Does EF Core's `.AsNoTracking()` Affect Database Writes When Updating Entities?

EF Core's .AsNoTracking() and Database Writes: A Clarification

Entity Framework Core (EF Core) offers .AsNoTracking() to optimize queries by disabling change tracking. This is beneficial when you only need to read data and don't intend to modify it within the current context. However, its impact on subsequent updates requires careful consideration.

Your example highlights a common point of confusion:

Scenario: Using a per-request context, you first retrieve a user with .AsNoTracking(), then attempt to update the same user.

Step 1: context.Set<user>().AsNoTracking() retrieves a user without tracking.

Step 2: context.Set<user>() attempts to update the untracked user.

The Crucial Difference:

The key difference between using .AsNoTracking() and not using it lies in how EF Core manages the entity's state.

• Without .AsNoTracking(): EF Core tracks the entity. When you update and save, EF Core automatically detects the changes and updates the database accordingly. This is the simpler, more straightforward approach if you intend to modify the entity.

• With .AsNoTracking(): The entity is not tracked. EF Core doesn't know about the changes you make. To update the database, you must explicitly attach the entity to the context using context.Entry(user).State = EntityState.Modified; before calling context.SaveChanges(). Failure to do so will likely result in a new record being inserted instead of the existing one being updated.

In short, .AsNoTracking() provides performance gains for read-only operations. For update operations, either avoid .AsNoTracking() for the initial retrieval or be prepared to manually manage the entity's state within the context before saving changes. The choice depends on your specific needs and whether you prioritize performance or simpler code.

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