SQLite3::SQLException: no such column - ruby-on-rails

Question

I'm trying to build an app where people can specify what posts need to be read before this one and here I'm trying to show them.
<%= #post.before.each do |before| %>
<li><%= before.title %></li>
<% end %>
This gets me this error:
SQLite3::SQLException: no such column: connections.post_id: SELECT "posts".* FROM "posts" INNER JOIN "connections" ON "posts"."id" = "connections"."after_id" WHERE "connections"."post_id" = ?
There isn't supposed to be a post_id column in connections, there is supposed to be an before_id column in it.
My models are:
post.rb:
class Post < ApplicationRecord
has_many :connections
has_many :before, through: :connections, source: :after, foreign_key: "before_id"
has_many :after, through: :connections, source: :before, foreign_key: "after_id"
end
connection.rb
class Connection < ApplicationRecord
belongs_to :before, class_name: "Post", foreign_key: "before_id"
belongs_to :after, class_name: "Post", foreign_key: "after_id"
end
The controller code for posts - automatically generated with scaffolding:
class PostsController < ApplicationController
before_action :set_post, only: [:show, :edit, :update, :destroy]
# GET /posts
# GET /posts.json
def index
#posts = Post.all
end
# GET /posts/1
# GET /posts/1.json
def show
end
# GET /posts/new
def new
#post = Post.new
end
# GET /posts/1/edit
def edit
end
# POST /posts
# POST /posts.json
def create
#post = Post.new(post_params)
respond_to do |format|
if #post.save
format.html { redirect_to #post, notice: 'Post was successfully created.' }
format.json { render :show, status: :created, location: #post }
else
format.html { render :new }
format.json { render json: #post.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /posts/1
# PATCH/PUT /posts/1.json
def update
respond_to do |format|
if #post.update(post_params)
format.html { redirect_to #post, notice: 'Post was successfully updated.' }
format.json { render :show, status: :ok, location: #post }
else
format.html { render :edit }
format.json { render json: #post.errors, status: :unprocessable_entity }
end
end
end
# DELETE /posts/1
# DELETE /posts/1.json
def destroy
#post.destroy
respond_to do |format|
format.html { redirect_to posts_url, notice: 'Post was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_post
#post = Post.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def post_params
params.require(:post).permit(:title, :text)
end
end

Answer 1

has_many :connections in your Post model is telling Rails that you have a post_id on the connections table. If this is not the case, I recommend deleting the association or defining a foreign_key for the association.
I would recode your model as follows:
class Post < ApplicationRecord
has_many :before, class_name: 'Connection', foreign_key: "before_id"
has_many :after, class_name: 'Connection', foreign_key: "after_id"
end
NOTE: You have source: :before and source: :after set opposite their respective association names and foreign_key names. I suspect that was not intentional. However, if it was intentional, you may want to swap foreign_keys between your two associations (i.e put the before_id on the after association and vis versa).