如何在外键列上更新和插入值？

Question

I want to insert and update my table. My query statement is only indicate primary key, item name, description, price and so on.. The problem is I have another column which is the FOREIGN KEY. When I try to insert values to my item database table the error is occurred. It said that the column count doesn't match value count at row 1. And also how can I update the table if I have a column of FOREIGN KEY?

class Item
    {
        public int ItemID { get; set; }
        public string ItemName { get; set; }
        public string Description { get; set; }
        public string Price { get; set; }
        public string Stocks { get; set; }

        public int GenerateID()
        {
            int newID = 0;
            Connection connection = new Connection();
            string sql = "SELECT ItemID FROM tbl_Item ORDER BY ItemID DESC Limit 1";
            MySqlConnection conn = new MySqlConnection(connection.ConnectionString);
            MySqlCommand cmd = new MySqlCommand(sql, conn);
            conn.Open();
            MySqlDataReader dr = cmd.ExecuteReader();
            if (dr.HasRows)
            {
                dr.Read();
                newID = dr.GetInt32("ItemID");
            }
            conn.Close();
            newID++;
            return newID;
        }

        public void UpdateRecord()
        {
            try
            {
                Connection connection = new Connection();
                string sql = "UPDATE Item SET ItemName=@itemName, Description=@desc, Price=@price, Stocks=@stocks WHERE ItemID=@itemId";
                MySqlConnection conn = new MySqlConnection(connection.ConnectionString);
                MySqlCommand cmd = new MySqlCommand(sql, conn);
                cmd.Parameters.AddWithValue("@itemId", ItemID);
                cmd.Parameters.AddWithValue("@itemName", ItemName);
                cmd.Parameters.AddWithValue("@desc", Description);
                cmd.Parameters.AddWithValue("@price", Price);
                cmd.Parameters.AddWithValue("@stocks", Stocks);

                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
                MessageBox.Show("Update Successfully", "Update Record", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
            catch (Exception e)
            {
                MessageBox.Show("An error occured: " + e, "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }

        public void InsertRecord()
        {
            Connection connection = new Connection();
            try
            {
                string sql = "INSERT INTO tbl_Account VALUES(@itemId, @itemName, @desc, @price, @stocks)";
                MySqlConnection conn = new MySqlConnection(connection.ConnectionString);
                MySqlCommand cmd = new MySqlCommand(sql, conn);
                cmd.Parameters.AddWithValue("@itemId", ItemID);
                cmd.Parameters.AddWithValue("@itemName", ItemName);
                cmd.Parameters.AddWithValue("@desc", Description);
                cmd.Parameters.AddWithValue("@price", Price);
                cmd.Parameters.AddWithValue("@stocks", Stocks);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();

                MessageBox.Show("Update Successfully", "Update Record", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }
            catch (Exception e)
            {
                MessageBox.Show("An error occurred: " + e, "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
    }
//for button ADD
private void btnAddItem_Click(object sender, EventArgs e)
        {
            Item item = new Item();

            item.ItemID = item.GenerateID();
            item.ItemName = txtINameItem.Text;
            item.Description = txtDescriptionItem.Text;
            item.Price = txtPriceItem.Text;
            item.Stocks = textStocksItem.Text;

            item.InsertRecord();
        }

Answer 1

Your SQL code is wrong. You must pass valid Foreign Key value while inserting the record. Valid Foreign Key value is the value already existing in the Parent Table OR NULL. However, setting NULL to Foreign Key column is based on how you have created the Foreign Key on the Child Table.

Try below code replacing @fkValue & FkValue with correct Foreign Key column order in the Child Table and value:

                string sql = "INSERT INTO tbl_Account VALUES(@itemId, @fkValue, @itemName, @desc, @price, @stocks)";
                MySqlConnection conn = new MySqlConnection(connection.ConnectionString);
                MySqlCommand cmd = new MySqlCommand(sql, conn);
                cmd.Parameters.AddWithValue("@itemId", ItemID);
                cmd.Parameters.AddWithValue("@fkValue", FkValue);
                cmd.Parameters.AddWithValue("@itemName", ItemName);
                cmd.Parameters.AddWithValue("@desc", Description);
                cmd.Parameters.AddWithValue("@price", Price);
                cmd.Parameters.AddWithValue("@stocks", Stocks);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();

Hope this helps!