如何獲得這個ActiveRecord :: Associations :: CollectionProxy的總和？

Question

[#<ActiveRecord::Associations::CollectionProxy [#<InvoiceServiceType id: 1, value_charged: 50.0, invoice_id: 4, service_type_id: 1>, #<InvoiceServiceType id: 2, value_charged: 50.4, invoice_id: 4, service_type_id: 2>]>, #<ActiveRecord::Associations::CollectionProxy [#<InvoiceServiceType id: 8, value_charged: 70.0, invoice_id: 1, service_type_id: 2>, #<InvoiceServiceType id: 9, value_charged: 50.0, invoice_id: 1, service_type_id: 6>]>] 

我想總結所有value_charged。

IM嘗試地圖（&：value_charged）的.sum 收集.. 並沒有什麼:(

謝謝

Answer 1

讓說你有一個has_many關係details一個@object，並details有現場通話:value_charged，你可以嘗試總結的@object.details所有:value_charged有：

@object.details.sum(:value_charged)