I need an idea!

Rails
#1

Hello here, I need to find an idea to solve a problem

I manage Events which are of kind :arrival or :departure
At first the two kind of events was unrelated but my client want to see
the :departure belonging to the :arrival and vice versa.

I’m searching for a solution to implement this ‘link’. I’ve thought
about an integer column containing an uniq id for the same pairs of
Events but I don’t like this solution because I don’t know how to
display the related event in a for loop

Events must be displayed ordered by date with for each (:arrival, the
corresponding :departure)

Eg.

  1. 12/04/2006 - 99AABB - Arrival
    20/05/2006 - 99AABB - Departure
  2. 15/04/2006 - 88CCAA - Arrival
    23/04/2006 - 88CCAA - Departure

Any idea is welcome, I’m stuck !! (And of course I would avoid running a
query for each line displayed )

Thanks

#2

Hi Nuno,

if I get you right you’ve got an arrival (let’s say from a plane) on
your
airport and a departure of that plane.

If that’s true, then a plane can’t arrive twice without being departured
as
well as a plane can’t departure without arriving earlier.

Wouldn’t than the natural way of modelling be:

class Arrival
has_one :departure, :include => :departure
end

class Departure
belongs_to :arrival
end

This way you should be able to iterate over arrivals to construct a list
like yours where the departures are eager loaded

@arrivals = Arrival.find(:all) # or limit and or paginate

<% for arrival in @arrivals -%>

<%= arrival.date %> ...
<%= departure.date %>

<% end -%>

Another way of doing things might be to Model from a class - ‘Flight’
which
has one arrival and one departure.

Cheers,
Jan

#3

On 8/4/06, nuno [email protected] wrote:

Events must be displayed ordered by date with for each (:arrival, the
corresponding :departure)

This sounds like a special case of the “has_many :through”
relationship, where you really only “have one”.

If you could have, for example, a “trips” table that stored an arrival
id and a departure id, you’d be able to easily relate the two. Plus,
you could then sort a list of Trip objects by dates from either
related table.

http://wiki.rubyonrails.org/rails/pages/ThroughAssociations

– James

#4

Thanks a lot for your help !

I dunno if I choosed the right way but following more or less your
advices I did this :

class ArrivalDeparture < ActiveRecord::Base
belongs_to :vehicle
has_one :arrival, :class_name => ‘Movement’, :dependant => :destroy
has_one :departure, :class_name => ‘Movement’, :dependant => :destroy
end

And

class Movement < ActiveRecord::Base
belongs_to :ArrivalDeparture

bunch of properties here including a :kind_of property feeded with

symbols

:departure or :arrival

end

And now I do
ArrivalDeparture .find(:all,
:include => [:arrival, :departure],
:conditions => [“movements.activ = ? AND movements.statut = ? AND
movements.date_programmed BETWEEN ? AND ?”, true, :not_handled,
Date.today, Date.today + some_days],
:order => “movements.date_programmed”)

Unit tests seems to be OK, I’ll will check later if the relationship for
special cases like ArrivalDeparture with a departure but NO arrival is
correctly handled.

#5

On 04/08/06, nuno [email protected] wrote:

Unit tests seems to be OK, I’ll will check later if the relationship for
special cases like ArrivalDeparture with a departure but NO arrival is
correctly handled.

Strictly speaking, I would think these “special cases” really should be
unit
tests.

#6

Hasan D. wrote:

On 04/08/06, nuno [email protected] wrote:

Unit tests seems to be OK, I’ll will check later if the relationship for
special cases like ArrivalDeparture with a departure but NO arrival is
correctly handled.

Strictly speaking, I would think these “special cases” really should be
unit
tests.

You are right and I think like you (I meant checking later = writing
more unit test)

BTW : there is something wrong with the solution I have choosen
How the has_one :arrival and :departure parameter can be related with
one movement ? How RoR can associate a particular Movement instance
with it ? I presume I should add a :condition eg. :
has_one :departure, :class_name => ‘Movement’, :dependant => :destroy,
:conditions => [‘kind = ?’, :departure]

I have the feeling that there’s something wrong somewhere…

#7

Hi Nuno,

now I’m getting things. You’ve got one model ‘events’, which might be of
kind ‘arrival’ or ‘departure’. IMHO you can model this by using
single-table-inheritance (STI) where the type column is either ‘arrival’
or
‘departure’. Then on this table you could model the has_one, belongs_to
relationship as a self-referring one. There are examples for such
self-referential relationships in RailsRecipes and on the wiki.

You could of course model this relationship :through another model as
described by james, especially if you are in need of a fine grained
control
over the relationship itself.

Cheers,
Jan

#8

Hasan D. wrote:

Yes, it’s probably not syntactically correct, but you get the idea.

Yes, this is far easier than what I was trying to do…

More or less, following your idea now I

arrivals = Movements.find(:all, :conditions => [“mov_type = ?”,
:departure], :order => “date_programmed”]

for arrival in arrivals

display arrival

dep = Movement.find(:first, :conditions => [“id_pair = ?”,
arrival.id_pair])
end

Each pair of arrival / departure is identified by an unique id

Thanks !!

#9

On 05/08/06, nuno [email protected] wrote:

BTW : there is something wrong with the solution I have choosen
How the has_one :arrival and :departure parameter can be related with
one movement ? How RoR can associate a particular Movement instance
with it ? I presume I should add a :condition eg. :
has_one :departure, :class_name => ‘Movement’, :dependant => :destroy,
:conditions => [‘kind = ?’, :departure]

Could you not have a movement_id foreign key in your :arrival or
:departure?
When you display, you’d do something like:
<% for arrival in @arrivals %>

<%=h arrival.send ('bleh') %> <%=h departure.find(:first, :id => arrival.movement_id) %> <% end %>

Yes, it’s probably not syntactically correct, but you get the idea.