Entity Framework Core issue: 'DbContext' creation error with defined primary key

Question

I'm developing an ASP.NET Core application and encountering an issue with Entity Framework Core. Despite having defined a primary key in my Task entity, I get an error when trying to create an instance of DbContext.

The error message is:

Unable to create a 'DbContext' of type ''. The exception 'The entity type 'Task' requires a primary key to be defined. If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'.

Here is the relevant code for my Task entity:

using System.ComponentModel.DataAnnotations;

namespace taskManager.Services.TaskApi.Models
{
    public class Task
    {
        [Key]
        public int TaskId {  get; set; }
        [Required]
        public string Title { get; set; }
        public string Description { get; set; }
        [Required]
        public DateTime DateTime { get; set; }
        public bool IsCompleted { get; set; }
        public bool IsImportant { get; set; }        
    }
}

And my AppDbContext looks like this:

using Microsoft.EntityFrameworkCore;
using taskManager.Services.TaskApi.Models;

namespace taskManager.Services.TaskApi.Data
{
    public class AppDbContext : DbContext
    {
        public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }
        public DbSet<Task> Tasks { get; set; }
    }
}

The DbContext is registered in my Program.cs as follows:

var builder = WebApplication.CreateBuilder(args);
// ... other configurations ...
builder.Services.AddDbContext<AppDbContext>(option =>
{
    option.UseSqlServer("Server=DESKTOP-39TI737\\SQLEXPRESS;Database=Manage_Task;Trusted_Connection=True;TrustServerCertificate=True");
});
// ... other configurations ...

Task exists in the framework already, perhaps you are referencing the wrong one. In the long run, it's probably better to rename it anyway. — DavidG
– DavidG, Commented Dec 21, 2023 at 22:47

DavidG · Accepted Answer · 2023-12-22 00:50:37Z

1

The code as you have posted will work perfectly fine. However, the .NET Framework already contains a type Task and you are almost certainly referencing that instead of the one you have defined. You have various options to fix this:

Rename your class to be something other than Task. This would be the preferred solution as having the conflict is only going to cause more problems in the future.
Make sure you are referencing the correct class. This may be done by ensuring you have the correct using .... import statements or by specifying the full namespace for the class, for example:
```
public DbSet<taskManager.Services.TaskApi.Models.Task> Tasks { get; set; }
```

answered Dec 22, 2023 at 0:50

DavidG

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