.NET Core 允许从配置文件中懒惰地读取设置,将其反序列化为POCO,然后使用一行代码将POCO注册到内置DI容器中:
.NET Core allows to lazily read settings from configuration file, de-serialize it to a POCO and register that POCO in built-in DI container with one line of code:
public void ConfigureServices(IServiceCollection services) { services.Configure<MyOptions>(Configuration.GetSection("MySection")); }然后,任何消费者都可以解析 IOptions< MyOptions> 访问该POCO:
Then any consumer can resolve IOptions<MyOptions> to access that POCO:
public HomeController(IOptions<MyOptions> optionsAccessor) { MyOptions options = optionsAccessor.Value; }这种方法有很多缺点:
-
Microsoft.Extensions.Options 包中不必要的依赖项:
Unnecessary dependency from Microsoft.Extensions.Options package:
模拟,测试和显式实例创建变得更加冗长。
Mocking, testing and explicit instance creation become a bit more verbose.
什么是没有 IOptions< T> 的最简单解决方案?
What is the easiest solution to resolve options without IOptions<T>?
推荐答案反序列化 configuration.Get< TOptions> 或 configuration.Bind 的选项,并在DI容器中将POCO明确注册为单例:
Deserialize options with configuration.Get<TOptions> or configuration.Bind call and register a POCO in DI container explicitly as singleton:
public void ConfigureServices(IServiceCollection services) { services.AddSingletonFromFile<MyOptions>(Configuration.GetSection("MySection")); } //... public static IServiceCollection AddSingletonFromFile<TOptions>( this IServiceCollection services, IConfiguration configuration) where TOptions : class, new() { //POCO is created with actual values TOptions options = configuration.Get<TOptions>(); services.AddSingleton(options); return services; }UPD:感谢@NPNelson提供的。Get< TOptions>()提示。
UPD: thanks to @NPNelson for .Get<TOptions>() hint.
然后 IOptions< T> 解析不再
public HomeController(MyOptions options) { _options = options; }仅供参考:也可以从外部服务(数据库等)读取方式:
FYI: reading from an external service (database etc.) is also possible this way:
public void ConfigureServices(IServiceCollection services) { services.AddTransientFromService<OptionsReader, MyOptions>(reader => reader.GetOptions()); } //... public static void AddTransientFromService<TReader, TOptions>( this IServiceCollection services, Func<TReader, TOptions> getOptions) where TReader : class where TOptions : class { services.AddTransient(provider => getOptions(provider.GetService<TReader>())); }备注:
- Singleton并不懒惰(总是在启动时实例化);
- 如果是单例注册,则在运行时会丢失任何更新选项的功能(.NET Core通过 reloadOnChange 选项设置本地支持运行时文件重新加载: .AddJsonFile( appsettings.json,false,reloadOnChange:true));
- Singleton is not lazy (it's always instantiated at startup);
- In case of singleton registration, any ability to update options at runtime is lost (.NET Core natively supports runtime file reloading with reloadOnChange option setup: .AddJsonFile("appsettings.json", false, reloadOnChange: true));
如果您确实需要重新加载文件,但仍然不想使用 IOptions ,请考虑临时解析。当然,按请求解决可能会导致性能显着下降。
If you really need the file reload and you still don't want to use IOptions, consider a transient resolving. Of course, per-request resolving can lead to the significant perfomance decrease.
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在没有IOptions< T>的情况下从appsettings.json中读取和使用设置吗?
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