I needed to create a Core Data Mapping Model today. The only value migration
necessary was to negate a boolean. It seems like one should be able to enter
such a simple expression into the "Value Expression" column of "Attribute
Mappings". Reading the Predicate Programming Guide, I tried, in turn, these
three…
!$source.foo
NOT $source.foo
NOT($source.foo)
However, in each case, Xcode complained of an invalid expression. At that
point I gave up and did the only thing I know that works, which is to subclass
NSMigrationPolicy, implement a method that negates a given NSNumber, and
reference it in the expression…
FUNCTION($entityPolicy, "negateBoolean:" , $source.foo)
It tested OK and is ready to ship. But, for next time, is there an easier way
to do this?
Thanks,
Jerry
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