOptions.Book));
        services.Configure<DateTimeOptions>(DateTimeOptions.Beijing, Configuration.GetSection($"DateTime:{DateTimeOptions.Beijing}"));
        services.Configure<DateTimeOptions>(DateTimeOptions.Tokyo, Configuration.GetSection($"DateTime:{DateTimeOptions.Tokyo}"));
    }
}

最后,通过构造函数的方式将选项注入到Controller中。需要注意的是,因为DateTimeOptions类绑定了两个选项类,所以当我们获取时选项值时,需要指定选项的名字。

public class ValuesController : ControllerBase
{
    private readonly DateTimeOptions _beijingDateTimeOptions;
    private readonly DateTimeOptions _tockyoDateTimeOptions;

    public ValuesController(IOptionsSnapshot<DateTimeOptions> dateTimeOptions)
    {
        _beijingDateTimeOptions = dateTimeOptions.Get(DateTimeOptions.Beijing);
        _tockyoDateTimeOptions = dateTimeOptions.Get(DateTimeOptions.Tokyo);
    }
}

程序运行后,你会发现变量 _beijingDateTimeOptions 绑定的配置是“Beijing”配置节点,变量 _tockyoDateTimeOptions 绑定的配置是“Tokyo” 配置节点,但它们绑定的都是同一个类DateTimeOptions

事实上,.NET Core 中所有 Options 都是命名选项,当没有显式指定名字时,使用的名字默认是Options.DefaultName,即string.Empty

使用 DI 服务配置选项

在某些场景下,选项的配置需要依赖DI中的服务,这时可以借助OptionsBuilderConfigure方法(注意这个Configure不是上面提到的IServiceCollection的扩展方法Configure,这是两个不同的方法),该方法支持最多5个服务来配置选项:

services.AddOptions<BookOptions>()
    .Configure<Service1, Service2, Service3, Service4, Service5>((o, s, s2, s3, s4, s5) => 
    {
        o.Authors = DoSomethingWith(s, s2, s3, s4, s5);
    });

Options 验证

配置毕竟是我们手动进行文本输入的,难免会出现错误,这种情况下,就需要使用程序来帮助进行校验了。

DataAnnotations

Install-Package Microsoft.Extensions.Options.DataAnnotations

我们先升级一下BookOptions,增加一些数据校验:

public class BookOptions
{
    public const string Book = "Book";

    [Range(1,1000,
        ErrorMessage = "必须 {1} <= {0} <= {2}")]
    public int Id { get; set; }

    [StringLength(10, MinimumLength = 1,
        ErrorMessage = "必须 {2} <= {0} Length <= {1}")]
    public string Name { get; set; }

    public string Author { get; set; }
}

然后我们在添加到DI容器时,增加数据注解验证:

public void ConfigureServices(IServiceCollection services)
{
    services.AddOptions<BookOptions>()
        .Bind(Configuration.GetSection(BookOptions.Book))
        .ValidateDataAnnotations();
        .Validate(options =>
        {
            // 校验通过 return true
            // 校验失败 return false
    
            if (options.Author.Contains("A"))
            {
                return false;
            }
    
            return true;
        });
}

ValidateDataAnnotations会根据你添加的特性进行数据校验,当特性无法实现想要的校验逻辑时,则使用Validate进行较为复杂的校验,如果过于复杂,则就要用到IValidateOptions了(实质上,Validate方法内部也是通过注入一个IValidateOptions实例来实现选项验证的)。

IValidateOptions

通过实现IValidateOptions<TOptions>接口,增加数据校验规则,例如:

public class BookValidation : IValidateOptions<BookOptions>
{
    public ValidateOptionsResult Validate(string name, BookOptions options)
    {
        var failures = new List<string>();
        if(!(options.Id >= 1 && options.Id <= 1000))
        {
            failures.Add($"必须 1 <= {nameof(options.Id)} <= {1000}");
        }
        if(!(options.Name.Length >= 1 && options.Name.Length <= 10))
        {
            failures.Add($"必须 1 <= {nameof(options.Name)} <= 10");
        }

        if (failures.Any())
        {
            return ValidateOptionsResult.Fail(failures);
        }

        return ValidateOptionsResult.Success;
    }
}

然后我们将其注入到DI容器 Singleton,这里使用了TryAddEnumerable扩展方法添加该服务,是因为我们可以注入多个针对同一Options的IValidateOptions,这些IValidateOptions实例都会被执行:

