How to join two tables using ruby on rails - ruby-on-rails

Question

I have two tables - positions table with the fields id, position_id, first_name and last_name. The other table is positionslist with the fields id, positions.How will i able to join that two tables?
Here's my positionscontroller:
class PositionsController < ApplicationController
def index
##positions = Position.all(:order=>'updated_at DESC')
#positions = Position.joins(:positions => :positionlists)
end
def new
#position = Position.new
end
def create
#position = Position.new(params.require(:position).permit(:position_id, :first_name, :last_name))
if #position.save
redirect_to(:controller=>'positions')
else
render 'new'
end
end
def edit
#position = Position.find(params[:id])
end
def update
#position = Position.find(params[:id])
if #position.update(params.require(:position).permit(:position_id, :first_name, :last_name))
redirect_to(:controller=>'positions')
else
render 'edit'
end
end
def destroy
#position = Position.find(params[:id])
#position.destroy
redirect_to(:controller=>'positions')
end
end
my models position.rb
class Position < ActiveRecord::Base
has_many :positionlists
has_many :positionlists , :through => :positions
validates :first_name, length: { in: 4..20}
validates :last_name, length: { in: 4..20}
end
my models positionlists.rb
class Positionlists < ActiveRecord::Base
has_many :positions
end
any my postions index.html.erb
<% content_for :title, "Positions" %>
<%= render "layouts/nav" %>
<div class="clear"></div>
<h1>Positions List</h1>
<%= link_to "Add", new_position_path, :class =>'btn btn-success' %>
<br />
<br />
<table class="table">
<tr>
<th>First Name</th>
<th>Last Name</th>
<th>Position</th>
<th>Options</th>
</tr>
<% #positions.each do |positions| %>
<tr>
<td><%= positions.first_name %></td>
<td><%= positions.last_name %></td>
<td><%= positions.position_id %></td>
<td>
<%= link_to "Edit", edit_position_path(positions)%> |
<%= link_to "Delete", position_path(positions),
method: :delete, data:{confirm: 'Are you sure you want to delete this?.' }%>
</td>
</tr>
<% end %>
</table>
any help is greatly appreciated! thanks

Answer 1

Rails takes care of this for you.
class PositionList < ActiveRecord::Base
has_many :positions
end
class Position < ActiveRecrod::Base
belongs_to :position_list
end
Also your position needs a position_list_id column for simplicity. If I'm understanding what you are trying to do here.
Other problems: naming your class PositionLists and not PositionList will confuse Rails automagic naming conventions.
Also you have an odd set of columns in your tables. For what you want as far as I can tell your positions table needs to have the columns:
first_name
last_name
id (automatic)
You don't appear to have anything in your position_list table so there's no column you need there outside of the automatic id column. The association is automatic from the belongs_to in the Position class and the position_list_id column in the positions table.
If you want to get an idea of how simple this all can be try running an automatic scaffolding, looking at how it's done there, and learning from that. Maybe a generate a fresh Rails app and then run something like this:
rails g scaffold position_list name
rails g scaffold position first_name last_name position_list:references
This will give you position_list.positions to get all positions for any position_list or Position.all for a list of all positions.
Also it sounds like a lot of Rails is new to you. Hartl's classic is a great intro: http://ruby.railstutorial.org/ruby-on-rails-tutorial-book