NSPredicate fetch Core Data objects with dates attribute within NSDate date range

Question

I'm using an NSPredicate with a couple of <= constructs to fetch objects from a Core Data store with a startDate attribute between 2 dates but I'm getting 0 objects fetched.

Here's my NSPredicate:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"( ( %@ <= %K ) && ( %K <= %@ ) )", fromDate, @"startTime", @"startTime", toDate];

Here's the console output:

predicate: CAST(336261600.000000, "NSDate") <= startTime AND startTime <= CAST(339285599.000000, "NSDate")
[sectionInfo numberOfObjects]: 0

Here are the dates that are in Core Data (the Attribute Type is set to Date):

startTime
---------
337249800
337309200
337318200

fromDate and toDate are both NSDate objects. I've tried substituting these with distantPast and distantFuture to make completely sure than my Core Data startTime attributes are within the date range and I still get 0 object fetched.

I have no idea why 0 objects are returned. Can anyone see where I'm going wrong?

score 2 · Answer 1 · answered Mar 12 '11 at 00:32

2

I'd start by adding the following executable argument:

-com.apple.CoreData.SQLDebug 1

This is going to spew a gigajazillion lines of debugging information to the console when you run your app, but it should also include information about the predicate its attempting to translate to SQL, and perhaps even why it's not working.

You'll obviously want to turn remove this before shipping your app :)

answered Mar 12 '11 at 00:32

Dave DeLong

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@MattVick: Glad you figured it out. The way we show thanks is by upvoting the answers to your questions that you've found helpful. – Dave DeLong Mar 14 '11 at 03:37

score 0 · Accepted Answer · answered Mar 14 '11 at 01:50

After looking at the generated SQL queries it appeared like the TIMESTAMP was being evaluated as a string and not an integer. This explained why my predicate wasn't working. I confirmed this by running the following SQL query on the SQLite db that I'm using to pre-populate Core Data.

SELECT DISTINCT typeof(ZSTARTTIME) FROM ZMATCH;

This showed that the TIMESTAMP field was of type BLOB!

Adding '+0' to my predicate so the startTime attribute was evaluated as an integer fixed the issue. However this seemed like a nasty solution. Also keeping the dates stored as blobs would most likely cause issues further down the road. So I went back and re-populated the the SQLite db from scratch making sure the TIMESTAMPs were inserted as integers and not strings. Now everything is working fine.

However this does mean that I'm going to have to do some more work with the next app update because I'll have to make sure the update overwrite the old SQLite db in the Documents folder with the new db. Is there a easy way to do this? Should I look at Core Data store migration??

NSPredicate fetch Core Data objects with dates attribute within NSDate date range

2 Answers2