CODEWITHSUNDEEP
ruby-on-railsrubypostgresql
Isaac Byrne
Isaac Byrne

Reputation: 613

PG::UndefinedColumn: ERROR: column comments.post_id does not exist

I cant seem to figure out why I keep getting this error. I am trying to add comment forms to a blog I am making and it wont work. Here is what the full error says.

ActiveRecord::StatementInvalid in Posts#show

Showing /Users/ipbyrne/FirstRailsApp/blog/app/views/posts/show.html.erb where line #17 raised:

PG::UndefinedColumn: ERROR: column comments.post_id does not exist LINE 1: SELECT COUNT() FROM "comments" WHERE "comments"."post_id" ... ^ : SELECT COUNT() FROM "comments" WHERE "comments"."post_id" = $1

</p>

   <div id="comments">
       <h2><%= @post.comments.count %> Comments</h2> <-- Says it breaks here
       <%= render @post.comments %>

       <h3>Add a comment:</h3>

From what i can understand there is a column missing in one of the tables in the schema.rb file? Incase this the case here is what mine looks like

# encoding: UTF-8
# This file is auto-generated from the current state of the database. Instead
# of editing this file, please use the migrations feature of Active Record to
# incrementally modify your database, and then regenerate this schema definition.
#
# Note that this schema.rb definition is the authoritative source for your
# database schema. If you need to create the application database on another
# system, you should be using db:schema:load, not running all the migrations
# from scratch. The latter is a flawed and unsustainable approach (the more migrations
# you'll amass, the slower it'll run and the greater likelihood for issues).
#
# It's strongly recommended that you check this file into your version control system.

ActiveRecord::Schema.define(version: 20140911230918) do

  create_table "comments", force: true do |t|
    t.string   "name"
    t.text     "body"
    t.integer  "post_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  add_index "comments", ["post_id"], name: "index_comments_on_post_id"

  create_table "posts", force: true do |t|
    t.string   "title"
    t.text     "body"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "users", force: true do |t|
    t.string   "email",                  default: "", null: false
    t.string   "encrypted_password",     default: "", null: false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          default: 0,  null: false
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  add_index "users", ["email"], name: "index_users_on_email", unique: true
  add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true

end

Upvotes: 5

Views: 16397

Answers (2)

Graham S.
Graham S.

Reputation: 1540

You probably just need to add the column into your comments table.

You can do that by creating a migration via the terminal to add the column in:

$ rails g migration add_post_id_column_to_comments post:belongs_to
$ rake db:migrate

The reason you want to use post:belongs_to is that Rails will automatically append the _id suffix and create a foreign key in the comments table to refer back to each other.

So essentially this part of the migration post:belongs_to will add the column post_id to your comments table. (Same thing if you did for example cars:belongs_to, you would get cars_id, etc)

That way you can be able to refer to the post's comments like this:

@post.comments

The reason why your @post.comments is failing now is that it is looking for that post_id column that you have not made yet which is probably also because you may not have defined the relationship between your Post and Comment models.

If you haven't done so already you just need to quickly define the relationship in each model:

  • A post has many comments.
  • A comment belongs to a post.

Get the lingo?

In your Post model, just add

class Post < ActiveRecord::Base
    has_many :comments   # make sure it's pluralized
end

and in your Comment model, add

class Comment < ActiveRecord::Base
    belongs_to :post  # and this one is singularized
end

Then try running your app again. Let me know how it goes.

Upvotes: 5

eirikir
eirikir

Reputation: 3842

Yes, you're missing the field post_id on the Comment model, which would tell Rails which comments belong to which posts.

You can add it by generating a migration from the command line like so:

rails generate migration AddPostIdToComments post:references
rake db:migrate

Upvotes: 1

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