Rails: HasManyThroughAssociationNotFoundError

I have problems with getting a has_many through association to work.

I keep getting this exception:

Article.find(1).warehouses.build
ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :entries in model Article

These are the models involved:

class Article < ActiveRecord::Base
  has_many :warehouses, :through => :entries
end

class Warehouse < ActiveRecord::Base
  has_many :articles, :through => :entries
end

class Entry < ActiveRecord::Base
  belongs_to :article
  belongs_to :warehouse
end

And this is my schema:

create_table "articles", :force => true do |t|
  t.string   "article_nr"
  t.string   "name"
  t.integer  "amount"
  t.string   "warehouse_nr"
  t.datetime "created_at"
  t.datetime "updated_at"
  t.integer  "unit"
end

create_table "entries", :force => true do |t|
  t.integer "warehouse_id"
  t.integer "article_id"
  t.integer "amount"
end

create_table "warehouses", :force => true do |t|
  t.string   "warehouse_nr"
  t.string   "name"
  t.integer  "utilization"
  t.datetime "created_at"
  t.datetime "updated_at"
end

You need to add

has_many :entries

To each of your models, since the :through option just specifies a second association which it should use to find the other side.

You would need to add

has_many :entries

To each model, and above has_many :through, like this:

class Article < ActiveRecord::Base
  has_many :entries
  has_many :warehouses, :through => :entries
end

class Warehouse < ActiveRecord::Base
  has_many :entries
  has_many :articles, :through => :entries
end

More detailed tutorial on how to handle view and controllers https://kolosek.com/rails-join-table/