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<BookOptions>(Configuration.GetSection(BookOptions.Book));
    services.TryAddEnumerable(ServiceDescriptor.Singleton<IValidateOptions<BookOptions>, BookValidation>());
}

Options后期配置

介绍两个方法,分别是PostConfigurePostConfigureAll,他们用来对选项进行后期配置。

  • 在所有的OptionsServiceCollectionExtensions.Configure方法运行后执行
  • ConfigureConfigureAll类似,PostConfigure仅用于对指定名称的选项进行后期配置(默认名称为string.Empty),PostConfigureAll则用于对所有选项实例进行后期配置
  • 每当选项更改时,均会触发相应的方法
public void ConfigureServices(IServiceCollection services)
{
    services.PostConfigure<DateTimeOptions>(options =>
    {
        Console.WriteLine($"我只对名称为{Options.DefaultName}的{nameof(DateTimeOptions)}实例进行后期配置");
    });

    services.PostConfigure<DateTimeOptions>(DateTimeOptions.Beijing, options =>
    {
        Console.WriteLine($"我只对名称为{DateTimeOptions.Beijing}的{nameof(DateTimeOptions)}实例进行后期配置");
    });

    services.PostConfigureAll<DateTimeOptions>(options =>
    {
        Console.WriteLine($"我对{nameof(DateTimeOptions)}的所有实例进行后期配置");
    });
}

Options 体系

IConfigureOptions

该接口用于包装对选项的配置。默认实现为ConfigureOptions<TOptions>

public interface IConfigureOptions<in TOptions> where TOptions : class
{
    void Configure(TOptions options);
}

ConfigureOptions

public class ConfigureOptions<TOptions> : IConfigureOptions<TOptions> where TOptions : class
{
    public ConfigureOptions(Action<TOptions> action)
    {
        Action = action;
    }

    public Action<TOptions> Action { get; }

    // 配置 TOptions 实例
    public virtual void Configure(TOptions options)
    {
        Action?.Invoke(options);
    }
}

ConfigureFromConfigurationOptions

该类通过继承类ConfigureOptions<TOptions>,对选项的配置进行了扩展,允许通过ConfigurationBinder.Bind扩展方法将IConfiguration实例绑定到选项上:

public class ConfigureFromConfigurationOptions<TOptions> : ConfigureOptions<TOptions>
    where TOptions : class
{
    public ConfigureFromConfigurationOptions(IConfiguration config)
        : base(options => ConfigurationBinder.Bind(config, options))
    { }
}

IConfigureNamedOptions

该接口用于包装对命名选项的配置,该接口同时继承了接口IConfigureOptions<TOptions>的行为,默认实现为ConfigureNamedOptions<TOptions>,另外为了实现“使用 DI 服务配置选项”的功能,还提供了一些泛型类重载。

public interface IConfigureNamedOptions<in TOptions> : IConfigureOptions<TOptions> where TOptions : class
{
    void Configure(string name, TOptions options);
}

ConfigureNamedOptions

public class ConfigureNamedOptions<TOptions> : IConfigureNamedOptions<TOptions> where TOptions : class
{
    public ConfigureNamedOptions(string name, Action<TOptions> action)
    {
        Name = name;
        Action = action;
    }

    public string Name { get; }

    public Action<TOptions> Action { get; }

    public virtual void Configure(string name, TOptions options)
    {
        // Name == null 表示针对 TOptions 的所有实例进行配置
        if (Name == null || name == Name)
        {
            Action?.Invoke(options);
        }
    }

    public void Configure(TOptions options) => Configure(Options.DefaultName, options);
}

NamedConfigureFromConfigurationOptions

该类通过继承类ConfigureNamedOptions<TOptions>,对命名选项的配置进行了扩展,允许通过ConfigurationBinder.Bind扩展方法将IConfiguration实例绑定到命名选项上:

public class NamedConfigureFromConfigurationOptions<TOptions> : ConfigureNamedOptions<TOptions>
    where TOptions : class
{
    public NamedConfigureFromConfigurationOptions(string name, IConfiguration config)
        : this(name, config, _ => { })
    { }

    public NamedConfigureFromConfigurationOptions(string name, IConfiguration config, Action<BinderOptions> configureBinder)
        : base(name, options => config.Bind(options, configureBinder))
    { }
}

