如何使用 EF Core 与孩子一起更新数据

Question

I have these two models:

public class Film
{
    public long Id { get; set; }
    [Required]
    public string Title { get; set; }
    [Required]
    public string Director { get; set; }
    public string Synopsis { get; set; }
    public int? Release { get; set; }
    [Required]
    public Genre Genre { get; set; }
}

public class Genre
{
    public long Id { get; set; }
    public string Description { get; set; }
}

And I want to be able to update a Film's Genre through a PUT method. I am currently trying this, but I get the following error:

[HttpPut]
public async Task<IActionResult> UpdateFilm(Film film)
{
    var existingFilm = await _context.Films
        .Include(f => f.Genre)
        .FirstOrDefaultAsync(f => f.Id == film.Id);

    if (existingFilm == null)
    {
        return NotFound(new JsonResponse { Success = false, Message = "Impossible to update, film was not found", Data = null });
    }

    existingFilm.Title = film.Title;
    existingFilm.Synopsis = film.Synopsis;
    existingFilm.Release = film.Release;
    existingFilm.Director = film.Director;

    if (existingFilm.Genre.Id != film.Genre.Id)
    {
        existingFilm.Genre.Id = film.Genre.Id;
        existingFilm.Genre.Description = film.Genre.Description;
        //_context.Entry(existingFilm.Genre).State = EntityState.Modified;
        _context.Entry(existingFilm).CurrentValues.SetValues(film);
    }

    _context.Films.Update(existingFilm);

    try
    {
        await _context.SaveChangesAsync();
    }
    catch (Exception e)
    {
        return BadRequest(new JsonResponse { Success = false, Message = e.Message, Data = null });
    }

    return Ok(new JsonResponse { Success = true, Message = "Film updated with success", Data = film });
}

The error message is:

System.InvalidOperationException: The property 'Id' on entity type 'Genre' is part of a key and so cannot be modified or marked as modified. To change the principal of an existing entity with an identifying foreign key first delete the dependent and invoke 'SaveChanges' then associate the dependent with the new principal.

Anyone able to help? Thanks a lot.

Answer 1

According to the error, its existingFilm.Genre.Id that you cannot update the id, if its not equal to the id.

My suggestion would be ignore the id update, but if it is necessary:

if (existingFilm.Genre.Id != film.Genre.Id)
{
    var genre = _context.Genre.FirstOrDefault(x => x.Id == film.Genre.Id);
    // Update the fields needed except the id

    existingFilm.Genre = genre;
}