foreign key rails, how to add? - ruby-on-rails

Question

To make more simple I do have
class User
has_many :questions, trough: votes
has_many :questions #(as the author)
has_many :votes
end
Forgot to add foreign_key when created, now I don't know how to add it to specific (has_many through) association
schema.rb
enable_extension "plpgsql"
create_table "answers", force: :cascade do |t|
t.text "body"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "question_id"
t.integer "user_id"
t.boolean "best", default: false
end
add_index "answers", ["question_id"], name: "index_answers_on_question_id", using: :btree
add_index "answers", ["user_id"], name: "index_answers_on_user_id", using: :btree
create_table "attachments", force: :cascade do |t|
t.string "file"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "attachable_id"
t.string "attachable_type"
end
add_index "attachments", ["attachable_id", "attachable_type"], name: "index_attachments_on_attachable_id_and_attachable_type", using: :btree
create_table "questions", force: :cascade do |t|
t.string "title"
t.text "body"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "user_id"
end
add_index "questions", ["title"], name: "index_questions_on_title", using: :btree
add_index "questions", ["user_id"], name: "index_questions_on_user_id", using: :btree
create_table "users", force: :cascade do |t|
t.string "name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
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.inet "current_sign_in_ip"
t.inet "last_sign_in_ip"
end
add_index "users", ["email"], name: "index_users_on_email", unique: true, using: :btree
add_index "users", ["name"], name: "index_users_on_name", unique: true, using: :btree
add_index "users", ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree
create_table "votes", force: :cascade do |t|
t.integer "votable_id"
t.string "votable_type"
t.integer "user_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "votes", ["user_id", "votable_id"], name: "index_votes_on_user_id_and_votable_id", unique: true, using: :btree
add_foreign_key "answers", "questions", on_delete: :cascade
add_foreign_key "questions", "users", on_delete: :cascade
end

Answer 1

Run this command on your console
rails g migration AddForeignKeyToVotes user:references question:references
This will generate a xxxx_add_foreign_key_to_votes.rb file under db/migrate/ with following contents
class AddForeignKeyToVotes < ActiveRecord::Migration
def change
add_reference :votes, :user, index: true, foreign_key: true
add_reference :votes, :question, index: true, foreign_key: true
end
end

Answer 2

Are you really need foreign keys?
Many of Rails developers are comfortable with the way Rails handles relationships in the application rather than the database.
for your case:
class User
has_many :questions, trough: votes
has_many :questions #(as the author)
has_many :votes
end
if votes table has question_id and user_id that is enough to define the relation without any foreign keys, unless you have a reason and really need this foreign keys to be defined database level.
Read THIS SECTION carefully, Rails is using Convention over Configuration.
As a small example: how your User model know which table to query in and retrieve the data, without any configuration it search for table with same name users (convention) and use it, same for foreign keys.
According to your comment you have a model something as Stackoverflow, you have a User who can ask a Question and can answer a Question in this case you may have something like:
class User
has_many :asked_questions, class_name: 'Question' # user can ask many questions
has_many :voted_questions, through: :votes, source: 'question'
has_many :votes # to get all votes this user did
end
class Question
has_many :votes # to get all votes for a question
belongs_to :user
end
class Vote
belongs_to :user
belongs_to :question
end
Database will be something like:
# Table User
# Table Question (user_id)
# Table Vote (user_id, question_id)
Let's say you want to get Questions user asked they it will be:
user = User.first
user.asked_questions
if you want get Questions who user votes for:
user.voted_questions