IPostConfigureOptions

该接口用于包装对命名选项的后期配置,将在所有IConfigureOptions<TOptions>执行完毕后才会执行,默认实现为PostConfigureOptions<TOptions>,同样的,为了实现“使用 DI 服务对选项进行后期配置”的功能,也提供了一些泛型类重载:

public interface IPostConfigureOptions<in TOptions> where TOptions : class
{
    void PostConfigure(string name, TOptions options);
}

public class PostConfigureOptions<TOptions> : IPostConfigureOptions<TOptions> where TOptions : class
{
    public PostConfigureOptions(string name, Action<TOptions> action)
    {
        Name = name;
        Action = action;
    }

    public string Name { get; }

    public Action<TOptions> Action { get; }

    public virtual void PostConfigure(string name, TOptions options)
    {
        // Name == null 表示针对 TOptions 的所有实例进行后期配置
        if (Name == null || name == Name)
        {
            Action?.Invoke(options);
        }
    }
}

AddOptions & AddOptions & OptionsBuilder

public static class OptionsServiceCollectionExtensions
{
    // 该方法帮我们把一些常用的与 Options 相关的服务注入到 DI 容器
    public static IServiceCollection AddOptions(this IServiceCollection services)
    {
        services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptions<>), typeof(OptionsManager<>)));
        services.TryAdd(ServiceDescriptor.Scoped(typeof(IOptionsSnapshot<>), typeof(OptionsManager<>)));
        services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitor<>), typeof(OptionsMonitor<>)));
        services.TryAdd(ServiceDescriptor.Transient(typeof(IOptionsFactory<>), typeof(OptionsFactory<>)));
        services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitorCache<>), typeof(OptionsCache<>)));
        return services;
    }
    
    // 没有指定 Options 名称时,默认使用 Options.DefaultName
    public static OptionsBuilder<TOptions> AddOptions<TOptions>(this IServiceCollection services) where TOptions : class
        => services.AddOptions<TOptions>(Options.Options.DefaultName);
    
    // 由于后续还要对 TOptions 进行配置,所以返回一个 OptionsBuilder 出去
    public static OptionsBuilder<TOptions> AddOptions<TOptions>(this IServiceCollection services, string name)
        where TOptions : class
    {
        services.AddOptions();
        return new OptionsBuilder<TOptions>(services, name);
    }
}

那我们看看OptionsBuilder<TOptions>可以配置哪些东西,由于该类中有大量重载方法,我只挑选最基础的方法来看一看:

public class OptionsBuilder<TOptions> where TOptions : class
{
    private const string DefaultValidationFailureMessage = "A validation error has occurred.";
    
    // TOptions 实例的名字
    public string Name { get; }
    
    public IServiceCollection Services { get; }
    
    public OptionsBuilder(IServiceCollection services, string name)
    {
        Services = services;
        Name = name ?? Options.DefaultName;
    }
    
    // 选项配置
    public virtual OptionsBuilder<TOptions> Configure(Action<TOptions> configureOptions)
    {
        Services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(Name, configureOptions));
        return this;
    }
    
    // 选项后期配置
    public virtual OptionsBuilder<TOptions> PostConfigure(Action<TOptions> configureOptions)
    {
        Services.AddSingleton<IPostConfigureOptions<TOptions>>(new PostConfigureOptions<TOptions>(Name, configureOptions));
        return this;
    }
    
    // 选项验证
    public virtual OptionsBuilder<TOptions> Validate(Func<TOptions, bool> validation)
        => Validate(validation: validation, failureMessage: DefaultValidationFailureMessage);
        
    public virtual OptionsBuilder<TOptions> Validate(Func<TOptions, bool> validation, string failureMessage)
    {
        Services.AddSingleton<IValidateOptions<TOptions>>(new ValidateOptions<TOptions>(Name, validation, failureMessage));
        return this;
    }
}

OptionsServiceCollectionExtensions.Configure

OptionsServiceCollectionExtensions.Configure<TOptions>实际上就是对选项的一般配置方式进行了封装,免去了OptionsBuilder<TOptions>

public static class OptionsServiceCollectionExtensions
{
    // 没有指定 Options 名称时,默认使用 Options.DefaultName
    public static IServiceCollection Configure<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
        => services.Configure(Options.Options.DefaultName, configureOptions);
        
    // 等同于做了 AddOptions<TOptions> 和 OptionsBuilder<TOptions>.Configure 两件事
    public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, Action<TOptions> configureOptions)
    where TOptions : class
    {
        services.AddOptions();
        services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(name, configureOptions));
        return services;
    }
    
    // 由于 ConfigureAll 是针对 TOptions 的所有实例进行配置,所以不需要指定名字
    public static IServiceCollection ConfigureAll<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
        => services.Configure(name: null, configureOptions: configureOptions);
}

