can anyone explain me this error? - ruby-on-rails

Question

I am getting this while i use Postgres.
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:
PG::UndefinedTable: ERROR: relation "retailers" does not exist
: ALTER TABLE "stations" ADD CONSTRAINT "fk_rails_57ee36b830"
FOREIGN KEY ("retailer_id")
REFERENCES "retailers" ("id")
/home/suyesh/Desktop/Petrohub_main/db/migrate/20160104152245_create_stations.rb:3:in `change'
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR: relation "retailers" does not exist
: ALTER TABLE "stations" ADD CONSTRAINT "fk_rails_57ee36b830"
FOREIGN KEY ("retailer_id")
REFERENCES "retailers" ("id")
/home/suyesh/Desktop/Petrohub_main/db/migrate/20160104152245_create_stations.rb:3:in `change'
PG::UndefinedTable: ERROR: relation "retailers" does not exist
/home/suyesh/Desktop/Petrohub_main/db/migrate/20160104152245_create_stations.rb:3:in `change'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)
Here are my stations and retailers model.
Retailer
class Retailer < User
has_many :stations
has_many :retailer_suppliers
has_many :suppliers , through: :retailer_suppliers, as: :connections
end
Stations
class Station < ActiveRecord::Base
belongs_to :retailer
has_many :tanks
end
Here is my Station Migration
class CreateStations < ActiveRecord::Migration
def change
create_table :stations do |t|
t.string :brand
t.string :business_name
t.string :tax_id
t.string :phone_number
t.string :contact_person
t.string :cell_number
t.string :address1
t.string :address2
t.string :city
t.string :state
t.string :zip
t.string :station_reg_number
t.references :retailer, index: true, foreign_key: true
t.timestamps null: false
end
end
end
I dont have retailer migration because its inheriting from the User. Here is my User migration
User
class DeviseCreateUsers < ActiveRecord::Migration
def change
create_table(:users) do |t|
## Database authenticatable
t.string :email, null: false, default: ""
t.string :encrypted_password, null: false, default: ""
## Recoverable
t.string :reset_password_token
t.datetime :reset_password_sent_at
## Rememberable
t.datetime :remember_created_at
## Trackable
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
## Confirmable
# t.string :confirmation_token
# t.datetime :confirmed_at
# t.datetime :confirmation_sent_at
# t.string :unconfirmed_email # Only if using reconfirmable
## Lockable
# t.integer :failed_attempts, default: 0, null: false # Only if lock strategy is :failed_attempts
# t.string :unlock_token # Only if unlock strategy is :email or :both
# t.datetime :locked_at
t.timestamps null: false
end
add_index :users, :email, unique: true
add_index :users, :reset_password_token, unique: true
# add_index :users, :confirmation_token, unique: true
# add_index :users, :unlock_token, unique: true
end
end
Add Type to User
class AddTypeToUsers < ActiveRecord::Migration
def change
add_column :users, :type, :string
end
end
Add extra attributes to user
class AddExtraToUsers < ActiveRecord::Migration
def change
add_column :users, :first_name, :string
add_column :users, :last_name, :string
add_column :users, :phone_number, :string
add_column :users, :cell_number, :string
add_column :users, :tax_id, :string
add_column :users, :business_name, :string
add_column :users, :address1, :string
add_column :users, :address2, :string
add_column :users, :city, :string
add_column :users, :state, :string
add_column :users, :zip_code, :string
add_column :users, :years_in_business, :string
end
end
And add account number to user
class AddAccountNumberToUsers < ActiveRecord::Migration
def change
add_column :users, :account_number, :string
add_index :users, :account_number
end
end
It works with no errors when i use Sqlite3 but i get errors in Production heroku using postgres. so i decided to use postgres in developemnt and i saw the above errors which i cannot understand. Thank you in advance

Answer 1

PG::UndefinedTable: ERROR: relation "retailers" does not exist
This error simply means that the retailers table is not present in your database when you try to reference this in another place. All you need is to make sure you create retailers table before you try to use/reference it in some some migration.

Answer 2

The error is coming from this line in your migration:
t.references :retailer, index: true, foreign_key: true
The foreign key option means that rails is trying to create a foreign key between retailer_id on the stations table and id on the non existant retailers table.
Although migrations are frequently created at the same time as a model, they're not really connected - the migration doesn't know that retailer is an STI model.
As far as I can tell you will need to remove the foreign key option from the call to references and add the foreign separately with add_foreign_key:
add_foreign_key :stations, :users, column: "retailer_id"
You probably didn't encounter this in development because earlier versions of sqlite3 didn't support foreign keys and current versions require that it be activated (see docs): unless activated it just ignores foreign key constraints (as long as they are syntactically correct)