Ruby on Rails

On 12 October 2014 12:28, Yongbiao Long <longyongbiao@gmail.com> wrote:
> On Sun, Oct 12, 2014 at 6:54 PM, Colin Law <clanlaw@gmail.com> wrote:
>> 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.
>
> It's the date of the journey. I once thought about this method, the
> problem is I don't know how to implement it in rails. In Rails
> tutorials and guidelines, there is a model file in app/model directory
> for every table. If I need to create new journey tables, what's the
> model files and migration files look like?(Or I don't need them any
> more?)
>
>> 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.
>
> According to your first and third point, It's because my design is
> different. In my design one booking might indicates more than one row.
> A row just means the state of a seat. So, if a seat is booked from
> station 1 to station 3, then rows representing 1->3, 1->2, 2->3, 1->4,
> 1->5.... all need to change. I do it in this way because I have
> another table representing the number of left seats, and I think it's
> easier to update this table in my way(in this case, the number of leaf
> seats from 1->3, 1->2, 2->3.... decreases by one).

In that case you have redundant data in your database (as 1->3 implies
1->2 and 1->3), which is almost always not the best way to do it.

Colin

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