OptionsConfigurationServiceCollectionExtensions.Configure

请注意,该Configure<TOptions>方法与上方提及的Configure<TOptions>不是同一个。该扩展方法针对配置(IConfiguration)绑定到选项(Options)上进行了扩展

Install-Package Microsoft.Extensions.Options.ConfigurationExtensions

public static class OptionsConfigurationServiceCollectionExtensions
{
    public static IServiceCollection Configure<TOptions>(this IServiceCollection services, IConfiguration config) where TOptions : class
        => services.Configure<TOptions>(Options.Options.DefaultName, config);

    public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, IConfiguration config) where TOptions : class
        => services.Configure<TOptions>(name, config, _ => { });

    public static IServiceCollection Configure<TOptions>(this IServiceCollection services, IConfiguration config, Action<BinderOptions> configureBinder)
        where TOptions : class
        => services.Configure<TOptions>(Options.Options.DefaultName, config, configureBinder);

    public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, IConfiguration config, Action<BinderOptions> configureBinder)
        where TOptions : class
    {
        services.AddOptions();
        services.AddSingleton<IOptionsChangeTokenSource<TOptions>>(new ConfigurationChangeTokenSource<TOptions>(name, config));
        return services.AddSingleton<IConfigureOptions<TOptions>>(new NamedConfigureFromConfigurationOptions<TOptions>(name, config, configureBinder));
    }
}

IOptionsFactory

IOptionsFactory<TOptions>负责创建命名选项实例,默认实现为OptionsFactory<TOptions>

public interface IOptionsFactory<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] TOptions> where TOptions : class
{
    TOptions Create(string name);
}

public class OptionsFactory<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> 
    : IOptionsFactory<TOptions> where TOptions : class
{
    private readonly IEnumerable<IConfigureOptions<TOptions>> _setups;
    private readonly IEnumerable<IPostConfigureOptions<TOptions>> _postConfigures;
    private readonly IEnumerable<IValidateOptions<TOptions>> _validations;

    // 这里通过依赖注入的的方式将与 TOptions 相关的配置、验证服务列表解析出来
    public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures) 
    : this(setups, postConfigures, validations: null)
    { }

    public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures, IEnumerable<IValidateOptions<TOptions>> validations)
    {
        _setups = setups;
        _postConfigures = postConfigures;
        _validations = validations;
    }

    public TOptions Create(string name)
    {
        // 1. 创建并配置 Options
        TOptions options = CreateInstance(name);
        foreach (IConfigureOptions<TOptions> setup in _setups)
        {
            if (setup is IConfigureNamedOptions<TOptions> namedSetup)
            {
                namedSetup.Configure(name, options);
            }
            else if (name == Options.DefaultName)
            {
                setup.Configure(options);
            }
        }
        
        // 2. 对 Options 进行后期配置
        foreach (IPostConfigureOptions<TOptions> post in _postConfigures)
        {
            post.PostConfigure(name, options);
        }

        // 3. 执行 Options 校验
        if (_validations != null)
        {
            var failures = new List<string>();
            foreach (IValidateOptions<TOptions> validate in _validations)
            {
                ValidateOptionsResult result = validate.Validate(name, options);
                if (result.Failed)
                {
                    failures.AddRange(result.Failures);
                }
            }
            if (failures.Count > 0)
            {
                throw new OptionsValidationException(name, typeof(TOptions), failures);
            }
        }

        return options;
    }

    protected virtual TOptions CreateInstance(string name)
    {
        return Activator.CreateInstance<TOptions>();
    }
}

OptionsManager

通过AddOptions扩展方法的实现,可以看到,IOptions<TOptions>IOptionsSnapshot<TOptions>的实现都是OptionsManager<TOptions>,只不过一个是 Singleton,一个是 Scoped。我们通过前面的分析也知道了,当源中的配置改变时,IOptions<TOptions>始终维持初始值,IOptionsSnapshot<TOptions>在每次请求时会读取最新配置值,并在同一个请求中是不变的。接下来就来看看OptionsManager<TOptions>是如何实现的:

public class OptionsManager<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> :
    IOptions<TOptions>,
    IOptionsSnapshot<TOptions>
    where TOptions : class
{
    private readonly IOptionsFactory<TOptions> _factory;
    // 将已创建的 TOptions 实例缓存到该私有变量中
    private readonly OptionsCache<TOptions> _cache = new OptionsCache<TOptions>(); 

    public OptionsManager(IOptionsFactory<TOptions> factory)
    {
        _factory = factory;
    }

    public TOptions Value => Get(Options.DefaultName);

    public virtual TOptions Get(string name)
    {
        name = name ?? Options.DefaultName;

