Rails 5: Add belongs_to association

Question

I have two tables, "users" and "friendships", I'm trying to make a relationship so that a user can have a friendship with other users, so generate this model friendships with rails g model Friendship user:references friend:references status

in the model friendship.rb:

class Friendship < ApplicationRecord
  belongs_to :user
  belongs_to :friend,class_name: "User"
end

but at the time of creating the record it shows me the following error:

Friendship.create(user_id: 1, friend_id:2, id: 1)

   (0.1ms)  begin transaction
  User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
  User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 2], ["LIMIT", 1]]
  SQL (0.4ms)  INSERT INTO "friendships" ("id", "user_id", "friend_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?)  [["id", 1], ["user_id", 1], ["friend_id", 2], ["created_at", "2018-02-26 19:39:57.865042"], ["updated_at", "2018-02-26 19:39:57.865042"]]
   (0.1ms)  rollback transaction
Traceback (most recent call last):
        1: from (irb):2
ActiveRecord::StatementInvalid (SQLite3::SQLException: no such table: main.friends: INSERT INTO "friendships" ("id", "user_id", "friend_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?))
irb(main):003:0> 

What could it be? I have Rails 5.1.5

Answer 1

Your Friendship model is set up correctly, but perhaps your migration is not. It should look like this:

class CreateFriendships < ActiveRecord::Migration[5.1]
  def change
    create_table :friendships do |t|
      t.references :user, index: true, foreign_key: true
      t.references :friend, index: true, foreign_key: { to_table: :users }
    end
  end
end

I've set this up in a new Rails 5.1.5 project and it is working for me:

>> User.create(name: 'First User')
>> User.create(name: 'Second User')
>> Friendship.create(user_id: 1, friend_id:2, id: 1)
   (0.1ms)  begin transaction
  User Load (0.7ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
  User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 2], ["LIMIT", 1]]
  SQL (0.8ms)  INSERT INTO "friendships" ("id", "user_id", "friend_id") VALUES (?, ?, ?)  [["id", 1], ["user_id", 1], ["friend_id", 2]]
   (0.8ms)  commit transaction
#<Friendship id: 1, user_id: 1, friend_id: 2>

Incidentally, you should avoid assigning id numbers to non-persisted objects. Better to let the database handle that job. I would create a Friendship simply as:

>> Friendship.create(user_id: 1, friend_id: 2)