undefined method `include?' for nil:NilClass w

问题:

I am trying to follow the guide for partial validation on object using the wizard gem, but I keep getting the error undefined method `include?' for nil:NilClass, cant understand what is wrong, have tried to follow the step by step instructions.

The error in the log shows.

NoMethodError - undefined method `include?' for nil:NilClass:
app/models/property.rb:22:in `active_or_tenants?'

Here is my steps controller.

class Properties::BuildController < ApplicationController
  include Wicked::Wizard

  steps :tenant, :confirmed 

  def show
    @property = Property.find(params[:property_id])
    @tenants = @property.tenants.new(params[:tenant_id])
    render_wizard
  end

  def update
    @property = Property.find(params[:property_id])
    params[:property][:status] = step.to_s
    params[:property][:status] = 'active' if step == steps.last
    @property.update_attributes(params[:property])
    render_wizard @property
  end

  def create
    @property = current_user.properties.build(params[:property])
      logger.info @property.attributes
    if @property.save
        flash[:success] = "Tenant Added"
        redirect_to wizard_path(steps.second, :property_id => @property.id)
    else
        render 'edit'
    end
  end
end

Property.rb

class Property < ActiveRecord::Base
  attr_accessible  :name, :address_attributes, :tenants_attributes, :property_id, :status
  belongs_to :user 

  has_one :address, :as => :addressable
  accepts_nested_attributes_for :address, :allow_destroy => true

  has_many :tenants 
  accepts_nested_attributes_for :tenants, :allow_destroy => true

  validates :name,        :presence => true
  validates :address,     :presence => true
  validates :tenants,     :presence => true, :if => :active_or_tenants?

  def active?
    status == 'active'
  end

  def active_or_tenants?
    status.include?('tenants') || active?
  end
end

Let me know if you need any other parts added to the question. Thanks in advance.

回答1:

From my comments:

The status is an attribute of your Property model. It can be nil which raises an error in certain cases:

undefined method include?' for nil:NilClass

It is actually trying to compare nil to 'tenants' (String).

To fix that, you can use an empty string to be compared if status is nil,

# an example (you can try in your IRB console):
nil || "No value"
# => returns "No value"

in your case:

def active_or_tenants?
  status.to_s.include?('tenants') || active?
end

nil.to_s return an empty string. Which solves your problem ;)

---

Actually, the methods to_s, to_i, to_f etc. are often used to remove the possible nil:

# in ruby console:
2.3.3 :018 > nil.to_i
# => 0 
2.3.3 :019 > nil.to_f
# => 0.0 
2.3.3 :020 > nil.to_s
# => "" 
2.3.3 :021 > nil.to_a
# => [] 

回答2:

There is another solution to this, you might want to set a default state upon object creation, preferable in the migration.

class AddStatusToProperties < ActiveRecord::Migration
  def change
    create_table :projects do |t|
      t.string :status, default: 'new'
    end
  end
end

Following this you'll never have nil for your state

回答3:

In Ruby 2.3 you can use the safe navigation operator, which will simply return nil when your object is nil and it won't throw an error.

def active_or_tenants?
  status&.include?('tenants') || active?
end