class ActiveRecord::Associations::JoinDependency::JoinAssociation

def append_constraints(join, constraints)
  if join.is_a?(Arel::Nodes::StringJoin)
    join_string = Arel::Nodes::And.new(constraints.unshift join.left)
    join.left = join_string
  else
    right = join.right
    right.expr = Arel::Nodes::And.new(constraints.unshift right.expr)
  end
end