quick way to check for duplicate values in Core Data

I need to quickly check to see if I have some duplicate values in CoreData. I am doing some background syncing and occasionally a dupe makes it into my system.

I have a ManufacturerID and an ItemID and I cannot have a duplicate value for both, example of bad data:

ManufacturerID   ItemID
35               IT001
35               IT001

So I would just want to know if that happened and maybe get a list of those ItemID's, then I need a way to figure out how to get rid of the dupes but this is a good start.

I just need a fast method figure out if they exist or not.


In my app I have a SynchManager that using NSoperations performs synch in background and store new records in the persistent sqlite store only if not alredy stored. Basically what I do is:

  1. execute a fetch request which retrieves a collections of stored ids (in my case these ids are strings representing urls)
  2. before insert a new object in the store I call a method like "shouldImportObject:", which basically test that the url is not already stored in the database. This is a simplified implementation sample:

    for (id objectID in ids) {
      if ([objectID isEqual:objectToImport.objectID]) {
         return NO;
    return YES;

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