Delete foreign Key

Question

I tried to delete foreign key in table NatureCharge that refer for primary key of Famille's table, because I need to delete a multiple row in Famille

For deleting multiple row, it works, but the problem with deleting row in NatureCharge The tables look like that
the Code :

private void DeleteFamBtn_Click(object sender, EventArgs e)
    {
        List<DataGridViewRow> selectedRows = (from row in DataGridViewFamille.Rows.Cast<DataGridViewRow>()
                                              where Convert.ToBoolean(row.Cells["checkBoxColumn"].Value) == true
                                              select row).ToList();


        if (MessageBox.Show(string.Format("Do you want to delete {0} rows?", selectedRows.Count), "Confirmation", MessageBoxButtons.YesNo) == DialogResult.Yes)
        {
            //delete Nature de Charge before delete Famille
            foreach (DataGridViewRow row in selectedRows)
            {
                try
                {
                    using (SqlConnection con = new SqlConnection(connstring))
                    {
                        con.Open();
                        using (SqlCommand command = new SqlCommand("DELETE NatureCharge FROM NatureCharge n INNER JOIN Famille f on n.IdFam = f.IdFam WHERE IdNat = @IdNat", con))
                        {
                            command.ExecuteNonQuery();
                        }
                        con.Close();
                    }
                }
                catch (SystemException ex)
                {
                    MessageBox.Show(string.Format("An error occurred: {0}", ex.Message));
                }
            }

            //Delete Famille
            foreach (DataGridViewRow row in selectedRows)
            {
                using (SqlConnection con = new SqlConnection(connstring))
                {
                    using (SqlCommand cmd = new SqlCommand("DELETE FROM Famille WHERE IdFam = @IdFam", con))
                    {
                        cmd.CommandType = CommandType.Text;
                        cmd.Parameters.AddWithValue("@IdFam", row.Cells["IdFam"].Value);
                        con.Open();
                        cmd.ExecuteNonQuery();
                        con.Close();
                    }
                }
            }

an error shows with line (it is for Famille part)

cmd.ExecuteNonQuery();

Additional information: The DELETE statement conflicted with the REFERENCE constraint "FK_NatureCharge_Famille". The conflict occurred in database "Tresorerie", table "dbo.NatureCharge", column 'IdFam'.

Answer 1

You forgot to add the @IdNat parameter here:

 using (SqlCommand command = new SqlCommand("DELETE NatureCharge FROM NatureCharge n INNER JOIN Famille f on n.IdFam = f.IdFam WHERE IdNat = @IdNat", con))
 {
     // you haven't added the @IdNat parameter
     command.ExecuteNonQuery();
 }

This would be more apparent if you tidied your code.

string sql = "DELETE NatureCharge 
              FROM NatureCharge n 
              INNER JOIN Famille f on n.IdFam = f.IdFam 
              WHERE IdNat = @IdNat";
                            ^^^^^^
using (SqlCommand command = new SqlCommand(sql, con))
{
    // you haven't added the @IdNat parameter
    command.ExecuteNonQuery();
}