How to create a migration

How to create a migration:

rails g migration migration_name 

This will create an empty migration:

class <MigrationName> < ActiveRecord::Migration[5.0]
  def change
  end
end

An example of changing the column name from name to full_name. Here's the existing code for name:

class CreateProfiles < ActiveRecord::Migration
  def change
    create_table :profiles do |t|
      t.references :user
      t.string :avatar
      t.string :name, null: false
    end
  end
end

And here's the change required to change from name to full_name:

class RenameProfileNameToFullName < ActiveRecord::Migration
  def change
    rename_column :profiles, :name, :full_name
  end
end

Then run

rails db:migrate

To make the change to the database.

Rename existing column

rails g migration rename_field

Which will create the migration file:

class UserAuth < ActiveRecord::Migration[5.2]
  def change
		rename_column :profiles, :name, :full_name
  end
end