What are the latest bugs and fixes in C# Entity Framework Core migrations in 2025 (.NET 9 / .NET 10)?

Fix #1 — EF Tools vs runtime version mismatch

Always keep your Tools and Design packages on the same major version as your runtime. Run these in your startup project:

dotnet add package Microsoft.EntityFrameworkCore.Tools --version 10.0.0
dotnet add package Microsoft.EntityFrameworkCore.Design --version 10.0.0

Pro tip: When upgrading EF Core, treat Tools, Design, and the core runtime packages as a single upgrade unit — never upgrade one without the others.

Fix #2 — Missing Design package

The Design package must be in your startup project, not just your infrastructure/data project. In your startup project's .csproj:

<PackageReference Include="Microsoft.EntityFrameworkCore.Design"
  Version="10.0.0">
  <PrivateAssets>all</PrivateAssets>
  <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
</PackageReference>

The PrivateAssets=all flag ensures it's a dev-only dependency and won't be published to production.

Fix #3 — Migration assembly mismatch (multi-project solutions)

Always specify both --project (where migrations live) and --startup-project (your API/web project) explicitly:

dotnet ef migrations add InitialCreate \
  --project src/MyApp.Infrastructure \
  --startup-project src/MyApp.Api

Also make sure your DbContext registration includes the migrations assembly:

options.UseSqlServer(connectionString, x =>
  x.MigrationsAssembly("MyApp.Infrastructure"));

Fix #4 — Safely removing a bad migration

Never manually delete migration files. Always follow this safe sequence:

Step 1: Roll back the database first
Update-Database -TargetMigration LastGoodMigration

Step 2: Then remove the bad migration file safely
dotnet ef migrations remove

If you already deleted the file manually, query __EFMigrationsHistory to find the last applied migration, then run Update-Database to that target to resync.

Bonus tip — never run migrations auto-apply in production

Avoid context.Database.Migrate() in your startup pipeline for production environments. Generate a SQL script instead and review it before applying: dotnet ef migrations script --idempotent

Quick reference checklist