↖️ Show all posts

Using class_eval

Sometimes it is quite handy to add some helping attributes or instance methods to an object, i.e. for calculation purposes. This code snip is stripped and is mainly for demonstrating a use case.

@units = Unit.all

def calc_units_empty_not_empty_time
        @units.each do |unit|
            unit.class_eval do
                # Adding two extra attributes to the model Unit
                attr_accessor :time_empty_in_period
                attr_accessor :time_not_empty_in_period
            period_tenants = get_period_tenants(unit)
            time_with_tenants = 0
            period_tenants.each do |tenant|
                time_with_tenants += calc_tenants_time_span_in_period(tenant) if tenant
            unit.time_empty_in_period = (period_duration - time_with_tenants).to_i
            unit.time_not_empty_in_period = time_with_tenants

Important! These two new attributes are not permanent and bound to the instance(s) you call class_eval on.

⬅️ Read previous Read next ➡️