Mark Gandolfo's Blog

Associated With is a simple ruby on rails plugin that will check if an object is associated with another object.

has_one and belongs_to

class Computer < ActiveRecord::Base
  belongs_to :programmer
end

class Programmer < ActiveRecord::Base
  has_one :computer
end

So if, Programmer with id 1, is associated with Computer 1, but not Computer 2 using associated_with? we will return

programmer = Programmer.find(1)
computer = Computer.find(1)
computer2 = Computer.find(2)

programmer.associated_with?(computer)
# => true

programmer.associated_with?(computer2)
# => false

We can even do it the other way around

computer.associated_with?(programmer)
# => true

This will work with all associations with ActiveRecord, for example, a has_many :through

class Analyst < ActiveRecord::Base
  has_many :document_stores
  has_many :documents, :through => :document_stores
end

class Document < ActiveRecord::Base
  has_many :document_stores
  has_many :analysts, :through => :document_stores
end

class DocumentStore < ActiveRecord::Base
  belongs_to :document
  belongs_to :analyst
end

so if document 1 is associated to analyst 1 & 2, but not 3. then

Analyst.find(1).associated_with(Document.find(1))
# => true

Analyst.find(3).associated_with(Document.find(1))
# => false

Check out the tests for more information.