Rails - Returning list of incorrect ids

I have an app including Dog, Events and Booking models. Each event has many bookings, each dog has many bookings but each booking belong to an event and has one dog.

On the view for Events it should list all bookings with that id and the details of the linked dog.

I was having a lot of trouble with "Rails Error: undefined method ` ' for nil:NilClass" but then realised the problem was that it is retrieving a list of dogs based on the booking id and not the dog_id field.

In the console I can see that this is the SQL query being generated and what I think is the source of the error but I can't figure out why:

SELECT "dogs".* FROM "dogs" INNER JOIN "bookings" ON "dogs"."id" = "bookings"."id" WHERE "bookings"."event_id" = ?  [["event_id", 1]]

I've spent days combing Stack Overflow and Google to figure out where I've gone wrong but am a bit lost. Here are the models:

class Event < ActiveRecord::Base
has_many :bookings
has_many :dogs, :through => :bookings, :foreign_key => "dog_id"
end

class Dog < ActiveRecord::Base
validates :name, presence: true, length: { maximum: 255 }
validates :breed, presence: true, length: { maximum: 255 }
belongs_to :owner
validates :owner_id, presence: true
has_many :bookings
has_many :events, through: :bookings, :foreign_key => "event_id"
end

class Booking < ActiveRecord::Base
belongs_to :event
has_one :dog, :foreign_key => "id"
validates :event_id, presence: true
validates :dog_id, presence: true
end

The controllers

class EventsController < ApplicationController
  before_action :logged_in_user

  def index
    @events = Event.paginate(page: params[:page])
  end


  def show
    @event = Event.find(params[:id])
    @bookings = @event.bookings.paginate(page: params[:page])

...

class DogsController < ApplicationController

  def show
    @dog = Dog.find(params[:id])
  end

  def new
    @dog = Dog.new
  end

...

class BookingsController < ApplicationController
end

And finally the show view for Events and the _booking partial it renders:

<% provide(:title, @event.name) %>
<div class="row">
  <aside class="col-md-4">      
    <section class="event_info">
      <h1><%= @event.name %></h1> - <%= @event.category %>
      <span><b><%= @event.date %></b> <%= @event.start %> - <%= @event.finish %>    </span>
      <span><b>Location:</b> <%= @event.location %></span>
      <%-# Calculated occupany figure goes in line below. -%>
      <span><b>Capacity: </b>X / <%=@event.capacity %></span>
    </section>
  </aside>
  <div class="col-md-8">
    <section class="event_notes_header">
      Description
    </section>
    <section class="event_notes_body">
      <%= @event.description %>
    </section>
    <section class="event_notes_header">
      Notes
    </section>
    <section class="event_notes_body">
      Event notes will be displayed here...
    </section>
  </div>
  <div class="col-md-8">
    <% if @event.bookings.any? %>
      <h3>Bookings (<%= @event.bookings.count %>)</h3>
      <ol class="bookings">
        <%= render @bookings %>
      </ol>
      <%= will_paginate @bookings %>
    <% end %>
  </div>
</div>   

_booking.html.erb

<li id="booking<%= booking.id %>">
  <span class="event"><%= link_to booking.event.name, booking.event %></span>
  <span class="dog"><%= link_to booking.dog.name, booking.dog %></span>
</li>

Apologies if I've missed anything or if the code has gotten a little convoluted - this is where I am after several days of plugging stuff in and out to try and fix this error.