Search if exist before insert in Linq DB in C# for WP8

Question

I am working on a WP8 questions application, the application send the data to the DB but will skip the exist data. I have a class called "DBHelper.cs" and it contains

public static void InsertQuestion(Question oQuestion)
{
    using (var context = new QuestionContext(ConnectionString))
    {
        if(context.DatabaseExists())
        {
            Question oQuestionWord = (from ostd in context.Questions where ostd.Word == oQuestion.Word select ostd).Single();
            if (oQuestionWord.Word == null)
            {
                context.Questions.InsertOnSubmit(oQuestion);
                context.SubmitChanges();
            }
        }
    }
}

And this code in the mainpage.xaml.cs

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    Question oQuestion = new Question();
    oQuestion.Word = "One";
    DBHelper.InsertQuestion(oQuestion);``
    oQuestion = new Question();
    oQuestion.Word = "Two";
    DBHelper.InsertQuestion(oQuestion);
    oQuestion = new Question();
    oQuestion.Word = "One";
    DBHelper.InsertQuestion(oQuestion);
    base.OnNavigatedTo(e);
}

There is no errors when Building the solution, but it crashes when launching the app.

score 3 · Accepted Answer · edited May 23 '17 at 11:57

3

I believe the reason of the error is the Single method. Single throws an exception if it finds more than one record. Try using FirstOrDefault instead:

var oQuestionWord = context.Questions.FirstOrDefault(q => q.Word == oQuestion.Word);
if (oQuestionWord != null && oQuestionWord.Word == null)
{
    context.Questions.InsertOnSubmit(oQuestion);
    context.SubmitChanges();
}

And probably you didn't get a useful exception message because it happened in OnNavigatedTo event.You might want to take a look at this question...

edited May 23 '17 at 11:57

Community

1
1

answered Jul 30 '14 at 17:01

Selman Genç

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This code works perfect, just edit "(oQuestionWord != null && oQuestionWord.Word == null)" to "(oQuestionWord == null)",thank you! :D – Afterlife Jul 30 '14 at 17:43

Search if exist before insert in Linq DB in C# for WP8

1 Answers1