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PG::UndefinedTable: ERROR:  relation "musicians" does not exist
: ALTER TABLE "orders" ADD CONSTRAINT "fk_rails_ad134589be"
FOREIGN KEY ("musician_id")
  REFERENCES "musicians" ("id")
   (0.9ms)  ROLLBACK
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:
PG::UndefinedTable: ERROR:  relation "musicians" does not exist
: ALTER TABLE "orders" ADD CONSTRAINT "fk_rails_ad134589be"
FOREIGN KEY ("musician_id")
Here is a link to the entire log: https://gist.github.com/helloravi/2cb69e0927e63e186b09
The following is the migration which does not get executed. The error is displayed below the migration code
class CreateAlbums < ActiveRecord::Migration
  def change
    create_table :albums do |t|
      t.string :album_name
      t.references :musician, index: true, foreign_key: true
      t.timestamps null: false
    add_foreign_key :albums, :users, column: :musician_id
I have a users table with a musician column which is boolean(some users are musicians)
I even tried using add_foreign_key and still I am not able to figure out what the problem is.
I tried rake db:schema:load and it worked. I want to be able to make rake db:migrate work because I need to be able to migrate in production.
                ` belongs_to :musician, class_name: User.name` `  has_many :songs` `  has_many :order_items`
– Ravikanth Andhavarapu
                Feb 12, 2016 at 10:19
SQLite does not check foreign keys, it simply ignores them. But PostgreSQL is very strict and raises an error when the foreign key constraint is not valid. 
Rails foreign_key does not support what you want it to do. When you write t.references :musician then there must be a musicians table. But you want the foreign key to point to a users table.
I see two options:
Use t.references :users and rename that association in your albums.rb like this:
belongs_to :musician, class_name: 'User', foreign_key: 'user_id'
Or: you just use t.integer :musician_id instead of references and define the foreign key constraint manually with an execute 'ALTER TABLE ...'
                1. I will probably go with option one. I am already using the association the way you suggested. 2. How would I manually execute the execute 'ALTER TABLE ...' in heroku ? 3. Would it work if I deleted the line with t.references and used add_foreign_key line in the migration?
– Ravikanth Andhavarapu
                Feb 12, 2016 at 10:15
Changing your migration to the following should work:

class CreateAlbums < ActiveRecord::Migration
  def change
    create_table :albums do |t|
      t.string :album_name
      t.integer :musician_id
      t.timestamps null: false
    add_foreign_key :albums, :users, column: :musician_id
    add_index :albums, :musician_id
                What would be the command which would create a migration of what you mentioned?(I was also planning to do what Speckerman said)
– Ravikanth Andhavarapu
                Feb 12, 2016 at 10:23
                You could just edit the migration. The existing migration will not work on postgresql. You will have to make a change to the existing migration. Making this change will not effect what happens with sqlite3.
– Satyaram B V
                Feb 12, 2016 at 10:27
        
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