data = [
  { name: 'Jones',
    post: 'President',
    city: 'Washington'
  },
  { name: 'Smith',
    post: 'Vice-President',
    city: 'Washington'
  },
  { name: 'Peters',
    post: 'Janitor',
    city: 'New York'
  }
]

data.each do |row|
  name = row[:name]; post = row[:post]; city = row[:city]
  person = Person.where(name: name).first_or_create
  post = Post.where(post: post).first_or_create
  location = Location.where(city: city).first_or_create
  post.people << person
  post.locations << location
  location.save; person.save; post.save
end

person1 = Person.find_by_name("Jones");
person1.posts.first.locations.first == nil
person2 = Person.find_by_name("Smith");
person2.posts.first.locations.first.city == "Washington"
person3 = Person.find_by_name("Peters");
person3.posts.first.locations.first.city == "New York"

class Location < ActiveRecord::Base
  belongs_to :post
  attr_accessible :city
end

class Person < ActiveRecord::Base
  attr_accessible :name
  has_many :occupations
  has_many :posts, through: :occupations
end

class Post < ActiveRecord::Base
  attr_accessible :post
  has_many :occupations
  has_many :people, through: :occupations
  has_many :locations
end

class Occupation < ActiveRecord::Base
  belongs_to :person
  belongs_to :post
  attr_accessible :person_id, :post_id, :since, :till
end

class Post
  has_and_belongs_to_many :locations
end

class Location
  has_and_belongs_to_many :posts
end

create_table :posts_locations, :id => false do |t|
  t.integer :post_id
  t.integer :location_id
end