Question

I have the following data model:

Group(name, color, activities*) // one group may have many activities
Activity(startTime, endTime, location, Group*) // startTime and endTime are NSDate, group is an inverse relationship

so if I want to get all Groups who have at least one activity which on on a specified NSDate, say theTime, what predicate should I construct?

My thoughts:

1. first get all activities
2. then put their groups into a Set in order to remove duplicate Groups
3. convert the Set to an array

so:

[NSPredicate predicateWithFormat:@"%@ >= startTime AND %@ <= endTime", theTime]

fetch an array of Activities then:

for (Activity *activity in activities)
{
    [theSet add:activity.group];
}

so I got an array of unique Groups that have at least one activity on theTime?

Is there any other way to just do a fetch without post-processing?

Thanks!

EDIT:

Can I do:

[NSPredicate predicateWithFormat:@"%@ >= activities.startTime AND %@ <= activities.endTime", theTime]

???

Answer 1

If I understood well your question, yes.

You can do it fecthing against Group instead of Activity entity. In this manner you can avoid to fetch first Activityies enitity and then apply a filter. Since activities is not a scalar value, you need a predicate modifier (ANY, ALL, etc.) or a SUBQUERY.

About your question I would do the following:

[NSPredicate predicateWithFormat:@"(SUBQUERY(activities, $x, $x.startTime >= %@ and $x.endTime <= %@).@count > 0)", theStartTime, theEndTime];

About the predicate, I suppose yuo want to find Groups that contain Activityies included in a specificified range.

Try and let me know. Hope that helps.