Adding A Column To An Existing Table In A Rails Migration

Answer :

If you have already run your original migration (before editing it), then you need to generate a new migration (rails generate migration add_email_to_users email:string will do the trick). It will create a migration file containing line: add_column :users, email, string Then do a rake db:migrate and it'll run the new migration, creating the new column.

If you have not yet run the original migration you can just edit it, like you're trying to do. Your migration code is almost perfect: you just need to remove the add_column line completely (that code is trying to add a column to a table, before the table has been created, and your table creation code has already been updated to include a t.string :email anyway).

Use this command at rails console

rails generate migration add_fieldname_to_tablename fieldname:string 

and

rake db:migrate 

to run this migration

Sometimes rails generate migration add_email_to_users email:string produces a migration like this

class AddEmailToUsers < ActiveRecord::Migration[5.0]   def change   end end 

In that case you have to manually an add_column to change:

class AddEmailToUsers < ActiveRecord::Migration[5.0]   def change     add_column :users, :email, :string   end end 

And then run rake db:migrate