Unable to resolve service for type while attempting to activate

Question

In my ASP.NET Core application, I get the following error:

InvalidOperationException: Unable to resolve service for type 'Cities.Models.IRepository' while attempting to activate 'Cities.Controllers.HomeController'.

I the HomeController I am trying to pass the Cities getter to the view like so:

public class HomeController : Controller {     private readonly IRepository repository;      public HomeController(IRepository repo) => repository = repo;      public IActionResult Index() => View(repository.Cities); } 

I have one file Repository.cs that contains an interface and its implementation like so:

public interface IRepository {     IEnumerable<City> Cities { get; }     void AddCity(City newCity); }  public class MemoryRepository : IRepository {     private readonly List<City> cities = new List<City>();      public IEnumerable<City> Cities => cities;      public void AddCity(City newCity) => cities.Add(newCity); } 

My Startup class contains the default-generated code from the template. I have made any changes:

public class Startup {     public Startup(IConfiguration configuration)     {         Configuration = configuration;     }      public IConfiguration Configuration { get; }      public void ConfigureServices(IServiceCollection services)     {         services.AddControllersWithViews();     }      public void Configure(IApplicationBuilder app, IWebHostEnvironment env)     {         ...     } } 

Answer 1

For the Dependency Injection framework to resolve IRepository, it must first be registered with the container. For example, in ConfigureServices, add the following:

services.AddScoped<IRepository, MemoryRepository>(); 

For .NET 6+, which uses the new hosting model by default, add the following in Program.cs instead:

builder.Services.AddScoped<IRepository, MemoryRepository>(); 

AddScoped is just one example of a service lifetime:

For web applications, a scoped lifetime indicates that services are created once per client request (connection).

See the docs for more information on Dependency Injection in ASP.NET Core.

Answer 2

We are getting this error in Entity frame work core database first approach. I followed below steps and error got resolvedenter code here

Step 1: Check Your context class constructor should be like this

public partial class ZPHSContext : DbContext {     public ZPHSContext(DbContextOptions<ZPHSContext> dbContextOptions)         : base(dbContextOptions)     {     } }      

Step 2: In Startup file

public void ConfigureServices(IServiceCollection services) {     services.AddMvc();     services.AddDbContext<ZPHSContext>(options =>         options.UseSqlServer(             Configuration.GetConnectionString("BloggingDatabase"))); }      

Step 3: Connection string in appsettings

"ConnectionStrings": {     "BloggingDatabase": "Server=****;Database=ZPHSS;Trusted_Connection=True;" } 

Step 4: Remove default code in OnConfiguring method in context class

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { }