NSPredicate from Core Data selecting by Object ID (and potentially summing)
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I'm finding my way to the advanced part of core data. I know it is not SQL, and there are limitations, however, how would I translate the code below to a NSPredicate to be applied in a fetch request?

    Product* p = self.product; //this is a managed object
    double vol=0;
    for (PlanningItem* pi in self.planitems) {
     if (pi.product==p)
    	vol+=pi.volume;

1. I want to fetch all plan items that have p as their product.
2. Next I want to sum all the volumes of that set.

How do I do 1 in a fetch request with a NSPredicate?
Can i do 2 at the same time?

I'm asking for the string for the NSPredicate. I am capable of building the Fetchrequest myself.

Tx!

	

