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5 posts

2026-10-27 errors ef-core dotnet

Fix: The property 'X' is part of a key and so cannot be modified or marked as modified in EF Core

EF Core never updates a key value on a tracked entity. Stop copying the key from DTOs, use a unique index instead of an alternate key, and change a real key by inserting a new row and deleting the old one. Tested on EF Core 10.0.14.

2026-10-11 ef-core dotnet-10 csharp

How to check whether an entity is already tracked by the DbContext before attaching it in EF Core

Use DbSet.Local.FindEntry(key) to ask the change tracker whether an entity with a given key is tracked, without a database round trip or a scan. Why Entry(entity).State lies for this question, why Find queries, and a tested AttachOrMerge helper for EF Core 10.

2026-09-09 errors ef-core ef-core-11

Fix: Complex entry original ordinal '-1' is invalid when saving a ToJson complex collection

Upgrade Microsoft.EntityFrameworkCore to 10.0.10 or later. Before that, growing a nested collection under a second ToJson complex property crashed SaveChanges.

2026-09-09 errors ef-core ef-core-11

Fix: The complex type collection must be initialized to a non-null value

On EF Core 10.0.x, nulling a complex property that holds a two-element collection inside a ToJson complex collection breaks DetectChanges. Fixed in 11.0.0-rc.1.

2026-05-07 errors csharp dotnet

Fix: The instance of entity type cannot be tracked because another instance with the same key value is already being tracked

EF Core 11 throws when two objects share a primary key inside one DbContext. Detach the old one or update it in place. AsNoTracking on the read prevents the collision.