在C＃中的列表中查找项目

Question

The code below contains a foreach loop that loops through a list of string collection which contains XML. While enumerating through the collection, it reads the question and answer elements and adds them to the list collection. I need to ensure that no repeated question is added to the list collection.

The code below questionnaire.QuestionAnswers.Add(fataQuestionsAnswers) adds the elements to the list collection. The problem that I am facing is that the repeated questions are getting added to the list. I tried to put the following condition that is:

if (questionnaire.QuestionAnswers.Find(a => a.Question != fataQuestionsAnswers.Question) == null) 

but that doesn't seem to work.

var fataQuestionnaireData = DbAccess.GetFatcaQuestionnaire(contactId);
if (fataQuestionnaireData != null)
{
    var questionnaire = new FatcaQuestionnaire();

    foreach (var fatcaQuestionnaire in fataQuestionnaireData)
    {
        //var QData = GetObjectFromStream<FatcaQuestionnaire>fataQuestionnaireData);
        //FatcaQuestionnaire.Deserialize(fataQuestionnaireData);

        XDocument doc = XDocument.Parse(fatcaQuestionnaire.ToString(CultureInfo.InvariantCulture));

        // w.WriteLine("The value of doc" + doc);

        doc.Descendants("QuestionAnswer").ToList().ForEach(questionAnswer =>
        {
            var fataQuestionsAnswers = new QuestionAnswers();
            {
                //var questionAnswer = qa.Element("QuestionAnswer");

                var questionElement = questionAnswer.Element("Question");


                if (questionElement != null )

                    fataQuestionsAnswers.Question = questionElement.Value;

                //if (questionElement != null)
                //    w.WriteLine("The value of questionElement" + questionElement.Value);

                var answerElement = questionAnswer.Element("Answer");
                if (answerElement != null)
                    fataQuestionsAnswers.Answer = answerElement.Value;

                //if (answerElement != null)
                //    w.WriteLine("The value of answerElement" + answerElement.Value);

                var sqa = questionAnswer.Element("SubQuestionAnswer");
                if (sqa != null)

                {
                    var subQuestionElement = sqa.Element("Question");
                    if (subQuestionElement != null)
                        fataQuestionsAnswers.SubQuestionAnswer.Question = subQuestionElement.Value;

                    //if (subQuestionElement != null)
                    //    w.WriteLine("The value of answerElement" + subQuestionElement.Value);


                    var subAnswerElement = sqa.Element("Answer");
                    if (subAnswerElement != null)
                        fataQuestionsAnswers.SubQuestionAnswer.Answer = subAnswerElement.Value;

                    //if (subQuestionElement != null)
                    //    w.WriteLine("The value of answerElement" + subQuestionElement.Value);
                }

                if (questionnaire.QuestionAnswers.Find(a => a.Question != fataQuestionsAnswers.Question) == null)
                questionnaire.QuestionAnswers.Add(fataQuestionsAnswers);
                //fatcaQuestionsList.Add(fataQuestionsAnswers);
            }

            fatca.Questionnaire.Add(fataQuestionsAnswers);
        });
    }
}

Answer 1

Use Any instead

if(!questionnaire.QuestionAnswers.Any(a => a.Question == fataQuestionsAnswers.Question)) 
{ 
    questionnaire.QuestionAnswers.Add(fataQuestionsAnswers); 
}

Answer 2

Is it possible there's trailing spaces / casing differences?

if(!questionnaire.QuestionAnswers.Any(a => a.Question.Trim().Equals(fataQuestionsAnswers.Question.Trim(), StringComparison.OrdinalIgnoreCase))) 
{ 
    questionnaire.QuestionAnswers.Add(fataQuestionsAnswers); 
}

Answer 3

You have your condition wrong, you are looking for questionanswers where the question does not match, you should be looking where they do match and checking that the result is null. (switch the != with ==)

It should be

if (questionnaire.QuestionAnswers.Find(a => a.Question == fataQuestionsAnswers.Question) == null)

However I would change it to Any() as it is a bit nearer and easier to read, it returns a true if one of the items in your list matches the condition that you specify.

if(!questionnaire.QuestionAnswers.Any(a => a.Question == fataQuestionAnswers.Question)) {
   questionnaire.QuestionAnswers.Add(fataQuestionsAnswers);
}