Core Data NSPredicate to filter results

Question

I have a NSManagedObject that contains a bID and a pID. Within the set of NSManagedObjects, I only want a subset returned and I'm struggling to find the correct NSPredicate or way to get what I need out of Core Data.

Here's my full list:

bid pid
41 0
42 41
43 0
44 0
47 41
48 0
49 0
50 43

There is a parent-child relationship above.

Rules:

If a record's PID = 0, it means that that record IS a parent record. If a record's PID != 0, then that record's PID refers to it's parent record's BID.

Example:

1) BID = 41 is a parent record. Why? Because records BID=42 and record BID=47 have PID's of 41, meaning those are children of its PID record.
2) BID = 42 has a parent record with a BID = 41.
3) BID = 43 is a parent record.
4) BID = 44 is a parent record.
5) BID = 47 has a parent record with a BID = 41 because its PID = 41. See #1 above.
6) BID = 48 is a parent record.
7) BID = 49 is a parent record.
8) BID = 50 is a child record, and its parent record has a BID = 43.

See the pattern?

Now, basically from that, I want only the following rows fetched:

bid pid
44 0
47 41
48 0
49 0
50 43

BID = 41, BID = 48, BID = 49 should all be returned because there are no records with a PID equal to their BID.

BID = 47 should be returned because it is the most recent child of PID = 41.
BID = 50 should be returned because it is the most recent child of PID = 43.

Hope this helps explain it more.

oops, even after you modified the question, it does not seem to be clear what you want to get from the data. Try to define a rule to fetch your data and you will see how to do it. With your explaination here, I don't see any rule to fetch the data you want. You said you want to get bid=44, but later on, you said 41? — Hoang Pham

Hoang Pham Hoang Pham · Accepted Answer · 2010-03-16T16:35:02

Ohh, this is pretty easy, you just need to set the predicate of bid >= 43.

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"bid >= %@", [NSNumber numberWithInt:43]];

I guess maybe you are having problem with the NSNumber, because Core Data saves many types under the NSNumber, includes: int, BOOL, etc... See here

Core Data NSPredicate to filter results

1 Answers