Undefined method `average'

Question

I'm trying to calculate the average star rating of a movie object in my rails app using raty.js. Here's a snippet of my code:

controllers/movies_controller.rb

def show
  @avg_review = @movie.average(:rating)
end

private
def set_movie
  @movie = Movie.find(params[:id])
end

schema.rb

create_table "movies", force: true do |t|
  t.integer  "user_id"
  t.string   "title"
  t.text     "description"
  t.integer  "image_id"
  t.string   "director"
  t.float    "rating"
  t.integer  "num_ratings"
  t.datetime "created_at"
  t.datetime "updated_at"
  t.text     "url"
  t.string   "tracking"
end

I keep getting the error:

undefined method `average' for #<.Movie:0x5b385d0>

From my understanding, this is a predefined method in rails. Yet, I'm getting the error. Can someone help me?

sjagr · Accepted Answer · 2015-09-04T17:03:34.773

7

From the docs you referenced, average is meant to be called on the Movie model itself, not an instance of it.

This will return the average of the column.

@avg_review = Movie.average(:rating)

You can also add conditions to the query (I made up a column for demonstration purposes):

# Get average of movie ratings from 2015
@avg_review = Movie.average(:rating).where(year: '2015')

edited Sep 04 '15 at 17:03

answered Sep 04 '15 at 16:56

sjagr

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Thank you, this fixed the problem for me :) – adventuredoge Sep 04 '15 at 17:34

score 1 · Answer 2 · answered Sep 04 '15 at 16:57

According to the average method documentation. it's a method for ActiveRecord::Calculations so you should use it on ActiveRecord collections or on the model directly, but you trying to use it on instance:

Wrong:

@avg_review = @movie.average(:rating)

Right:

@avg_review = Movie.average(:rating)

Undefined method `average'

2 Answers2