Unable to create an object of type 'DataContext'

Question

I've created default DB context as I do always and tried to add migration. I got an error:

"Unable to create an object of type 'DataContext'. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728"

My DB Context:

public class DataContext : IdentityDbContext<User, ApplicationRole, Guid>
{
    public DataContext(DbContextOptions<DataContext> opts) : base(opts) { }


    public DbSet<User> Users { get; set; }

    public DbSet<Coach> Coaches { get; set; }

    public DbSet<Coaching> Coachings { get; set; }

    public DbSet<CoachingVideo> CoachingVideos { get; set; }

    public DbSet<AppFile> Files { get; set; }
}

My DB Context injection (already in Program.cs)

public static class DataContextExtension
{
    public static IServiceCollection AddDataContext(this IServiceCollection services, IConfiguration builder)
    {
        services.AddDbContext<DataContext>(
                o => o.UseSqlServer(builder.GetConnectionString("DefaultConnection")));
        return services;
    }
}

I tried to install different versions, but nothing...

score 1 · Accepted Answer · answered Jun 28 '23 at 16:51

1

First, make sure the connection string is correct

Then use this code

services.AddDbContext<DataContext>(options =>
            {
                options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection"));
            });

or

services.AddDbContext<DataContext>(options =>
            {
                options.UseSqlServer("Conection string");
            });

If the above code does not work , use this code section 1

public DataContext(DbContextOptions options) : base(options)
    {
    }

    protected override void OnConfiguring(DbContextOptionsBuilder options)
    {
        if (!options.IsConfigured)
        {
            options.UseSqlServer("CONNECTION STRING");
        }
    }

If the above code does not work, disable your code temporarily and enter this code and after updating the database, comment this code and activate your code.

//public DataContext(DbContextOptions options) : base(options)
  //  {
   // }

protected override void OnConfiguring(DbContextOptionsBuilder options)
    {
        
      options.UseSqlServer("CONNECTION STRING");
        
    }

answered Jun 28 '23 at 16:51

abolfazl sadeghi

2,277
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My connection string is correct, I've added an empty constructor to my db context and OnConfiguring method. Migrations are creating, but when I want to apply them to DB, I get new error "Instance failure.". It seems that EF doesn't see my conn string – Ярослав Терех Jun 28 '23 at 17:03
first Test Conectionstring with udl file "https://www.c-sharpcorner.com/blogs/database-connection-string-mssql-server-easy-steps2" after use last step – abolfazl sadeghi Jun 28 '23 at 17:06
It's OK. Even my previous projects worked with this connection string (of course with other Database name.)\ Maybe problem in package versions? – Ярослав Терех Jun 28 '23 at 17:13
And make sure that the data access project(DAL) is in the console and the final project(UI) is the default.https://stackoverflow.com/a/44788785/10193401 – abolfazl sadeghi Jun 28 '23 at 17:14
I already made it – Ярослав Терех Jun 28 '23 at 17:16
ah, ok, it works. But how to get connection string from appsetting in OnConfiguring method? – Ярослав Терех Jun 28 '23 at 17:36
Or the connection string in the app setting is not correct. Or it "builder.GetConnectionString("DefaultConnection")" doesn't work properly here,i have two solution(1.use this code and try to solve problem 2.segregate program to "Startup.cs or program" and use this code "https://github.com/abolfazlSadeqi/Net7JwtAuthentication/blob/master/UI/API/Startup.cs") – abolfazl sadeghi Jun 28 '23 at 17:46
1

Please, check my code in github. https://github.com/YaroslavTerekh/FeelYourBody/tree/feature/add-new-entities – Ярослав Терех Jun 28 '23 at 18:05
@ЯрославТерех .I checked your Code,your problem is related line "builder.Services.AddValidatorsFromAssemblies(AppDomain.CurrentDomain.GetAssemblies());" ,when I commented This line,your code corrected – abolfazl sadeghi Jun 28 '23 at 23:05
1

Thanks, you really helped me, but why when I use .AddValidatorsFromAssembly it works? Can you give me a link to an article about it? – Ярослав Терех Jun 29 '23 at 12:02
you're welcome,I so sorry, I don't know the exact reason,I used Trial(Test) and error to reach a conclusion(result) – abolfazl sadeghi Jun 29 '23 at 12:34
1

Ah, ok, anyway thanks so much, you helped me. Have a nice day – Ярослав Терех Jun 29 '23 at 12:43

Unable to create an object of type 'DataContext'

1 Answers1