连接多个表时如何处理jdbc中的重复值

Question

Following is my jdbc code to fetch data from multiple tables

public Set<Bill> fetch(long billNo) {

        System.out.println(" BillProductDetailsBusiness fetch()");
        status = "success";

        Set st = new HashSet();
        con = ConnectionFactory.getConnection();

        try {

            String query = "select distinct bpd.product_id,bpd.bill_no,"
                    + "bpd.qty, bpd.unit_price as up,bpd.selling_price sp,"
                    + "bpd.discount_percent as dp, "
                    + "bd.*,cu.*,pr_dl.*, "
                    + " colors.color,pmodeld.model_no, ptype.product_type,  "
                    + "sizes.size, pbrand.brand,suppd.name  "
                    + "from bill_product_details as bpd  "
                    + "left join bill_details as bd "
                    + "on  bd.bill_no=bpd.bill_no "
                    + "left join product_details as pr_dl "
                    + "on bpd.product_id=pr_dl.barcode "
                    + "left join  "
                    + "colors  "
                    + "on pr_dl.color_id=colors.color_id  "
                    + "left join  "
                    + "product_model_details as pmodeld  "
                    + "on pr_dl.model_id=pmodeld.model_no_id  "
                    + "left join  "
                    + " product_brand as pbrand  "
                    + "on pr_dl.brand_id=pbrand.id  "
                    + "left join  "
                    + "product_types as ptype  "
                    + "on pr_dl.product_type_id=ptype.product_type_id  "
                    + "left join  "
                    + "sizes  "
                    + "on pr_dl.size_id=sizes.size_id  "
                    + "left join  "
                    + "supplier_details as suppd  "
                    + " on pr_dl.supplier_id=suppd.id   "
                    + "left join customer_details as cu "
                    + "on bd.customer_id=cu.id "
                    + "where bpd.bill_no=? ";

            ps = con.prepareStatement(query);
            ps.setLong(1, billNo);

            System.out.println("Before execution");
            res = ps.executeQuery();
            Bill b;
            ProductDetailsAction pb = null;
            while (res.next()) {
                b = new Bill();
                long product_id = res.getLong("product_id");
                int qty = res.getInt("qty");
                float unit_price_s = res.getFloat("up");
                float sell_price_s = res.getFloat("sp");
                int dis_per_s = res.getInt("dp");

                long bill_no = res.getLong("bill_no");
                long customer_id = res.getLong("customer_id");
                float sub_total = res.getFloat("sub_total");
                float vat = res.getFloat("vat");
                float total = res.getFloat("total");
                String payment_type = res.getString("payment_type");
                Timestamp add_date = res.getTimestamp("add_date");

                long bar_code = res.getLong("barcode");
                String color = res.getString("color");
                String model_no = res.getString("model_no");
                String brand = res.getString("brand");
                String product_type = res.getString("product_type");
                String size = res.getString("size");
                String supplier_name = res.getString("name");
                long quntity = res.getLong("quntity");
                float unit_price = res.getLong("unit_price");
                float selling_price = res.getLong("selling_price");
                int discount_percent = res.getInt("discount_percent");

                long id = res.getLong("id");
                String name = res.getString("name");
                String address = res.getString("address");
                String mobno = res.getString("mobno");
                Date dob = res.getDate("dob");
                Date anniversery = res.getDate("anniversery");
                Timestamp adddate = res.getTimestamp("add_date");
                //setting bill bean
                System.out.println(bill_no + "  " + sub_total);
                b.getBillDetails().setBillNo(bill_no);
                b.getBillDetails().setSubTotal(sub_total);
                b.getBillDetails().setVat(vat);
                b.getBillDetails().setTotal(total);
                b.getBillDetails().setPaymentType(payment_type);

                SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("dd-MMM-yy hh:mm aaa");
                String pur_date = DATE_FORMAT.format(add_date);
                b.getBillDetails().setDispDate(pur_date);

                b.getCustomerDetails().setCustomerName(name);
                b.getCustomerDetails().setAddress(address);
                b.getCustomerDetails().setMobno(mobno);
                pb = new ProductDetailsAction();
                pb.setBarCode(bar_code);
                pb.setProductType(product_type);
                pb.setProductSize(size);
                pb.setQuantity(qty);
                pb.setUnitPrice(unit_price_s);
                pb.setSellingPrice(sell_price_s);
                pb.setTotalSellingPrice(sell_price_s * qty);
                pb.setDiscountPercentage(dis_per_s);
                b.getProductDetails().add(pb);
                st.add(b);

            }

            con.close();
        } catch (SQLException s) {
            status = "failure";
            System.out.println("SQL code does not execute." + s);
        } finally {
            try {
                if (con != null) {
                    con.close();
                }
            } catch (SQLException sqe) {
                status = "failure";
                System.out.println("SQLException " + sqe);
            }
        }
        System.out.println("Returning from BillProductDetailsBusiness fetch() ");

        return st;
    }

Bill.java

 public class Bill {

        private CustomerAction customerDetails = new CustomerAction();
        private Set<ProductDetailsAction> productDetails = new          HashSet<ProductDetailsAction>(0);
        private BillAction billDetails = new BillAction();
 //getter and setter 
 }

I am fetching data from multiple table and showing in jsp page. This code is fetching proper data. Problem is that if productDetails are more that one then it is repeating customerDetails and billDetails as much as productDetails are there.

I want one customerDetails one billDetails and one or more productDetails as available in database

How to resolve this.

Answer 1

I believe the issue is that you are joining the tables to get your data back from SQL, which means the database will be returning multiple rows:

customer1 bill1 product1
customer1 bill1 product2
etc

There are a few ways to solve this. The simplest, depending on if you have enough memory to keep data in memory, is to store your Bill in a hashmap, and as you iterate through the rows, check to see if the Bill is already in the hashmap. If it is, add the product to the product list in the bill, otherwise, create a new Bill object and add to the map.

Then when you display it on the page, you would display:

Bill1
  - product1
  - product2

Etc. Hope that helps.