No relationship between tables shown in schema diagram when using add_reference in Rails

I am working on a Rails application where I need to add some of the Foreign keys for existing columns from Rails migrations and few people working on same as well. I am adding this way:

class AddUserRefToEvents < ActiveRecord::Migration[5.2]
  def change
    add_foreign_key :events, :users, name: :index_events_on_user_id
  end
end

and one of my mate is adding this way:

class AddUserToParts < ActiveRecord::Migration[5.0]
  def up
    add_reference :parts, :user
  end

  def down
    remove_reference :parts, :user
  end
end

When we use SchemaCrawler for building schema diagram, the relation is built in between user and events (with add_foreign_key) but there is no relation between users and parts (when added add_reference).

Can you tell me why? Can we use both (with reference to this link) or only add_foreign_key? Please help.

The fact is that add_reference does not add a foreign key by default. The API Docs for v5.2 or v5.0 state that the options hash can include a :foreign_key key to set the appropriate foreign key constraint.

So, to use add_reference just change your code to include foreign_key: true as an option.

add_reference :parts, :user, foreign_key: true