How can I do exception handling in C#?

Question

I am using a try / catch block. The query is executed successfully and gives a message, but after that it gives nullvalue massage for Householdid column which is foreign key, although the text box took the value and data is inserted. I want that this error message is not shown.

private void OK_HouseHoldMember_Click_1(object sender, EventArgs e)
{
     //Datagrid view

     string ConString = @"Data Source=.;Initial Catalog=HouseHoldProfile;Integrated Security=True";
     SqlConnection conn = new SqlConnection(ConString);
     conn.Open();
     textBox13.Text = textBox3.Text;

     try
     {
         foreach (DataGridViewRow dr in dataGridView1.Rows)
         {
             textBox13.Text = textBox3.Text;

             SqlCommand sqlCommand_3 = new SqlCommand();
             sqlCommand_3.CommandType = CommandType.StoredProcedure;
             sqlCommand_3.Connection = conn;
             sqlCommand_3.CommandText = "InsertHouseHoldMembertbl";

             sqlCommand_3.Parameters.AddWithValue("@HouseHoldID", dr.Cells["آی دی خانواده"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@Gender", dr.Cells["جنسیت"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@Age", dr.Cells["سن تکمیل شده"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@MaritalStatus", dr.Cells["حالت مدنی"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@HeadRelationship", dr.Cells["قرابت با رییس خانواده"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@Student", dr.Cells["شاگرد"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@EducationLevelMature", dr.Cells["سطح سواد"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@HighestEducationLevel", dr.Cells["بلند ترین درجه تحصیل"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@job", dr.Cells["شغل اصلی"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@TemporaryJob", dr.Cells["شغل فرعی"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@Disability", dr.Cells["معلولیت"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@Addict", dr.Cells["اعتیاد"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@addictType", dr.Cells["نوعیت اعتیاد"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@Pregnant", dr.Cells["حاملگی"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@MilkChildwoman", dr.Cells["طفل سو تغذی"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@UnderNutrationChild", dr.Cells["طفل سو تغذی"].Value ?? DBNull.Value);
             sqlCommand_3.Parameters.AddWithValue("@CauseNotSchool", dr.Cells["علت مکتب نرفتن"].Value ?? DBNull.Value);

             sqlCommand_3.ExecuteNonQuery();
         }
     }
     catch (Exception ex)
     {
         MessageBox.Show(ex.Message);
     }
}

Answer 1

It looks as though you are coercing the value of HouseHoldID , which might be allowing it to get through without throwing an exception.

I suggest trying to remove the:

?? DBNull.Value

From that line, so that it throws an exception if it's null , as the value shouldn't be null .