Net core学习系列（十）—

一、前言

选项（Options）模式是对配置（Configuration）的功能的延伸。在12章（ASP.NET Core中的配置二）Configuration中有介绍过该功能（绑定到实体类、绑定至对象图、将数组绑定至类）而选项模式又有个选项类（TOptions），该选项类作用是指：把选项类中的属性与配置来源中的键关联起来。举个例，假设json文件有个Option1键，选项类中也有个叫Option1的属性名，经过选项配置，这样就能把json中的键的值映射到选项类属性值中。也可以理解在项目应用中，把一个json文件序列化到.net类。

二、常规选项配置

选项类必须为包含公共无参数构造函数的非抽象类。在appsettings.json文件中添加option1、option2、subsection的配置：

{

  "option1": "value1_from_json",

  "option2": -1,

  "subsection": {

    "suboption1": "subvalue1_from_json",

    "suboption2": 200

  },

  "Logging": {

    "LogLevel": {

      "Default": "Warning"

    }

  },

  "AllowedHosts": "*"

}

新建MyOptions类(Models/MyOptions.cs)，以下类MyOptions具有三种属性：Option1和 Option2。设置默认值为可选，但以下示例中的类构造函数设置了Option1的默认值。Option2具有通过直接初始化属性设置的默认值：

public class MyOptions

{

    public MyOptions()

    {

        // Set default value.

        Option1 = "value1_from_ctor";

    }

    public string Option1 { get; set; }

    public int Option2 { get; set; } = 5;

}

而MyOptions类通过Configure添加到服务容器并绑定到配置：

public void ConfigureServices(IServiceCollection services)

{

    // Example #1: General configuration

    // Register the Configuration instance which MyOptions binds against.

    services.Configure<MyOptions>(Configuration);

}

也可以使用自定义ConfigurationBuilder从设置文件加载选项配置时，确认基路径设置正确，添加到服务容器并绑定到配置：

var configBuilder = new ConfigurationBuilder()

   .SetBasePath(Directory.GetCurrentDirectory())

   .AddJsonFile("appsettings.json", optional: true);

var config = configBuilder.Build();

services.Configure<MyOptions>(config);

以下页面模型通过IOptionsMonitor<TOptions>使用构造函数依赖关系注入来访问设置 (Pages/Index.cshtml.cs)：

public class IndexModel

{

    public IndexModel(IOptionsMonitor<MyOptions> optionsAccessor)

    {

        _options = optionsAccessor.CurrentValue;

    }

    private readonly MyOptions _options;

    public void OnGet()

    {

        // Example #1: Simple options

        var option1 = _options.Option1;

        var option2 = _options.Option2;

        var simpleOptions = $"option1 = {option1}, option2 = {option2}";

    }

}

在Home/Index控制器Action下调用IndexModel.OnGet方法返回包含选项值的字符串：

public HomeController(IOptionsMonitor<MyOptions> optionsAccessor)

{

    _optionsAccessor = optionsAccessor;

}

private readonly IOptionsMonitor<MyOptions> _optionsAccessor;

public IActionResult Index()

{

    IndexModel indexModel = new IndexModel(_optionsAccessor);

    indexModel.OnGet();

    return View();

}

三、通过委托配置简单选项

使用委托设置选项值。此示例应用程序使用新建MyOptionsWithDelegateConfig类 (Models/MyOptionsWithDelegateConfig.cs)：

public class MyOptionsWithDelegateConfig

{

    public MyOptionsWithDelegateConfig()

    {

        // Set default value.

        Option1 = "value1_from_ctor";

    }

    public string Option1 { get; set; }

    public int Option2 { get; set; } = 5;

}

向服务容器添加IConfigureOptions<TOptions>服务。它通过MyOptionsWithDelegateConfig使用委托来配置绑定：

public void ConfigureServices(IServiceCollection services)

{

    // Example #2: Options bound and configured by a delegate

    services.Configure<MyOptionsWithDelegateConfig>(myOptions =>

    {

        myOptions.Option1 = "value1_configured_by_delegate";

        myOptions.Option2 = 500;

    });

