Ruby On Rails-使用HAVING覆盖作用域的JOIN

Question

I tried to ask this question previously and it didn't go well - hopefully I do it better this time.

I have three models

class Flavor < ActiveRecord::Base
  has_many :components
  has_many :ingredients, through: :components
end

class Ingredient < ActiveRecord::Base
  has_many :components
  has_many :flavors, through: :components
end

class Component < ActiveRecord::Base
  belongs_to :ingredient
  belongs_to :flavor

  validates :percentage, presence: true 
end

Batches are made of flavors, but a flavor can only be made into a batch if it's components add up to 100 percent (hence why I put the percentage validation in there so it was represented).

At first I tried to write this as a scope, but could never get it to work, the model testing i created worked using

def self.batch_eligible
  self.find_by_sql("Select flavors.* FROM flavors 
  INNER JOIN components on flavors.id = components.flavor_id 
  GROUP BY flavors.id, flavors.name 
  HAVING SUM(percentage)=100")
end

I did make an attempt at the scope and it failed. Here is the final version of the scope I came up with:

scope :batch_eligible, -> {joins(:components).having('SUM(percentage) = 100').group('flavor.id')}

The resultant object will be used to populate a selection list in a form for batches (flavors can exist before the components are fully worked out).

I figure the limitation here is my understanding of scopes - so how would the scope be built properly to produce the same results as the find_by_sql expression?

All help is appreciated, thanks.

In response to the first comment - I tried a variety of scopes without capturing the errors - the scope above returns this error:

 ActiveRecord::StatementInvalid:
   PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "flavor"
   LINE 1: SELECT COUNT(*) AS count_all, flavor.id AS flavor_id FROM "f...
                                         ^
   : SELECT COUNT(*) AS count_all, flavor.id AS flavor_id FROM "flavors" INNER JOIN "components" ON "components"."flavor_id" = "flavors"."id" GROUP BY flavor.id HAVING SUM(percentage) = 100

changing it to flavors id makes it 'work' but it doesn't return the proper information.

One more piece of code - models testing

require 'rails_helper'

RSpec.describe Flavor, type: :model do
  let!(:flavor) {FactoryGirl.create(:flavor)}
  let!(:flavor2) {FactoryGirl.create(:flavor)}
  let!(:ingredient) {FactoryGirl.create(:ingredient)}
  let!(:component) {FactoryGirl.create(:component, flavor: flavor, ingredient: ingredient, percentage: 25)}
  let!(:component1) {FactoryGirl.create(:component, flavor: flavor2, ingredient: ingredient, percentage: 100)}

  it "should have a default archive as false" do
    expect(flavor.archive).to be(false)
  end

  it "should only have valid flavors for batch creation" do
    expect(Flavor.batch_eligible.count).to eq 1
    expect(Flavor.batcH_eligible.first).to eq flavor2
  end
end

Even with a clean test database - the batch_eligible count is 4 - not one

One more note - the tests DO pass with the find_by_sql function being used - I just think a scope should be possible?

Answer 1

Props to @taryneast for the help - I was pointed in the right direction by this.

After correcting the scope issue with flavors.id - I did run the inspect to see what was happening but I also ran a variety of functions.

puts Flavor.batch_eligible.count or puts Flavor.batch_eligible.size both yield the same thing, for example, the hash {312 => 1} - 312 would be the id of the Factory Created Flavor.

So the problem (once I solved flavors.id) wasn't in the scope - it was in the test. You need to test the LENGTH, Flavor.batch_eligible.length yields the integer 1 that I wanted.

Perhaps everyone else knew that - I didn't.

Thank you Taryn