.net core Mvc Unable to create a DbContext of type AppDbContext. The exception Object reference

trisetia...

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User: trisetia302
Posted: on Sep 01, 2025 01:40 PM
Forum: ASP.Net Web Forms
Answer: 1
Views: 182

I was tried to solve thi problem but until now I can't find the problem. I was search the solution from over internet but still get same error and can't fix it. in many my privious project work fine but now I get this problem.

AppDbContext.cs

using Microsoft.EntityFrameworkCore; using POS_System.Models;

namespace POS_System.DbCtx { public class AppDbContext:DbContext { public AppDbContext(DbContextOptions<AppDbContext> options):base(options) { } public DbSet<Karyawan> Karyawans { get; set; } public DbSet<PeranUser> PeranUsers { get; set; } public DbSet<Permission> Permissions { get; set; } public DbSet<RolePermission> RolePermissions { get; set; } public DbSet<RoleUser> RoleUsers { get; set; } public DbSet<Pelanggan> Pelanggans { get; set; } public DbSet<JenisPelanggan> JenisPelanggans { get; set; } public DbSet<Kategori> Kategoris { get; set; } public DbSet<Produk> Produks { get; set; } public DbSet<ProdukGambar> ProdukGambars { get; set; } public DbSet<Inventori> Inventoris { get; set; } public DbSet<Transaksi> Transaksis { get; set; } public DbSet<AlurKas> AlurKass { get; set; } public DbSet<MetodeBayar> MetodeBayars { get; set; } public DbSet<LaporanKeuangan> LaporanKeuangans { get; set; }

protected override void OnModelCreating(ModelBuilder modelBuilder) { base.OnModelCreating(modelBuilder); } } } Program.cs

using Microsoft.EntityFrameworkCore; using POS_System.DbCtx; using POS_System.Repository;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container. builder.Services.AddControllersWithViews(); builder.Services.AddDbContext<AppDbContext>(options => options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"))); builder.Services.AddScoped<IPeranUserRepository, PeranUserRepository>();

var app = builder.Build();

// Configure the HTTP request pipeline. if (!app.Environment.IsDevelopment()) { app.UseExceptionHandler("/Home/Error"); // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts. app.UseHsts(); }

app.UseHttpsRedirection(); app.UseRouting();

app.UseAuthorization(); the error is PM> dotnet ef migrations add Init Build started... Build succeeded. Unable to create a 'DbContext' of type 'AppDbContext'. The exception 'Object reference not set to an instance of an object.' was thrown while attempting to create an instance. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

app.MapStaticAssets();

app.MapControllerRoute( name: "default", pattern: "{controller=Dashboard}/{action=Index}/{id?}") .WithStaticAssets();

app.Run();

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Mudassar

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User: Mudassar
Replied: on Sep 01, 2025 01:44 PM
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The error "Unable to create a 'DbContext' of type 'AppDbContext'. The exception 'Object reference not set to an instance of an object.'" indicates that during the design-time operations of Entity Framework Core (such as adding migrations), the tooling is unable to instantiate your AppDbContext due to a NullReferenceException. This typically arises when a dependency required by your DbContext or its configuration is not properly initialized or available at design time.

Common causes and solutions include:

Missing or Incorrect Constructor in AppDbContext:
- Ensure your AppDbContext has a public constructor that accepts DbContextOptions<AppDbContext> as a parameter. This is the standard way EF Core injects options.
- If you have other constructors, ensure they are also properly handled or that the DbContextOptions constructor is the one being used by the design-time tooling.

Code

    public class AppDbContext : DbContext
    {
        public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
        {
        }

        // ... your DbSets
    }

Dependency Injection Issues at Design Time:
- If your AppDbContext or its configuration relies on other services registered in your Program.cs (or Startup.cs in older .NET versions), ensure these services are available and correctly configured when EF Core attempts to create the DbContext instance during design time.
- Scoped services, in particular, can be problematic in design-time scenarios if not handled correctly. Consider using AddTransient for services that don't need a single instance per request if this is causing issues.
- For complex scenarios with dependency injection, consider implementing IDesignTimeDbContextFactory<AppDbContext> to explicitly control how your DbContext is created during design time.

Code

    public class AppDbContextFactory : IDesignTimeDbContextFactory<AppDbContext>
    {
        public AppDbContext CreateDbContext(string[] args)
        {
            var optionsBuilder = new DbContextOptionsBuilder<AppDbContext>();
            // Configure your options here, e.g., for a local database
            optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=YourDesignDb;Trusted_Connection=True;");

            return new AppDbContext(optionsBuilder.Options);
        }
    }

Incorrect Startup Project or Default Project:
When running EF Core commands (like Add-Migration) from the Package Manager Console or command line, ensure the correct project is set as the "Startup Project" in Visual Studio, and if using a multi-project solution, the "Default Project" in the Package Manager Console should be the project containing your AppDbContext.
Null References in OnConfiguring or Model Configuration:
If you are overriding the OnConfiguring method in your AppDbContext or performing model configuration, ensure that no NullReferenceException occurs within these methods during design time. This can happen if you are trying to access uninitialized variables or services.
Incompatible Package Versions:
Verify that your Entity Framework Core NuGet packages (e.g., Microsoft.EntityFrameworkCore, Microsoft.EntityFrameworkCore.SqlServer, Microsoft.EntityFrameworkCore.Tools) are compatible and of consistent versions within your project.

By addressing these potential areas, the NullReferenceException preventing the creation of your AppDbContext during design-time operations should be resolved.

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.net core Mvc Unable to create a DbContext of type AppDbContext. The exception Object reference

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