ruby on rails - Automatic naming of objects based on associations with other models -


i have 3 models "input", "mechanism", , "output".

mechanism 'has_one' :input , 'has_one' :output.

i want make mechanism object has name attribute "the effect of input x on output y".

here tried:

class mechanism   include neo4j::activenode   property :name, default: 'newmechanism#{self.class.count}'   has_one :in, :input,  class_name: 'input'   has_one :out, :output,  class_name: 'output'   after_create :name_mechanism   def name_mechanism      self.update_attributes(name: "effect of #{self.input.name} on #{self.output.name}")   end end

but when initialize object in console, error

nomethoderror: undefined method `name' nil:nilclass app/models/mechanism.rb:12:in 'name_mechanism'

so yeah using neo4j database, suspect isn't neo4j issue, rather weak understanding of callbacks in rails. advice?

your code assuming every mechanism have associated input , output. need cater situations not. this

class mechanism   include neo4j::activenode   property :name, default: 'newmechanism#{self.class.count}'   has_one :in, :input,  class_name: 'input'   has_one :out, :output,  class_name: 'output'   before_create :name_mechanism    def name_mechanism     if self.name.blank?       self.name = self.default_name     end   end    def default_name     "effect of #{self.input ? self.input.name : "<input not set>"} on #{self.output ? self.output.name : "<output not set>"}"   end  end

note i've changed callback before_create since better place set default name. note name_mechanism keeps name if it's got non-blank one.


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