Issue on delete record from SQL Server database through C# program

Question

I'm new to C# programming. I've written a program in C# which has been connected to a SQL Server database through LINQ connector. Everything ran smoothly. But now I get below error when I want to delete a record from program with a specific condition:

An unhandled exception of type 'System.ArgumentNullException' occurred in EntityFramework.dll

Additional information: Value cannot be null.

This is my C# code:

private void btnDel_Click(object sender, EventArgs e)  
{
    DialogResult result = MessageBox.Show("Sales system ", "Are you sure to delete", MessageBoxButtons.YesNo, MessageBoxIcon.Question);

    if (result == DialogResult.Yes)
    {
        string photo = txtPhoto.ToString();

        var edit = db.tblPersons.Where(c => c.PhotoNo == photo || c.ReceiptNo == photo).FirstOrDefault();
        db.tblPersons.Remove(edit);
        db.SaveChanges();

        MessageBox.Show("Info deleted");
    }
}

Does anyone know about my issue in this occasion?

I suspect that you need to check how the txtPhoto field is getting populated. It looks like maybe photo is an invalid value, which is causing edit to be null, and entity framework cannot remove a null value from tblPersons. — jwatts1980
– jwatts1980, Commented May 29, 2019 at 20:22

Anas Alweish · Accepted Answer · 2019-05-29 20:48:39Z

1

I believe that control is a textbox, however, get the text.

example:

string photo = txtPhoto.Text;

edited May 29, 2019 at 20:48

Anas Alweish

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answered May 29, 2019 at 19:55

Leandro Bianch

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1 Comment

Mitch Over a year ago

The .ToString() is not neccessary. Should be just var photo = txtPhoto.Text;

Paulo Campez · Accepted Answer · 2019-05-29 20:29:52Z

0

You should check if your var edit is not null before try to remove

private void btnDel_Click(object sender, EventArgs e)   {
        DialogResult result = MessageBox.Show("Sales system ", "Are you sure to delete", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
        if (result == DialogResult.Yes)
        {
            string photo = txtPhoto.ToString();

            var edit = db.tblPersons.Where(c => c.PhotoNo == photo || c.ReceiptNo == photo).FirstOrDefault();
            if(edit != null)
            {
              db.tblPersons.Remove(edit);
              db.SaveChanges();
              MessageBox.Show("Info deleted");
            }
            else
            {
             MessageBox.Show(photo + " Incorrect");
            }
        }
    }

edited May 29, 2019 at 20:29

answered May 29, 2019 at 19:57

Paulo Campez

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1 Comment

jwatts1980 Over a year ago

This will stop the error from throwing, but it will not solve the issue of why the variable txtPhoto has an invalid value which is likely the root cause of the issue.

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