Forum: Ruby on Rails A custom method for models

Rails 3.1.3

Say, I have models and associations like
models:
  Plan               :flight_name_id: integer

  FlightName    :departure_id    :integer
                        :destination_id  :integer

  Place              :city_id              :integer

  City                :name                :string


Plan  1--n  FlightName  n--1  Place  n--1 City


Apparently, a flight_name has connections to TWO places, where one of
them refers to departure_id and another to destination_id.
Corresponding place.id's are stored in them.

In a view, I would like to generate City.name's (string) for both
departure place and destination place.

My question is: How can I achieve this?

in a view (html.erb template)

  plan.flight_name.plan

gives an error, "undefined method `place' for" obviously.
I am guessing that a custom method needs to be defined in order to pull
out City,name from a Plan.

Can anyone give me advice?

soichi

On 15 October 2012 08:08, Soichi Ishida <lists@ruby-forum.com> wrote:
>
>   City                :name                :string
>
>
> Plan  1--n  FlightName  n--1  Place  n--1 City
>
>
> Apparently, a flight_name has connections to TWO places, where one of
> them refers to departure_id and another to destination_id.
> Corresponding place.id's are stored in them.

Show us the class definitions with has_many and belongs_to
specifications.  If the problem is that you do not know how to specify
two places in the flight name then you need to do something like
class Flightname
  belongs_to :destination, :class_name => "Place", :foreign_key =>
"destination_id"
  belongs_to :departure,   :class_name => "Place", :foreign_key =>
"departure_id"

Then you can say flightname.destination and flightname.departure.  You
also have to put two equivalent has_many definitions in class Place.
Have a look at the rails guide on activerecord associations and the
rails docs for more details.

Colin

>   belongs_to :destination, :class_name => "Place", :foreign_key =>
> "destination_id"
>   belongs_to :departure,   :class_name => "Place", :foreign_key =>
> "departure_id"
>

I didn't know anything about ":foreign_key" option.

I put

class Place < ActiveRecord::Base
  has_many :flight_names, :foreign_key => :departure_id
  has_many :flight_names, :foreign_key => :destination_id
end

class FlightName < ActiveRecord::Base
  belongs_to :departure, :class_name => "Place", :foreign_key => 
:departure_id
  belongs_to :destination, :class_name => "Place", :foreign_key => 
:destination_id
...


It works fine!  Thanks Colin as always!

soichi

On 15 October 2012 10:30, Soichi Ishida <lists@ruby-forum.com> wrote:
> class Place < ActiveRecord::Base
>   has_many :flight_names, :foreign_key => :departure_id
>   has_many :flight_names, :foreign_key => :destination_id

That won't work properly when you come to do place.flight_names,
though the code you have so far may be ok.  You did not look at the
examples in the guide carefully enough.  Check out section 2.10 and
you will see that you need something like
has_many :departure_flight_names, :class_name => "FlightName",
:foreign_key => :departure_id
has_many :destination_flight_names, :class_name => "FlightName",
:foreign_key => :destination_id
then you can say place.departure_flight_names and 
place.destination_flight_names

Though I am not sure about your choice of class name as FlightName.
Should it not just be Flight or something similar?

Colin

> That won't work properly when you come to do place.flight_names,
> though the code you have so far may be ok.  You did not look at the
> examples in the guide carefully enough.  Check out section 2.10 and
> you will see that you need something like
> has_many :departure_flight_names, :class_name => "FlightName",
> :foreign_key => :departure_id
> has_many :destination_flight_names, :class_name => "FlightName",
> :foreign_key => :destination_id
> then you can say place.departure_flight_names and
> place.destination_flight_names

Rails is amazingly fun to deal with...Now I have learned a lot. Thanks.

> Though I am not sure about your choice of class name as FlightName.
> Should it not just be Flight or something similar?

FlightName only contains integer identification codes, and Flight 
includes Airline.company and Date as well, which are not apparent in 
this thread. So it's OK.
Thanks, though.

soichi