Question

Here is a simple mySQL request :

UPDATE myTable SET X=X-1 WHERE (X>100)

Now my question goes like this.
How would I write a similar request in Core Data ?

I am starting to find out my way in Core Data; but the last part of the above SQL order gives me problems in Core Data.

In other word : how do I handle the WHERE (X>100) part.

If the mySQL request concerned one record only, I would use some thing like this :

[matchItem setValue:VALUE forKey:@"X"];

But how do I do if is a range of records, like here, where I want to perform some actions for all records where X>100.

Answer 1

Use an NSPredicate and add it to your NSFetchRequest.

NSPredicate *predicate = [NSPredicate predicateWithFormat:
    @"X > %@", [NSNumber numberWithInt:100]];

Iterate through your results array and set the value as appropriate.

for (NSManagedObject *match in resultsArray) {
    NSInteger newValue = [[match objectForKey:@"X"] intValue] +1;
    [match setValue:[NSNumber numberWithInt:newValue] forKey:@"X"];
}