how to increment invoice no. whenever I click order? - php

Question

My table columns are invoiceid (primary AI), invoiceno, purchaseorderno, userid. I figured I couldn't use invoiceid since for example: when a customer buys 2 products, the 2 invoiceid will be diff. So I decided to use invoiceno that whenever the user will click order and he bought for example 2 products, they will have the same invoiceno. I have this code below:
$invoice = 0000000;
$invoiceno = $invoice + 1;
$sqlString1 = "INSERT INTO invoice
(invoiceno, purchaseorderno, userid)
VALUES ('$invoiceno', '$purchaseorderno', '$userid');";
$result1 = mysqli_query($conn, $sqlString1);
It works but then the invoice no stay as 1. It doesn't increment when I click order. If my idea is wrong, suggestions would be greatly appreciated.

Answer 1

I would do it in two tables not one.
You have invoice and invoice_item Which have a One to Many relationship.
If you make another table for the line items, all you problems evaporate.
Table invoice
id
date
total
status etc...
Table invoice_item
id
invoice_id - foreign key
product_id
quantity
etc...
Selecting them is no problem
SELECT
{fields}
FROM
invoice AS i
JOIN
invoice_item AS l ON i.id = l.invoice_id
WHERE
i.id = :id
And so on....
Then you can just use the Primary key from invoices and your all set. It will also be more robust (less prone to breaking) probably faster, probably easier to code in the long run and so on.
It does add a tiny bit of complexity to the data model, and a bit more caution when doing inserts and deletes and what not, but if you setup the foreign key restraints correctly, use transactions when doing inserts, you should be fine.
UPDATE
Here is a DBfiddle (click it) with a number of examples of how to setup the forign key and how to build the basic table relationship. I just guessed at these fields you can of course make any changes you need to, to add or remove them. This is just for the sake of explaining it.
CREATE TABLE invoice(
id INT(10) unsigned NOT NULL AUTO_INCREMENT,
total DECIMAL(6,2) unsigned NOT NULL,
email VARCHAR(100),
submission_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY ( id )
) ENGINE=InnoDB;
CREATE TABLE invoice_item(
id INT(10) unsigned NOT NULL AUTO_INCREMENT,
invoice_id INT(10) unsigned NOT NULL,
product_id INT(10) unsigned NOT NULL,
qty INT(3) unsigned NOT NULL,
sub_total DECIMAL(6,2) unsigned NOT NULL,
PRIMARY KEY ( id ),
CONSTRAINT FK_InvoiceItems FOREIGN KEY(invoice_id) REFERENCES invoice(id) ON DELETE CASCADE ON UPDATE CASCADE,
KEY(product_id)
) ENGINE=InnoDB;
Just a few Query examples:
Insert invoice
#in the example fiddle this is AI #2 so invoice.id=2
INSERT INTO invoice (total,email) VALUES ('100.00','user2#example.com');
Insert related invoice items
#both of these line items have same invoice,
INSERT INTO invoice_item (invoice_id,product_id,qty,sub_total) VALUES ('2','200','7','70.00');
INSERT INTO invoice_item (invoice_id,product_id,qty,sub_total) VALUES ('2','270','2','30.00');
Basic Inner Join (selects all invoices that have items, and their items)
SELECT
i.*, l.id AS invoice_item_id, l.product_id, l.qty
FROM
invoice AS i
LEFT JOIN
invoice_item AS l ON i.id = l.invoice_id;
Count the number of unique Items
SELECT
invoice_id, COUNT(id) AS unique_items
FROM
invoice_item
GROUP BY invoice_id;
Count the number of total items. You can sum, sub_total to get total the same way. You could remove invoice.total if you want to. It can be nice to have the total counted up in there, but you also have to keep it updated when/if you change the number of items in an invoice.
SELECT
invoice_id, SUM(qty) AS total_items
FROM
invoice_item
GROUP BY invoice_id;
Find any invoices without items (its impossible to add items without invoices with the fk constraint, which is exactly what we want)
SELECT
i.*, l.id AS invoice_item_id, l.product_id, l.qty
FROM
invoice AS i
LEFT JOIN
invoice_item AS l ON i.id = l.invoice_id
WHERE
l.id IS NULL;
And Last, Delete an invoice, because of the constraint this will cascade and delete the related items from invoice_item with no extra work,in other words the items are auto-magicaly deleted. I've also found letting the database do the cascade delete is significantly faster then manually deleting them.
DELETE FROM invoice WHERE id=2;
In this data model, I have the invoice_items grouped by products. So for invoice.id #2, we have two items, one with product id #200, which is toy ufo's. The other is #270 which is metallic weather balloons. Tiny Tim got 7 UFO's for $10 each for a sub_total of $70, and then he got 2 weather balloons for $15 each (nothing our government does is cheap).
Ok that is my DB 101 lesson for the day.
UPDATE1
Based on this error
Cannot add or update a child row: a foreign key constraint fails
This is actually a good thing, it's the purpose of the foreign key. I will try to explain
If you do this insert
INSERT INTO invoice (total,email) VALUES ('100.00','user2#example.com');
This creates a row in invoice, it's the purpose of insert. Now because it's Auto Increment Id and this is the first row it's id is 1. Because it's the first row its also the only record in invoice. We can all agree on that, I insert 1 row in a new table, that makes it the first and only row. And it has an AI id of 1
Now if I try to insert
INSERT INTO invoice_item (invoice_id,product_id,qty,sub_total) VALUES ('2','200','7','70.00');
This row has an invoice_id of 2, and we just said we have one invoice with an id of 1. So there is no invoice with an id of 2. This will give you the same error you just got, because you are trying to add an invoice_item without having it's associated invoice, which is something we never want to happen. This is called an "orphan" row because it's parent row does not exist. If we allowed this our Database could be filled with invoice items that have no invoice. Then if we later add an invoice with the id of one of those orphan rows we have just associated things that should not be associated. This is why that error makes sense and why it's a good thing.
The obvious way to fix this is to not insert invoice_items that don't belong to an invoice.
I really hope that makes sense.
So how do we insert invoice_items that do have an invoice?
In PHP you want to insert the invoice then get it's id, then insert the invoice_item. See this page.
http://php.net/manual/en/mysqli.insert-id.php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
//insert invoice
$query = "INSERT INTO invoice (total,email) VALUES ('100.00','user2#example.com')";
$mysqli->query($query);
//insert invoice item with last insert id
$query = "INSERT INTO invoice_item (invoice_id,product_id,qty,sub_total) VALUES ('".$mysqli->insert_id."','200','7','70.00')";
The important part here is to use, $mysqli->insert_id when inserting invoice items. Now if you want to add an invoice item to an existing invoice that was inserted some time ago. Then you just query the invoice, and pull it's id out and use that for the new invoice item.
Hope that helps, enjoy!