How to pass argument to delegate method in Rails
I would like to have a Dashboard to display summary of multiple models, and I implemented it using Presenter without its own data. I use an ActiveModel class (without data table):
class Dashboard
attr_accessor :user_id
def initialize(id)
self.user_id = id
end
delegate :username, :password, :to => :user
delegate :address, :to => :account
delegate :friends, :to => :fr开发者_JS百科iendship
end
By delegate, I want to be able to call Dashboard.address
and get back Account.find_by_user_id(Dashboard.user_id).address
.
If Dashboard was an ActiveRecord class, then I could have declared Dashboard#belongs_to :account
and delegate would work automatically (i.e., Account would know it should return address attribute from account with user_id
equals to user_id
in Dashboard instance).
But Dashboard is not an ActiveRecord class, so I can't declare belongs_to
. I need another way to tell Account to lookup the right record.
Is there a way to overcome this problem? (I know I can fake Dashboard to have an empty table, or I can rewrite User's instance methods to class methods that take argument. But these solutions are all hacks).
Thank you.
When you write delegate :address, :to => :account
, this creates a new address
method on Dashboard which basically calls the account
method on the same object and then calls address
on the result of this account
method. This is (very roughly) akin to writing:
class Dashboard
...
def address
self.account.address
end
...
end
With your current class, all you have to do is to create an account
method which returns the account with the correct user_id
:
class Dashboard
attr_accessor :user_id
def initialize(id)
self.user_id = id
end
delegate :username, :password, :to => :user
delegate :address, :to => :account
delegate :friends, :to => :friendship
def account
@account ||= Account.find_by_user_id(self.user_id)
end
end
This would allow you to access the address like this:
dashboard = Dashboard.new(1)
# the following returns Account.find_by_user_id(1).address
address = dashboard.address
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