Simple role system through associative table

Rails
1

So I have the Ninja model which has many Hovercrafts through
ninja_hovercrafts (which stores the ninja_id and the hovercraft_id).

It is of my understanding that this kind of arrangement should be set
in a way that the associative table stores only enough information to
bind two different classes.

But I’d like to use the associative table to work as a very
streamlined authorization hub on my application. So i’d also like this
table to inform my system if this binding makes the ninja the pilot or
co-pilot of a given hovercraft, through a “role” field in the table.

My questions are:

Is this ugly?

Is this normal?

Are there methods built into rails that would help me to automagically
create Ninjas and Hovercrafts associations WITH the role? For exemple,
could I have a nested form to create both ninjas and hcs in a way that
the role field in ninjas_hovercrafts would be also filled?

If managing my application roles this way isn’t a good idea, whats the
non-resource heavy alternative (my app is being designed trying to
avoid scalability problems such as excessive joins, includes, etc)

thank you

2

Daniel,

Adding attributes to the HMT model is an acceptable practice.
Originally
HABTM was used for many-to-many relationships and it assumed a simple
table
in the middle with the related ids. The problem was that the
relationship
table often needed to become a model of its own with additional
attributes.
This is why HMT came about and is the preferred method for many-to-many
relationships.

I am not aware of a way to create all three models with the role in the
field as you described. I believe you will have to code that in the
controller.

If you do something like this and the association will set the role
value
for you…

class Pilot < ActiveRecord::Base
belongs_to :ninja
belongs_to :hovercraft
end

class Hovercraft < ActiveRecord::Base
has_many :pilots
has_many :piloted, :conditions => {:role => ‘pilot’}, :class_name =>
“Pilot”
has_many :copiloted, :conditions => {:role => ‘co-pilot’}, :class_name
=>
“Pilot”

has_many :ninjas, :through => :pilots
has_many :copilot_ninjas, :through => :copiloted, :source => :ninja
has_many :pilot_ninjas, :through => :piloted, :source => :ninja
end

class Ninja < ActiveRecord::Base
has_many :pilots
has_many :piloted, :conditions => {:role => ‘pilot’}, :class_name =>
“Pilot”
has_many :copiloted, :conditions => {:role => ‘co-pilot’}, :class_name
=>
“Pilot”

has_many :hovercrafts, :through => :pilots
has_many :copiloted_hovercrafts, :through => :copiloted, :source =>
:hovercraft
has_many :piloted_hovercrafts, :through => :piloted, :source =>
:hovercraft
end

Then you can do stuff like this…

Create hovercraft

hovercraft = …

Create pilot ninja

pilot_ninja = …

Create co-pilot ninja

copilot_ninja = …

Associate ninjas to hovercrafts

hovercraft.piloted.create(:ninja => pilot_ninja)
hovercraft.copiloted.create(:ninja => copilot_ninja)

Anthony C.