public async Task SaveAsync(IEnumerable <FileInfoDto> newDtoFiles)
{
var categories = await GetOrCreateCategoriesFor(newDtoFiles);
var newFiles = newDtoFiles.Select(dto =>
{
var withCategory = categories.Single(c => c.Name == dto.Category);
return(FileInfo.From(dto, withCategory));
}).ToList();
await MakeIndexesUniqueFor(newFiles);
await db.Files.SaveAsync(newFiles);
await db.CommitChangesAsync();
}