Fix issue on UnitOfWork.Save

[Ian-Webster]

This code from the UnitOfWork class assume that there were be a non zero result from the SaveChangesAsync method;

public async Task<bool> Save(CancellationToken token)
{
    try
    {
        return await _context.SaveChangesAsync(token) > 0;
    }
    catch (Exception ex)
    {
        _logger.LogError(ex, "UnitOfWork failed to save changes");
        return false;
    }
}

this is an invalid assumption - SaveChangesAsync only returns a positive number when there are rows inserted (i.e. an addition) for updates the value will be zero.

The code should be as follows instead;

public async Task<bool> Save(CancellationToken token)
{
    try
    {
        await _context.SaveChangesAsync(token);
        return true;
    }
    catch (Exception ex)
    {
        _logger.LogError(ex, "UnitOfWork failed to save changes");
        return false;
    }
}

To see a live example of this bug look at MovieRepository.SaveMovie in the Movies repo;

public async Task<bool> SaveMovie(Movie movie, CancellationToken token)
{
    var movieDao = movie.Id != Guid.Empty ? await _movieRepository.FirstOrDefault(m => m.Id == movie.Id, token): null;

    if (movieDao == null)
    {
        movieDao = new Repo.Movie
        {
            Id = movie.Id,
            Title = movie.Title,
            GenreId = (short)movie.Genre,
            YearOfRelease = movie.YearOfRelease,
            RunningTime = movie.RunningTime
        };
        if (!await _movieRepository.Add(movieDao, token)) return false;
    }
    else
    {
        movieDao.GenreId = (short)movie.Genre;
        movieDao.RunningTime = movie.RunningTime;
        movieDao.Title = movie.Title;
        movieDao.YearOfRelease = movie.YearOfRelease;
    }

    return await _unitOfWork.Save(token);
}

the final line returns false on edits.