Rails csv import with associations

Question

I am building a rails application that associates posts with many different categories. For example, I have a Post and need to be able to assign it to the categories Sports, News and Science through csv import via rake task.

My question is how can I import an array of multiple category_ids into my Post model? I have it working where I can manually create a new Post and assign multiple categories to the post, but I am confused as to how to complete this through csv. I need help figuring out the best way to accomplish this.

Here is what I have so far:

Schema

  create_table "posts", force: :cascade do |t|
    t.string   "name"
    t.text     "description"
  end

  create_table "styles", force: :cascade do |t|
    t.datetime "created_at",  null: false
    t.datetime "updated_at",  null: false
    t.integer  "post_id"
    t.integer  "category_id"
  end

  create_table "categories", force: :cascade do |t|
    t.string   "name"
    t.datetime "created_at",        null: false
    t.datetime "updated_at",        null: false
  end

Post.rb

class Post < ApplicationRecord  
  has_many :styles
  has_many :categories, through: :styles
end

Category.rb

class Category < ApplicationRecord
  has_many :styles
  has_many :posts, through: :styles
end

Style.rb

class Style < ApplicationRecord
  belongs_to :post
  belongs_to :category
end

Rake Task

require 'csv'
require 'open-uri'
namespace :post_import do
  desc "Import posts daily"
  task posts: :environment do
    filename = File.join Rails.root, "posts.csv"
    counter = 0

    CSV.foreach(filename) do |row|
      name, category, description = row
      post = Post.create(name: name, category_ids: category, description: description)
      counter += 1 if post.persisted?
    end

    puts "Imported #{counter} [posts]"
  end
end

Answer 1

require 'csv'
require 'open-uri'
namespace :post_import do
  desc "Import posts daily"
  task posts: :environment do
    filename = File.join Rails.root, "posts.csv"
    counter = 0

    CSV.foreach(filename) do |row|
      name, category, description = row

      #you can user find or create, but for clarity I split it
      post = Post.where(name: name).first
      post = Post.new(name: name, description: description) if post == nil

      #now we can simply add the style which joins to the category
      post.styles.build(category_id: category)
      post.save
      counter += 1 if post.persisted?
    end

    puts "Imported #{counter} [posts]"
  end
end

Answer 2

I was able to solve this with help from Chris at gorails.com. Here is my (rough) working solution. Hope this helps anyone else with this issue!

require 'csv'
require 'open-uri'
namespace :post_import do
  desc "Import posts daily"
  task posts: :environment do
    filename = File.join Rails.root, "posts.csv"
    counter = 0

    CSV.foreach(filename) do |row|
      name, category_ids, description = row
      post = Post.new(name: name, description: description) if post == nil
      post.save 

      #separate string of category ids into array
      a_categories = category_ids.split(",")

      a_categories.each do |category_id|
        post.styles.where(category_id: category_id).first_or_create
      end

      counter += 1 if post.persisted?
    end

    puts "Imported #{counter} [posts]
  end
end