feature: has_many & has_one model_labels: [] option (instead of model_class)

[jorroll]

Problem

Currently, when defining a has_many or has_one association, you indicate what the association's targets are using model_class. This can be limiting. For example, given the models below, I want the person's has_many association to target current signup questions AKA nodes with (:`Question::Signup`:`Current`) labels. This could be accomplished by creating a class specifically for this purpose (i.e. Current = Class.new(Question::Signup){mapped_label_name = "Current"}) but the class would only exist to work around neo4jrb's limitations.

class Person
  has_many :out, :signups, type: :SIGNUP, model_class: ???
end

class Question
  self.mapped_label_name = "Question"

  class Signup < Question
    self.mapped_label_name = "Question::Signup"

    class List < Signup
      self.mapped_label_name = "Question::Signup::List"

      class Current < List
        self.mapped_label_name = "Current"
      end

      class Destroyed < List
        self.mapped_label_name = "Destroyed"
      end
    end

    class Shift < Signup
      self.mapped_label_name = "Question::Signup::Shift"

      class Current < Shift
        self.mapped_label_name = "Current"
      end

      class Destroyed < Shift
        self.mapped_label_name = "Destroyed"
      end
    end
  end
end

Proposal

Would you accept a pull request to add a model_labels option to has_many() and has_one()? This option could be used instead of model_class (an ArgumentError would be raised if they both were included) and would indicate the labels to match against. To use the option, you would include an array of strings where each string was formatted like the label part of a cypher query.

  has_many :out, :children, type: nil, model_labels: [":Current:`Question::Signup`", ":Person:Current"]