}

以下页面模型通过IOptionsMonitor<TOptions>使用构造函数依赖关系注入来访问设置 (Pages/Index.cshtml.cs)：

public class IndexModel

{

    private readonly MyOptionsWithDelegateConfig _optionsWithDelegateConfig;

    public IndexModel(IOptionsMonitor<MyOptionsWithDelegateConfig> optionsAccessorWithDelegateConfig)

    {

        _optionsWithDelegateConfig = optionsAccessorWithDelegateConfig.CurrentValue;

    }

    public void OnGet()

    {

        // Example #2: Options configured by delegate

        var delegate_config_option1 = _optionsWithDelegateConfig.Option1;

        var delegate_config_option2 = _optionsWithDelegateConfig.Option2;

        var simpleOptionsWithDelegateConfig =

                $"delegate_option1 = {delegate_config_option1}, " +

                $"delegate_option2 = {delegate_config_option2}";

    }

}

在Home/Index控制器Action下调用IndexModel.OnGet方法返回包含选项值的字符串：

public HomeController(IOptionsMonitor<MyOptionsWithDelegateConfig> optionsAccessorWithDelegateConfig)

{

    _optionsAccessorWithDelegateConfig = optionsAccessorWithDelegateConfig;

}

private readonly IOptionsMonitor<MyOptionsWithDelegateConfig> _optionsAccessorWithDelegateConfig;

public IActionResult Index()

{

    IndexModel indexModel = new IndexModel(_optionsAccessorWithDelegateConfig);

    indexModel.OnGet();

    return View();

}

每次调用Configure都会将IConfigureOptions<TOptions>服务添加到服务容器。在前面的示例中，Option1和Option2的值同时在appsettings.json中指定，但Option1和Option2的值被配置的委托替代。当启用多个配置服务时，指定的最后一个配置源优于其他源，由其设置配置值。运行应用程序时，页面模型的OnGet方法返回显示选项类值的字符串。

四、子选项配置

将选项绑定到配置时，选项类型中的每个属性都将绑定到窗体property[:sub-property:]的配置键。例如，MyOptions.Option1属性将绑定到从appsettings.json中的option1属性读取的键Option1。在以下代码中，已向服务容器添加IConfigureOptions<TOptions>服务。它将MySubOptions绑定到appsettings.json文件的subsection部分：

public void ConfigureServices(IServiceCollection services)

{

    // Example #3: Suboptions

    // Bind options using a sub-section of the appsettings.json file.

    services.Configure<MySubOptions>(Configuration.GetSection("subsection"));

}

新建MySubOptions类(Models/MySubOptions.cs)将属性SubOption1和SubOption2定义为保留选项值：

public class MySubOptions

{

    public MySubOptions()

    {

        // Set default values.

        SubOption1 = "value1_from_ctor";

        SubOption2 = 5;

    }

    public string SubOption1 { get; set; }

    public int SubOption2 { get; set; }

}

以下页面模型通过IOptionsMonitor<TOptions>使用构造函数依赖关系注入来访问设置(Pages/Index.cshtml.cs)：

public class IndexModel

{

    private readonly MySubOptions _subOptions;

    public IndexModel(IOptionsMonitor<MySubOptions> subOptionsAccessor)

    {

        _subOptions = subOptionsAccessor.CurrentValue;

    }

    public void OnGet()

    {

        // Example #3: Suboptions

        var subOption1 = _subOptions.SubOption1;

        var subOption2 = _subOptions.SubOption2;

        var subOptions = $"subOption1 = {subOption1}, subOption2 = {subOption2}";

    }

}

在Home/Index控制器Action下调用IndexModel.OnGet方法返回包含选项值的字符串：

public HomeController(IOptionsMonitor<MySubOptions> subOptionsAccessor)

{

    _subOptionsAccessor = subOptionsAccessor;

}

private readonly IOptionsMonitor<MySubOptions> _subOptionsAccessor;

public IActionResult Index()

{

    IndexModel indexModel = new IndexModel(_subOptionsAccessor);

    indexModel.OnGet();

    return View();

