Unable to create an object of type 'GameContext'

Question

I have created an asp.net core project, And also i have created one ClassLibrary and i have joined them to one solution. I write my way step by step :

1-dotnet new sln 2-dotnet new mvc -o GameShop 3-dotnet new classlib -o GameShop.Data Then i created a class in GameShop.Data/Domain/User, I named it "User.cs"

using System;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;

namespace GameShop.Data.Domain.User
{
    public class User
    {
          [Key]
        public int UserId { get; set; }
        [Display(Name = "نام کاربری")]
        [Required(ErrorMessage = "لطفا {0} را وارد کنید")]
        [MaxLength(200, ErrorMessage = "{0} نمی تواند بیشتر از {1} باشد")]
        public string UserName { get; set; }
        [Display(Name = "ایمیل")]
        [Required(ErrorMessage = "لطفا {0} را وارد کنید")]
        [MaxLength(400, ErrorMessage = "{0} نمی تواند بیشتر از {1} باشد")]
        [EmailAddress(ErrorMessage = "ایمیل وارد شده معتبر نمی باشد")]
        public string Email { get; set; }

        [Display(Name = "کلمه عبور")]
        [Required(ErrorMessage = "لطفا {0} را وارد کنید")]
        [MaxLength(200, ErrorMessage = "{0} نمی تواند بیشتر از {1} باشد")]
        public string Password { get; set; }

        [Display(Name = "تاریخ ثبت نام")]
        public DateTime RegisterDate { get; set; }
        [Display(Name = "کد فعال سازی")]
        public string ActiveCode { get; set; }

       

    }
}

This is my startup :

 public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
             services.AddDbContext<GameContext>(option =>
            {
                option.UseSqlServer(Configuration.GetConnectionString("GameShop"));
            });
        }

This my ConnectionString :

{
  "ConnectionStrings": {
    "GameShop": "Data Source=.;Initial Catalog=GameShop-DB;Integrated Security=True"
  }

And this is my Context that its address is :(GameShop.Data/Context/GameContext)

using System;
using Microsoft.EntityFrameworkCore;
using GameShop.Data.Domain.User;

namespace GameShop.Data.Context
{
    public class GameContext:DbContext
    {
        public GameContext(DbContextOptions<GameContext> option):base(option)
        {
            
        }
        public DbSet<User> Users { get; set; }
        
    }
}

Thats my codes. But whn i want to "add migrations", i have an error that says : Unable to create an object of type 'GameContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

These are the packages that i have in both GameShop.csproj and Gameshop.csproj :

<ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="5.0.3" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="5.0.3">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="5.0.3" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="5.0.3">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.3" />
     <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="5.0.2" />
  </ItemGroup>

(I tried this without any ClassLibrary(just one "asp.net core mvc project ") and i didn`t have any error)

So can anyone help me what to do ???

Answer 1

If you're running "add migrations" from the command line, the project GameShop.Data does not have access to the connection string in your MVC project's appsettings.json file.

I think you need an implementation of IDesignTimeDbContextFactory in your Data project so that the migration engine can connect to the appropriate database and determine the 'gap' between target database and model. Something like:

class GameShopDbContextFactory : IDesignTimeDbContextFactory<GameContext>
{
   public GameShopDbContextFactory CreateDbContext(string[] args)
   {
      var builder = new DbContextOptionsBuilder<GameContext>();
      var connStr = {ADD YOUR CONNECTION STRING HERE}
      dbContextBuilder.UseSqlServer(connStr);
      return new GameContext(builder.Options);
   }
}