ASP.NET Core Web API InvalidOperationException: Unable to resolve service

Question

i'm trying to build a simple api as a test to a future api for a project. But i keep having this error

InvalidOperationException: Unable to resolve service for type 'AspnetCore_WebApi.Models.TarefaContext' while attempting to activate 'AspnetCore_WebApi.Models.TarefaRepositorio'.

Here is TarefaContext.cs

using Microsoft.EntityFrameworkCore;
namespace AspnetCore_WebApi.Models
{
    public class TarefaContext : DbContext
    {
        public TarefaContext(DbContextOptions<TarefaContext> options)
            : base(options)
        { }
        public DbSet<TarefaItem> TarefaItens { get; set; }
    }
}

TarefaRepositorio.cs

using System.Collections.Generic;
using System.Linq;
namespace AspnetCore_WebApi.Models
{
    public class TarefaRepositorio : ITarefaRepositorio
    {
        private readonly TarefaContext _context;
        public TarefaRepositorio(TarefaContext context)
        {
            _context = context;
            Add(new TarefaItem { Nome = "Item1" });
        }
        public IEnumerable<TarefaItem> GetAll()
        {
            return _context.TarefaItens.ToList();
        }
        public void Add(TarefaItem item)
        {
            _context.TarefaItens.Add(item);
            _context.SaveChanges();
        }
        public TarefaItem Find(long key)
        {
            return _context.TarefaItens.FirstOrDefault(t => t.Chave == key);
        }
        public void Remove(long key)
        {
            var entity = _context.TarefaItens.First(t => t.Chave == key);
            _context.TarefaItens.Remove(entity);
            _context.SaveChanges();
        }
        public void Update(TarefaItem item)
        {
            _context.TarefaItens.Update(item);
            _context.SaveChanges();
        }
    }
}

TarefaController.cs

using System.Collections.Generic;
using AspnetCore_WebApi.Models;
using Microsoft.AspNetCore.Mvc;
namespace AspnetCore_WebApi.Controllers
{
    [Route("api/[controller]")]
    public class TarefaController : Controller
    {
        private readonly ITarefaRepositorio _tarefaRepositorio;
        public TarefaController(ITarefaRepositorio tarefaRepositorio)
        {
            _tarefaRepositorio = tarefaRepositorio;
        }
        [HttpGet]
        public IEnumerable<TarefaItem> GetAll()
        {
            return _tarefaRepositorio.GetAll();
        }

        [HttpGet("{id}", Name = "GetTarefa")]
        public IActionResult GetById(long id)
        {
            var item = _tarefaRepositorio.Find(id);
            if (item == null)
            {
                return NotFound();
            }
            return new ObjectResult(item);
        }

        [HttpPost]
        public IActionResult Create([FromBody] TarefaItem item)
        {
            if (item == null)
            {
                return BadRequest();
            }
            _tarefaRepositorio.Add(item);
            return CreatedAtRoute("GetTarefa", new { id = item.Chave }, item);
        }
    }
}

ITarefaRepositorio.cs

using System.Collections.Generic;
namespace AspnetCore_WebApi.Models
{
    public interface ITarefaRepositorio
    {
        void Add(TarefaItem item);
        IEnumerable<TarefaItem> GetAll();
        TarefaItem Find(long key);
        void Remove(long key);
        void Update(TarefaItem item);
    }
}

Answer 1

Error message describes that dependency injection cannot resolve your TarefaContext class. You should register your db context in your startup ConfigureServices method using services.AddDbContext method. For more information see Microsoft documentation: https://learn.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext