Getting Error While trying to connect to a SQL Server database

Question

I'm new to .NET Core. While I'm connecting to a SQL Server database, I'm getting an error:

Unable to resolve service for type 'MVC_Core.Business.Repo' while attempting to activate 'MVC_Core.Controllers.AbcController

My StartUp.cs:

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<DbContext>(options =>
              options.UseSqlServer(Configuration.GetConnectionString("BloggingDatabase")));
    services.AddTransient<IRepo,Repo>();
}

Application.js:

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning"
    },
    "ConnectionStrings": {
      "BloggingDatabase": "Data Source=MD\\MD;Initial Catalog=Ems_local;User ID=sa;Password=123"
    }
  },
  "AllowedHosts": "*"
}

My DbContext:

public class ConnectToDb : DbContext
{
        //public DbConnection(){}

        public ConnectToDb(DbContextOptions<ConnectToDb> options) : base(options)
        {
        }

        public virtual DbSet<Country> Country { get; set; }
    }

This connection I'm calling like this:

public class Repo : IRepo
{
        private ConnectToDb db = null;

        public Repo(ConnectToDb _db)
        {
            db = _db;
        }

While I'm calling this in my controller as

Repo ObjRepo;

public AbcController(Repo _objRepo)
{
    ObjRepo = _objRepo;
}

[Route("Hello")]
public IActionResult Index()
{
    var x = ObjRepo.GetCountry();
    return Json("abc" + x);
}

Please guide me - why am I getting this error?

Is this an Instanced Sql Server Install or default? Pretty sure your connection string is wrong — mvermef
– mvermef, Commented Dec 29, 2018 at 22:10
Then how in heck do you plan on this working? Kinda need it to have this work, since that what you are telling it to connect to with whole configuration, MD\\MD is what then? — mvermef
– mvermef, Commented Dec 30, 2018 at 6:19

Vadim Martynov · Accepted Answer · 2018-12-29 21:22:13Z

2

You have two problems with dependency injection in ASP.NET Core.

When you call AddTransient method you add new service of the type specified in the first type parameter with an implementation type specified in the second one. It allows you to use service as an dependency without specifying its implementation.

You've registered class Repo as an implementation for the interface IRepo and then should use interface to resolve it:

public AbcController(IRepo _objRepo)

Aslo, AddDbContext is an extension method for registration DbContext and EF infrastructure as a service and it works in the same way. Here is an important part of the implementation for your example:

// TContextService is the type parameter
serviceCollection.TryAdd(new ServiceDescriptor(typeof(TContextService), typeof(TContextService), ServiceLifetime.Scoped));

It means that in the serviceCollection adds new service of the type TContextService with implementation type TContextService.

So, you should fix registration for your DbContext with specific class name as a generic parameter to resolve it in class Repo:

services.AddDbContext<ConnectToDb>(options =>
          options.UseSqlServer(Configuration.GetConnectionString("BloggingDatabase")));

edited Dec 29, 2018 at 21:22

answered Dec 29, 2018 at 20:00

Vadim Martynov

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3 Comments

JOHN Mickh Over a year ago

Im Getting Error as Unable to resolve service for type 'MVC_Core.ConnectionString.ConnectToDb' while attempting to activate 'MVC_Core.Business.Repo'

Vadim Martynov Over a year ago

@JOHNMickh I'm trying to find potential problems with DbContext registration but can't find anything. You can register ConnectToDb directly as a service with services.AddScoped<ConnectToDb>(); but it'll be workaround for the real problem. Is there any additional info about exception?

Edward Over a year ago

@VadimMartynov Have you changed services.AddDbContext<DbContext> to services.AddDbContext<ConnectToDb>? Share us your current startup.cs.

Derviş Kayımbaşıoğlu · Accepted Answer · 2018-12-29 20:00:49Z

0

Your registration is with IRepo. You need to chang below code from Repo to IRepo

IRepo ObjRepo;
public AbcController(IRepo _objRepo)
{
    ObjRepo = _objRepo;
}

besides you need to use ConnectToDb DbContext as interface when you are registering your DbContext

 services.AddDbContext<ConnectToDb>(options => options.UseSqlServer(
    Configuration.GetConnectionString("BloggingDatabase")));

answered Dec 29, 2018 at 20:00

Derviş Kayımbaşıoğlu

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1 Comment

JOHN Mickh Over a year ago

Im Getting Error as Unable to resolve service for type 'MVC_Core.ConnectionString.ConnectToDb' while attempting to activate 'MVC_Core.Business.Repo'

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