Ruby on Rails

On 12 October 2014 11:54, Colin Law <clanlaw@gmail.com> wrote:
> On 12 October 2014 11:34, Yongbiao Long <longyongbiao@gmail.com> wrote:
>> On Sun, Oct 12, 2014 at 5:17 PM, Colin Law <clanlaw@gmail.com> wrote:
>>> Are you sure your basic design is appropriate? Having 100,000
>>> associated records per user seems very high. Are you able to explain
>>> what is in those records in case an alternative can be suggested?
>>
>> Thank you Colin! I'm implementing a railway ticket-booking system just
>> for learn purpose, not for production.
>> Now I try to explain it:
>> Suppose a train has 20 stations along the way. It has 1000 seats to
>> sell. Table A store one train's information in a row. I want table B
>> to store every seat's information. I design table B as follow
>>
>> train_id:
>> start_city_id:
>> end_city_id:
>> seat_id:
>> availability: boolean type
>> date:
>>
>> For one train, the number of start_city_id and end_city_id's
>> combinations is 19+18+...+1=190, the number of possible date is
>> 20(people can book tickets in 20 days), and possible seat_id's number
>> is 1000. The total number of rows for one train is
>> 190*1000*20=3,800,000. So huge..
>
> The first point is that you should only add rows as seats are booked,
> use that fact that there is no row to indicate that there is no
> booking.
> Secondly, what is the date? Is that the date of the journey or the
> date of the booking? I don't understand why you have multiplied the
> number of trains by 20 days. If it is the date of the journey then
> consider having a Journeys table which is a particular train on a
> particular day.
> Thirdly I don't understand why you have 20 factorial for the city
> combinations. Is it not true that if a seat is booked from station 1
> to station 3 then that implies a booking 1 to 2 and 2 to 3? In which
> case you do not separate rows for bookings 1 to 2, 2 to 3, and 1 to 3.

In fact thinking further, I would probably turn the problem around and
have a bookings table, specifying the journey, the stations, and the
seat (or seats).

Colin

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