has_many through association dependent error is still referenced in table users

Question

Before I start, I should say I have already checked out Rails 5.1.: destroy records in "has_many: through" association with restriction and has_many through association dependent destroy under condition of who called destroy without results.

My app consist in USERS that has_one EMPRESA. An EMPRESA may have several TAGS A TAG may have several EMPRESAS (To do this I have used has_many :through)

My case: I got this screen error:

And I know the origin of this error is because I'm trying to destroy items with pending references. But I can't identify th issue.

By looking at server console I can guess the problem involve empresa, tag, and tagging.

Models involved

class Empresa < ApplicationRecord

  skip_callback :validate, after: :create
  after_initialize :set_default_plan, :if => :new_record?

  attr_accessor :tag_list

  enum plan: [:noplan, :basic, :plus, :premium]

  belongs_to :user
  belongs_to :category, optional: true
  has_many :promos, dependent: :destroy

  has_many :taggings, dependent: :destroy
  has_many :tags, through: :taggings

  mount_uploader :logo, LogoUploader
  mount_uploaders :fotos, FotosUploader

  def tag_list
    tags.join(", ")
  end

  def tag_list=(names)
    tag_names = names.split(",").collect {|str| str.strip.downcase}.uniq
    new_or_existing_tags = tag_names.collect {|tag_name| Tag.find_or_create_by(name: tag_name)}

    self.tags = new_or_existing_tags
  end

  def set_default_plan
    self.plan ||= :noplan
  end

end

class Tag < ApplicationRecord
  has_many :empresas, through: :taggings
  has_many :taggings, dependent: :destroy

  def to_s
    name
  end

end

class Tagging < ApplicationRecord
  belongs_to :empresa
  belongs_to :tag
end

class Category < ApplicationRecord
  validates :name, presence: true, length:{ minimum: 3 }, uniqueness: true
  has_many :empresas, dependent: :nullify

end
class User < ApplicationRecord

  enum role: [:user, :editor, :admin, :superadmin]
  after_initialize :set_default_role, :if => :new_record?

  has_one :empresa, dependent: :destroy
  has_many :incidents, dependent: :destroy
  has_many :comments, dependent: :destroy
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable


  def set_default_role
    self.role ||= :user
  end


  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable


end

schema.rb (irrelevant tables removed)

ActiveRecord::Schema.define(version: 20180531033550) do

  enable_extension "plpgsql"

  create_table "empresas", force: :cascade do |t|
    t.string   "logo"
    t.string   "name"
    t.text     "description"
    t.text     "excerpt"
    t.string   "address"
    t.string   "web"
    t.string   "email"
    t.string   "tel"
    t.string   "video"
    t.json     "fotos"
    t.integer  "plan",        default: 0
    t.float    "mlon"
    t.float    "mlat"
    t.string   "schedule0"
    t.string   "schedule1"
    t.string   "schedule2"
    t.string   "schedule3"
    t.string   "schedule4"
    t.string   "schedule5"
    t.string   "schedule6"
    t.string   "schedule7"
    t.string   "schedule8"
    t.string   "schedule9"
    t.string   "schedule10"
    t.string   "schedule11"
    t.string   "schedule12"
    t.string   "schedule13"
    t.string   "schedule14"
    t.string   "schedule15"
    t.string   "schedule16"
    t.string   "schedule17"
    t.string   "schedule18"
    t.string   "schedule19"
    t.string   "schedule20"
    t.string   "schedule21"
    t.string   "schedule22"
    t.string   "schedule23"
    t.string   "schedule24"
    t.string   "schedule25"
    t.string   "schedule26"
    t.string   "schedule27"
    t.integer  "tag_id"
    t.integer  "offer_id"
    t.integer  "user_id"
    t.datetime "created_at",              null: false
    t.datetime "updated_at",              null: false
    t.integer  "category_id"
    t.index ["category_id"], name: "index_empresas_on_category_id", using: :btree
  end


  create_table "taggings", force: :cascade do |t|
    t.integer  "empresa_id"
    t.integer  "tag_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["empresa_id"], name: "index_taggings_on_empresa_id", using: :btree
    t.index ["tag_id"], name: "index_taggings_on_tag_id", using: :btree
  end

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

  create_table "users", force: :cascade do |t|
    t.string   "email",                  default: "", null: false
    t.string   "encrypted_password",     default: "", null: false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          default: 0,  null: false
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.string   "current_sign_in_ip"
    t.string   "last_sign_in_ip"
    t.integer  "creditos",               default: 0,  null: false
    t.datetime "created_at",                          null: false
    t.datetime "updated_at",                          null: false
    t.integer  "empresa_id"
    t.integer  "role"
    t.string   "first_name"
    t.string   "last_name"
    t.date     "birthdate"
    t.string   "dni"
    t.string   "phone"
    t.string   "address"
    t.string   "gender"
    t.index ["email"], name: "index_users_on_email", unique: true, using: :btree
    t.index ["empresa_id"], name: "index_users_on_empresa_id", using: :btree
    t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true, using: :btree
  end

  add_foreign_key "comments", "incidents"
  add_foreign_key "comments", "users"
  add_foreign_key "incidents", "users"
  add_foreign_key "promos", "empresas"
  add_foreign_key "taggings", "empresas"
  add_foreign_key "taggings", "tags"
  add_foreign_key "users", "empresas"
end

Answer 1

You do not need empresa_id in users.
Remove the referential integrity and column via:

rails g migration remove_constraint_from_users

Edit the newly created migration file to add the following in def change block

def change
  remove_foreign_key :users, :empresas
  remove_column :users, :empresa_id
end