CoreData等价于sum ... group by [英] CoreData equivalent of sum...group by

问题描述

我有以下伪SQL模式：

I have the following pseudo-SQL schema:

table flight
  id int primary key
  date timestamp
  aircraft_id int (foreign key to aircraft.id)

table flight_component
  flight_id int (foreign key to flight.id)
  component_id int (foreign key to component.id)
  duration double

如果我将它转换为使用CoreData，等效的方式来获得每个组件的总持续时间与另一个查询谓词？我认为SQL等效项将是

If I convert this to using CoreData, is there an equivalent way to get the total duration for each component with another query predicate? I think the SQL equivalent would be

select component_id, sum(duration)
from flight_component
join flight on (flight_component.flight_id = flight.id)
where flight.date between ? and ?
group by component_id

或者我必须进行查询，然后总结所有组件自己？

Or am I going to have to make my query and then sum up all the components myself?

推荐答案

可以查询@someArray。在 Collection Operators page。

You can query for @"someArray.@sum". There's a list of such operators on the Collection Operators page.

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