ASP.NET Core中的Options選項(xiàng)模式
1.前言
選項(xiàng)（Options）模式是對(duì)配置（Configuration）的功能的延伸。在12章（ASP.NET Core中的配置二）Configuration中有介紹過該功能（綁定到實(shí)體類、綁定至對(duì)象圖、將數(shù)組綁定至類）而選項(xiàng)模式又有個(gè)選項(xiàng)類（TOptions），該選項(xiàng)類作用是指：把選項(xiàng)類中的屬性與配置來源中的鍵關(guān)聯(lián)起來。舉個(gè)例，假設(shè)json文件有個(gè)Option1鍵，選項(xiàng)類中也有個(gè)叫Option1的屬性名，經(jīng)過選項(xiàng)配置，這樣就能把json中的鍵的值映射到選項(xiàng)類屬性值中。也可以理解在項(xiàng)目應(yīng)用中，把一個(gè)json文件序列化到.net類。
2.常規(guī)選項(xiàng)配置
選項(xiàng)類必須為包含公共無參數(shù)構(gòu)造函數(shù)的非抽象類。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類(Models/MyOptions.cs)，以下類MyOptions具有三種屬性：Option1和 Option2。設(shè)置默認(rèn)值為可選，但以下示例中的類構(gòu)造函數(shù)設(shè)置了Option1的默認(rèn)值。Option2具有通過直接初始化屬性設(shè)置的默認(rèn)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類通過Configure添加到服務(wù)容器并綁定到配置：
public void ConfigureServices(IServiceCollection services)
{
// Example #1: General configuration
// Register the Configuration instance which MyOptions binds against.
services.Configure<MyOptions>(Configuration);
}也可以使用自定義ConfigurationBuilder從設(shè)置文件加載選項(xiàng)配置時(shí)，確認(rèn)基路徑設(shè)置正確，添加到服務(wù)容器并綁定到配置：
var configBuilder = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json", optional: true);
var config = configBuilder.Build();
services.Configure<MyOptions>(config);以下頁(yè)面模型通過IOptionsMonitor<TOptions>使用構(gòu)造函數(shù)依賴關(guān)系注入來訪問設(shè)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下調(diào)用IndexModel.OnGet方法返回包含選項(xiàng)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();
}
3.通過委托配置簡(jiǎn)單選項(xiàng)
使用委托設(shè)置選項(xiàng)值。此示例應(yīng)用程序使用新建MyOptionsWithDelegateConfig類 (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;
}向服務(wù)容器添加IConfigureOptions<TOptions>服務(wù)。它通過MyOptionsWithDelegateConfig使用委托來配置綁定：
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;
});
}以下頁(yè)面模型通過IOptionsMonitor<TOptions>使用構(gòu)造函數(shù)依賴關(guān)系注入來訪問設(shè)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下調(diào)用IndexModel.OnGet方法返回包含選項(xiàng)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();
}
每次調(diào)用Configure都會(huì)將IConfigureOptions<TOptions>服務(wù)添加到服務(wù)容器。在前面的示例中，Option1和Option2的值同時(shí)在appsettings.json中指定，但Option1和Option2的值被配置的委托替代。當(dāng)啟用多個(gè)配置服務(wù)時(shí)，指定的最后一個(gè)配置源優(yōu)于其他源，由其設(shè)置配置值。運(yùn)行應(yīng)用程序時(shí)，頁(yè)面模型的OnGet方法返回顯示選項(xiàng)類值的字符串。
4.子選項(xiàng)配置
將選項(xiàng)綁定到配置時(shí)，選項(xiàng)類型中的每個(gè)屬性都將綁定到窗體property[:sub-property:]的配置鍵。例如，MyOptions.Option1屬性將綁定到從appsettings.json中的option1屬性讀取的鍵Option1。在以下代碼中，已向服務(wù)容器添加IConfigureOptions<TOptions>服務(wù)。它將MySubOptions綁定到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類(Models/MySubOptions.cs)將屬性SubOption1和SubOption2定義為保留選項(xiàng)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; }
}以下頁(yè)面模型通過IOptionsMonitor<TOptions>使用構(gòu)造函數(shù)依賴關(guān)系注入來訪問設(shè)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下調(diào)用IndexModel.OnGet方法返回包含選項(xiàng)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();
}
5.通過IOptionsSnapshot重新加載配置數(shù)據(jù)
IOptionsSnapshot針對(duì)請(qǐng)求生命周期訪問和緩存選項(xiàng)時(shí)，每個(gè)請(qǐng)求只能計(jì)算一次選項(xiàng)。以下示例演示如何在更改appsettings.json(Pages/Index.cshtml.cs)后創(chuàng)建新的 IOptionsSnapshot<TOptions>。在更改appsettings.json文件和重新加載配置之前，針對(duì)服務(wù)器的多個(gè)請(qǐng)求返回appsettings.json文件提供的配置鍵值。
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}";
}
}下面顯示從appsettings.json文件加載的初始o(jì)ption1和option2值：
snapshot option1 = value1_from_json, snapshot option2 = -1
將appsettings.json文件中的值更改為value1_from_json UPDATED和200。保存appsettings.json 文件。刷新瀏覽器，查看更新的選項(xiàng)值：
snapshot option1 = value1_from_json UPDATED, snapshot option2 = 200
6.包含IConfigureNamedOptions的命名選項(xiàng)支持
命名選項(xiàng)支持允許應(yīng)用程序在命名選項(xiàng)配置之間進(jìn)行區(qū)分。命名選項(xiàng)通過OptionsServiceCollectionExtensions.Configure進(jìn)行聲明，其調(diào)用擴(kuò)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";
});
}通過OnGet(Pages/Index.cshtml.cs)訪問命名選項(xiàng)：
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下調(diào)用IndexModel.OnGet方法返回包含選項(xiàng)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();
}
使用ConfigureAll方法配置所有選項(xiàng)
使用ConfigureAll方法可以配置所有選項(xiàng)實(shí)例。以下代碼將針對(duì)包含公共值的所有配置實(shí)例配置Option1。將以下代碼手動(dòng)添加到Startup.ConfigureServices方法：
services.ConfigureAll<MyOptions>(myOptions =>
{
myOptions.Option1 = "ConfigureAll replacement value";
});在Home/Index控制器Action下調(diào)用IndexModel.OnGet方法返回包含選項(xiàng)值的字符串：
以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。
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