Core Data Versioning: Non-trivial Value Expressions?
Core Data Versioning: Non-trivial Value Expressions?
- Subject: Core Data Versioning: Non-trivial Value Expressions?
- From: Jerry Krinock <email@hidden>
- Date: Mon, 3 May 2010 18:53:36 -0700
When doing Core Data versioning, when creating a Mapping Model, when writing Custom Value Expressions, I understand that the syntax to be used is that described in the Predicate Programming Guide > Predicate Format String Syntax.
But I can't figure out how to do non-trivial mappings like these...
Example 1: Old data model attribute type is an Integer16. I want to map this to a Boolean which is NO if the old value was 0 and YES if != 0.
Example 2: Old and new data model attribute types are both String. If the string is "Joe", I want to map it to "Jose"; else, map the original value.
It seems like the concept of "mapping" should support stuff like this, but I can't find any such examples. In MigratingDepartmentAndEmployees, all I see is mapping from one attribute name to another.
Relations get a complicated expression like this generated automatically:
FUNCTION($manager, "destinationInstancesForEntityMappingNamed:sourceInstances:" , "EmployeeToEmployee", $source.employees)
but I have no idea where that FUNCTION keyword comes from (it's not listed as a reserved word in the Predicate Programming Guide). It seems like I should be able to make my own FUNCTION to implement the stuff I need in my examples. Is this possible?
Thanks,
Jerry Krinock
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