Use hash conditions instead of SQL's IN

This is what we're doing in most places.

app/models/budget/investment.rb

@@ -167,7 +167,7 @@ class Budget
       ids += results.where(selected: true).pluck(:id)       if params[:advanced_filters].include?("selected")
       ids += results.undecided.pluck(:id)                   if params[:advanced_filters].include?("undecided")
       ids += results.unfeasible.pluck(:id)                  if params[:advanced_filters].include?("unfeasible")
-      results = results.where("budget_investments.id IN (?)", ids) if ids.any?
+      results = results.where(id: ids) if ids.any?
       results
     end
 
@@ -194,7 +194,7 @@ class Budget
         ids += Investment.where(heading_id: hid).order(confidence_score: :desc).limit(max_per_heading).pluck(:id)
       end
 
-      results.where("budget_investments.id IN (?)", ids)
+      results.where(id: ids)
     end
 
     def self.search_by_title_or_id(title_or_id)

app/models/community.rb

@@ -45,9 +45,7 @@ class Community < ApplicationRecord
   private
 
     def users_who_commented
-      topics_ids = topics.pluck(:id)
+      User.by_comments(topics)
-      query = "comments.commentable_id IN (?)and comments.commentable_type = 'Topic'"
-      User.by_comments(query, topics_ids)
     end
 
     def users_who_topics_author

app/models/user.rb

@@ -108,8 +108,10 @@ class User < ApplicationRecord
   scope :active,         -> { where(erased_at: nil) }
   scope :erased,         -> { where.not(erased_at: nil) }
   scope :public_for_api, -> { all }
-  scope :by_comments,    ->(query, topics_ids) { joins(:comments).where(query, topics_ids).distinct }
+  scope :by_authors,     ->(author_ids) { where(id: author_ids) }
-  scope :by_authors,     ->(author_ids) { where("users.id IN (?)", author_ids) }
+  scope :by_comments,    ->(commentables) do
+    joins(:comments).where("comments.commentable": commentables).distinct
+  end
   scope :by_username_email_or_document_number, ->(search_string) do
     string = "%#{search_string}%"
     where("username ILIKE ? OR email ILIKE ? OR document_number ILIKE ?", string, string, string)

spec/models/community_spec.rb

@@ -13,11 +13,13 @@ RSpec.describe Community, type: :model do
       community = proposal.community
       user1 = create(:user)
       user2 = create(:user)
+      user3 = create(:user)
 
       topic1 = create(:topic, community: community, author: user1)
       create(:comment, commentable: topic1, author: user1)
       create(:comment, commentable: topic1, author: user2)
       create(:topic, community: community, author: user2)
+      create(:comment, commentable: proposal, author: user3)
 
       expect(community.participants).to match_array [user1, user2, proposal.author]
     end