无法从关联的模型导轨访问属性

Question

I have three models, ingredient, recipe_ingredient and recipy

class Ingredient < ApplicationRecord
  has_many :recipe_ingredients
end

class RecipeIngredient < ApplicationRecord
 belongs_to :recipy, :dependent => :destroy
 belongs_to :ingredient
end

class Recipy < ApplicationRecord
  has_many :recipy_steps
 has_many :recipe_ingredients, :dependent => :delete_all
end

I am trying to access the ing_name attribute in the ingredients table from recipies show page.

<% @recipe_ingredients.each do |ing| %>
<p> <%= ing.amount  %> <%= ing.unit %>
<%= ing.ingredient.ing_name %>
</p>

def Show from the recipies controller:

def show
 @recipe_ingredients = @recipy.recipe_ingredients
end

But I keep receiving the following error msg: undefined method `ing_name' for nil:NilClass

My ingredient_params:

def ingredient_params
params.require(:ingredient).permit(:ing_name)
end

It does seem to work like this:

    <%= Ingredient.where(id: ing.ingredient_id).pluck(:ing_name) %>

But this does not use the connection between the tables if I understand correctly? Any help? Thanks.

Answer 1

You have ingredient nil thats why you got the error.

Must be your controller has some before_action hook to load recipy

class RecipesController < ApplicationController
  before_action :load_recipy, only: :show

  def show
    @recipe_ingredients = @recipy.recipe_ingredients
  end

 private
 def load_recipy
   @recipy = Recipy.find(params[:id])
  end
end

You can try this to avoid this nil error( undefined method 'ing_name' for nil:NilClass )

<% @recipe_ingredients.each do |ing| %>
<p> <%= ing.amount  %> <%= ing.unit %>
<%= ing.try(:ingredient).try(:ing_name) %>
</p>

From Rails 5 by default you got one required option to make ingredient always not nullable

like below

belongs_to :ingredient, required: true

It will also prevent this error of

class RecipeIngredient < ApplicationRecord
 belongs_to :recipy, :dependent => :destroy
 belongs_to :ingredient, required: true
end

Answer 2

the problem is because inside your show method @recipy is nil, here is usually code for show

controller

def show
  @recipy = Recipy.find(params[:id]) # --> you missed this line
  @recipe_ingredients = @recipy.recipe_ingredients # @recipy will be null without line above
end

view

<% @recipe_ingredients.each do |ing| %>
  <p> <%= ing.amount  %> <%= ing.unit %> <%= ing.ingredient.ing_name %> </p>
<% end %>

I would like also add some suggestion to your model relationship as follow since Ingredient and Recipy shows many to many relationship

class Ingredient < ApplicationRecord
  # -> recipe_ingredients -> recipies
  has_many :recipe_ingredients, :dependent => :destroy
  has_many :recipies, through: :recipe_ingredients
end

class RecipeIngredient < ApplicationRecord
 belongs_to :recipy
 belongs_to :ingredient
end

class Recipy < ApplicationRecord
  has_many :recipy_steps
  # -> recipe_ingredients -> ingredients
  has_many :recipe_ingredients, :dependent => :destroy
  has_many :ingredients, through: :recipe_ingredients
end