iphone - CoreData 相当于 sum...group by

Question

我有以下伪 SQL 架构:

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

如果我将其转换为使用 CoreData，是否有等效的方法可以使用另一个查询谓词获取每个组件的总持续时间？我认为 SQL 等效项是

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

或者我是否必须进行查询，然后自己总结所有组件？

Answer 1

您可以查询@"someArray.@sum"。 Collection Operators 上有此类运算符的列表。页。