CODEWITHSUNDEEP
c#
tariq
tariq

Reputation: 43

Prevent duplicate names in a DataGridView

I am using this code to check and prevent duplicate names when I insert names in a database table. So if the name exists it will prevent the insert and a MessageBox will be displayed warning that the name exists. if not, a MessageBox is displayed confirming the operation is done.

string Coonstring = "datasource=localhost;port=3306;username=root;password=****;Charset=utf8";

using (MySqlConnection connectionDatabase = new MySqlConnection(Coonstring))
{
    try
    {
        connectionDatabase.Open();
        using (MySqlCommand select = new MySqlCommand("SELECT COUNT(*) FROM project.name_registry WHERE Name=@NM", connectionDatabase))
        {
            select.Parameters.AddWithValue("@NM", txt.Text);
            if (select.ExecuteScalar() != 0)
            {
                MessageBox.Show("Name exists");
                return;
            }
        }
        using (MySqlCommand cmddata = new MySqlCommand("INSERT INTO project.name_registry (name) VALUES(@NM)", connectionDatabase))
        {
            cmddata.Parameters.AddWithValue("@NM", txt.Text);
            cmddata.ExecuteNonQuery();
            MessageBox.Show("Done");
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

My problem is when I run the code above, the following error is thrown

Specified cast is not valid.

What does this mean?

Upvotes: 0

Views: 183

Answers (4)

M P
M P

Reputation: 2337

Maybe something like this?

var count = 0;
var obj = select.ExecuteScalar();
if(obj != null)
{
    count = Convert.ToInt32(obj);

    if(count != 0)
    {
        MessageBox.Show("Name exists");
        return;
    }
}
else
{
    throw new Excepion();
}

Upvotes: 0

Sreenath Ganga
Sreenath Ganga

Reputation: 736

use parse or cast

if ((Int32)select.ExecuteScalar() != 0)
{
    MessageBox.Show("Name exists");
    return;
}

or 

if(int.parse(select.ExecuteScalar().ToString())!=0)
{
MessageBox.Show("Name exists");
        return;
}

Upvotes: 0

user3584428
user3584428

Reputation: 

if (select.ExecuteScalar() != 0)
{
    MessageBox.Show("Name exists");
    return;
}

use 

if(int.Parse(select.ExecuteScalar()) !=0)

Upvotes: 1

leskovar
leskovar

Reputation: 661

Both with parse

if (int.Parse(select.ExecuteScalar()) != 0)
{
    MessageBox.Show("Name exists");
    return;
}

or casting

if (((int)select.ExecuteScalar()) != 0)
{
    MessageBox.Show("Name exists");
    return;
}

should work.

Upvotes: 0

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