active_admin_hbtm_association

How to have active_admin filters working with a has_and_belongs_to_many association.

The issue:

Let's have two models: Post and Category related via a has_and_belongs_to_many association. Let's try to make a filter for the Post index admin page:

ActiveAdmin.register Post do
  # just putting "filter :categories" does not show up any filters in the view.
  filter :category_ids,
    label: 'categories',
    as: :select,
    collection: Category.all.collect { |category| [category.name, category.id] }
end

The following exception is thrown:

undefined method `category_ids_eq' for #<MetaSearch::Searches::Post:0x007fcc483bf918>

Related discussions:

activeadmin/activeadmin#1093 activeadmin/activeadmin#1928 activeadmin/activeadmin#515

The solution:

Create the method MetaSearch is looking for as a scope and make it 'findable' to MetaSearch declaring it as a 'search method':

class Post < ActiveRecord::Base
  attr_accessible :body, :title
  has_and_belongs_to_many :categories

  search_methods :category_ids_eq

  scope :category_ids_eq, lambda { |category_id|
    Post.joins(:categories).where("category_id = ?", category_id)
  }
end

The set up from scratch:

rails new active_admin_hbtm_association -T

• Add gem active_admin to gem file

bundle
rails g active_admin:install
rake db:migrate

• Generate the models:

rails g model post title:string body:text -T
rails g model category name:string -T

• Create the association table:

rails g migration CreateTableCategoriesPosts

# and fill the migration file:
class CreateTableCategoriesPosts < ActiveRecord::Migration
  def change
    create_table :categories_posts do |t|
      t.references :post
      t.references :category
    end
  end
end

# then run migrate
rake db:migrate

• Add associations to models:

class Post < ActiveRecord::Base
  attr_accessible :body, :title, :categories
  has_and_belongs_to_many :categories
end

class Category < ActiveRecord::Base
  attr_accessible :name
  has_and_belongs_to_many :posts
end

# create admin views
rails g active_admin:resource post
rails g active_admin:resource category

• Active admin does not have (afaik) direct support to HABTM associations so at this point we three options:
  • A) customize the active admin forms to be able to manage the association throw the admin views.
  • B) use the console to create some associations.
  • C) go to the database itself and create some associations in SQL.

I am going to use B for clarity and simplicity:

rails c
sports_category = Category.create(name: "sports")
news_category = Category.create(name: "news")
cooking_category = Category.create(name: "cooking")
post_about_cooking = Post.create(title: "about cooking 1", body: "about cooking 1 body")
post_about_news = Post.create(title: "about news 1", body: "about news 1 body")
news_category.posts << post_about_news
cooking_category.posts << post_about_cooking