class ActiveRecord::ConnectionAdapters::Table

See {connection.add_reference}[rdoc-ref:SchemaStatements#add_reference] for details of the options you can use.

t.belongs_to(:supplier, foreign_key: true)
t.references(:user)

Adds a reference.

def references(*args, **options)
  raise_on_if_exist_options(options)
  args.each do |ref_name|
    @base.add_reference(name, ref_name, **options)
  end
end