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Entity Framework Code Stopped Working

Kmcnet 1,236 Reputation points
2025-10-04T15:32:34.34+00:00

Hello everyone and thanks for the help in advance. I have a Visual Studio 2022 project that utilizes Entity Framework. I last opened the project 3 days ago and the project worked fine. Today, I opened the project and immediately was met with several errors type used in a using statement must implement System.IDisposable. The code throwing the error:

            using (var ctx = new myDbContext())
            {

            }

which is used multiple times throughout the project, but only throws the error within one controller. There is another error in myDbContext:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)

throws no suitable method found to override. These errors happened without any changes to the project. I tried cleaning the project, but that did not work. Any help would be appreciated.

Developer technologies | Visual Studio | Other
Developer technologies | Visual Studio | Other
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  1. Leon Tran (WICLOUD CORPORATION) 350 Reputation points Microsoft External Staff
    2025-10-06T04:24:31.7633333+00:00

    Hi Kmcnet,

    Thank you for your response. I’ve updated the solution based on your answer.

    1. Kill namespace/alias collisions in the failing controller

    Remove any aliases or wrong usings:

    // BAD (causes EF6 or custom DbContext to be used)
using System.Data.Entity;
using DbContext = Some.Other.Namespace.DbContext;
using myDbContext = Some.Other.Namespace.MyDbContext;

    Explicitly use your EF Core context

    using YourApp.Data; // where myDbContext is declared
using var ctx = new YourApp.Data.myDbContext();
    1. Align EF Core 9 with .NET 9 and keep provider versions in lockstep In .csproj:
    <PropertyGroup>
  <TargetFramework>net9.0</TargetFramework>
</PropertyGroup>
<ItemGroup>
  <PackageReference Include="Microsoft.EntityFrameworkCore" Version="9.0.9" />
  <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="9.0.9" />
</ItemGroup>

    Then:

    dotnet clean
dotnet restore --force
dotnet build
dotnet list package

    Ensure no EF6 (EntityFramework) sneaked in.

    1. Delete bin/obj and NuGet caches to fix stale type resolution
    dotnet nuget locals all --clear
rm -rf bin obj  # (Windows: rd /s /q bin && rd /s /q obj)
dotnet restore
dotnet build
    1. Prefer DI over new myDbContext() to avoid mismatches
    // Program.cs / Startup.cs
services.AddDbContext<myDbContext>(options =>
    options.UseSqlServer(Configuration.GetConnectionString("Default")));

// Controller
public class FooController : Controller
{
    private readonly myDbContext _ctx;
    public FooController(myDbContext ctx) => _ctx = ctx;
}

    If #1 fixes it, you had a namespace/alias conflict. If #2 fixes it, you had a framework/package mismatch. If #3 fixes it, it was cache corruption. If you still see the error after these, rename the context to a unique name (e.g., AppDbContext) to break collisions across the solution.

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