        // 若缓存不存在,则通过工厂新建 Options 实例,否则直接读取缓存
        return _cache.GetOrAdd(name, () => _factory.Create(name));
    }
}

OptionsMonitor

同样,通过前面的分析,我们知道OptionsMonitor<TOptions>读取的始终是配置的最新值,它的实现在OptionsManager<TOptions>的基础上,除了使用缓存将创建的 Options 实例缓存起来外,还增添了监听机制,当配置发生更改时,会将缓存移除。

public class OptionsMonitor<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> :
    IOptionsMonitor<TOptions>,
    IDisposable
    where TOptions : class
{
    private readonly IOptionsMonitorCache<TOptions> _cache;
    private readonly IOptionsFactory<TOptions> _factory;
    private readonly IEnumerable<IOptionsChangeTokenSource<TOptions>> _sources;
    private readonly List<IDisposable> _registrations = new List<IDisposable>();
    internal event Action<TOptions, string> _onChange;

    public OptionsMonitor(IOptionsFactory<TOptions> factory, IEnumerable<IOptionsChangeTokenSource<TOptions>> sources, IOptionsMonitorCache<TOptions> cache)
    {
        _factory = factory;
        _sources = sources;
        _cache = cache;

        // 监听更改
        foreach (IOptionsChangeTokenSource<TOptions> source in _sources)
        {
            IDisposable registration = ChangeToken.OnChange(
                  () => source.GetChangeToken(),
                  (name) => InvokeChanged(name),
                  source.Name);

            _registrations.Add(registration);
        }
    }

    // 当发生更改时,移除缓存
    private void InvokeChanged(string name)
    {
        name = name ?? Options.DefaultName;
        _cache.TryRemove(name);
        TOptions options = Get(name);
        if (_onChange != null)
        {
            _onChange.Invoke(options, name);
        }
    }

    public TOptions CurrentValue => Get(Options.DefaultName);

    public virtual TOptions Get(string name)
    {
        name = name ?? Options.DefaultName;
        return _cache.GetOrAdd(name, () => _factory.Create(name));
    }

    // 通过该方法绑定 OnChange 事件
    public IDisposable OnChange(Action<TOptions, string> listener)
    {
        var disposable = new ChangeTrackerDisposable(this, listener);
        _onChange += disposable.OnChange;
        return disposable;
    }

    public void Dispose()
    {
        // 移除所有 change token 的订阅
        foreach (IDisposable registration in _registrations)
        {
            registration.Dispose();
        }

        _registrations.Clear();
    }
}

总结

  • 所有选项均为命名选项,默认名称为Options.DefaultName,即string.Empty
  • 通过ConfigurationBinder.GetConfigurationBinder.Bind手动获取选项实例。
  • 通过Configure方法进行选项配置:
    • OptionsBuilder<TOptions>.Configure:通过包含DI服务的委托来进行选项配置
    • OptionsServiceCollectionExtensions.Configure<TOptions>:通过简单委托来进行选项配置
    • OptionsConfigurationServiceCollectionExtensions.Configure<TOptions>:直接将IConfiguration实例绑定到选项上
  • 通过OptionsServiceCollectionExtensions.ConfigureAll<TOptions>方法针对某个选项类型的所有实例(不同名称)统一进行配置。
  • 通过PostConfigure方法进行选项后期配置:
    • OptionsBuilder<TOptions>.PostConfigure:通过包含DI服务的委托来进行选项后期配置
    • OptionsServiceCollectionExtensions.PostConfigure<TOptions>:通过简单委托来进行选项后期配置
  • 通过PostConfigureAll<TOptions>方法针对某个选项类型的所有实例(不同名称)统一进行配置。
  • 通过Validate进行选项验证:
    • OptionsBuilderDataAnnotationsExtensions.ValidateDataAnnotations:通过数据注解进行选项验证
    • OptionsBuilder<TOptions>.Validate:通过委托进行选项验证
    • IValidateOptions<TOptions>:通过实现该接口并注入实现来进行选项验证
  • 通过依赖注入读取选项:
    • IOptions<TOptions>:Singleton,值永远是该接口被实例化时的选项配置初始值
    • IOptionsSnapshot<TOptions>:Scoped,每一次Http请求开始时会读取选项配置的最新值,并在当前请求中保持不变
    • IOptionsMonitor<TOptions>:Singleton,每次读取都是选项配置的最新值

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转载请注明原文链接:理解ASP.NET Core – 选项(Options)
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