Dependency Injection в ASP.NET Core

1public interface IEmailService
2{
3    Task SendAsync(string to, string subject, string body);
4}
5
6public class SmtpEmailService : IEmailService
7{
8    private readonly SmtpClient _client;
9    
10    public SmtpEmailService(SmtpClient client)
11    {
12        _client = client;
13    }
14    
15    public async Task SendAsync(string to, string subject, string body)
16    {
17        await _client.SendMailAsync("from@example.com", to, subject, body);
18    }
19}

1// Program.cs
2builder.Services.AddControllers();
3
4// Scoped — один экземпляр на запрос
5builder.Services.AddScoped<IEmailService, SmtpEmailService>();
6
7// Singleton — один экземпляр на всё приложение
8builder.Services.AddSingleton<ICacheService, MemoryCacheService>();
9
10// Transient — новый экземпляр каждый раз
11builder.Services.AddTransient<ILogger, ConsoleLogger>();

1[ApiController]
2[Route("api/[controller]")]
3public class UsersController : ControllerBase
4{
5    private readonly IUserService _userService;
6    private readonly IEmailService _emailService;
7    private readonly ILogger<UsersController> _logger;
8
9    public UsersController(
10        IUserService userService,
11        IEmailService emailService,
12        ILogger<UsersController> logger)
13    {
14        _userService = userService;
15        _emailService = emailService;
16        _logger = logger;
17    }
18
19    [HttpPost]
20    public async Task<IActionResult> Create(CreateUserDto dto)
21    {
22        _logger.LogInformation("Creating user {Email}", dto.Email);
23        
24        var user = await _userService.CreateAsync(dto);
25        await _emailService.SendAsync(dto.Email, "Welcome", "...");
26        
27        return CreatedAtAction(nameof(GetById), new { id = user.Id }, user);
28    }
29}

1// Использование фабрики для создания сервисов
2builder.Services.AddScoped<IRepositoryFactory, RepositoryFactory>();
3
4public interface IRepositoryFactory
5{
6    IRepository<T> Create<T>() where T : class;
7}
8
9public class RepositoryFactory : IRepositoryFactory
10{
11    private readonly IServiceProvider _provider;
12    
13    public RepositoryFactory(IServiceProvider provider)
14    {
15        _provider = provider;
16    }
17    
18    public IRepository<T> Create<T>() where T : class
19    {
20        return _provider.GetRequiredService<IRepository<T>>();
21    }
22}

1// Регистрация декоратора
2builder.Services.AddScoped<IUserService, UserService>();
3builder.Services.AddScoped<IUserService>(sp =>
4{
5    var inner = sp.GetRequiredService<IUserService>();
6    return new LoggingUserService(inner);
7});
8
9public class LoggingUserService : IUserService
10{
11    private readonly IUserService _inner;
12    
13    public LoggingUserService(IUserService inner)
14    {
15        _inner = inner;
16    }
17    
18    public async Task<User> GetByIdAsync(int id)
19    {
20        Console.WriteLine($"Getting user {id}");
21        var result = await _inner.GetByIdAsync(id);
22        Console.WriteLine($"Got user {result.Name}");
23        return result;
24    }
25}

1// Регистрация всех сервисов из assembly
2builder.Services.Scan(scan => scan
3    .FromAssemblyOf<Startup>()
4    .AddClasses(classes => classes.Where(t => t.Name.EndsWith("Service")))
5    .AsImplementedInterfaces()
6    .WithScopedLifetime());

1// Мокирование для тестов
2var mockService = new Mock<IUserService>();
3mockService.Setup(s => s.GetByIdAsync(1))
4    .ReturnsAsync(new User { Id = 1, Name = "Test" });
5
6var controller = new UsersController(mockService.Object, ...);