Creating associated objects - Rails 4.2

Question

I'm trying to create a few simple relations in my Rails 4 application. I have three models: user, list, word.

This is for a simple 'list' application, where each user has_many words through lists.

I currently have the following associations...

User model

class User < ActiveRecord::Base
  has_many :lists
  has_many :words, through: :lists
end

List model

class List < ActiveRecord::Base
  has_many :words
  belongs_to :user
end

Word model

class Word < ActiveRecord::Base
  belongs_to :list
end

DB Scheme

ActiveRecord::Schema.define(version: 20150320200247) do

# These are extensions that must be enabled in order to support this database
enable_extension "plpgsql"

create_table "users", force: :cascade do |t|
  t.string   "name"
  t.string   "email"
  t.datetime "created_at",  null: false
  t.datetime "updated_at",  null: false
end

create_table "lists", force: :cascade do |t|
  t.string   "name"
  t.text     "description"
  t.datetime "created_at",  null: false
  t.datetime "updated_at",  null: false
end

create_table "words", force: :cascade do |t|
  t.string   "word"
  t.datetime "created_at", null: false
  t.datetime "updated_at", null: false
end
  add_index "words", ["word"], name: "index_words_on_word", using: :btree

end

creating objects:

> user = User.create(name: "Kyle")
> list = List.create(name: "List One")
> word = Word.create(word: "StackOverflow")

# Display words in list
> list.words

The above association object gives an error: PG::UndefinedColumn: ERROR: column words.list_id does not exist.

I've also tried creating migrations with foreign key constraints using the Foreigner gem, but am still getting errors. Please help!

your are missing list_id in your words table and user_id in the lists table, these are required for the association to work correctly. — mtkcs
– mtkcs, Commented Mar 23, 2015 at 0:58

mtkcs · Accepted Answer · 2015-03-23 00:51:09Z

3

From what the error tells, the list_id column is not present, your migration should look something like this

 class CreateWords < ActiveRecord::Migration
  def change
    create_table :words do |t|
      t.string :word
      t.integer :list_id

      t.timestamps null: false
    end
  end
end

then when creating your records:

> user = User.create(name: "Kyle")
> list =  List.create(name: "List One", user_id: user.id)
> word = Word.create(word: "StackOverflow", list_id: list.id)

# Should work
> list.words

answered Mar 23, 2015 at 0:51

mtkcs

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Creating associated objects - Rails 4.2

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