class Ransack::Adapters::ActiveRecord::Context

def extract_correlated_key(join_root)
  case join_root
  when Arel::Nodes::OuterJoin
    # one of join_root.right/join_root.left is expected to be Arel::Nodes::On
    if join_root.right.is_a?(Arel::Nodes::On)
      extract_correlated_key(join_root.right.expr)
    elsif join_root.left.is_a?(Arel::Nodes::On)
      extract_correlated_key(join_root.left.expr)
    else
      raise 'Ransack encountered an unexpected arel structure'
    end
  when Arel::Nodes::Equality
    pk = primary_key
    if join_root.left == pk
      join_root.right
    elsif join_root.right == pk
      join_root.left
    else
      nil
    end
  when Arel::Nodes::And
    extract_correlated_key(join_root.left) || extract_correlated_key(join_root.right)
  else
    # eg parent was Arel::Nodes::And and the evaluated side was one of
    # Arel::Nodes::Grouping or MultiTenant::TenantEnforcementClause
    nil
  end
end