C# 10 - Problems with Entity Framework Core Tracking and Detached Entities in ASP.NET Core API
I'm working with unexpected behavior with Entity Framework Core 6 when dealing with detached entities in my ASP.NET Core 6 Web API. I have a method that retrieves a user object from the database, modifies it, and then I attempt to update it. However, I'm running into the scenario where the changes are not being saved to the database, and I'm getting the following behavior: ```plaintext InvalidOperationException: The entity type 'User' is not being tracked by the context. ``` Here’s a simplified version of my code: ```csharp public class UserController : ControllerBase { private readonly AppDbContext _context; public UserController(AppDbContext context) { _context = context; } [HttpPut("{id}")] public async Task<IActionResult> UpdateUser(int id, User updatedUser) { if (id != updatedUser.Id) { return BadRequest(); } var existingUser = await _context.Users.FindAsync(id); if (existingUser == null) { return NotFound(); } // Detach the existing user to simulate a detached entity _context.Entry(existingUser).State = EntityState.Detached; // Update fields from the updated user existingUser.Name = updatedUser.Name; existingUser.Email = updatedUser.Email; await _context.SaveChangesAsync(); return NoContent(); } } ``` The question seems to stem from the fact that I'm detaching the `existingUser` before saving. I thought this would allow me to update the properties, but now EF Core is complaining about the entity not being tracked. I've tried using `Attach` instead, but that leads to another behavior: ```plaintext DbUpdateConcurrencyException: The database operation was expected to affect 1 row(s) but actually affected 0 row(s). ``` I’ve also considered using AutoMapper to handle the mapping, but I would prefer to understand the underlying EF Core behavior first. What’s the best practice here for updating detached entities without running into tracking issues? Any insights would be appreciated!