CODEWITHSUNDEEP
sqlsilverlightwcflinq
Schoof
Schoof

Reputation: 2855

LINQ to SQL in silverlight exception

This is a continution of my previous question: Could not find an implementation of the query pattern

Now I managed to query my database I can't seem to get the content on my webpage.

I try to return the code using the following code: 

private void button1_Click(object sender, RoutedEventArgs e)
{
    Service1Client client = new Service1Client();

    client.GetPersoonByIDCompleted += new EventHandler<GetPersoonByIDCompletedEventArgs>(client_GetPersoonByIDCompleted);
    client.GetPersoonByIDAsync("1");
}

void client_GetPersoonByIDCompleted(object sender, GetPersoonByIDCompletedEventArgs e)
{
    if (e.Error != null)
        textBox1.Text = e.Error.ToString();
    else
        label1.Content = e.Result.Voornaam.ToString();
}

However when I press the button I get the following errors:

Object reference not set to an instance of an object.

at SilverlightApplication1.MainPage.client_GetPersoonByIDCompleted(Object sender, GetPersoonByIDCompletedEventArgs e) at SilverlightApplication1.ServiceReference1.Service1Client.OnGetPersoonByIDCompleted(Object state)

The weird thing is it works when I do not use LINQ, but normal SQL.

    string sql = "SELECT ID, naam, voornaam, leeftijd FROM tblPersoon WHERE id=@pmID";
    Persoon pers = null;
    string connstr = ConfigurationManager.ConnectionStrings["connDB"].ConnectionString;

    using (SqlConnection cn = new SqlConnection(connstr))
    {
        SqlCommand com = new SqlCommand(sql, cn);
        com.Parameters.AddWithValue("pmID", id);
        cn.Open();
        SqlDataReader reader = com.ExecuteReader();
        if (reader.Read())
        {
            pers = new Persoon();
            pers.ID = reader.GetString(0);
            pers.Naam = reader.GetString(1);
            pers.Voornaam = reader.GetString(2);
            pers.Leeftijd = reader.GetInt32(3);
        }
    }

    return pers;
}

LINQ result:

LINQ

SQL result:

SQL

Thank you for helping me, I grealy appreciate it! Thomas

Upvotes: 0

Views: 207

Answers (1)

Ken Smith
Ken Smith

Reputation: 20445

You get that particular exception by trying to reference the "e.Result" property when it's not valid, i.e., when the method call returned an exception instead of a value. Before you reference e.Result, confirm that e.Error == null, and if it doesn't, indulge yourself in some error handling or messaging code, e.g.:

void client_GetPersoonByIDCompleted(object sender, GetPersoonByIDCompletedEventArgs e)
{
    if (e.Error != null)
    {
        MessageBox.Show("An error occurred: " + e.Error.ToString());
    }
    else
    {
        label1.Content = e.Result;
    }
}

Or something of that sort.

Upvotes: 2

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