Rails 4 x PostgreSQL：ActiveRecord :: InvalidForeignKey

Question

In my Rails 4 app, which uses postgresql , I am running into an error that I cannot seem to understand:

Completed 500 Internal Server Error in 6ms (ActiveRecord: 1.2ms)

ActiveRecord::InvalidForeignKey (PG::ForeignKeyViolation: ERROR:  insert or update on table "comments" violates foreign key constraint "fk_rails_2fd19c0db7"
DETAIL:  Key (commentable_id)=(52) is not present in table "posts".
: INSERT INTO "comments" ("body", "commentable_id", "commentable_type", "user_id", "created_at", "updated_at") VALUES ($1, $2, $3, $4, $5, $6) RETURNING "id"):
  app/controllers/comments_controller.rb:52:in `block in create'
  app/controllers/comments_controller.rb:51:in `create'

This is the code from comments_controller.rb :

def create
    @commentable = load_commentable
    @comment = @commentable.comments.build(comment_params)
    @comment.user_id = current_user.id
    respond_to do |format|
      if @comment.save
        format.html { redirect_to :back }
        format.json { render :show, status: :created, location: @comment }
        format.js
      else
        format.html { render :new }
        format.json { render json: @comment.errors, status: :unprocessable_entity }
      end
    end
  end

And here is how the routes were setup:

resources :posts, shallow: true do
  resources :comments, shallow: true
end
resources :ads, shallow: true do
  resources :comments, shallow: true
end

With a polymorphic association:

class Post < ActiveRecord::Base
  has_many :comments, as: :commentable, dependent: :destroy
end

class Ad < ActiveRecord::Base
  has_many :comments, as: :commentable, dependent: :destroy
end

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
end

—————

UPDATE:

As per @RuNpiXelruN's request, here the DB schema for comments:

create_table "comments", force: :cascade do |t|
  t.integer  "user_id"
  t.string   "body"
  t.datetime "created_at",       null: false
  t.datetime "updated_at",       null: false
  t.integer  "commentable_id"
  t.string   "commentable_type"
end

  create_table "ads", force: :cascade do |t|
    t.string   "campaign"
    t.string   "text"
    t.string   "headline"
    t.text     "description"
    t.string   "url"
    t.string   "cta"
    t.text     "context"
    t.string   "status"
    t.string   "approval"
    t.integer  "calendar_id"
    t.datetime "created_at",         null: false
    t.datetime "updated_at",         null: false
    t.string   "image_file_name"
    t.string   "image_content_type"
    t.integer  "image_file_size"
    t.datetime "image_updated_at"
  end

create_table "posts", force: :cascade do |t|
    t.integer  "calendar_id"
    t.datetime "date"
    t.string   "subject"
    t.string   "format"
    t.text     "copy"
    t.datetime "created_at",         null: false
    t.datetime "updated_at",         null: false
    t.string   "image_file_name"
    t.string   "image_content_type"
    t.integer  "image_file_size"
    t.datetime "image_updated_at"
    t.string   "short_copy"
    t.integer  "score"
    t.boolean  "facebook"
    t.boolean  "twitter"
    t.boolean  "instagram"
    t.boolean  "pinterest"
    t.boolean  "google"
    t.boolean  "linkedin"
    t.boolean  "tumblr"
    t.boolean  "snapchat"
    t.string   "approval"
  end

—————

How can I fix the error I am getting in the logs?

Answer 1

The error is telling you that no post with id = 52 exists in the database when your trying to add a comment with a commentable_id = 52 . I'm going to guess that column used to be post_id and was renamed in a migration when you swapped over to the polymorphic commentable relation? If so I think you still have a foreign key constraint in your database and will need to delete it.