在Linq中过滤掉空值

Question

我有以下（工作）代码。它非常不优雅，我认为它只能使用Linq重构，因此避免了foreach循环并且不得不依赖外部List＆lt;＆gt;。这该怎么做？谢谢

  List<string> answerValues = new List<string>();
  foreach (Fillings filling in fillings)
  {
      string answer = filling.Answers.Where(a => a.Questions == question)
          .Select(a => a.Answer).FirstOrDefault();
      if (!string.IsNullOrEmpty(answer)) answerValues.Add(answer);
  }

Answer 1

IEnumerable<string> answerValues = fillings
                                    .SelectMany(f => f.Answers)
                                    .Where(a => a.Questions == question)
                                    .Select(a => a.Answer)
                                    .Where(ans => !string.IsNullOrEmpty(ans));

或者如果您需要一个清单：

IList<string> answerValues = fillings
                                    .SelectMany(f => f.Answers)
                                    .Where(a => a.Questions == question)
                                    .Select(a => a.Answer)
                                    .Where(ans => !string.IsNullOrEmpty(ans))
                                    .ToList();

Answer 2

var answerValues = (
    from f in fillings
    from a in f.Answers
    where a.Question == question
    where !String.IsNullOrEmpty(a.Answer)
    select a.Answer).ToList();

Answer 3

fillings.SelectMany(x => x.Answers.Where(a => a.Question == question)
                                  .Select(a => a.Answer)
                                  .FirstOrDefault())
        .Where(x => !string.IsNullOrEmpty(x));