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 Crumley
http://commonthread.com
On Sun, Apr 11, 2010 at 5:01 AM, Daniel Drehmer <[email protected]>wrote:
> 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
>
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