ASP.NET Core 5: Make your options immutable
source link: https://anthonygiretti.com/2020/08/19/asp-net-core-5-make-your-options-immutable/
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ASP.NET Core 5: Make your options immutable
Introduction
If you’ve been using ASP.NET Core 5 for a while, you’ll be delighted to learn that a major improvement of C# 9, in other words C# 9 (delivered with .NET 5) that allows the creation of immutable objects through Init-only properties. As a result, you’ll have the ability to set up your application options so that they’re immutable. After all, these are a kind of constants that you don’t necessarily want to change after initialization, or even ban it. So it’s possible with ASP.NET Core 5 and C# 9.
If you don’t know what are Init-only properties, you can read my article here: https://anthonygiretti.com/2020/06/16/introducing-c-9-init-only-properties/
Prerequisites
For now, .NET 5 and ASP.NET Core 5 are still in preview, if you want to be able to reuse the code I will show you you’ll need to install:
<Project Sdk="Microsoft.NET.Sdk"> <PropertyGroup> <TargetFramework>net5.0</TargetFramework> <LangVersion>preview</LangVersion> </PropertyGroup> </Project>
Configure options as immutable
I have already written an article you can read for more details here if you want to configure your options in a simpler way: https://anthonygiretti.com/2019/09/15/simplified-options-usage-in-asp-net-core-2/
I will take the same sample to show you how to make your options immutable, you just need to replace in your options class set by init:
namespace DemoAspNet5.Models { public class SmtpConfiguration { public string Domain { get; init; } public int Port { get; init; } } }
Once done, you’ll need to register your options:
using DemoAspNet5.Models; using Microsoft.AspNetCore.Builder; using Microsoft.AspNetCore.Hosting; using Microsoft.AspNetCore.Http; using Microsoft.Extensions.Configuration; using Microsoft.Extensions.DependencyInjection; using Microsoft.Extensions.Hosting;
namespace DemoAspNet5 { public class Startup { public Startup(IConfiguration configuration) { Configuration = configuration; }
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services) { services.AddControllers();
var smtpConfiguration = new SmtpConfiguration(); Configuration.Bind("SmtpConfiguration", smtpConfiguration);
services.AddSingleton(smtpConfiguration); }
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline. public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { if (env.IsDevelopment()) { app.UseDeveloperExceptionPage(); }
app.UseRouting();
app.UseEndpoints(endpoints => { endpoints.MapControllers();
endpoints.MapGet("/", async context => { await context.Response.WriteAsync("Hello World!"); }); }); } } }
And now you are ready to consume them, and you won’t be able to modify your options, example:
using DemoAspNet5.Models; using Microsoft.AspNetCore.Mvc;
namespace DemoAspNet5.Controllers { [Route("api/[controller]")] [ApiController] public class ConfigController : ControllerBase { private readonly SmtpConfiguration _smtpConfiguration;
public ConfigController(SmtpConfiguration smtpConfiguration) { _smtpConfiguration = smtpConfiguration; }
[HttpGet("smtp")] public IActionResult GetSmtpConfig() { // _smtpConfiguration.Port = 570; Error CS8852 Init-only property or indexer 'SmtpConfiguration.Port' can only be assigned in an object initializer, or on 'this' or 'base' in an instance constructor or an 'init' accessor.
return Ok(_smtpConfiguration); } } }
As you can see you are not able to modifie your options, you’ll get a compiler exception: Error CS8852 Init-only property or indexer ‘{your property}’ can only be assigned in an object initializer, or on ‘this’ or ‘base’ in an instance constructor or an ‘init’ accessor.
Very practical feature isn’t it ? 
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