在Linq中过滤出空值

Question

我有以下（工作）代码。这是非常不雅观的，我认为它可以使用Linq来重构，因此避免了foreach循环，并且不得不依赖外部列表<>。这个怎么做？由于

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，如果你需要一个列表：

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));