PHP Booking System自动更新MySQL数据库，无需任何用户交互。

Question

I have created a booking system for a car rental company, and I have an issue with setting the availability of cars.

A brief example of how it works is that a single car, when it is booked out recieves a value of yes in a field within the database called bookedout

Ok, so say for examples sake that there is 10 cars (this is unrealistically small but demonstrates the point)

1 of these is a Audi R8.

Today's date is the 6th of march 2012.

A user books the car from the 26th of march to the 31st of march. But they place that booking through the website today. I cannot set the bookedout value to yes straight away or the website will actually consider that car unavailable from the 6th of march to the 31st of march.

This scenario would loose a company money.

So I am looking for something like a script that sits on the server, checks the current date and then checks the database every day. And for example if there is a booking due to start on today's date, it would change the value within the database so the car is unavailable to book from this day.

In turn I could also adapt it to change the value back on the date on which the car is due to be returned.

I am not specifically looking for code (although I wouldn't say no to examples), just a starting point for figuring things like this out as I have never done this before.

Basically, I need a way to trigger a query, without any user interaction, on a certain date.

Any help would be seriously appreciated. :)

Answer 1

I'll flesh this out a little more in answer-form for you, though I'm not going to post any code because I don't think it's necessary to answer this particular question.

Your database structure should look something like this (a lot of fields that a car rental company would want - such as mileage, damage, etc - are left out for brevity):

cars

• car_id
• make
• model
• year

customers

• customer_id
• first_name
• last_name
• email_address

reservations

• reservation_id
• car_id
• customer_id
• start_date
• end_date

The idea is that you never store a booking status with the car . Rather, you create a reservation with start_date and end_date set to the dates of the reservation.

Your query to check cars that are available for a given date range would be:

SELECT
    c.car_id
FROM
    cars c 
    LEFT JOIN reservations r ON (
       c.car_id = r.car_id
       AND r.start_date <= $reservationEndDate
       AND r.end_date >= $reservationStartDate
    )
WHERE
    r.reservation_id IS NULL

And with this model, you never need to worry about running time-based jobs to update a cars reserved status. Although, to optimize your application, you may run a daily job that updates the cars status so you can quickly find out how many cars are available today .

Additional Note

As NB pointed out in the comments - you'll want to make sure your application doesn't allow conflicting date ranges in the reservations table. There's no unique index that can solve for this, so you'll need to handle this in your application logic - beware of race conditions. A possible solution would be to create a temporary reservation as soon as someone looks at a car for a certain date range.

Another Additional Note

NB Also had a good suggestion to avoid the above problem: use database triggers to validate it server-side. The database can reject the INSERT in the trigger if another booking was created that conflicts. This solution may very well be the best, as it keeps the validation as close to the data as possible (so you can't "forget" it in your application).

Answer 2

The literal answer to your question is cron (assuming you're running on a *nix system).

However, you really don't want to do that - it's very fragile, because you still have to query a table with bookings whenever you run the cron job; that means that now there are 3 places which know how car bookings work (the cron job, the bookings table, and your application).

It's far simpler to say that a car is unavailable to book by joining it to the bookings table; if there's a valid booking for a given date, the car can be considered unavailable.

Making some assumptions about your schema, it might be something like

select 'booked'
from   cars c, 
       bookings b
where  c.car_id = b.car_id
and    b.start_date < ?required_date 
and    b.end_date   > ?required_date
union
select 'free'
from   cars c, 
       bookings b
where  c.car_id = b.car_id
and    b.start_date >= ?required_date 
or    b.end_date   <= ?required_date