}

五、通过IOptionsSnapshot重新加载配置数据

IOptionsSnapshot针对请求生命周期访问和缓存选项时，每个请求只能计算一次选项。以下示例演示如何在更改appsettings.json(Pages/Index.cshtml.cs)后创建新的 IOptionsSnapshot<TOptions>。在更改appsettings.json文件和重新加载配置之前，针对服务器的多个请求返回appsettings.json文件提供的配置键值。

public class IndexModel

{

    private readonly MyOptions _snapshotOptions;

    public IndexModel(IOptionsSnapshot<MyOptions> snapshotOptionsAccessor)

    {

        _snapshotOptions = snapshotOptionsAccessor.Value;

    }

    public void OnGet()

    {

        // Example #5: Snapshot options

        var snapshotOption1 = _snapshotOptions.Option1;

        var snapshotOption2 = _snapshotOptions.Option2;

        var snapshotOptions = $"snapshot option1 = {snapshotOption1}, " + $"snapshot option2 = {snapshotOption2}";

    }

}

下面显示从appsettings.json文件加载的初始option1和option2值：

snapshot option1 = value1_from_json, snapshot option2 = -

将appsettings.json文件中的值更改为value1_from_json UPDATED和200。保存appsettings.json 文件。刷新浏览器，查看更新的选项值：

snapshot option1 = value1_from_json UPDATED, snapshot option2 =

六、包含IConfigureNamedOptions的命名选项支持

命名选项支持允许应用程序在命名选项配置之间进行区分。命名选项通过OptionsServiceCollectionExtensions.Configure进行声明，其调用扩展方法ConfigureNamedOptions<TOptions>.Configure：

public void ConfigureServices(IServiceCollection services)

{

    // Example #6: Named options (named_options_1)

    // Register the ConfigurationBuilder instance which MyOptions binds against.

    // Specify that the options loaded from configuration are named

    // "named_options_1".

    services.Configure<MyOptions>("named_options_1", Configuration);

    // Example #6: Named options (named_options_2)

    // Specify that the options loaded from the MyOptions class are named

    // "named_options_2".

    // Use a delegate to configure option values.

    services.Configure<MyOptions>("named_options_2", myOptions =>

    {

        myOptions.Option1 = "named_options_2_value1_from_action";

    });

}

通过OnGet(Pages/Index.cshtml.cs)访问命名选项：

public class IndexModel

{

    private readonly MyOptions _named_options_1;

    private readonly MyOptions _named_options_2;

    public IndexModel(IOptionsSnapshot<MyOptions> namedOptionsAccessor)

    {

        _named_options_1 = namedOptionsAccessor.Get("named_options_1");

        _named_options_2 = namedOptionsAccessor.Get("named_options_2");

    }

    public void OnGet()

    {

        // Example #6: Named options

        var named_options_1 =

            $"named_options_1: option1 = {_named_options_1.Option1}, " +

            $"option2 = {_named_options_1.Option2}";

        var named_options_2 =

            $"named_options_2: option1 = {_named_options_2.Option1}, " +

            $"option2 = {_named_options_2.Option2}";

        var namedOptions = $"{named_options_1} {named_options_2}";

    }

}

在Home/Index控制器Action下调用IndexModel.OnGet方法返回包含选项值的字符串：

public HomeController(IOptionsSnapshot<MyOptions> namedOptionsAccessor)

{

    _namedOptionsAccessor = namedOptionsAccessor;

}

private readonly IOptionsSnapshot<MyOptions> _namedOptionsAccessor;

public IActionResult Index()

{

    IndexModel indexModel = new IndexModel(_namedOptionsAccessor);

    indexModel.OnGet();

    return View();

}

七、使用ConfigureAll方法配置所有选项

使用ConfigureAll方法可以配置所有选项实例。以下代码将针对包含公共值的所有配置实例配置Option1。将以下代码手动添加到Startup.ConfigureServices方法：

services.ConfigureAll<MyOptions>(myOptions =>

{

    myOptions.Option1 = "ConfigureAll replacement value";

});

在Home/Index控制器Action下调用IndexModel.OnGet方法返回包含选项值的字符串：

参考资料：https://www.cnblogs.com/lonelyxmas/p/10302449.html

巴特西

Net core学习系列（十）——Net Core配置

一、前言

二、常规选项配置

三、通过委托配置简单选项

四、子选项配置

五、通过IOptionsSnapshot重新加载配置数据

六、包含IConfigureNamedOptions的命名选项支持

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