1. Introduction
In ASP.NET Core web.config is no longer a proper place for storing application settings. New framework introduces the concept of a json based configuration and the default file which stores the settings now is appsettings.json. Here is a quick tutorial how to use new features.
2. Reading configuration
Let’s assume that our appsettings.json file looks as follows.
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{ "Logging": { "IncludeScopes": false, "LogLevel": { "Default": "Debug", "System": "Information", "Microsoft": "Information" } }, "AvailabilitySearchOptions": { "FlexDaysIn": 2, "FlexDaysOut": 3 } } |
Thanks to ConfigurationBuilder we can parse this config and later on materialize sections or entire file into strongly typed configuration classes. Let’s say we want to parse AvailabilitySearchOptions node to following class
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public class AvailabilitySearchOptions { public int FlexDaysIn { get; set; } public int FlexDaysOut { get; set; } public TimeSpan MinimumConnectionTime { get; set; } public TimeSpan MinimumDepartureTime { get; set; } } |
We can achieve that with following steps. First of all, we need to read entire configuration
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public IConfigurationRoot Configuration { get; } public Startup(IHostingEnvironment env) { var builder = new ConfigurationBuilder() .SetBasePath(env.ContentRootPath) .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true) .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true) .AddEnvironmentVariables(); Configuration = builder.Build(); } |
And in the next step we have to register IOptions<AvailabilitySearchOptions> in the container using services.Configure<TOptions>(IConfiguration section) method
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// This method gets called by the runtime. Use this method to add services to the container. public void ConfigureServices(IServiceCollection services) { // Add framework services. services.AddMvc(); services.Configure<AvailabilitySearchOptions>(Configuration.GetSection("AvailabilitySearchOptions")); } |
Note Configuration.GetSection(“AvailabilitySearchOptions”) passed as argument to services.Configure method.
From now on we can access AvailabilitySearchOptions settings via IOptions<AvailabilitySearchOptions> interface, which you can easily inject into your classes.
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[Route("api/[controller]")] public class OptionsController : Controller { private readonly IOptions<AvailabilitySearchOptions> availabilitySearchOptions; public OptionsController(IOptions<AvailabilitySearchOptions> availabilitySearchOptions) { this.availabilitySearchOptions = availabilitySearchOptions; } public AvailabilitySearchOptions Get() { return availabilitySearchOptions.Value; } } |
3. Populating IOptions<T> from external data source
From time to time, reading configuration just from JSON file might not be enough and for instance you would like to add additional configuration read from some external data source. Fortunately you don’t have to resign from the IOptions<T> class as it is possible to read additional data for literally any other source thanks to IConfigureOptions<T> class. All we have to do is to create a setup class which implements IConfigureOptions<T> interface
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public class AvailabilitySearchOptionsSetupService : IConfigureOptions<AvailabilitySearchOptions> { private readonly ILogger<AvailabilitySearchOptionsSetupService> logger; private readonly IReservationSettingsService reservationSettingsService; public AvailabilitySearchOptionsSetupService(ILogger<AvailabilitySearchOptionsSetupService> logger ,IReservationSettingsService reservationSettingsService) { this.logger = logger; this.reservationSettingsService = reservationSettingsService; } public void Configure(AvailabilitySearchOptions options) { this.logger.LogInformation($"Calling first {typeof(IConfigureOptions<AvailabilitySearchOptions>)} service"); options.MinimumConnectionTime = reservationSettingsService.GetMinimumConnectionTime(); } } |
And then registering this class in our container
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// This method gets called by the runtime. Use this method to add services to the container. public void ConfigureServices(IServiceCollection services) { // Add framework services. services.AddMvc(); services.Configure<AvailabilitySearchOptions>(Configuration.GetSection("AvailabilitySearchOptions")); services.AddSingleton<IConfigureOptions<AvailabilitySearchOptions>, AvailabilitySearchOptionsSetupService>(); } |
From now on, when value of IOptions<AvailabilitySearchOptions> is accessed for very first time, Configure method from AvailabilitySearchOptionsSetupService will be called and you will be able to set additional values for your settings. Note that values from appsettings.json will already be there.
In addition, it is possible to have multiple implementations of IConfigureOptions<T> so if you want your setup to be split into multiple classes you are good to go.
Source code for this post can be found here
very good thanks